3800 4T80E>4t60/65/hd
- Thread starter Turbocharged400sbc
- Start date
the extreeme load you speak of is the sprag freewheeling, then locking, then freewheeling, then locking as you throttle the engine in and out of power.
im sure you can readily tell that the sprag is sliding and damaging the rollers/ramps while doing the burnout. just as you can when it gets full load for a far longer duration before slipping.
saying it never broke during a burnout but only when under max load isnt taking into acount that the burnout is often the hardest on a trans as far as shock loading
the th400's sprag is readily damaged by freewheeling and then locking under shock loads....so burnouts are done in a certain way to keep the sprag from having to do anything but freewheel since the trans is not shifting 1-2 and trying to stop a sprag on a dime....
it'll even kill the turbine sprag (one reason why people use spragless converters is to eliminate slip and inconsistency at the drawback of less efficiency at coupling speed.
the descriptions you gave of having "hard drive" then losing drive entirely is listed as the forward sprag/clutch. and since sprags tend to be damaged by high load freewheeling to holding transitions...what would you think would kill your sprag?
anytime you shock the drivetrain in any forward gear outside of manual 2nd/1st those two items are handling direct turbine shaft power/rpm.
it would make sense to me. pull apart your forward drum, id bet the band is glazed and the sprag has flat spots on the rollers and dimples on the ramps
it appears if you have the manual valve in manual 2nd it does lock the coast clutch to keep it from freewheeling...but then your pedaling of the throttle will be far more dramatic as you enter engine braking as you let off instead of the sprag freewheeling.
a sprag is a sprag, and roller/ramp sprags are great at friction free freewheeling, which is important on an OD fwd v8 trans to try and keep the CAFE ratings up. they are however bad at locking up with an oil wedge acting as a bearing before the rollers finally touch metal before slipping a little then holding once wedged.
no other sprag is of the roller type, all others are 30+ element dogbone sprags and arent as heavily integral to trans function as that single forward sprag.
it would still be prudent to change your driving technique to TRY minimize damage.
especially since unlike the 400, we dont have a ready replacement for a known weak sprag design.
your new low mile units would probably last longer, even if not "built" other than accum mods and line pressure bump via a boost valve spring.
3rd has more than a few checkballs, so replacing the steel with the teflon would probably help alot, 2 passages in the seperator plate could get drilled for faster apply
im sure you can readily tell that the sprag is sliding and damaging the rollers/ramps while doing the burnout. just as you can when it gets full load for a far longer duration before slipping.
saying it never broke during a burnout but only when under max load isnt taking into acount that the burnout is often the hardest on a trans as far as shock loading
the th400's sprag is readily damaged by freewheeling and then locking under shock loads....so burnouts are done in a certain way to keep the sprag from having to do anything but freewheel since the trans is not shifting 1-2 and trying to stop a sprag on a dime....
it'll even kill the turbine sprag (one reason why people use spragless converters is to eliminate slip and inconsistency at the drawback of less efficiency at coupling speed.
the descriptions you gave of having "hard drive" then losing drive entirely is listed as the forward sprag/clutch. and since sprags tend to be damaged by high load freewheeling to holding transitions...what would you think would kill your sprag?
anytime you shock the drivetrain in any forward gear outside of manual 2nd/1st those two items are handling direct turbine shaft power/rpm.
it would make sense to me. pull apart your forward drum, id bet the band is glazed and the sprag has flat spots on the rollers and dimples on the ramps
it appears if you have the manual valve in manual 2nd it does lock the coast clutch to keep it from freewheeling...but then your pedaling of the throttle will be far more dramatic as you enter engine braking as you let off instead of the sprag freewheeling.
a sprag is a sprag, and roller/ramp sprags are great at friction free freewheeling, which is important on an OD fwd v8 trans to try and keep the CAFE ratings up. they are however bad at locking up with an oil wedge acting as a bearing before the rollers finally touch metal before slipping a little then holding once wedged.
no other sprag is of the roller type, all others are 30+ element dogbone sprags and arent as heavily integral to trans function as that single forward sprag.
it would still be prudent to change your driving technique to TRY minimize damage.
especially since unlike the 400, we dont have a ready replacement for a known weak sprag design.
your new low mile units would probably last longer, even if not "built" other than accum mods and line pressure bump via a boost valve spring.
