TBRTGP Posted September 5, 2020 Report Share Posted September 5, 2020 My ABS has hardly ever worked properly.. the Anti Lock light is almost always flashing.. now lately the brake system continues to run after i shut the car off.. so i need to yank the brake relay to get it to stop or it runs the battery down. Why does it do that? The brakes also sometimes make a chirping noise from near the master cylinder when i depress the pedal. Is there a reasonable way to swap out this system for a more recent GP or any GM vehicle ABS system? Quote Link to comment Share on other sites More sharing options...
Psych0matt Posted September 5, 2020 Report Share Posted September 5, 2020 If it’s still stock (and has the pm3 brakes) it’s basically a matter of time until they’re non functioning, at least safely. You can swap vacuum brakes in with some effort, but I was lucky enough to have bought my TGP with that swap already done when I owned it. TBRTGP 1 Quote Link to comment Share on other sites More sharing options...
digitaloutsider Posted September 6, 2020 Report Share Posted September 6, 2020 The pump is continuing to run because the relay has failed. It's been a long time since I've dicked around with PM3, but IIRC, those relays are out of production. Likely other shit is beginning to fail too. You can convert to vacuum brakes with some work. If you search around the forum, I believe @White93z34 did a writeup on how to convert. TBRTGP 1 Quote Link to comment Share on other sites More sharing options...
White93z34 Posted September 6, 2020 Report Share Posted September 6, 2020 I was going to but never got around to it. I'll have to come back to this thread and describe my lessons learned from converting my car when I have more time. Long story short... and this is just my opinion: The PMIII was a ill-conceived idea in the mid 1980s, and then we add 30 years of living next to a hot turbocharger onto that and its gone from a questionable system to flat out unsafe. It adds in entirely too many faults and fail scenarios that just shouldn't exist. On top of that critical components are just not available anymore. Believe me, I tried like hell to make it reliable. I stopped just short of making my own controller for it namely because the cost of a modern safe pressure switch that I needed completely eclipsed the cost of replacing it wholesale. TBRTGP 1 Quote Link to comment Share on other sites More sharing options...
55trucker Posted September 8, 2020 Report Share Posted September 8, 2020 Some time ago a forum member did this conversion, the usual approach is to remove the PMIII firewall adapter plate & install the regular plate that supports the vacuum booster/master cyl. Can't remember who it was but he didn't remove the adapter plate, instead he drilled it, did some light machine work/welding to it to accept a vacuum booster. If memory serves because he was in Europe he didn't have access to the needed parts so he improvised. The rear brakes lines need to be formed as the ABS system makes use of a single brake line that tees off at the rear wheels whereas the vacuum system makes use of 4 independent lines. TBRTGP 1 Quote Link to comment Share on other sites More sharing options...
White93z34 Posted September 9, 2020 Report Share Posted September 9, 2020 (edited) I've done it both ways. Doing a factory vacuum swap is a gigantic pain, but possible if you want to pull the dashboard apart and most of the engine bay. It also comes with issues of its own. the factory non ABS master is at a different angle to PMIII and comes VERY close to the turbo. I've thought about this and in my junkyard trips it looks like J and N cars of the era used the same master but angled up slightly, that may help the issue of it being close to the Turbo but it may also bring its own set of issues. never done it but its been on the back of my mind. Also you'll need to run 2 new rear brake lines. making absolutely sure to not get them backwards since you'll no longer be running a Front-Rear Split setup but a Cross- diagonal so the Front left needs to be on the same side of the master as right rear and front right needs to be on the same side as left rear. You can't get away with just one as the factory rear brake line is 1/4" or something like that and standard are much smaller. What I did on my Red Turbo GP was remove everything PMIII off the firewall and use a 4th gen F body booster and master. It has the advantage of also being Front rear split so you don't have to mess with the brake lines to the rear of the car and it can be done in a day or 2, not weeks. What I did, and I know others have done it differently I made an adapter plate of aluminum to bolt to the factory bolts then put my own holes in for the F body booster. You DO have to cut holes in your factory firewall plate for this. and in the future i'd do it a bit different and cut most of it away so I could access the booster bolts easily from the inside of the car I did have to cut and extend the pushrod from the booster so it was the same length as PMIII Was. Just cut and welded that. I considered threading the rod and putting a turnbuckle on it to get it proper. Now the fun part is the brake lines. Since we live in america getting metric fittings is a bigger pain then it should be. I changed everything to 1/4 fittings, took the front brake lines and put them into a t fitting, and then made a brake line to go from that to the master. For the rear I also changed the fittings to SAE but then put it into a reducer to get the size of the line down to fit into the master, again just made and extension tube to get it how it needed to be. Not the cleanest part of the install but it does work quite well. If I ever get around to working on TGPs again i'll be doing this same modification to my Black TGP as I fully believe PMIII is not fit for purpose at this point. I'll revisit the modification at that time and fine tune it then. Edited September 9, 2020 by White93z34 grammar TBRTGP and digitaloutsider 2 Quote Link to comment Share on other sites More sharing options...
55trucker Posted September 10, 2020 Report Share Posted September 10, 2020 It's not a fun job............. Quote Link to comment Share on other sites More sharing options...
jiggity76 Posted September 10, 2020 Report Share Posted September 10, 2020 14 minutes ago, 55trucker said: It's not a fun job............. Hey, you see my PM? Quote Link to comment Share on other sites More sharing options...
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