multiple bleeds, still no brakes after vacuum brake swap

[stockgp]

first, for those who don't know, i swapped the pmIII on my tgp to vacuum brakes

 

i've bled the brakes on my tgp MANY times now. still, i barely have the braking power to stop the car from a creep. i can't see that i'm leaking fluid anywhere, so i'm assuming i'm not sucking air back into the lines anywhere. this was a concern for me, as i ran 1-piece lines to the rear brakes and flared them myself. flaring isn't something i have a ton of experience with.

 

so, i'd like to hear suggestions as to what my problem may be, if anyone has any.

[19Cutlass94]

aside from the actual brake system part, like bleeding, the pads calipers lines etc etc, are all your vaccum lines hooked up? Does the engine have the correct vaccum to be running it?

[stockgp]

all vac lines are hooked up.

 

what do you mean by correct vacuum? do you mean pressure? if so, i have no idea. i don't have a vacuum gauge, nor do i know how much vac pressure it should have

[stockgp]

also, in my experience, when a vac line is unhooked the pedal is very firm along with no braking power. my problem is that the pedal is very soft with no braking power.

[BXX]

If you screw up a flare, it will cause that exact issue.. Go through an redo any flare that doesn't look exactly like ones on pre-fab line.. Odds are, the flare(s) are screwed up, causing only a certain percentage of fluid flow.

[19Cutlass94]

yes engine vaccum in PSI. The engine should have a certain amount of vaccum. If you dont have that vaccum needed, especially to run the brakes now that you have vaccum brakes, it will make a difference.

[BXX]

Soft pedal and everything was properly bleed, then the master cylinder is bad. Replace it with a new one... Also, did you bleed the master cylinder correctly??? If not, go and redo that, then rebleed all the lines in the correct order... Same issue, then get a new master cylinder..

[stockgp]

If you screw up a flare, it will cause that exact issue.. Go through an redo any flare that doesn't look exactly like ones on pre-fab line.. Odds are, the flare(s) are screwed up, causing only a certain percentage of fluid flow.

 

well, i'm going to let someone else do it, then. i know i'm not great with flaring.

 

 

what should the vac pressure be for a tgp?

 

i bench bled the master, but possibly not perfectly. i was a little...distracted whilst i was doing it.

[BXX]

well if you have soft pedal, then it's an issue with air in the system or a bad master cylinder...

[stockgp]

well, i can get a new master for like 38 bux. i'll give that a shot and hope i don't have to redo my flares

[z34duck]

get a new master cylinder and make sure you bench bleed it before installing it

[GOT2B GM]

yes engine vaccum in PSI.

 

Actually, vacuum is measured in inches of mercury.

[stockgp]

the gauges are in hg increments, no?

 

i'll pick one up when i get a new master cylinder. anyone know what the correct vacuum pressure should be

[GOT2B GM]

Yes. Mercury is Hg on the periodic table. Unfortunately I don't know officially what the vacuum should be, but I do have a boost gauge in my TGP....... I could see what it reads at idle if that helps........

[Chancho]

an aftermarket Vac/Boost Gauge will be your best bet to get, it will give you both acurate boost readings and accurate Vac readings in PSI and In/HG respectivly

[stockgp]

well, i'm going to get some aftermarket gauges eventually. i'm just wondering right now what would be an appropriate vac level for a tgp with vac brakes

 

matt, is your tgp still abs infested?

[GOT2B GM]

Yes it still has the PM3........that still works amazingly enough.

 

I have an Autometer boost gauge that is attached to the port at the back of the plenum (exactly where the brake booster vacuum line goes).

[GOT2B GM]

I know Kyle's Turbo Cutlass and Psychomatt's TGP are both vacuum brake equipped.......

[stockgp]

ok. i may be sending them some pms, depending on what happens with the new master and shit

[GOT2B GM]

cool

[Crazy K]

speaking for psychomatt's tgp, It is supposed to use 100% stock hardware front to rear from a donor car. I haven't crawled beneath to check, but the underhood looks correct.

 

I would recommend discarding the single line you have used.... and go with a 100% stock setup, as the OEM master cylinder was a split diagonal system with the opposite corners of the car in the same circuit. This means the if one circuit fails, you will still have opposing corners of the car providing braking instead of a complete failure. Having one line to the back may mean you either have your lines crossed resulting in incorrectly proportioned pressure and flow, or that you have mixed your circuits and defeated the safety feature.

 

start over on your lines, get some hardware from a donor etc etc...

 

the rear lines that used to link to the rear PMIII proportioning block and back are the same as the vac cars, so you can grab lines from there forward.

[Bake82]

I know Kyle's Turbo Cutlass and Psychomatt's TGP are both vacuum brake equipped.......

 

I think if I remember correctly my boost gauage at idle read around -17psi... Can't remember 100%, and I won't be able to find out until the Spring....Cutlass is sleeping for the winter.

 

 

[Schurkey]

also, in my experience, when a vac line is unhooked the pedal is very firm along with no braking power. my problem is that the pedal is very soft with no braking power.

Lack of vacuum causes a HARD pedal, not a soft pedal. There's no point in playing games checking vacuum--that's not the problem.

 

Several questions:

 

1. I don't understand what you mean by swapping to "vacuum brakes". What did you have before? Hydroboost hydraulic assist? Manual (no assist) brakes? I though vacuum-assist was standard equipment on all W bodies.

 

2. Is the pedal at the same height as it was before when making a normal stop? Or is it very low? (In general, and if there's no other guidelines: The brake pedal should be at the same height or higher than the gas pedal during a normal stop.)

 

3. Does the fluid level in the master cylinder go down over time? If air can get IN past a bad flare--fluid can get out. The resulting leakage makes the level in the reservoir go down. After ANY brake work, I perform a "sixty second test" which is to start the engine (so the power booster is active) then apply the brakes with medium force for 60 seconds, feeling for any dropping of the brake pedal which would indicate fluid leakage. Of course, there's no point in doing that until you've achieved a high, firm pedal to begin with.

 

4. You did remember that the flares on W bodies are not the old-style 45 degree double-flare, right? The W uses ISO bubble flares.

 

5. Any chance the rear brakes are way out of adjustment because you haven't used the park brake enough?

 

 

[mfewtrail]

Several questions:

 

1. I don't understand what you mean by swapping to "vacuum brakes". What did you have before? Hydroboost hydraulic assist? Manual (no assist) brakes? I though vacuum-assist was standard equipment on all W bodies.

 

TGP's(and some early W's) have a fully hydraulic(integrated ABS) brake setup called the "Powermaster III(aka Delco-Morraine ABS 3)." When it's functioning properly, the PMIII setup will stop these cars very quickly. One magazine test got some 112ft 60-0mph stops out of a TGP when it was new.

[stockgp]

ken, i have yet to see a w in a yard here that would be worth getting lines off of. might as well just go poke some holes in my brand new lines, you know? rust sucks.

 

anyhow, the pressure to the rear calipers would be the same regardless of whether or not i crossed the lines. i may defeat the opposing corner safety feature, but that would just mean the car would pull to the side that stil has pressure to both calipers. also, i can't possibly have mixed up the front and rear lines. the front line fittings are different from the rear line fittings.

 

kyle, i'll keep that in mind when i test my vac pressure