3rd has more than a few checkballs, so replacing the steel with the teflon would probably help alot, 2 passages in the seperator plate could get drilled for faster apply
Took a break from it all.
starting back the work, ran out of time for this weekened.
Bought a old Motorhome to make the race track experience more fun for the GF and myself.
Fixed the trailblazer SS stage 7 trans. Went through the 4t80e GM course and learned some good stuff. Helped my pinpoint my 4l70e problem right away and fixed it quickly. Now trailblazer SS shifts like a top again.
Looking to upgrade the 4t80e transmission and increase pressure in key areas.
Any info that you go james on which springs spacers that would fit the 4t80e accumulators and boost valve etc... that would save time, or I will have to find it the hard way, take measurement and compare to existing products.
I believe more pressure on the clutch pack will help holding capacity. That is the first thing I want to do.
starting back the work, ran out of time for this weekened.
Bought a old Motorhome to make the race track experience more fun for the GF and myself.
Fixed the trailblazer SS stage 7 trans. Went through the 4t80e GM course and learned some good stuff. Helped my pinpoint my 4l70e problem right away and fixed it quickly. Now trailblazer SS shifts like a top again.
Looking to upgrade the 4t80e transmission and increase pressure in key areas.
Any info that you go james on which springs spacers that would fit the 4t80e accumulators and boost valve etc... that would save time, or I will have to find it the hard way, take measurement and compare to existing products.
I believe more pressure on the clutch pack will help holding capacity. That is the first thing I want to do.
Here's some more info for you. Wasted an hour researching this crap...
My 3 2006 2008 2011 torque converters look Identical to my 99-2000 Viccous torque converters. No way to see the difference. THere is a date stamp that says the year on the converter, only way to tell.
The 2005 + ECCC Torque converters look the same as the Viscous.
The only one that looks different is the old 1994 allante non viscous non ECCC converter.
The ECCC torque converter needs a different programming and valvebody to operate correctly or it will apply very harshly (alledgedly)
So I will let you know what I find.
AND the bolt pattern is slightly wider (so I again need to redrill god dammit !!
My 3 2006 2008 2011 torque converters look Identical to my 99-2000 Viccous torque converters. No way to see the difference. THere is a date stamp that says the year on the converter, only way to tell.
The 2005 + ECCC Torque converters look the same as the Viscous.
The only one that looks different is the old 1994 allante non viscous non ECCC converter.
The ECCC torque converter needs a different programming and valvebody to operate correctly or it will apply very harshly (alledgedly)
So I will let you know what I find.
AND the bolt pattern is slightly wider (so I again need to redrill god dammit !!
from everything in the manual i have there's negligible differences in the ECCC vb over the viscus. so little in fact other than talking about the conver, they dont point out any differences. it may be more of the PCM logic and maybe a couple spring changes or restricter changes
but on the other side of things....
holy hell did they design this thing to be hydraulic intensive. that probably explains the 2 line pressure pumps....
anyways after a bit of research and tracing hydraulic diagrams it does appear that GM was sensible enough to design the trans that in R/N and first gear (in D4, D3 to the manual 1st position) the solenoids are in the same position and the apply's jive with each other.
so while in D4-L1 reverse actuation is just a mater of the reverse clutch needing to be applied to lock the trans into 1st and reverse.
problem is that its difficult to do using the oem passages since some passages are passing through the main shift valves and exhausts at the manual valve (since it'll be in D not R).
the good news is that the tap in for main line pressure is already there, the passage is large enough to handle any extra fluid flow, and the reverse clutch passage is fairly readily accessible in one area for a tie in for the external solenoid.
problem is much like the old th400 brake's.... this removes the ability for the trans to use its reverse circuits since any reverse apply with the oem passages allowing bleed off through 2 restricters and the manual valve.
while it might work the problem lies in whether the crossing of the shift valves of the pressure would screw with anything (im still tracing out possible interference issues on the hydraulic paths with the accumulator valves)
so the best solution so far is to block off the 2 branches, and use the brake solenoid to allow for reverse operation. either manually through the Tbrake switch or possibly via an "automatic" reverse can be done with a microswitch on the shifter.
