I just got my 56 F100 that I started restoring 10 years ago running this week. Im having problems with my brakes locking up after about a 1/4 mile of driving it. After 10-15 minutes with the car off, the brakes released and then I could drive it back home. The suspension bits were installed by industrial Chassis and we used their front end kit that was from a Dodge Dakota with that had all the parts replaced. We re-purposed a hydroboost off a 2007 chevy Express 2500 with a mid 70's chevy master cylinder that we already had available. It also has a wilwood proportioning valve installed that I havent tried to adjust yet. The rod the attaches the brake pedal to the hydroboost doesn't have any adjustment, but seems like it has a tiny bit of play. The power steering fluid was a bit low and after filling it up it I took it out again and went about a mile and it didn't lock up, but it still seems like it was starting to build up pressure as I had a hell of a time getting it back up the driveway without stalling. Does anyone have any idea of why this might be happening?
Check the rear brake hardware..Return springs ? Hydrabooster may have residual built in..Bypass it and see if they stay free...
Just a couple things to check, start the car with the brakes free (rolling, not dragging) crank the steering wheel from full right to full left several times then see if the truck will still roll. If not, the problem is in the hydroboost system not in the wheel brakes as you have not applied the brakes. When the brakes do drag, stop and shut off the engine, pump the pedal several times untill it is rock hard (brakes should be free at this point) then hold the pedal down while starting the engine. You should feel the pedal drop as soon as the engine starts. This will verify the hydroboost is somewhat working as intended, further testing should be done with a gauge on the power steering lines. If the return hose to the steering fluid reservoir is restricted it will cause a build up in pressure and gradually apply the brakes as pressure builds too high. Some of those power steering fluid hoses are lined with a teflon liner in the hose that can break free and get trapped in the valves in the hydroboost assembly. Saw this many times on Dodge diesel pickups. Hope this helps, Mark
Do all four wheels seem to lock up, or just the front or rears only? Is it a disk/drum system or four wheel disk? Or maybe it's a brake on just one side that's locking up?
Double check that the "tiny" amount of play in the pedal pushrod is actually there when it's running. And that the pedal return spring is doing its job. If that checks out, loosen the master cylinder mount bolts and slip a shim or washer between the master and the booster and take a drive to see if the problem goes away. If it does adjust booster pushrod properly.
Sounds like the piston in the master cylinder not returning far enough for the fluid to vent back into the resovoir. Check the rod has the correct free play,
Ummm… it is strictly for power assist, no brake fluid goes through the hydraboost. For the op definitely check pedal pushrod length
The master cylinder pushrod clearance has been mentioned. If the master cylinder is too full, it can cause what you are describing. The hydroboost by it self will not cause what you are describing. The brake pedal to hydroboost rod can also be too tight.
I had a similar problem with a hydro boost in my 55 bird. Not enough slack from in pedal rod. Probably would have been fine on a master cylinder, but the hydro boost just needed more. Gave it another 1/8”, been fine for 15 years.
Thanks for all the responses. I took it out again today for another test drive. After 10 minutes around the neighborhood the pads started smoking. I took some shots with an infared camera. 3 of the 4 rotors were above 266 degrees the passenger rear was 205 degrees which makes sense that it would be less because its the furthest from the master cylinder. Heres some more info... It has disks brakes on all 4 wheels. If I have the pedal pumped up and depressed, it compresses about another 1/2 inch when I start the truck so I believe the hydroboost is working. Im guessing that the proportioning valve isnt the issue because its locking up the front & rear brakes. From the comments, it sounds like I need to shorten the rod a 1/8" to get a little more free play. I'll do that tomorrow and report. back.
I didn’t have a heat gun with me, but the brakes were hot and dragging. I ended up in an empty parking lot, got the tool roll out, and cracked the brake lines. Spurted pressure, so it was there. Using lower gears and driving cautiously, I got to work without locking them again. I had a full auto shop there, so at the end of the day I shortened the rod. Problem gone. Could have been a combined problem of lack of clearance on the rod and under hood temperature, the header is really close on a 55 bird. But done. I also have 4 wheel disc, I don’t think that was part of it.
Watch the whole video https://bangshift.com/general-news/...oting-problems-before-the-deck-goes-together/
It is definitely the rod. I added a a 1/8" of washers between the hydraboost and the master cylinder and now I have about a 3/8" free play in the pedal. I took it out on the same trip that I did yesterday and took some more thermal images. Everything feels fine now and the caliper temps are good. I was even able to drive it to the DMV and also put a couple freeway miles on her. Thanks for all your help.
I’m glad it worked, but that’s a band aid solution. Figure out if the rod from the pedal to booster is too long, or the rod from the booster to master is too long. Bandaids are great for some things, but steering, brakes and throttle linkages need to be right. I could go on. Enjoy your ride.
My hydro needed the push rod slightly shortened the front was getting hot. Did a roadside washers behind the master cyl and it stopped doing that.
FEL-PRO 35595 plastic thermostat gasket will fit on the booster studs and give enought space for the pushrod and seal water out of the master cylinder too..
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