I read all 11 pages but still couldn't find the size of the piston in mc

 

.....ok, humnnn...sorry 'bout that!.(it was 6-8 months ago) .however i know that there is a recent post on the piston sizes as mentioned in/by a previous poster....do a search using the forum search engine and you should find it...

..edit; i just found it, try the engine and you should too!

 

whats that supposed to mean?

 

I think it's about 0.93" on your vette. 85-87 was about .875" and 84 was much smaller than both.

I haven't driven an 84 hard, but I would expect the pedal effort to be much much less on it.

 

.....ck your pm's....

 

Since the 11 pages of this thread are intriguing, thought I would chime in with info on our car.

100k miles on 1994 LT1 coupe, JL9 brakes (standard). 100% stock car.

Original brake booster with new check valve, which 'tests' good (holds vacume for 2-3 pedal pumps and no hissing) -- engine maintains vacume of about 20"/mercury at idle.

Original master cylinder and brake lines (both hard and flexible).

all new OEM/PBR brake pads & caliper rebuild kits (all 4). Only RF caliper had slightly tight pistons, all other where perfect.

Numerous manual 2-person brake bleedings following 1994 FSM sequence -- MC prime pipe via ABS bleeder, RR, LR, RF, LF. Started with Castrol LMA DOT-4 brake fluid and finished with GM brake fluid (DOT-3).

New GM OEM rotors (12"?) with proper break-in braking to 'deposit' brake pad material on rotors.

And after all that, the brakes are still only so-so and still make me slightly nervous, albeit generally acceptable unless a panic stops is required. Thankfully they are solid and consistent and I am sure there is no air in the lines. But whereas they will stop the car in a reasonable distance, they are nothing like the brakes on our 2000 Vette and TA (which would put you through the windshield without a seatbelt).

Based on all the posts, my corrective approach may be as follows:
1. try different bleeding sequence (FSM may be incorrect)
2. replace flexible brake lines to slightly improve the brakes
3. replace hard brake lines with slightly larger ID if available
4. replace master cylinder with OEM or NAPA stock unit

I offer the following lessons learned so far to others for their challenges:

1. The C4 brakes/abs/asr systems changed frequently throughout the years, so equal comparisions are difficult at best

2. Review bleeding sequence and assure it is correct for your year -- if possible verify via multiple sources.

3. DOT-4 brake fluid is not better than DOT-3, just different -- and might be causing some of the problems. DOT-4 is thicker and more caustic than DOT-3, which will slow response, trap more air, and possibly damage ABS units -- along with retaining more water over time which can result in a lower boiling point and a spongy pedal).

4. All brake pads are not created equal -- The PBR pads are 'semi-metallic', but AC/Delco also offers 'durastop', then there are ceramic pads, along with various aftermarket pads of varying compositions. Did you ever installed a inexpensive set of aftermarket pads and then replaced them with OEMs because they squealed? Different pads are going to react differently, albeit I agree they should all stop the car better than most C4s are presently stopping.

Respectfully submitted,

 

^^^^^^^^^^^^^^^^^^^^^^^^^

Since the 11 pages of this thread are intriguing, thought I would chime in with info on our car.

100k miles on 1994 LT1 coupe, JL9 brakes (standard). 100% stock car.
***80k on my 88

Original brake booster with new check valve, which 'tests' good (holds vacume for 2-3 pedal pumps and no hissing) -- engine maintains vacume of about 20"/mercury at idle.
***same here except applied vacuum from an external source and checked good along with the "pedal pump" test...
Original master cylinder and brake lines (both hard and flexible).

all new OEM/PBR brake pads & caliper rebuild kits (all 4). Only RF caliper had slightly tight pistons, all other where perfect.
***stock calipers and new stock pads and new rotors...

Numerous manual 2-person brake bleedings following 1994 FSM sequence -- MC prime pipe via ABS bleeder, RR, LR, RF, LF. Started with Castrol LMA DOT-4 brake fluid and finished with GM brake fluid (DOT-3).
...multiple complete flushes with dot 3 fluid and again with synthetic (which remains)...
New GM OEM rotors (12"?) with proper break-in braking to 'deposit' brake pad material on rotors.
***new rotors here too...

