I have an '89 with the J55 big brake setup. Recently my car had spongy brakes. When I checked the fluid level, I found the front level completely low, down to the bottom of the cup. The rear cup overflowed when I removed the lid. I have the Doug Rippie brake bias spring installed. Could this be the problem or do you think my master cylinder has developed an internal leak and need new O rings? Thanks for the help.

Edit: I have recently replaced the front lines with SS Braided lines. I also removed all old fluid from reservoirs and replaced with fresh, then flushed and bled the entire system once. Brake light is on and pedal is spongy.

 

If your reservoirs where correctly filled to the "FULL" line when you did the bleeding and fluid replacement....and now the fluid is out of the front reservoir..you either have a leak coming out of the back of the master cylinder where it connects to the power brake booster...or you have a leak somewhere in your front brake system. Because the fluid has to be going somewhere.

QUESTION: When you did the fluid change out and bleeding...did your brake system ever feel correct?

You still have air in the system to allow the light to come on. And depending on the method you are using to bleed the brake system. It may need to be bled again. I use a pressure bleeder that has a fixture that attaches to the top of the reservoir and I can force fluid through the brake system under pressure...which is rather high due to the ABS system. I believe I pressurize my tool to 20+ psi. The reason I am mentioning this is because when you thoroughly drain the system and allow the master cylinder to get air into it...you have to get this air out...which means you have to be able to force the air through your ABS unit. Using the "old" pump up the pedal and crack open the bleeder...might not work because you might not be able to move the bubble ir air out of the system due to the way your brake lines can hold air back where they are secured to your ABS unit behind your drivers seat. I can not comment on using a vacuum bleeder and sucking the fluid out of the bleeder... because I do not have one...maybe someone else can comment on that type of bleeding procedure.

When I do a brake system "refreshing" much like you have done...and I allow air into the master cylinder and the lines are free of old fluid and cleaned out...I can EASILY use 2 to 3 quarts through the entire system to make sure the air is out. And then...the next day...I will bleed it again...and while doing the bleeding process...I use an air hammer and light shock/vibrate the frame. I do not damage anything...I am using the shocking effect so that I can get any bubbles of air that have attached themselves to the inner walls of the brake lines to release...much like you tapping the side of your glass of "Sprite" to release the bubbles of carbonation. I also tap on the calipers with the end of my screwdriver...to do the same thing...trying to shock "things" to get the bubbles of air to move out of the system while I am pumping the fluid through the system. I have found...in some cases...when the system was dry and cleaned out...repeating the bleeding procedure the next day will often times show some more air getting out. I do not know why because I have done the bleeding procedure to the best of my ability...but it seems there are very, very,very small bubbles still in the system...that collect together to create a much larger bubble...that will now come out. This does not occur all the time...but I do not take chances and I ALWAYS re-bleed the system.

DUB

 

yes, if the fluid is transferring from one cup to the other, the MC internal seals are l;eaking past the plunger and being forced out of one back to the other...internal bypass.

rebuild, replace.

 

I went ahead and bled the front two lines again which solved my brake light and spongy pedal problem.

This does not take care of the master cylinder problem though. I suppose it's time for a rebuild. But brakes do feel great now.

 

I have an '89 with that has been upgraded to C5 front brakes with the exact same problem;
http://forums.corvetteforum.com/c4-t...-89-coupe.html

I replaced my M/C with no effect at all! Don't waste your time and money on this as it will not solve the problem! The new, not rebuilt M/C was having the same front to back fluid reservoir issue. Very strange.

I think the problem is with the antilock brake module and hardware found in the storage compartment behind the drivers side seat. I've bleed and rebleed several times and my brakes seem to work great.... Although I still haven't figured it out?

 

Yes I thought that would solve the problem but it didn't! Any other ideas??

 

Do you have a DRM bias spring installed?

Now that I think about it, isn't 89 the only year there were two separate cups on the MC?


I know that earlier cars had one cup on the back with a tube to the front.



Later C4's have a large reservoir that covers both.


I suppose if I changed to one of those, I wont notice the problem anymore.

 

Here is my 91 when I first got it home. Looks like dual cups for that year too.

 

My 87 came with 1 cup, but I converted to the 2 cup simply because I hold more fluid in reserve (for many reasons) and the 2 can be easier to ID which system has a leak if one is low.
Not sure where to get the single cup cross-over pipe...if you wanted to go back to a 1 cup system to solve the back-flow issue. Is that why GM did the 1 cup I wonders? nawww

They'd fix it right if they were aware of an annoying issue like this.

 

Yes I have a DRM bias spring installed in the new M/C. But I had this strange issue in the original OEM M/C before I installed the DRM spring and the new M/C??