Brakes lock up!!!

wartruk44 · Post by **wartruk44** » Fri May 12, 2006 2:45 pm

Has anyone had their brakes lock up after do a complete bleed job from Hydro.. to brake cylinders. Starting with Hydrovac #1 bleeder (rear one) then #2 (front one) then going to the nearest wheel cylinder and on thru to the furtherest. Just can seem to get all the air out of the system or what. Master cylinder is NOS, flex lines are new, have flushed out all lines completely. Have honed out all wheel cylinders and replaced the rubber (which most auto parts store carries the 11/2 and the 11/4 rubber). If someone can please help I would be grateful and maybe even let you drive my 1944 CCKW 353 Tipper! Thanks, Drew

pfarber · Post by **pfarber** » Sat May 13, 2006 10:21 am

Lock up as in you touched the brakes and all the wheels locked, or only the rears or fronts?

Did you adjust the brakes after rebuiding/bleeding?

wartruk44 · Post by **wartruk44** » Sat May 13, 2006 1:33 pm

The front brakes stay locked up. I can bleed the whole system and it will roll fine until I apply the brakes then they lock solid. I adjusted the brake shoes before bleeding according to the manual. I read where someone talks about the M-35 Master cylinder may have a check valve and the later Hydrovac's also has one. I think Mr. Gopan said that can cause a problem. Not sure yet about the rear brakes locking, will know today. Thanks for your reply.

Jeroen Sleijpen · Post by **Jeroen Sleijpen** » Sun May 14, 2006 1:47 am

what kind of fluid do you use?
Silicon will often solute the nos rubber in cylinders and flexible lines.

Sounds like the flexibles are the problem...you push through fluid so they get wider...but when the spring force has to push the fluid back.... the hoses are not wide enough to let the fluid through....when you bleed the cylinders the problem is gone...but returns after you brake again....get someone to push the brakes and take a good look if the diameter of the flexibles is increasing while braking...if so....they fail!

good luck

Karoshi · Post by **Karoshi** » Sun May 14, 2006 7:58 am

Drew, is the hydrovac the late type "j" bolt canister or the earlier thro' bolt type with nuts at each end ? The later type "J" bolt has a built in check valve.

Try isolating the front brakes with the "shut off" valve in the front feed line, brass tap, roughly under the pasenger seat area. And see if cures the brake hold-up.

Alternatively think about weak return springs on the front shoes.

wartruk44 · Post by **wartruk44** » Sun May 14, 2006 7:29 pm

The flex lines are new, should i still have problems with them being too small? And I'm using Prestone synthetic fluid. Thanks Drew.

Jeroen Sleijpen · Post by **Jeroen Sleijpen** » Mon May 15, 2006 1:24 am

with the lines being to small....the brake lock up should solve itself after a few minutes.
take a look through the refill cap of the mastercylinder and gently apply the brakes. there are 2 holes in the bottem. A small one and a larger one.... make sure that when you release the brake pedal the small hole is completely open. (If you cant see this feel with a needle)
If it is covered up adjust the link between pedal and cylinder to see if you can get it open. if not, the cylinder is not good....either is the rubber cup soluted or the parts are not mounted correct.

good luck

wartruk44 · Post by **wartruk44** » Mon May 15, 2006 9:41 am

Many thanks for you help, I closed the valve on the passenger side for the front brake line . I then released a little fluid pressure at the front wheels and then was able to drive the truck. It seems that only the front 2 wheels are giving the problem. Remember I have new lines (Wagner) the cylinders are honed , new rubber cups and the brakes adusted 4 turns counter clockwise from dragging. Thanks again, Drew.

Karoshi · Post by **Karoshi** » Mon May 15, 2006 9:50 am

Glad you're getting somewhere. The master cylinder is a single line system, so that's not holding up. I would suspect incorrect adjustments or more probably the return springs are weak on the front.

They are animals so please be careful.

wartruk44 · Post by **wartruk44** » Mon May 15, 2006 4:48 pm

I'm begining to suspect the return spring myself. Will let you know soon as I get 2, Thanks a million.

dr deuce · Post by **dr deuce** » Mon May 15, 2006 5:10 pm

Is this truck banjo or split?

Banjo's tend to have the shoes stick in the guides, that is why I recommend that you drive a tapered punch into the to open them up a little so that you have more clearance.

wartruk44 · Post by **wartruk44** » Tue May 16, 2006 2:16 pm

They are banjo, I'm able to move it now since I closed the front lines off. I will try your solution thanks.
What is your opinion of the 270 engine temp running under the required 160 to 205F. Mine is at 150F. New "Chinese gage" from Beechwood!

dr deuce · Post by **dr deuce** » Tue May 16, 2006 6:54 pm

Get a candy thermomoter and put it in the radiator when running and see what the temp is.

Karoshi · Post by **Karoshi** » Tue May 16, 2006 10:44 pm

We dont have a location for you, and so dont know your climate conditions, but I temporarily ran my 270 without a thermostat, and it only indicated about 150/160, here in Europe.

Do you have a thermostat fitted?

wartruk44 · Post by **wartruk44** » Wed May 17, 2006 10:14 am

Yes I have a thermostat it is 160-F and the climate is 70-F to 95-F until about October, November.

dr deuce · Post by **dr deuce** » Wed May 17, 2006 5:19 pm

Do you have the steam relief tube (SRT) installed? If so, is the one to the radiator (early) or the later one to the thermo housing?

That back corner of the engine tends to be the hottest

I 'believe' that the SRT screws up the circulation in the engine. The civy engines did not have it AND the mil Chevys, both US and CMP had a valve to shut it off. It was only to be opened when going up and down steep grades...

wartruk44 · Post by **wartruk44** » Thu May 18, 2006 10:56 am

I have the late steam relief tube on mine. It seems to get an air lock if the engine coolant is drained from the engine. The engine will reach around 210-F and finally the coolant will travel through it and cause the thermostat to open. But after it cools very good. Thanks

dr deuce · Post by **dr deuce** » Thu May 18, 2006 5:41 pm

The air lock is a problem that can be caused by the thermostat not having a hole (or clogged) and fitting too well.

If I replace a thermostat and it does not have a hole in it, I drill a small hole (maybe 1/32) in it so that air can bleed out of it when doing a refill after a complete drain. Some thermostats come with that hole in them.