And after all that, the brakes are still only so-so and still make me slightly nervous, albeit generally acceptable unless a panic stops is required. Thankfully they are solid and consistent and I am sure there is no air in the lines. But whereas they will stop the car in a reasonable distance, they are nothing like the brakes on our 2000 Vette and TA (which would put you through the windshield without a seatbelt).
***i too have absolutely no air in the lines but, a rather hard pedal and the crappiest brakes on the planet..no kinks or bends in the lines, s/s flex lines, no leaks whatsoever...while the hard pedal seems to indicate a bad booster, my booster cks ok as mentioned in previous posts..

Based on all the posts, my corrective approach may be as follows:
1. try different bleeding sequence (FSM may be incorrect)
***i used what gm has stated in their HELMS manual and used both speed bleeders as well as 2-man bleeding..2. replace flexible brake lines to slightly improve the brakes
3. replace hard brake lines with slightly larger ID if available
***if larger hard lines were needed, gm would not let their cars roll out for sale w/o them...when the cars came off of the line the brakes were good so, what changed duriung time?..the only thing nobody changes is the abs. however, member pcolt did his and it had no effect...
4. replace master cylinder with OEM or NAPA stock unit
***had one originally and just replaced it (defective) with one 2 weeks ago...
I offer the following lessons learned so far to others for their challenges:

1. The C4 brakes/abs/asr systems changed frequently throughout the years, so equal comparisions are difficult at best
***but most of the "80's" c-4's used the exact same components and eflect the same part numbers and yet, the brakes remain crappy...

2. Review bleeding sequence and assure it is correct for your year -- if possible verify via multiple sources.
***has been done...

3. DOT-4 brake fluid is not better than DOT-3, just different -- and might be causing some of the problems. DOT-4 is thicker and more caustic than DOT-3, which will slow response, trap more air, and possibly damage ABS units -- along with retaining more water over time which can result in a lower boiling point and a spongy pedal).
***agreed but as for me, i attained the same performance with dot and synthetic...

4. All brake pads are not created equal -- The PBR pads are 'semi-metallic', but AC/Delco also offers 'durastop', then there are ceramic pads, along with various aftermarket pads of varying compositions. Did you ever installed a inexpensive set of aftermarket pads and then replaced them with OEMs because they squealed? Different pads are going to react differently, albeit I agree they should all stop the car better than most C4s are presently stopping.
***the stock generic pad for STREET driving should effectively stop the car w/o having to go to ceramic, or carbon, or whatever..

 

Hi Da Mail Man,

thanks for the comparision reply, it should help us both as well as others.

A couple of thoughts on your reply...

1. you mention now using synthetic brake fluid -- I thought all brake fluid was synthetic, might you mean silicone (i.e. DOT-5)? If so, I thought silicone was very bad for the brake system seals and ABS units.

2. My reason about replacing the hard brake lines is they are suposedly double-walled. So, the inner wall could give way due to corrosion/age. However, the outer wall is probably thicker and would last longer. If there are 'leaks' between the inner and outer walls, it might account for some of our problems by preventing all the MC pressure from reaching the wheel calipers.

I was talking to a car nut/buddy of mine tonight and he came up with the same idea as one of our fellow forum members. Try putting a pressure gauge at each wheel and see what the pressure is per wheel and if it is the same/close side-to-side and front-to-rear.

Another thought we discussed is that whereas the C4 brake boosters might not be leaking, they might not be adequately sized to do the job on the C4's, especially the plastic single-diaphram versions.

So as time and age adversly affect the internal diaphram and seals, and the engine vacume falls off, and perhaps small vacume leaks develop, the barely adequate booster starts to fall quite short.

I wonder if anyone actually tested and has the results of a brand new C4's vacume at idle, to which we could compare our current numbers. I would love to know if my 20 reading is at or under what it was new.

