Lose brakes if car sits in traffic too long and clanking in rear end?

[KDR83]

I have two issues in the car that I want to address asap.

First one is that I lose my brakes if the car sits in traffic or idle too long. The first time this happened was right after I bought the car and we took it into New Orleans and drove down Bourbon Street, there was a lot of very slow traffic, idling, and I noticed the brake pedal kept getting softer and softer until it basically went all the way to the floor before there was any stopping power. Once I stopped and let the car cool down for 30 minutes the brake pedal came back. Even in stop and go traffic if its heavy I start feeling the pedal getting soft. I heard of fluid boiling but I thought that would be due to ******* the brakes on a track, I dont see the fluid getting hot in stop and go traffic unless my headers are heating it up?

Second is that when I reverse my car and hit the brakes I feel something clanking and shift to the back, it will only do this once unless I go forward again and then reverse again. Seems like there is something loose that moves forward when I first start reversing and than hits the back when I hit the brakes. I only feel it in reverse, seems like something maybe loose in the suspension but no idea where to start?

My car is due for an oil change so I will probably take it to Doug Levin soon however wanted to see if anyone has any ideas before I do so.

 

[Steve-Indy]

Have you changed brake fluid yet...if not, you need to...along with clutch as they are same fluid and gather moisture with time.

 

[heliguy25]

Have you changed brake fluid yet...if not, you need to...along with clutch as they are same fluid and gather moisture with time.

sounds more like a booster/vacuum problem to me.

 

[KDR83]

It seems to occur only if under hood temps go up, I drove the car for hrs and hrs as I drove it back from Austin to Miami and there was no issues, its once I sit in traffic for 20-30 min that I feel the brake pedal travel slowly starts to increase.

 

[bluesrt]

booster /vacuum problem

 

[KDR83]

I forgot to add that when I completely lost the brakes the dummy light for brakes came on

 

[jdeft1]

Failing master cylinder. ? Is the fluid level dropping? If not, replace the master. The problem will only get worse. As for the 'clunk', I'd need a short test drive... Perhaps check the U-joints.

Good luck with it.

 

[dave6666]

The brake booster going bad will not change the pedal travel. Just the force. The master cylinder however will if it is bypassing internally. Heat could be amplifying the problem once it heat soaks from under hood temps rising in traffic.

On the clunking, check your diff mounts, axle hub torque, control arm mounts for tightness.

 

[KDR83]

Yeah the force doesn't change, just the travel distance before it engages.

Would something like this work?
http://www.amazon.com/Raybestos-MC3...r=2002|2002&carId=004&n=15684181&s=automotive

I realize the ABS and non ABS cars have different master cylinders, could I use one from a 2002 or should I stick to the non-ABS units as the bore size is different

 

[heliguy25]

The brake booster going bad will not change the pedal travel. Just the force. The master cylinder however will if it is bypassing internally. Heat could be amplifying the problem once it heat soaks from under hood temps rising in traffic.

On the clunking, check your diff mounts, axle hub torque, control arm mounts for tightness.

Just depends how he's interpreting the feel. You can sit in a car with power assisted brakes and pump the pedal and hold it and it will sink further...... I'll still say booster or a vacum problem...

 

[KDR83]

The pedal simply feels like you are just pushing a soft spring and then engages at a further point down. The one time it went completely to the floor the pedal had the pressure of basically a loose gas pedal and didnt engage until the very last cm...if that, also the parking brake dummy light started flashing, I wasnt going over 5 mph and just limped it into a gas station. I let the car cool off for about 15-20 min and the brake pedal got better but wasnt back to normal, after about an hr or so of driving on the interstate the brake light on the dash stopped flashing and the pedal worked fine again.

Basically the engagement point of the brake changes not just the force, I am thinking of changing the master cylinder and bleeding brakes as those are two cheap fixes and see if I still experience the problem. I see the booster becomes a little more expense but I do see a used one on ebay. Not sure how a vacuum problem could be effected by stop and go traffic or the car idling?

