calipers not releaseing

[rubicon]

After driving for about ten minutes at 45mph the front and rear calipers get hot. I pulled into the garage, put car in neutral and was unable to push the car forward or reverse. Jacked it up and the front wheels would not move. Back wheels moved but hard. After about 10 minutes the front wheels were free.
I have disc all around. (Wilwood) The other day when I check the temp only the left rear was hot and both fronts were around 98 degrees. I re-shimmed the left rear to make sure it was centered. I also adjusted the proportioning valve. Decreasing the line pressure to the rear which allows the front to do most of the work when braking. My MC with booster is under the floor. I also have a remote reservoir for the brake fluid on the firewall. What could be causing this and what should I do first?

 

[Spanky]

I had a similar problem with my fronts, and it turned out to be a pedal issue. The pedal was not moving far enough up to release all the line pressure, so I had to cut a small relief in the floor to allow the pedal to fully retract. No more problems!

 

[rubicon]

I just checked the pedal. Everything looks good. I made sure I have play on the rod before it pushes on the MC. Started raining so I won't be able to take it out for a short run. Tomorrow I may bleed the brakes to eliminate that. I have a remote reservoir and residual valves front and back. (2 lbs) could they be causing the problem? I don't think I need them with the remote reservoir that is above the calipers. Does anyone have this set up?

 

[fletcherson]

I don't know if the remote resevour eliminates the usefulness of residual valves, are you absolutely sure that the correct residual valve is installed in its designed location? Some use different valves for front and rear, I'm not sure about four wheel disc, they may be the same. A properly functioning residual valve should not cause the problem you are having if it's the correct one. Look closely to be sure your calipers are spaced and mounted correctly so they can float and that the piston side pads have some breathing room when the piston is fully released. A quick test would be when the brakes are hot and not releasing, crack open a bleader and see if it releases. If so, you have a hydraulic issue, i.e. mc not releasing, etc.. if not, you have a mechanical issues with the caliper or its installation. Good luck!

 

[T-Test]

Residual valves installed backwards? Don't really need them. anywho.

 

[Bagman]

I had a similar issue with my Wilwood fronts when i built mine. I re bled and have had no issues since.

 

[rubicon]

The residual valves are installed correctly and they are the right ones. I will re-bleed the brakes hopefully that's solves the problem. Weather today is awesome. Good day for a ride.

 

[rubicon]

I bled the brakes twice one day apart. First time there was air in the lines. Second time everything was good. Took the car out twice today and both times the car ran fine. The only thing I notice is I have about 3.5 inches of pedal travel. Also, on a quick stop the brakes do not lock up. I have power brakes and I'm not sure if 3.5 inches is a lot or the norm.

 

[tfeverfred]

Maybe check pedal ratio?

 

[fletcherson]

That seems like a lot of travel. I would expect about half of that. Are both axles getting fluid? Did you bench bleed the master? Is the master bore diameter sufficient for four wheel disk? Are the calipers moving and requiring the fluid to flow to obtain pad contact? Just thinking aloud on possibilities. I would expect power four wheel disk brakes on such a light car to be very good and not require much effort to apply.

 

[2old2fast]

I'll assume this is a vacuum boost system , do you have a very radical cam ? Could be you don't have enough vacuum to run the booster ??

 

[choppinczech]

I'll assume this is a vacuum boost system , do you have a very radical cam ? Could be you don't have enough vacuum to run the booster ??

That sure could be it. My 383 has no decent port for my booster anyway. So I'll be running one of these.

I have a lot of space to mount it under the dash.

 

[Swampdog]

I had to put one on my 62 Dodge. Beware you will know when it kicks on. I also put a switch so I could turn it off during starting so there won't be so much draw in the battery.

 

[Swampdog]

 

[rubicon]

I have a vac pump in stalled. Even made a muffler for it. Chopp bench run yours to see how loud it is. If its anything like mine you wont want it under the dash. The pedal could be a 6 to 1 ratio. It looks long but i have not measured it yet. Cant get under the car right now. The brakes are not rubbing anymore after i bled them. The pedal does not seem spungy at all. I believe i got all the air out.

 

[choppinczech]

If its anything like mine you wont want it under the dash.

Where'd you mount yours?

 

[fletcherson]

There are belt driven vacuum pumps also. Look at diesel applications. The one on my Ford with the IH 7.3 is a fairly compact unit and would be easy to adapt. Just a different idea... options are good to have. I had a fairly radical 383 in my iroc with over .600 lift and just over 300 duration, lumpy, stout, hi rev. I had vacuum boosted brakes and they worked fine with only a vacuum resevour installed.

 

[rubicon]

Chopp, here's a picture of the set up I have. The pump with muffler and the reservoir tank. My pump is mounted on rubber stand offs. There is a vain pump that's supposedly less vibration and quieter. I would have tried that if I known about. The vac pumps are quite big. The muffler is a piece of pvc pipe with rubber grommets on both ends and foam spunge in between. This cut the noise way down.

 

[choppinczech]

There is a vain pump that's supposedly less vibration and quieter.

Thanks. After reading your post I checked out the feedback on the Summit pump. There is a lot complaints on the noise.

I don't have one yet. So now I'm steering toward the Hella UP30. It can be used as a stand alone for brakes.