I also wonder if anyone with problem brakes, has tested the vacume at cruising speed to see if the vacume stays in the good range (15-20+) and if that vacume level is retained within the vacume system and maybe even the booster once the engine drops to idle during braking.

 

Its interesting to look at that comparison because it reads like a mirror image of my 94s problem. I did all of that stuff and of course found my solution when I started this thread.
Mailman, I breezed back through these pages looking to see if you have actually had someone hook up a tech 2, take it through all of the valve activation sequences and tests and check it for codes. Perhaps I missed it but I didnt see anywhere that you state that was done. Was it?
Roy

 

^^^^^^^^^^^^^^^^^^^^^^^

1. you mention now using synthetic brake fluid -- I thought all brake fluid was synthetic, might you mean silicone (i.e. DOT-5)? If so, I thought silicone was very bad for the brake system seals and ABS units.
***not as far as i know (synthetic). the previous dot 3 fluid said nothing about being synthetic. the stuff that is in there says it is....i am also VERY aware that silicone brake fluid is BAD for the system

2. My reason about replacing the hard brake lines is they are suposedly double-walled. So, the inner wall could give way due to corrosion/age. However, the outer wall is probably thicker and would last longer. If there are 'leaks' between the inner and outer walls, it might account for some of our problems by preventing all the MC pressure from reaching the wheel calipers.
***i wouldn't think so that this is a concern or would matter. as far as my situation and if you read the 11 pages in this thread, that is NOT MY problem. cars are on the road many more years then mine and most others and only if damaged, would they need replacing. i HAVE a lot of fluid going through the lines and also coming out the caliper bleeders.

I was talking to a car nut/buddy of mine tonight and he came up with the same idea as one of our fellow forum members. Try putting a pressure gauge at each wheel and see what the pressure is per wheel and if it is the same/close side-to-side and front-to-rear.
***this was thought of some time ago and i believe in this thread or similar and the problem is finding the gauge and adapters to achieve this. in Florida, they used to have inspection stations near me and one would place there car on the rollers that would spin...you would apply your brakes and it would measure braking resistance at each wheel. if i could do that, i would. so, this leaves me and some others back to where they started. i was however thinking about using an infrared temperature "gun" and maybe making a comparison as to the heat on each wheel but, that would provide little in revealing brake torque "balance between each of the wheels.

Another thought we discussed is that whereas the C4 brake boosters might not be leaking, they might not be adequately sized to do the job on the C4's, especially the plastic single-diaphram versions.
***no way..as i have stated in this thread many times, gm would not let their cars off the line with inadequate braking systems (ROTORS, PADS, CALIPERS, M/C'S, BOOSTERS).besides, they came off of the line with GOOD brakes that somehow turned $hitty over time. forum members have replaced entire component assemblies (abs included) except hard lines and it made no difference causing them to do the brake package upgrade.

So as time and age adversly affect the internal diaphram and seals, and the engine vacume falls off, and perhaps small vacume leaks develop, the barely adequate booster starts to fall quite short.
***engine vacuum has remained generally the same with mine and other forum members. at one point i gave plans to another member to make a vacuum reservoir for his brakes. the purpose of that was he was running a modified engine and the engine didn't produce a high enough vacuum at idle....either way, he tried it and it made no difference...i have 2 spare boosters here and all have passed as for holding vacuum.

I wonder if anyone actually tested and has the results of a brand new C4's vacume at idle, to which we could compare our current numbers. I would love to know if my 20 reading is at or under what it was new.
***not an issue here for the most part as most new and "used" c-4's would be about the same. even if the "used" c-4 was lower, a person could increase the idle or place their foot on the gas and release it (which will bring the vacuum up) and throw the car in neutral and apply the brakes which would simulate "a higher vacuum) wile coasting to check differences. now, the brakes may be just a little bit better because it doesn't have the rotating assembly torque to contend with, only the mass/momentum of the vehicle.