 

[daveg]

I agree with dave. Brake booster / vacuum issue will give you a harder pedal. An example is if you turn your car off and press the brake a couple times to bleed off the vacuum and then step on it again, it will be hard to press but travel will remain the same. What happens if you start the car, press the brake and leave it pressed for a bit, does it slowly fade (as dave indicated an internal bypass in the master cylinder)

 

[KDR83]

The pedal definitely never gets hard, I am about to drive home so I will look test it out and see what the pedal does. I found a brake booster out of a 98 which I can probably get for about $50 bucks and I see I can get a oem replacement master for around $70.

 

[GTS Dean]

Booster is my first guess. Air in the MC or proportioning valve would be my second guess. Water in the brake fluid third.

Do you have headers without heat shields? Radiant heat could be boiling the moisture in old brake fluid.

 

[99 R/T 10]

Sounds like the Master Cyl. is going bad. What year is your car?

 

[Fatboy 18]

Do you have headers without heat shields? Radiant heat could be boiling the moisture in old brake fluid.

This is what I was thinking

Wonder also what other engine mods have been done? It would be worth checking all brake lines and calipers to make sure everything is in order and replace the brake fluid.

 

[dave6666]

You don't need a booster. But buy one, and then bill all the people that think pedal fade = booster issues.

All the booster does is alter the force required. Not the ultimate distance the pedal travels. You are displacing a non compressible fluid. The only reason the distance the pedal travels can change, is a mechanical malfunction in the process of moving the fluid volume like a leak, or a bypass in the fluid displacement mechanism aka fluid bypassing the master cylinder plunger.

This all assumes the pedal is not altering the force as things change. Just the travel.

BTW, I have run headers no shields in Texas heat and never had brake fade.

 

[viper04]

Sounds like a Master Cyl. to me. With the car not running pump the pedal and see if there is more travel, if there is my guess is Master.

 

[Mopar Steve]

Fluid is boiling. Booster and Master are likely fine. Grab all the low hanging fruit first. Get good quality fluid and flush and fill (bleed) the lines strating at the right rear wheel first and working your way to the left front. The clunk/clank noise is likely universals either on the frive shaft or the half shafts. If one is gone, change them all. Good luck, and be sure to post the final results so that future searches can benefit from this thread.

 

[KDR83]

I started the car and pressed and held the brake, it did not move down. I was stuck in traffic for about 20 minutes, I didnt experience the problem but it was raining and the temps were pretty cool.

I do have Bellanger headers with no heat shields on them, the car has headers, high flow cats, and exhaust. I see some master cylinders for sale online for around 80 bucks that say they fit my car, should those be fine? I want to replace the master cylinder and replace the brake fluid, hence my other thread about speed bleeders versus motive bleeder

 

[KDR83]

Fluid is boiling. Booster and Master are likely fine. Grab all the low hanging fruit first. Get good quality fluid and flush and fill (bleed) the lines strating at the right rear wheel first and working your way to the left front. The clunk/clank noise is likely universals either on the frive shaft or the half shafts. If one is gone, change them all. Good luck, and be sure to post the final results so that future searches can benefit from this thread.

I thought it might be the fluid boiling due to no heat shield, only happening when car sits in traffic or idle, and not knowing when the last time the brake fluid was changed, what is a good fluid for street driving? BTW for someone that asked the car is a 97 with 28k miles.

 

[AZTVR]

I thought it might be the fluid boiling due to no heat shield, only happening when car sits in traffic or idle, and not knowing when the last time the brake fluid was changed, what is a good fluid for street driving?

For street driving , I usually use Castrol LMA or Valvoline Synthetic in my vehicles. If your problem is boiling fluid;then just new fluid may solve it. ATE Blue/TYP 200 has a higher boiling point but, still pretty long lasting for street/track; but if the headers have been on your car for quite a while and didn't give problems to the PO, then I don't think you need that upgrade, especially based on dave's input with similar setup. If new fluid doesn't solve it, then change the master.

 

[Allan]

All the 'boiling fluid' guys are correct. ......The clunking on first apply in reverse, with repeat noise only after stopping with a forward brake apply, is more than likely loose caliper bolts. I had this happen on my car. Took a while to figure out, really wierd that it would only make the noise in reverse, but mine did the same thing.