pressure would still stroke the reverse accumulator against the main forward accumulator, but the reverse accumulator can be limited (with the usual spacers or springs) to make the rise/fall of Rclutch apply as rapid as possible.
the reverse clutch housing feed path is large enough but the primary fluid exhaust path is the same (exhausts at manual valve at all positions besides R) so for the pressure to drop enough to unseat the Rclutch bleedoff valve it'd take time. this valve is designed so centrifugal force is supposed to allow for faster release but is not applicable since it'll be stationary.
so likely much like the old 400 it'll need bleed holes in the piston housing and stiffer piston return springs (though i recall unused spots on the last trans i tore apart...so it may just be adding 3 springs in the empty spots...)
so yeah...4t80e can be trans braked just like the original GMR design on the 65e
im still looking at things but it looks like the coast clutch can be manually actuated the same way allowing for you to hold the forward sprag and keep it from overrunning during pedaling/coasting.
it means engine braking upon liftoff of the throttle but its an option if the forward sprag ends up hating lowly old v6's
so at least it looks like the 80e can be trans braked with a couple seperator plate changes/staked bearings in the reverse paths, and some linework and solenoid block.
locking 2.96 forward to 2.13 reverse would probably do it....plus who gives a shit if its hard on the reverse clutches as they release....at least with two yer likely to still have reverse on the other.
and now to some interesting facts
4t80e plant in Ypsilanti michigan
266.75 lbs dry
293.21lbs wet
12-14.6 liters fluid capacity (dry sump-internal drain plugs for upper sump)
it IS a 265mm converter, pattern is different but the converter shell is the same diameter and likely identical to the 65e unit aside from the stator/turbine spline size increase.
and most interesting, hard proof of the early 2.84 FDR being part of the range (3.11,3.48,3.71)
CLIFFS:
this one sexy beast
but on the other side of things....
holy hell did they design this thing to be hydraulic intensive. that probably explains the 2 line pressure pumps....
anyways after a bit of research and tracing hydraulic diagrams it does appear that GM was sensible enough to design the trans that in R/N and first gear (in D4, D3 to the manual 1st position) the solenoids are in the same position and the apply's jive with each other.
so while in D4-L1 reverse actuation is just a mater of the reverse clutch needing to be applied to lock the trans into 1st and reverse.
problem is that its difficult to do using the oem passages since some passages are passing through the main shift valves and exhausts at the manual valve (since it'll be in D not R).
the good news is that the tap in for main line pressure is already there, the passage is large enough to handle any extra fluid flow, and the reverse clutch passage is fairly readily accessible in one area for a tie in for the external solenoid.
problem is much like the old th400 brake's.... this removes the ability for the trans to use its reverse circuits since any reverse apply with the oem passages allowing bleed off through 2 restricters and the manual valve.
while it might work the problem lies in whether the crossing of the shift valves of the pressure would screw with anything (im still tracing out possible interference issues on the hydraulic paths with the accumulator valves)
so the best solution so far is to block off the 2 branches, and use the brake solenoid to allow for reverse operation. either manually through the Tbrake switch or possibly via an "automatic" reverse can be done with a microswitch on the shifter.
pressure would still stroke the reverse accumulator against the main forward accumulator, but the reverse accumulator can be limited (with the usual spacers or springs) to make the rise/fall of Rclutch apply as rapid as possible.
the reverse clutch housing feed path is large enough but the primary fluid exhaust path is the same (exhausts at manual valve at all positions besides R) so for the pressure to drop enough to unseat the Rclutch bleedoff valve it'd take time. this valve is designed so centrifugal force is supposed to allow for faster release but is not applicable since it'll be stationary.
so likely much like the old 400 it'll need bleed holes in the piston housing and stiffer piston return springs (though i recall unused spots on the last trans i tore apart...so it may just be adding 3 springs in the empty spots...)
so yeah...4t80e can be trans braked just like the original GMR design on the 65e
im still looking at things but it looks like the coast clutch can be manually actuated the same way allowing for you to hold the forward sprag and keep it from overrunning during pedaling/coasting.
