Anyone got ideas for a cheap or DIY vacuum regulator?

ZephTheChef

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Ok, so let me start off by saying that I'm not trying to be shady and hide problems here. I deal with a very low income, high-risk customer and need to perform repairs as cheaply as possible in order to keep things within their budget otherwise they're walking (literally). The backstory is that I had a customer who wrecked their LeSabre a month after we put a $1,500 transmission rebuild into it. I kept the salvage because I knew it had a new transmisssion. Recently, I pulled that transmission to put into another car and come to find out after the fact, the case is cracked at or around one or more of the threaded mount holes (presumably from the wreck). I have epoxied and silicone'd the damn thing to hell and back and it still seeps just a little bit when warmed up. It's not a pressure leak, just leaking from the side case a little bit presumably when the fluid level gets above the crack. Not a bad leak, just a steady drip.

Point of the story is, I really don't want to throw away a $1,500 transmission due to some simple problem like this. I have verified I can "fix" it by running a vacuum line to the transmission vent. I used a clear hose at first to verify that it does not actually suck any fluid out of the trans. All is good. I've used this trick on oil leaks a lot in the past by installing a check valve in the vent line of a PCV system to actually build crankcase vacuum. Works wonders for worn VSS and pan/other crankcase seal leaks. Effectively, it turns a fluid leak to the atmosphere into a vacuum leak, which can be more easily compensated for.

So basically, the problem is that often if you do have a leak, and you draw full manifold vacuum, the leak will go to squeaking/squealing badly (almost sounds like a bad pulley bearing on the belt). I can solve this problem with an adjustable check valve/vacuum regulator, and in fact did just that by going to the hardware store today. All is well. The problem is, the damn thing cost around $25 in parts/fittings to make. Still much more cost effective than finding them another transmission, but not something I would want to spend in every case. I would love to figure out how to build or buy something that would create a couple PSI (or preferably adjustable) pressure differential between the vacuum source and the target (trans or crankcase) that cost more like $10 in parts, not $20-30. Ideas?

Am I dumb and overthinking it again?
 

ZephTheChef

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modify a cheap manual boost controller with a cut spring/unscrewed

but not much chance of less than 25$
Yeah, that's the problem. Even the cheap MBCs that I could use are now the same price range. Since when did brass fittings and hose barbs get to be $4-5 each? I mean $25 really isn't the end of the world. It just seems like it should be able to be done for $10.
 

ZephTheChef

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It's more that this would be a beneficial preventive thing for me to do on every vehicle in the fleet, if it were cost effective. I mean our average vehicle these days is a 200k mile late 90s, early 2000s. It's common for our customers to not keep an eye on the fluids, and it's pretty rare I get one that stays 100% dry underneath so we do get occasional mechanical failures that I think could be prevented. This type of modification dramatically reduces oil seepage or consumption in most cases. The total number of vehicles in the fleet floats somewhere around 300. So the difference between $10 and $25 might not seem like a lot, but when you're talking about having that expense 300 times it turns into a big number. If I can get the cost down I could rationalize/justify it on every car as preventive maintenance as opposed to just the occasional use as a problem solver.
 

ZephTheChef

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Really, I guess the answer if I can't find a cost-effective adjustable solution is to just figure out what pressure differential most vehicles will tolerate without squeaking and get some fixed cracking pressure barbed spring and ball check valves. But cost can still be an issue there.
 

ZephTheChef

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The plastic ones with barbs already would be great, except that they are all like .25-1psi cracking pressure. I believe I need something that's going to be more in the 3psi range. Some stock PCV valves do an ok job of regulating pressure differential to a reasonable amount on their own if you just check valve the vent line...but many don't.
 

Turbocharged400sbc

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id stil go with a boost conroller deal, with that youd have to have a post maf air supply to the relief valve and at least an orifice in the man vac line.

at least this total circuit system would reduce spikes that would cause dirt/debris at the seals to allow grime in and accelerate seal wear at the least
 

ZephTheChef

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id stil go with a boost conroller deal, with that youd have to have a post maf air supply to the relief valve and at least an orifice in the man vac line.

at least this total circuit system would reduce spikes that would cause dirt/debris at the seals to allow grime in and accelerate seal wear at the least
I'm having a hard time picturing what you're saying exactly but the vacuum leak is unavoidable for my purposes. It's always going to be unmetered air if the purpose is to draw fresh air in through the seal leaks as opposed to seeping fluids out.

Boost controllers typically have a relief hole drilled that would be a full-time vacuum leak whether the spring pressure was overcome or not if not sealed up anyway. I was thinking one of these vacuum relief valves adjusted to maintain the pressure differential I want, then the adjustment locked in place and slip the entire assembly inside a hose. Connect to manifold vacuum and the crankcase or trans case or whatever. Yes, it's a small vacuum leak, but that's infinitely better than a small external fluid leak from the perspective of longevity. I mean we're talking about your average everyday unmodified stock vehicles with tons of miles. Very basic transportation vehicles. People with subzero credit scores and no automotive knowledge. Since it's only a leak under significant vacuum it won't affect drivability under any load.

The idea in general is mostly just to create a couple PSI vacuum under most idle/cruise conditions to slow fluid leaks to a less problematic level. I don't really even care about the fuel trims as long as they are within the smooth-running or correctable limits of the computer, even IF it does set a CEL. It's a rare case that these vehicles don't have half a dozen trivial MIL codes anyway.
 

ZephTheChef

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Or are you suggesting a two-pipe system? Either way, only the portion going through the relief valve would potentially be metered...the air flowing past the seals that's preventing the fluid leaks will always be a vacuum leak. I think. I'm open to suggestions otherwise...but typically on 3800 cars I just use the adjustable factory regulator when possible to compensate for slight intentional vacuum leaks like this and get the fuel trims in a happy medium during vacuum vs during load.
 

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