Smoking Brakes

[carlo]

Need some insight, less than a hundred miles on car/svo rear disc/gm calipers w/granada rotors/front.temp around 78 deg, dual master cylinder with balance bar( as suplied by shell valley. Heres the problem,cruising at around 50 when I noticed the stink, pulled over and smoke was coming from the rear wheels, I don't remmember the fronts smoking( but later I sniffed the fronts and they had that burnt brake smell, the brake pedal was hard no movement, i let it cool for 10 min, and stabbed at the pedal a few times and it seemed to return to normal. I'm using DOT3 fluid, and it was hot under the hood, I limped back home safely.Prior to noticing the problem I hadn't used the brakes for 10 minutes, also the car just slowed down by itself. it seemed to be laboring. It's evening and cooler now and it's working normal, ANY IDEAS?, BOILED FLUID, SLEAZY PARTS ????????tHANKS

[Whaler]

Hi I am totally taking a stab at this.

Is this the first time you have had the car out for a road test and long enough to generate a little heat? I note you say you have 100 miles on it. But this is the first time this has happened?

If so is there a chance the brake masters or lines feeding the masters or the lines out have got hot?

Is there shielding in the brake and tubing areas to protect from header heat?

Also as you said, the car was labouring...I would guess that's because it was actually braking. Therefore the smoke. Hope it wasn't hot enough to warp the rotors. Just thinking that if the heat in the engine bay could have caused the fluid to expand creating braking force. But this seems too extreme.
Actually hot fluid is supposed to cause brakes to fade doen't it?
Sure its not the e-brake sticking? I assume your calipers are floating freely on the slides?

Hard to guess without being there to see this and troubleshoot it methodically

Tim

[Excaliber]

Sounds like back brakes are the primary culprit here. It was unclear to me if the front brakes were really an issue or not?

Things to look for on the rear:
Emergency brake cable binding?
Automatic adjusters on the rear brakes "adjusting themselves" to tight?


Things that might apply to front and/or back brakes:
Brake pedal binding and holding pressure on the master cylinder?
Pistons in the master cylinder binding and not returning to normal position?

Binding pistons could be caused by: Oil contamination, which swells the rubber, this would apply to ALL rubber parts in the brake system. Wheel cylinders, brake lines, etc. Bear in mind brake fluid is NOT in ANY WAY "oil" based. It is compatible with WATER, not OIL. A small amount of oil contamination would take some time to swell the parts and eventually cause trouble.

Water/Rust/Contamination in general:
Same basic effect as the "oil" scenario above. The very close tolerance parts in the "brake system" can bind/stick with even a little bit of contamination, such as "moisture" being sucked in by the brake fluid. Thus a brake system can "go bad" after simply sitting for a long time and rarely if ever used.

There is ONE great law that ALWAYS applies to vehicles:
If "miles" don't get you, "time" will. Don't drive that many miles? Change your oil ANYWAY every few months! Wether you drive or not, your "stuff" is breaking down, use it or loose it.

Ernie

[auto10x]

Make sure the brake linkage is adjusted correctly. It must have some free play. The front of the primary piston MUST return back far enough to uncover the compensating port in the bore of the master cylinder. If not the fluid is trapped in the system and as the system temperature goes up the fluid expands and gradually applies the brakes. As it cools down then things will seem to return to normal.
auto10x
Bill

[carlo]

I'm going to re/do the rear master cylinder, Zoomer from Shell Valley is going to 2 day it to me so I have it for Friday( since I'm off. At wich point I will double ck, everything). Whaler, I'm hoping nothing warped BigTime, this is the 5 th time I had it out and the warmest day so I figured the dot 3 wasn't up to the job, thats not it, that pedal was like a rock, no movement until I repeatedly jabbed at it and it freed up. I'll find out Fri.One thing about SVM, they are allways willing to make good on a part.

[Gary Baxter]

sounds like piston in master cyl is not venting fluid back to reservoir.Make sure rod pushing piston from pedal has clearence[1/16 to 1/8]. Is there a spring to return pedal fully.

[carlo]

No Gary, it didn' come with a external spring, just the ones in the separate master cyl. Do other cars have them?

[Gary Baxter]

Not sure on floor mounted pedals if they have return springs on pedals.On hanging pedals they should have springs to ensure piston rod doesn't shove piston down when pedal is at rest. Fluid heats up and can't return to resivoir and drags brakes.The more you drive the worse it gets.

[gfridland]

Well, I went out for my first ride and just like Carlo, my brake pedal go hard after driving for about 50 miles. The same hot brake smell was coming out of the rear rotors and the pedeal was hard and made the stopping pretty difficult. After letting it cool down, the brakes came back and felt normal. I am running wilwood disc brakes on all 4 wheels and have a power brakes., the rear has an e-brake, but I dont think that it is dragging. I am sure this it temperature related, but I am not sure if it is a result or the cause of the brake overheating problem. All brake lines are run away from the headers, but as we all know, you cant get too far away in a cobra. My pedal is mounted from the top (hanging) but also does not have a spring, but it seems to return completely.

Any feedback from Carlo? Any other suggestions? I hope that Carlo fixed his and knows what caused this problem. Hopefully something simple.

Thanks,
Gene

[carlo]

Gene, all's well with the brakes for now, I went through everything a second time, changed the rear master cyl.( because shell valley are good about that), drained the dot3 and put in dot4, and made a stainless clamp ( 1") that mounts to the back side of the brake pedal and keeps constant return pressure on the pedal. I also found the svo backing plates that mount to the axle needed snugging up, I don't drive like a kook so the car stops allright, if I did I'd want power brakes. I suggest switching to castrol 4 ( highest boiling point of the non silicone type) fashioning a return spring affair ( pain in the ass ) and go around and re affirm tightness and clearances. You may also want to carry a line wrench and some throw away rags your first few times out to bleed off pressure at the master cyl. should it happen again. good luck Gene.

[gfridland]

Carlo, can you describle the clamp that you made for the pedal return? I assume it has a spring for the return? Any help is appreciated.

Gene

[carlo]

Gene, send me an E mail at cad@adelphia.net, I will take a pic and send you a jpg. I think that will help you more than a written description.