it means engine braking upon liftoff of the throttle but its an option if the forward sprag ends up hating lowly old v6's
so at least it looks like the 80e can be trans braked with a couple seperator plate changes/staked bearings in the reverse paths, and some linework and solenoid block.
locking 2.96 forward to 2.13 reverse would probably do it....plus who gives a shit if its hard on the reverse clutches as they release....at least with two yer likely to still have reverse on the other.
and now to some interesting facts
4t80e plant in Ypsilanti michigan
266.75 lbs dry
293.21lbs wet
12-14.6 liters fluid capacity (dry sump-internal drain plugs for upper sump)
it IS a 265mm converter, pattern is different but the converter shell is the same diameter and likely identical to the 65e unit aside from the stator/turbine spline size increase.
and most interesting, hard proof of the early 2.84 FDR being part of the range (3.11,3.48,3.71)
CLIFFS:
this one sexy beast
If those pages are loose, I have a portable scanner. We could scan them and put them into a PDF.
Went through 2 of my broken 4t80e and found some interesting stuff.
I will do a report on it tonight or tomorrow.
I have another trans to inspect (One of the two I broke last year). And if I can find it I have the 1st one I broke.
Most of them were broken at high boost with a 2nd gear launch with slicks (rear engine). Lots of traction, lots of torque. Most of them fail right when peak torque hits around 3500-4800rpm (full boost). I estimate torque to be ridiculous. I have yet to break one of these trans at "normal" boost level.
in a FWD, I think I would have had zero failures at the same power level. Maybe some burnt clutch in 3rd gear because of slow shifting after many runs.
Trying 2 4t65e-HD in the rear setup of the GTP, I broken them immediately on the street with little traction. That's how much load it sees and how stronger the 4t80e is.
Yet it's still not even close to what I was hoping for. I need to hold 800HP and a lot of torque for at least half a season or it's not worth continuing.
I found many problems with the trans and many ways to improve it.
I'm happy to report the "Built" trans I bought from Jeff didn't fail in the same manner which is a good sign some of the stuff he did, helped. It did have something odd, a broke/burnt plastic spacer which went everywhere. Perhaps blocking some hydraulic passages. As it melted it really went in places I wouldn't have expected.
The main problem I have with my type of use (2nd gear starts mostly) that is common in all of the damaged 4t80e I have opened.
Destroyed coast clutch packs. Most of them really bad... and Jeff's was badly burnt but no missing pieces.
And all of them showed some stress on the 3rd clutch packs as well, some pretty blacked out, but none destroyed. Jeff's trans had the best looking clutch pack. It does help he put new clutches in and it wasn't an original 60-100k transmission.
Jeff's 4th band was in very rough shape and the drum it was riding on is burned lots of hot spots. I did put Jeff's trans threw a lot of 4th gear full power runs. Which I didn't do to other trans (maybe 1 run by mistake)
Other trans show some stress on the 4th band but not burnt and little heat marks on the drum.
On my last broken 4t80e (which broke during a hard 2nd gear launch with 100 shot of NOS and lots of boost). It loaded really hard and hooked. I saw 4800rpm huge amount of boost and the nitrous was probably still under effect (although shut off almost immediately after the launch).
That trans (not Jeff's but a low miles 4t80e) broke the forward sprag. It spins in both directions. The car was still able to move but only in Low gear. The coast clutch was annihilated in that one. Lots of clutch debris which didn't help sealing or hydraulic functioning right (and probably hurt the sprag too).
We need to get the coast clutch problem resolved. The design is strange and I wonder if it hangs or sticks (doesn't disengage). That trans was run mostly in Drive but using manual shifting.
The sprag problem will be probably be less if I start in 1st gear vs 2nd gear (less boost too) and using more progressive boost off the line. And it will help if not a huge amount of gritty clutch material doesn't pollute the trans in that area as well.
Another possible culprid is tired valve body in general. Leaky valves etc... causing cross talk and poor hydraulic control.
This low miles trans was BY FAR the best shifting 4t80e I have ever had. It shifted clean with zero apparent slip (although 3rd shift was slow but clean once engaged). The logs showed a clean shift. I attribute that to the fact it had lower miles and was in better shape then the others.
