Here's a question for you all.Anyone bypassed the ABS.I don't want to remove it entirely for several reason but I wish I was totally in control rather than have a computer thinking for me.I'm so old when i started driving most cars had cable operated drum brakes!!When I did the C5 conversion on the front I took it out and stood on the brakes and the fronts locked and flat spotted!Then the abs light came on for a couple of minutes and then went off.Before the upgrade my brakes were so bad I couldn't understand how GM could sell a car like that.Reading these forums apparently I'm not the only one and I,like some others am wondering if it's an inherent abs problem.What's your thoughts?

 

.....my comments go back to the previous posts in this long thread which i hope to keep going as these brake problems come up often and until "there is a cure"....gm wouldn't sell a car with crappy brakes off of the assembly line nor am i aware that there was any recall on the particular abs units used in c-4's...

.....you may have read in my previous posts that i have replaced everything in my system that checked to be defective or just ready for replacement due to maintenance and still the fred flintstone brakes remain....

...there was a part in the threads that dealt with the friction "number" (coefficient) of the pads but, when ya go to the average parts house and they sell you stock street pads, they should damn well stop your car!.....no other car i have ever owned had me asking what type, etc etc......and that includes my 74 and 81 vettes....

.....reading these posts, most all whom had ventured out to solve this crappy brake problem and problem with hard pedal but good m/c and boosters, and calipers, have replaced just about everything EXCEPT the abs pump..

....pcolt had crappy brakes and he replaced his and there was little if any change at all!..a lot of work for no return!.....he finally threw in the towel and j55'd the car and it was over...

....do the internals of the standard (stock) calipers wear out in some way w/o leaking?......does the abs have a maintenence function that nobody told us about?...who knows?...

.....i heard many many years ago that when you change out your pads, you must change out your calipers!..i don't (and didn't) believe it then nor do i believe it now!...however it is to note (jokingly) that since c4'ers are having so many brake problems, they are just about doing that with the changeover to 55's!..ugh!...

....if you eliminate the abs i don't see any difference in the results you are now getting except that you will have no abs capabilities (of course!)..

....unless the abs is a major contributing factor in low fluid output/distribution to the calipers or similar, i believe it would be an excercise in futility...

 

DaMailMan, before you go postal, try this idea.

Stick a 1984 master cylinder on there. It has the smallest piston size of any C4. It will bolt up to your booster fine. You will need to have enough flex in the front brake line to attach it 2" further back on the master cylinder though.

An 85-87 m/c would also help, but not as much.

Whatever is causing it, this will give you 35% more leverage to all fours at the expense of more pedal travel. The 85-87 will give 15% more leverage.

 

..you )(*&%%*^ (grin) why would i go postal?...i have a high pedal and very strong legs from years of weight training and martial arts so, leverage or "push" on the pedal may not be the answer.....wadda ya think?....would love ta find a good used one or one that someone didn't "want"....

 

Ok then, disconnect your brake booster and then see how well you can stop.

The piston ratio gives leverage. The pedal gives leverage. The booster gives leverage. The J55 upgrade gives leverage.

 

.... ...(i am not fighting with you in this thread )..i have disconnected the booster and i have no noticable brakes at all!...now, to find someone that wants to part with a mc!........what does the 84 mc look like?....does it look like the 81 or similar to the 87 (single or dual)....
EDITED; when someone upgrades to 55's, their brakes improve w/o the extra "leverage" and they don't change out the m/c......i also do realize the additional contact area between the stock and upgrade 55's.....soooooo..?

 

That's PRECISELY what changes when upgrading to J55s. And it only helps the fronts too.

 

 

...??....wait a second...i can "jump" on my brake pedal with both feet and still have crappy brakes...disconnection of the booster as previously stated yeilds virtually no brakes...we are taking about a master cylinder here....you have infered that the changing of the master cylinder MAY yeild better braking power due to "leverage" on a stock system...however, if the only thing changed out when upgrading to 55's are the calipers and rotors with the master cylinder remaining "intact", how then will the master cylinder make a difference on a "stock" braking system with the standard brakes and rotors remaining intact?..the only thing that is usually changed out on an upgrade (excluding pads) are at the wheels whith reported substantial gains in braking power....follow?

 

Smaller piston deliever more PRESSURE to calipers (not leverage, there is no mechanical link between the two). A smaller piston also delivers less volume - hence the reason you need to push it further.

The only way to get more leverage is trhough changing the pivot point on the brake peddle itself.

Hopefully this week I can see how my new master cylinder plays into the effect of these brakes.

