Heartbeat1991 Posted April 27, 2014 Report Share Posted April 27, 2014 So, I need some PMIII expert advice. My master cylinder appears to be leaking from the rear of the unit. Not a lot, more of a drip. I recently put a new accumulator on it. When I removed the PMIII today, I saw an o-ring laying on the transmission. I am wondering if maybe it fell off the accumulator before I put it in. Can I remove the accumulator without replacing it again? Or will it leak out its charge when removed? Also, the place where the accumulator and pressure switch, etc bolt to the rear of the master was covered in a sealant of some sort that appears to be brittle and breaking off. Should I remove that whole assembly from the rear of the unit and re-seal it somehow? Quote Link to comment Share on other sites More sharing options...
Heartbeat1991 Posted April 27, 2014 Author Report Share Posted April 27, 2014 OK.. So I got brave and took that housing off of the back of the motor. There is an o-ring in there that seals it to the motor. I am thinking I will change that, in the event that is what's leaking. The o-ring on the accumulator was still on there, and didn't seem to be leaking. I'm not sure where it was coming from. I don't see any apparent cracks in that housing. Quote Link to comment Share on other sites More sharing options...
mfewtrail Posted April 28, 2014 Report Share Posted April 28, 2014 Considering the rear housings were common to crack, that could be what you're dealing with. Throwing this out there as an idea: You could get it tested with a dye penetrant kit at a local machine shop or engine builder for a reasonable price. Since the part is small, I don't think they should charge much to do that. For what it's worth, kits can be purchased to do it yourself for about $60ish. Quote Link to comment Share on other sites More sharing options...
Heartbeat1991 Posted April 28, 2014 Author Report Share Posted April 28, 2014 I know they were common to crack, I just don't see one. I will look into the dye. I have 2 spare PMIII units. .So I'm sure I'll have 1 good part somewhere. LOL. I just need to verify where it's leaking. I suppose it could be from that big allen head bolt in the housing too. There must he a seal on that. Quote Link to comment Share on other sites More sharing options...
White93z34 Posted April 28, 2014 Report Share Posted April 28, 2014 MY PMIII used to be great, but sometime over the winter it decided to leak all its fluid out, and continue to pump it onto the ground as fast as it can be put in. Haven't felt spicy enough to open it up to find out what went wrong though. I'm going through the motions of just replacing the whole dang thing and hoping for the best. Quote Link to comment Share on other sites More sharing options...
Heartbeat1991 Posted April 28, 2014 Author Report Share Posted April 28, 2014 Are you replacing it with a re-man, Chris? Or swapping to vacuum? I pulled mine out, but I haven't found where it's leaking. I noticed this morning that the cover seems like it doesn't seal all the way down at the rear. I'm wondering if that is the problem. I will have to get some plugs for the brake line ports and pressurize it to see if it leaks anywhere. Since I already have the rear housing off, I'll replace the o-ring. Does anyone have torque specs for the 4 bolts holding that housing to the motor? Quote Link to comment Share on other sites More sharing options...
mfewtrail Posted April 28, 2014 Report Share Posted April 28, 2014 I'll check for a rear housing torque spec, but I'm not certain there will be one in the factory manual. I've been meaning to pick up one of the Delco Moraine ABS III books on ebay for a while now to see if they're more in-depth about the internal works of the unit. A crack might not be obvious without dye testing. The unit gets pressurized up to 2700psi. Even a microscopic crack is going to get fluid pushed through it at pressures like that. Quote Link to comment Share on other sites More sharing options...
Heartbeat1991 Posted April 28, 2014 Author Report Share Posted April 28, 2014 A crack might not be obvious without dye testing. The unit gets pressurized up to 2700psi. Even a microscopic crack is going to get fluid pushed through it at pressures like that. Yeah, I get that. I should be able to pressurize it without bolting it back in and see if I can locate the leak. Quote Link to comment Share on other sites More sharing options...
White93z34 Posted April 28, 2014 Report Share Posted April 28, 2014 Are you replacing it with a re-man, Chris? Or swapping to vacuum? I pulled mine out, but I haven't found where it's leaking. I noticed this morning that the cover seems like it doesn't seal all the way down at the rear. I'm wondering if that is the problem. I will have to get some plugs for the brake line ports and pressurize it to see if it leaks anywhere. Since I already have the rear housing off, I'll replace the o-ring. Does anyone have torque specs for the 4 bolts holding that housing to the motor? Replacing with a spare PMIII unit that I have of unknown origin. I replaced the whole deal and swapped my nearly-new accumulator over. Good thing is no fluid on the ground now, pump motor seems to work fine, bad pump motor won't stop running. Maybe I need to bleed it down, maybe the pressure switch is bad. I was irritated and tired at that point so I walked away from it, I also didn't have my Tech1 or accumulator pressure gauge with me. Quote Link to comment Share on other sites More sharing options...