Jeff's trans was mated with a really loose 1st try precision converter. Which went straight to 7K at full power. We could never see or feel any shift. Was like a CVT transmission. So his trans couldn't be reviewed.
Oddly the newer trans I put in which had the lowest miles never shifted as clean. No apparent slip though after the shift. It did something funky last even, after a 4th gear run it was stuck in very high gear. 3rd or 4th gear. wouldn't downshift. After sitting a few days, all gears work perfect and it passes a 1st, 2nd and 3rd gear burnout. Which is a great sign. But what happened at the track ? Warped channel plate, issue in the valve body solenoid etc...
I will do a report on it tonight or tomorrow.
I have another trans to inspect (One of the two I broke last year). And if I can find it I have the 1st one I broke.
Most of them were broken at high boost with a 2nd gear launch with slicks (rear engine). Lots of traction, lots of torque. Most of them fail right when peak torque hits around 3500-4800rpm (full boost). I estimate torque to be ridiculous. I have yet to break one of these trans at "normal" boost level.
in a FWD, I think I would have had zero failures at the same power level. Maybe some burnt clutch in 3rd gear because of slow shifting after many runs.
Trying 2 4t65e-HD in the rear setup of the GTP, I broken them immediately on the street with little traction. That's how much load it sees and how stronger the 4t80e is.
Yet it's still not even close to what I was hoping for. I need to hold 800HP and a lot of torque for at least half a season or it's not worth continuing.
I found many problems with the trans and many ways to improve it.
I'm happy to report the "Built" trans I bought from Jeff didn't fail in the same manner which is a good sign some of the stuff he did, helped. It did have something odd, a broke/burnt plastic spacer which went everywhere. Perhaps blocking some hydraulic passages. As it melted it really went in places I wouldn't have expected.
The main problem I have with my type of use (2nd gear starts mostly) that is common in all of the damaged 4t80e I have opened.
Destroyed coast clutch packs. Most of them really bad... and Jeff's was badly burnt but no missing pieces.
And all of them showed some stress on the 3rd clutch packs as well, some pretty blacked out, but none destroyed. Jeff's trans had the best looking clutch pack. It does help he put new clutches in and it wasn't an original 60-100k transmission.
Jeff's 4th band was in very rough shape and the drum it was riding on is burned lots of hot spots. I did put Jeff's trans threw a lot of 4th gear full power runs. Which I didn't do to other trans (maybe 1 run by mistake)
Other trans show some stress on the 4th band but not burnt and little heat marks on the drum.
On my last broken 4t80e (which broke during a hard 2nd gear launch with 100 shot of NOS and lots of boost). It loaded really hard and hooked. I saw 4800rpm huge amount of boost and the nitrous was probably still under effect (although shut off almost immediately after the launch).
That trans (not Jeff's but a low miles 4t80e) broke the forward sprag. It spins in both directions. The car was still able to move but only in Low gear. The coast clutch was annihilated in that one. Lots of clutch debris which didn't help sealing or hydraulic functioning right (and probably hurt the sprag too).
We need to get the coast clutch problem resolved. The design is strange and I wonder if it hangs or sticks (doesn't disengage). That trans was run mostly in Drive but using manual shifting.
The sprag problem will be probably be less if I start in 1st gear vs 2nd gear (less boost too) and using more progressive boost off the line. And it will help if not a huge amount of gritty clutch material doesn't pollute the trans in that area as well.
Another possible culprid is tired valve body in general. Leaky valves etc... causing cross talk and poor hydraulic control.
This low miles trans was BY FAR the best shifting 4t80e I have ever had. It shifted clean with zero apparent slip (although 3rd shift was slow but clean once engaged). The logs showed a clean shift. I attribute that to the fact it had lower miles and was in better shape then the others.
Jeff's trans was mated with a really loose 1st try precision converter. Which went straight to 7K at full power. We could never see or feel any shift. Was like a CVT transmission. So his trans couldn't be reviewed.
