Hello all,

Everything was fine with my 2000 C5 coupe (21k miles, all stock) today at lunch, and then when I left to go home...the brakes felt normal for about 1/3 of the pedal travel, then lost braking pressure for the next 1/4 travel (spongy feel), and then regained their bite the rest of the way down. This problem continued all the way home. I bought the car only two weeks ago and it was my first time driving in 87 degree weather, but this was very unnerving to say the least. This shouldn't happen in a C5 when it's hot, correct? The braking is basically unsafe right now. Could a brake line have cracked while the car was sitting outside this afternoon? Any suggestions regarding the likely problem? The brake master cylinder level is between the minimum and maximum marks.

Thanks!

 

First off, you do not have a leak or break in the brake line.

If you had a leak at those pressures in a brake system you'd be in a tree somewhere already.

Most likely have air in the system somewhere, or maybe there was air in the ABS unit and it escaped after doing some ABS stops. You also might have old fluid with water trapped in it, the water boiled and now you have air.

Best bet is to get some decent fluid and do a bleed of the system.

You also could have pad taper but that would be inconsistent pedal at the top not really what you are describing but its still not a bad idea to check for. The C5 caliper will wear pads unevenly under hard braking causing the pads to taper, or wear on one edge more than the other. This leads to a long pedal and inconsistent braking.

Have you ever bled brakes before?

Have you ever changed pads before?

To answer the last part of the question, no the C5 should never do this, nor should any brake system on any vehicle.

Its something simple that will take you more time than money to fix unless it is pad taper in which case you'd need new pads.

I'll take the guess that when you bought the car the person before you installed new pads, bled the system, and failed to bleed the ABS unit. You got into some ABS stops and introduced air and old fluid into the system.

If this is the case you should see if you can bleed it with a Tech II to cycle the ABS pump and flush all of the fluid.

In the Roadracing forum there is a post by me about pressure bleeding with a Motive Power Bleeder. I'm told that they create sufficient pressure to push open the valves in the ABS unit so that would also work.

Let us know your experience level on what you've done before and it can be better explained what to do.

 

Spongy brake peddle may be many things:

1. vacuum leak
2. old brake fluid
3. pad taper
4. bent caliper braket
5. old warn out brake pads.

when was the last time you had a full brake fluid flush, not just bleeding, and changed your brake pads??

 

Thanks for the responses. I don't believe that the pads or brake fluid has been replaced, but I bought the car from the original owner (an older gentleman) who supposedly babied the car. Unfortunately, he is unavailable for a month so I don't know for sure. But his records only show oil changes (8 already!) and a new air filter. The car passed a MD inspection two weeks ago, which includes a check of pad thickness, so they should be okay and the problem is probably not pad taper. I may have gotten into the ABS unit once, but not yesterday when the problem started.

So is a brake fluid flush the best place to start? If so, I have replaced the pads with a mechanic friend on a Passat, but my experience is limited at best. So I've seen the bleeding process once. Basic questions, though: Do you need to remove the wheels to do this job, or can the wheels remain on the car (which brings up the tire pressure monitoring issue)? I assume that I'd need to buy a jack for the car and a Tech II system as you mentioned. Are two people required for the bleed with this system?

 

Car needs to be on a lift or 4 jack stands with all 4 wheels removed to flush the brakes.

 

If you've never done this before I might suggest a dealer...

Otherwise, like AU N EGL said, car needs to be up on STANDS, not a jack and wheels off.

You do not need a techII, they are thousands of dollars. If there's air in the ABS a tuner or dealer will need to do it.

A flush is really a pretty simple routine on the mechanical difficulty scale, but with every operation there are steps to follow and procedures to do it right that if not followed can result in problems.

You will need a jack, jack stands, wrench sets, a torque wrench and either a power bleeder, speed bleeders (need to install) OR a wife or friend willing to push the brake pedal while you man the bleeder screws. Bleeding without a power bleeder or special bleed screws is a 2 man job.

If you decide to do it yourself, there's plenty of help available on this forum. Just make sure you do the procedure in your head 10 times before actually doing it on the car for the first time.

 

Ok, here is a question I have then.

Why do you need to have 4 wheels off on jack stands?

If you are doing a pressure bleed/flush why should it matter?

If it does matter from a caliper to master cylinder height/level standpoint, could you jack up the car, remove the tire and then lower the car down to the point where the caliper would be at its normal at rest position?

I'm interested in this since I ordered my Motive and SRF today and plan on doing a complete flush this weekend.

My garage is on a slight incline and jack stands do not excite me in that regard.

My lift is coming as soon as the garage is finishing being done but in the meantime I'm normally lifting a corner at a time, actually the rear at once, then side by side for the front.

I vote for trying to fix it yourself. Its not a difficult job, can be done with simple tools and a little bit of time. There is plenty of help available and after your done you'll be amazed how easy of a job it is. It takes me longer to put the car in the air and get the tire off than it does to change the pads. I just picked up a cheapo piston depresser at Harbor Freight that would cut even more time out of the job.

I always look at it this way. A dealer is going to ding you for some decent cash to do the work. You can spend that money on tools instead and be farther ahead equipment and knowledge wise.

As far as the Tech II, I'm bad for that I can throw a tennis ball in my subdivision and hit 4 GM Engineers homes so I'm used to using a Tech II.

If they checked for pad thickness they still couldn't see the taper unless they physically pull the caliper apart and inspect the pad which I highly doubt they do, even then someone who is not looking for it might not catch it.

 

Speed Bleeders. They work well for me. No jacking, no tire/wheel removal. I do like to attach a short piece of clear vinyl hose over the nipple and direct it into a clear container. One man job too.

HTH,
Robert

 

Once in a while you have to re bleed a caliper. Just makes it much easier when the car is on four jack stands and the wheels are off.
I do my brake bleeding, brake pad change and generl inspection at the same time. One wheel well at a time.

And since you are changing to SRF you will need to do each caliper twice, do all four, then do all four again, to assure all the old brake fluid is out of the lines.

Then blow all the crap and road clagg out of the radiators with an air hose.

is your lift a two post or four post drive on?? if it is a drive on lift you will still need to remove the wheels to bleed the brakes.

Good Luck

 

It will be a 2 post, when it gets put in.

So the 4 wheels off/jackstands is a convienance thing or a neccessity?

I was thinking that you were saying it had to be on jackstands to keep the MC/Caliper angle/height differences the same, not just it makes it easier.

 

convienance only.