Bob S

I have that classic problem.4 wheel disc (87 GTA), Hard pedal, All 4 rotors surfaced, M/C replaced, Rear calipers have GM sevice kit upgrade, PFCM pads, clean fluid, bleed thoroughly, Blood sweat and tears, but still brakes exibit no where near the stoping power that they should. Even if I where to two foot it I couldn't even get close to a lock up.I have read about people here having the same problem and they talked about replacing the brake booster. I was just wondering if anyone has gone and done this and solved there problems. If anyone has any input on a cure other than a total upgrade ( I would love to but limited $$ at the moment) please chime in. Much thanks in advance

breathment

maybe u should think about upgrading to 1LE brakes... see the sticky thread.

AFrikinGoodTime

Ive replaced my booster. It went bad- hard pedal just as you stated. Now its Much better but I still get a hard pedal once in a while at low rpm's once in a while mainly when I first start the car and back it out of the garage. Once the R's come up so does the vacuum and then it works fine. Sometimes it will happen in heavy stop and go traffic, when car is mainly at idle.

This problem is indigenous to high profile cams, however , mine is stockprofile and I don't have any vacuum leaks or blockage.

Does this sound familiar to anyone?

urbman

Never had a problem with the booster, just a bunch
of problems with old vacuum lines...

This months carcraft seemed to cover brake boosters
and line pressure in fair detail...

Momar

Hey Frikin. I have been told that there is a valve in the vacuum line for the breaks somewhere that only allows the vacuum to travel one way and allows you to build enough vacuum to power the breaks at idle at least with the stock cam. Disclaimer: I don’t have experience here, this is just what I was told. But anyway I think that would be something to look into because if what I was told was right then if that valve was leaking on your car that could be what causes you to have a lack of vacuum to your breaks at idle.

Ben

AFrikinGoodTime

Thank you Ben. I see that valve and will check for one way flow.

Momar

Let me know how it goes.

Ben

AFrikinGoodTime

I checked the flow valve and gasket into the booster and both are brand new and working properly. also free of any particles of debris that would hamper a good seal. I also applied a bit of silicone o-ring type grease to see if that would help any and no difference.

I checked the booster vacuum pressure before and after and am reading about 10-10 1/2 ins. vacuumof max. hold pressure. It will slightly pump up higher but then self bleed back down to this.

There is another guy posting about booster pressure right now that claims he gets about the same (roughly 11 ins of vacuum).

I am trying to determine if maybe my new booster is bad. Does anyone Know factually what pressure the booster should hold at?

When the rpm's are up the brakes work great.Again its only at idle and there are absolutely/positively no vacuum leaks.(I sound like O.J.)

urbman

For what its worth...
The car craft guys measured their booster ...
"Held 18inches of vacuum easily"

My 95 Helms manual (4ht gen) indicates that the
rod extension measurement should be done with
25 inches on the booster...

Sorry Icouldn't find any mention of the subject in my 90 manua...

AFrikinGoodTime

Thank you for looking Urbman, I check my manual also and no info.

Tom84L69

i changed mine because it was damaged from an engine fire. what a pain in the ***, those nuts are hard to get at.

Bob S

Has anybody priced a new booster? I was away for the weekend and was glad to see all the responses. Gonna do a little messing around with the vac pump tomorow and see what I come up with . I'll keep you guys informed. Thanks again

Bob S

Well now I'm totally confused. I tested the booster with my mighty vac and it would pull down to 20in and hold just fine. Tested the check valve for one way operation and it seems fine. Measured vac going to the booster and its 20in at Idle. Also tried with vac pump holding at 20in pumping the brakes and Vac would bleed down to 0 after third pump (seemed correct to me). If it was a prop valve wouldn't I still get full pressure to one end (front or rear) and be weak on the other? I also have an IROC with disc/drum setup and It is a total difference in brake performance (It will actually stop). I know the 4 disk setup should be the better of the two but I'm running out of things to replace. Oh well the next step might be replacing the carbon metalic pads with a set from EBC or Hawk. I will keep every one posted if I do find a cure.

Bob S

Just Edited last message and moved ttt

Bob S

Just Found something interesting. This was posted last year by Apeiron

Master Cylinder Differences
I just came across this today, and thought it might shed some light on the reasons for the various M/C sizes for those swapping disc and drum rears, or doing the 1LE conversion:

Number: 84-88

Section: 5 (V)

Date: Mar., 1984
Subject: REDUCING BRAKE PEDAL EFFORT ON CAMAROS WITH FOUR WHEEL DISC BRAKES

Model and Year: ALL 1982-84 CAMAROS
TO: ALL CHEVROLET DEALERS


The higher brake pedal effort associated with 1982-84 Camaro cars equipped with four wheel disc brakes may be a source of some customer comments. The J65 brake system was designed with a low pedal ratio for reduced free travel and a firmer and higher effort pedal for the high performance buyer. Owners of J65 equipped Camaro cars not sharing this interest and desiring reduced brake pedal effort can be accommodated by replacing the original production master cylinder assembly with the appropriate J50 master cylinder unit specified below.

MODEL YEAR / ORIGINAL J65 MC / REPLACEMENT J50 MC
1982-83 / 18009370 / 18009367
1984 / 18010574 / 18010572
END
_________________________________________________

I wonder if changing to the J50 master cyl would offer an inprovement. Has any one tried this? Might explain why my 87 Iroc (disc/drum) stops so much better than my 87 GTA (disc/disc). Of course I would have to use 87 PN master cyl's

AFrikinGoodTime

Update on what I've found out about vacuum pressure. The vacuum at idle should set at aprox. 16ins., mine was at 8 while at idle. Found a little slit in the diaphram of my EGR. I replace it and the brakes feel great. Again my vacuum leakdown test of the booster is at 10 1/2 ins.- it will pump up higher but leaks down and holds at this.

Check your vacuum while the car is running. This was my first fault, I did a dry check from hose to hose the first time around and everything was showing 30+ins of vacuum. I thought the system was fine until I did a running test that revealed only 8 ins. of vacuum. Thats when I decided to check the EGR, etc...
Also, my computer never revealed any fault codes on this.

Bob S

Got a good 20in at idle and egr is fairly new also booster would hold 20in without leaking down (5 min). Gonna try the other mater cyl (J50) hopefully soon. Will keep every one posted. Just ordered a catgo cat so when I replace that I'm gonna try to replace the master cyl too.

99Hawk120

My ZZ4 pulls 18" of vacuum, I would think a weaker cam would pull more.

AFrikinGoodTime

Mines only a little V6, not alot of suction. Bought this car for handling purposes.

99Hawk120

Little V6s usually pull tons of vacuum. Small cams and badly restricted intakes usually does that. I think my 3.8L olds pulls almost 21".

AFrikinGoodTime

A 3.8 is not a little V6, A 2.8 is.