Oddly the newer trans I put in which had the lowest miles never shifted as clean. No apparent slip though after the shift. It did something funky last even, after a 4th gear run it was stuck in very high gear. 3rd or 4th gear. wouldn't downshift. After sitting a few days, all gears work perfect and it passes a 1st, 2nd and 3rd gear burnout. Which is a great sign. But what happened at the track ? Warped channel plate, issue in the valve body solenoid etc...
coast clutch is "assisting" holding the forward sprag under acceleration, it is disengauged when at coast, and reengages.
its one of the issues with the pedaling of a burnout and one reason i suggest a full coast lockup all the time with some sort of external solenoid that wont release it till the brake pedal is pressed. this should keep the relativly weak forward sprag from taking as much abuse. an old trans guy i know is a pretty fart smeller said a good option during our "rebuilds is to get rollers .005" larger dia to put the sprag on a clean section of the ramp and no longer have flat spots.
dont know on that last one but it bears investigation after failure.
its one of the issues with the pedaling of a burnout and one reason i suggest a full coast lockup all the time with some sort of external solenoid that wont release it till the brake pedal is pressed. this should keep the relativly weak forward sprag from taking as much abuse. an old trans guy i know is a pretty fart smeller said a good option during our "rebuilds is to get rollers .005" larger dia to put the sprag on a clean section of the ramp and no longer have flat spots.
dont know on that last one but it bears investigation after failure.
This statement is unclear.
From what I know about the 4t80e course and the details on the hydraulic flow and application is that the coast clutch is used whenever in Manual range. That means all the time in Manual. But not applied in Drive mode which I was in during the failures in some cases (others I was in manual 2nd with the GTP)
I do believe you on the sprag issue during burnout. It has to be hard on it, the big power and high MPH (high rpm inside the trans) and then hooks hard. I try to stop before it hooks naturally but that means the wheels stop moving very quickly after the burnout. A hard stop to prevent breaking through the beams (which the track officials don't enjoy)
That said I have never broken during a burnout. I do believe the problem is NOT related to pedaling the throttle like you think. It always happens during the launch when peak torque is reached. To me it just seems I reach the breaking point of the weak link in the trans (the forward sprag)...
Although I wonder why is the coast clutch always destroyed when it's not supposed to be engaged with my shifter in Drive position.
the only range not applying coast is D4 (aka OD)
D,2,L all use it. D not until third gear for towing/hauling and engine braking.
the forward sprag is holding in all except 4th, but the clutches dont assist untill D3 or lower
you sure your looking at the two frictions from the coast clutch or the more numerous plates of the forward clutch? the forward and coast clutches are concentric pistons, from the look of it,
apply passages are adjacent in the drum center bushing, so wear could factor into cross talk and partial apply/draging
but since the forward sprag is likly to get damaged during burnouts/shock loadings, we cant expect it to handle peak tq after the rollers develop hot spots or end up with divots in the ramps that prevent proper wedging (why it was suggested oversize rollers be installed).
but maybe with some work, somewhere there's an adjacent passage that can apply the coast clutch or just an external solenoid to force the coast to hold the sprag stationary and keep it from dying....then at least we can find the next weak link.
by its design as a MPG device allowing the wheels to overrun the engine rpm it spends alot of time freewheeling which is the roller/ramps forte'.... dogbone sprags dont like to freewheel without eventual flat spotting of the heels.
if we're looking at the sprag not holding (look at the rollers/ramps, i found the wear on the two ive torn down) as being an issue, certainly easier to deal with permanent engine braking or external solenoid activation than trying to ge tthe sprag to hold via an upgrade or brand new parts.
via the mechanical drive charts, that forward sprag is holding quite a bit of Tq as its holding the ring gear on the input in all gears except 4th where it overruns.
so its dealing with full engine Tq plus the Tq multiplication of the tq converter, plus the leverage of 1st (and less leverage with 2nd)
that little fucker is carrying more load than you realize and abuse isnt helping it do its job.
weld it solid and delete 4th was the only other suggestion i got. id rather have a solenoid triggered coast apply so i can at least manually control it and maintain streetability.
case passage access for rev and coast circuits look to be fairly easy at the drivers rear lower corner where they go through the driven sprocket support
D,2,L all use it. D not until third gear for towing/hauling and engine braking.