I also wonder if anyone with problem brakes, has tested the vacume at cruising speed to see if the vacume stays in the good range (15-20+) and if that vacume level is retained within the vacume system and maybe even the booster once the engine drops to idle during braking.[/QUOTE]
***see above

 

.....thanks for the reply...no, i have not had a tech 2 on this unit..(cost?...where? (except a dealer!)...i think the abs units for yours and mine are different..(88 obd1 - 94 obd2) i also know that the unit would not throw a code (visible). the unit however does self check...refresh my memory, what corrected your problem?

 

I was talking to a local guy, he also has a 93 Vette with only 30k miles on it. He stated that he had the same problem as I do and the way they were able to solve the issue was....................... I need a drum roll..... by resetting or clearing the computer.

My buddy works for a GM dealer ship and in a week or two I will have him take the Vette and work on it the including resetting the computer and all that good stuff. We will see.

HTH
Prasad

 

......if there is a computer to be reset, it would have to be an ABS brake computer and it would have to be done by a shop....i think you are obd2 and i am obd1....killing the battery power to the car will not reset any brake computer that i know of.......let me know how you make out and run my scenerio by him and tell me what he says....

 

FYI, in 1992, ASR was added to the brake system, so what works for 1992+ may not work for earlier years, but we can hope nonetheless.

Also, only the 1996 C4's are OBD-II. Some C4's (e.g. 94 & 95) have the 16 pin Data Link Connector (DLC) as used with OBD-II, but the system behind the connector is still OBD-I.

 

Which is exactly what I was referring to that fixed my 94.
Roy

 

.....you have obd 1 or 2?........did you have everything in your brake system checking good but still $hitty fred flintstone brakes?

 

Precisely my dear Watson.
94 models are obd1.
I replaced everything on my system, bled it a million times, nothing helped. ABS went through its check everytime, every test I performed inicated I should have had excellent brakes. But they were so bad I could not even hold the car on the line if I brake torqued it. And I was being outbraked by minivans on a regular basis.
You can go back and read the very first post in this thread.
I know my system is different than yours but if I was you after all you have been through I would certainly have it checked out.
Roy

 

.......holmes was a coke addict!.....i tis hard to believe that the abs has to be reset i some way which leads to my next question ; what causes the computer to go "out of whack" to necessitate it having to be reset and how often does it do it?.....only the obd1's, 2's, or both?

 

I just completed doing some part # analysis for our brake systems using a circa 2002 parts catalog.

I was very surprised at all the differences year to year and model to model.

This may play into why some brakes work great and others don't.

Brake Booster (there were at least six (6) different Boosters !!!):

earlier years = combo unit(s) including the master cylinder
1989 = AC/Delco # 178-509
1990-1991 = AC/Delco # 178-515
1990-1991 (LT5, ML9, ZR1)(J55) = discontinued (dual diaphram)
1992-1995 (LT5,J55) = AC/Delco # 178-523 (dual diaphram)
1992-1996 (LT1, J55) = AC/Delco # 178-534


ABS (/ASR) (there were at least 4 different ABS (/ASR) !!!:

1986-1991 = GM # 12506759
1992-1994 = GM # 12516323
1995 (LT5) = GM # 12516323
1995 (LT1) = GM # 12521971
1996 = GM # 12525023



Master Cylinder (there were at least 4 different Master Cylinders !!!):

1986 = AC/Delco # 174-830
1988 = AC/Delco # 174-831
1989-1991 = AC/Delco # 174-820
1992-1996 = AC/Delco # 174-828


So, is there any wonder that some cars have wonderful brakes and others close or far from it !!!

Further, I am sure some of the above part numbers have been discontinued or substituted, so even with new/replacement parts, there would be limited assurance of being able to replicate the original configuration and thereby the original, from the factory performance.

 

........other then the numbers of the parts being different, there is little on the specs of each item (not that the addition to this post is not appreciated!) such as the INTERNAL CAPACITY of the booster for example....

..........i am sure that part number changes may reflect engine compartment layout and positioning...i have used a m/c off of an 86 and an 88 and another later year which escapes me at the moment with no changes whatsoever...i have a listing of the bore sizes somewhere too.....would like to hear from someone whom had there abs "tech 1 or tech 2'd" and the before and after results, if any.....