high pedal when hot

[rockdogz]

I just ran into a problem today at the end of a 50 mile trip. It was HOT here today, not sure if that contributed to the problem...

About 2 miles from home, I noticed that the brakes were partially applied - all the time. The pedal was super high and hard. I made it home and the engine was hot from having to fight the brakes, and the rotors looked kindof bluish from being so hot. Once it cooled down for 5 minutes then the pedal was fine again.

I came across a post on lateral-g from Mecom Racer who had the same problem, and the fix for him was to shim the master cylinder some. I can try the same thing - actually I have an adjustable brake pedal pushrod, but I'm curious what the cause of this is - and if I do indeed have the same condition since I have manual brakes. Do I need to try to bleed the brakes again - could an air pocket have caused this?

My setup is 4 wheel Wilwood dynalites 4 pistons, with an aftermarket plastic master cylinder - I think it's from a Corvette. I don't remember the bore size right off but I can look it up. Any comments appreciated :twothumbs.

Thanks,

[Madspeed]

No its not air
Its because your pedal and master are adjusted improperly
you need to adjust your brke rod so that you can feel a VERY smal amount of play before it enguages
Can you wiggle the pedal a little? like about 1/116" should work
just back the rod down a little
Once the brakes dragg long enough the fluid swells and so does everything else untill it just applys the brake even more and the problem just compunds itself from there

[David Pozzi]

The brake pedal should not hit a stop or hit the brake light switch so hard it bottoms out, nothing should prevent the pedal from returning fully. With the pedal fully released, the master cyl should have no pressure on the piston, if there is pressure on the master cyl piston, it may not vent the brake lines and you can get a pressure buildup as you discribe.
David

[rockdogz]

Ok, thanks...
Currently I'm using the top hole in the brake pedal arm - should I use the lower? It would bring the pushrod further away, but then I lose leverage, right?

[rockdogz]

Ok, never mind I found another post that said the bottom hole is for power brakes. I adjusted the pushrod all the way in, about 3/8" from where it was. I still don't feel any play before it engages...

[Madspeed]

Rock. Can you see the plunger from the backside of the master under the dash?
Make a board out of thick enough plywood to hold your weight and narrow enough to fit on the rocker kind of under the dash Id say about 4 feet long then prop it up outside so it lays flat on the rocker
Now you can lay down under your dsash for this work Im about to explain


lay down Nice and comfy on your new tool =) and look up at the master pull the boot off. If you have to remove th master then take the rubber boot of so you can see the plunger .
now see if when you move the pedal all the way up it has slack between the rod and the plunger.
If there is no slack and you can not adjust it any more.
take the pin out of the clevis and see how much you need to shorten the rod.
take the rod and cut it shorter with a dremel or air powered cutoff wheel.
Now take the clevis off and the nut and install the cut rod into a drill motor ( be carefull not to damage the threads with the chuck)
go to your bench grinder and grind the rod end round again using the drill motor to turn it while your grinding wil get it pretty accurately rounded again (you will love that one and ill bet youl find many other uses)
I call it the south of the border lathe technique (srry no offense inteded)

You need more info Holla Im allways around =)

[rockdogz]

Thanks Mad, I will check it out.