Heartbeat1991 Posted April 29, 2014 Author Report Share Posted April 29, 2014 I sent my housing off to be checked for cracks. I hope there isn't one. I have 2 spare PMIII also with unknown past. One I think just needs an accumulator. But I can't be sure. Quote Link to comment Share on other sites More sharing options...
Heartbeat1991 Posted April 29, 2014 Author Report Share Posted April 29, 2014 No cracks. So maybe the drip was a failed o-ring or just leaking out the top cover. I'll throw a little UV dye in the fluid so if it leaks again I can find the source. Quote Link to comment Share on other sites More sharing options...
mfewtrail Posted April 29, 2014 Report Share Posted April 29, 2014 No cracks. So maybe the drip was a failed o-ring or just leaking out the top cover. I'll throw a little UV dye in the fluid so if it leaks again I can find the source. Good to hear. Unfortunately, I've yet to come across a torque spec for the rear housing. Most service manuals/resources pretty much treat the unit as "replaceable" rather than listing detailed information on it. I would judge what to torque it by going off of the fastener size and the standard amount of torque an aluminum part w/ that size fastener typically receives. Besides the housing itself, it is possible that the check valve in the housing could leak. I have no idea if that part can still be found, but I know I can provide you an old part number for it. Quote Link to comment Share on other sites More sharing options...
Heartbeat1991 Posted April 30, 2014 Author Report Share Posted April 30, 2014 I took the check valve out. I will replace the 2 o-rings on it and try again. I should be able to plug this assembly in and power it up without bolting it to the firewall or attaching lines, right? At least that way I can see the back of the thing while it's pressurized. Maybe then I can see if it's leaking and where. As far as I know, unless the pedal is pressed, there shouldn't be any fluid pushing out the ports to the wheels, right? Quote Link to comment Share on other sites More sharing options...
Heartbeat1991 Posted May 2, 2014 Author Report Share Posted May 2, 2014 So, it is leaking from the accumulator. I have the Hydac unit. The o-ring does not seal in the same place as the original one did. Instead of seating against the outer surface of the housing, It goes down in, counter-sunk into the housing. So it's not sandwiching the o-ring, the o-ring just sort of pinches between the nipple of the accumulator and the inside of the housing. Anyone else have this problem? Quote Link to comment Share on other sites More sharing options...
55trucker Posted May 2, 2014 Report Share Posted May 2, 2014 Here are a few of the torque specs as well an exploded view of the *dreaded* PMIII, I thank Christ I didn't order this when we purchased the car. Quote Link to comment Share on other sites More sharing options...
mfewtrail Posted May 3, 2014 Report Share Posted May 3, 2014 So, it is leaking from the accumulator. I have the Hydac unit. The o-ring does not seal in the same place as the original one did. Instead of seating against the outer surface of the housing, It goes down in, counter-sunk into the housing. So it's not sandwiching the o-ring, the o-ring just sort of pinches between the nipple of the accumulator and the inside of the housing. Anyone else have this problem? I have a Hydac unit on my Black car and haven't had an issue with it. Did you take any photos of your accumulator while it was off? I possibly have old pictures of mine before I installed it. I could search for it and then look to see if ours have any noticeable differences. Quote Link to comment Share on other sites More sharing options...
Heartbeat1991 Posted May 3, 2014 Author Report Share Posted May 3, 2014 It's not even back on the car yet. The whole master is on my work bench. I will take pics tomorrow of both the accumulators and the housing. Quote Link to comment Share on other sites More sharing options...
Heartbeat1991 Posted May 3, 2014 Author Report Share Posted May 3, 2014 It turns out the Hydac unit has a shorter nipple on it. The o-ring on the original accumulator went further into the housing and seated between a collar on the housing and a collar on the accumulator. The Hydac one doesn't have the same length or collar on it, so the o-ring isn't seating at the bottom of the housing. Quote Link to comment Share on other sites More sharing options...
mfewtrail Posted May 3, 2014 Report Share Posted May 3, 2014 Can you post a picture of the accumulator? Quote Link to comment Share on other sites More sharing options...
Heartbeat1991 Posted May 3, 2014 Author Report Share Posted May 3, 2014 New Hydac Accumulator: Old GM accumulator: Rear Housing : Quote Link to comment Share on other sites More sharing options...
mfewtrail Posted May 4, 2014 Report Share Posted May 4, 2014 Not certain if it's the picture, but that o-ring looks to be rather loose on there. I don't know if the length of my hydac accumulator is any different but I'm curious enough to almost want to remove it and check now. Quote Link to comment Share on other sites More sharing options...
Heartbeat1991 Posted May 4, 2014 Author Report Share Posted May 4, 2014 Yeah, I swapped the o-ring for another one. I'll power up the master cylinder today and see what happens. I put some teflon tape on there too. Quote Link to comment Share on other sites More sharing options...
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