the forward sprag is holding in all except 4th, but the clutches dont assist untill D3 or lower
you sure your looking at the two frictions from the coast clutch or the more numerous plates of the forward clutch? the forward and coast clutches are concentric pistons, from the look of it,
apply passages are adjacent in the drum center bushing, so wear could factor into cross talk and partial apply/draging
but since the forward sprag is likly to get damaged during burnouts/shock loadings, we cant expect it to handle peak tq after the rollers develop hot spots or end up with divots in the ramps that prevent proper wedging (why it was suggested oversize rollers be installed).
but maybe with some work, somewhere there's an adjacent passage that can apply the coast clutch or just an external solenoid to force the coast to hold the sprag stationary and keep it from dying....then at least we can find the next weak link.
by its design as a MPG device allowing the wheels to overrun the engine rpm it spends alot of time freewheeling which is the roller/ramps forte'.... dogbone sprags dont like to freewheel without eventual flat spotting of the heels.
if we're looking at the sprag not holding (look at the rollers/ramps, i found the wear on the two ive torn down) as being an issue, certainly easier to deal with permanent engine braking or external solenoid activation than trying to ge tthe sprag to hold via an upgrade or brand new parts.
via the mechanical drive charts, that forward sprag is holding quite a bit of Tq as its holding the ring gear on the input in all gears except 4th where it overruns.
so its dealing with full engine Tq plus the Tq multiplication of the tq converter, plus the leverage of 1st (and less leverage with 2nd)
that little fucker is carrying more load than you realize and abuse isnt helping it do its job.
weld it solid and delete 4th was the only other suggestion i got. id rather have a solenoid triggered coast apply so i can at least manually control it and maintain streetability.
case passage access for rev and coast circuits look to be fairly easy at the drivers rear lower corner where they go through the driven sprocket support
Remember i dont have a position leverthe only range not applying coast is D4 (aka OD)
D,2,L all use it. D not until third gear for towing/hauling and engine braking.
the forward sprag is holding in all except 4th, but the clutches dont assist untill D3 or lower
you sure your looking at the two frictions from the coast clutch or the more numerous plates of the forward clutch? the forward and coast clutches are concentric pistons, from the look of it,
apply passages are adjacent in the drum center bushing, so wear could factor into cross talk and partial apply/draging
but since the forward sprag is likly to get damaged during burnouts/shock loadings, we cant expect it to handle peak tq after the rollers develop hot spots or end up with divots in the ramps that prevent proper wedging (why it was suggested oversize rollers be installed).
but maybe with some work, somewhere there's an adjacent passage that can apply the coast clutch or just an external solenoid to force the coast to hold the sprag stationary and keep it from dying....then at least we can find the next weak link.
by its design as a MPG device allowing the wheels to overrun the engine rpm it spends alot of time freewheeling which is the roller/ramps forte'.... dogbone sprags dont like to freewheel without eventual flat spotting of the heels.
if we're looking at the sprag not holding (look at the rollers/ramps, i found the wear on the two ive torn down) as being an issue, certainly easier to deal with permanent engine braking or external solenoid activation than trying to ge tthe sprag to hold via an upgrade or brand new parts.
via the mechanical drive charts, that forward sprag is holding quite a bit of Tq as its holding the ring gear on the input in all gears except 4th where it overruns.
so its dealing with full engine Tq plus the Tq multiplication of the tq converter, plus the leverage of 1st (and less leverage with 2nd)
that little fucker is carrying more load than you realize and abuse isnt helping it do its job.
weld it solid and delete 4th was the only other suggestion i got. id rather have a solenoid triggered coast apply so i can at least manually control it and maintain streetability.
case passage access for rev and coast circuits look to be fairly easy at the drivers rear lower corner where they go through the driven sprocket support
When i say drive i mean the position where 4th can be used. OD... right below neutral.
Yes im sure its the coast clutch there are less frictions. 3rd also show that its been hot but not near as bad.
Like i said the gm tech cd I got clearly shows and says coast is not applied in drive... but it is in all manual ranges
look at the size of the restrictor holes in the separator plate then look at the volume of the accumulators versus the smaller 65 E stuff and realize that not only did that volume increase the piston volume increase that's a lot more fluid to move and it was designed for old people towing boats or grandkids around
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