Again what I have done with my brakes is: Removed the ABS unit; removed the master cyliner; and changed the pivot point - brakes are still less than good in my book.

What I have now is a VERY spongy feeling peddle and all lines have been evacuted using a vacuum pump system - so no air is present. My thought is the spongy, long travel feel is due to the increased leverage (at the peddle) with the small piston in place. The new MC I got is a 1.031 bore, and should increase the volume (decrease peddle travel) and make the peddle feel better and hopefully resolve the poor brake issue as well.

If this does not work, I may purchase a gage to check individual pressure at each caliper to see what they are getting. Something like that might show an inbalance of pressure. MANY racers use proportioning valves, as do many OEM cars - but these cars have nothing. Perhaps the rear brakes are virtually useless......I can say I have only replaced my back pads 1 time in the last 8 years - and there are MANY MANY MANY 100+ MPH stops on them. The fronts have been changed several times.

I have a feeling our capiler design is pretty crappy and that is part of the problem - again time will tell; I have eliminated nearly every possible variable from the system.

 

...i follow what you are saying however, i cannot stop thinking about what seems to go "bad" on c-4s that cause the brakes to be this crappy...i understand the leverage effect and did so from the beginning in regards to the pivot point on the frame for the brake pedal...however, if the brakes worked fine from the factory, what seems to cause them to become so $hitty "down the road" with the only typical fix being a "55" upgrade?...they would not have been able to market the car with the brakes in the condition that they wind up being in........i think what i am looking for is the actual solution using the "stock" parts with the reason why the brakes in c-4's keep going "south".....your text is well accepted..

 

Nothing wrong with those calipers Ski_dwn_it, other Australian cars use simular PBR and Repco calipers and same PBR pads with no issues. Not the booster either, a good amount of Australian made cars use the same PBR booster (Ford Falcons and VR Holden Commodores) and they both stop fine. (i know it is the same booster cause i just bought the parts for a Falcon booster to rebuild one from another 94 Corvette)

Im sure when these cars left the factory they stopped fine, so no idea what has changed to prevent that.

 

If the J55 calipers are the solution (how do we know this for sure?). Then the problem lies in the caliper design as I expressed before. Perhaps the casting becomes "bulged" or looses its shape and causes piston bind, but I rebuilt mine last year and they seemed to come out pretty easy and also push back in without too much pressure.

What specifically is different with the J55 calipers? Are they bigger or smaller.....or what? Will they work with a 15" rim?

 

^^^^^^^^^^^^^^^^^^^^^^^^
If the J55 calipers are the solution (how do we know this for sure?).
***i would surmise that is answered when the only thing changed out on the upgrade are the calipers and rotors and maybe pads...whack in a store bought set of generic pads and the brakes are "fine" again....i understand the larger surface area on the rotors and the caliper pistons.....so, the problem leans to what is at the wheels.......

 

Good points case.....

have the people that have been experiencing problem tried changing their rubber lines to the calipers? I do recall reading in here somewhere that people went to stainless lines with no improvement......mine are just the stock rubbers, so that is something to consider.

What are the J55 calipers? Where did they come from (new vettes?), I am not familiar with their name - can you explain.....and will they fit a 15" wheel?

PS: Case I got to visit the Holden Austalia plant last year at this time and got to see some of the "secret" cars they were going to be launching. We make internal engine component for the cars you mentioned above.

Very beautiful country you have - loved everything EXCEPT the plane ride. 28 hours of fly time - ONE WAY! They had to practically drag me back on the plane for the ride home. If I did not sink like a rock in water; I was considering a boat home - but that would have even taken longer. You need to float a little closer thisa-way!

 

Mine has a proportioning valve and I just changed the bias spring in it.I agree about the rears.Even if you had a 50/50 set up just comparing the swept area the fronts are doing four times as much work.Did you pull your abs unit out or just repipe around it?

 

Pulled it out and reran all new lines.

 

^^^^^^^^^^^^^^^^^^^^^^^^^^^
have the people that have been experiencing problem tried changing their rubber lines to the calipers? I do recall reading in here somewhere that people went to stainless lines with no improvement......mine are just the stock rubbers, so that is something to consider.

***if you read one of my earlier posts in this thread, you will find what i replaced and yes, i replaced my flex lines with s/s......

 

.....same as i

 

No ****. Smaller piston = more hydraulic advantage = more leverage.

Your car does have a proportioning, it's accomplished by the combination valve in the master cylinder. It reduces rear line pressure the harder the brakes are pushed, and the weight transfers towards the front tires. If you removed the combination valve, you'd probably lock up your rear brakes first.