CCKW Brakes locked up

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Bean
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CCKW Brakes locked up

Post by Bean » Sat Jul 06, 2013 12:13 pm

I have a 44 CCKW that I completely restored frame off many years ago.The brakes always worked fine,But from lack of use these past few years I noticed some leaks.I replaced the master cylinder with a newer M35 type.It was a direct bolt in.Thats when the problems started.The two rear drivers side wheels are locked up tight.The wheel cylinders are rebuilt and not leaking.When I release the bleeder screws fluid shoots out and the wheels unlock.I have read the other posts about locked up brakes on a CCKW,But they seem to be as you are driving and braking.Mine are locked up when you just sit in the garage and pump the brake pedal.It is as if you are standing on the pedal,The system is always under pressure.Could this be a check valve issue?


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Re: CCKW Brakes locked up

Post by Joe Gopan » Sat Jul 06, 2013 12:50 pm

It could be a check valve issue only if you have the Series 3 Hydrovac, I would check the linkage adjustment instructions in the CCKW TM, it has to do with the back of the Master Cylinder, next would be to start pulling the wheels.
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Re: CCKW Brakes locked up

Post by Bean » Sat Jul 06, 2013 1:53 pm

Ben,I believe the truck has the original series 2 booster.It is a long booster that mounts in the original booster brackets behind the fuel tank.I have pulled the wheels and took the wheel cylinders apart.I rebuilt them a few years ago.Everything is clean and the cylinders move freely.Like i said.When you open the bleeder screws after pumping the brakes fluid will shoot out.This will happen even if you let the truck sit a day or two.It is like someone is stepping on the pedal when I open the screw.Some how the system is holding pressure and not releasing the wheel cylinders.Once I bleed the wheel cylinders the truck will move,But when I apply the brake again they lock up tight?????????

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Re: CCKW Brakes locked up

Post by Joe Gopan » Sat Jul 06, 2013 5:58 pm

There is a test to see if the Hydrovac is functioning properly when the brakes do not release. If disconnecting the Vacuum Hose at the Hydrovac releases the brakes, then the Hydrovac is suspect, but this test is only good for a short period after the engine is shut off. you should start by pulling one of the problem wheels and checking to see if the Wheel Cylinder is sticking, or for swelling of the rgubber cups. You didn't by any chance lubricate the outer ends of the Wheel Cylinder Covers with grease or never sieze in order to make adjusting easier?
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Re: CCKW Brakes locked up

Post by motto » Sat Jul 06, 2013 7:52 pm

If it's not locking up all wheels, only one or two, it doesn't sound like a booster problem. This sounds more like a hose problem. Brake hoses don't normally fail by bursting or leaking as you would expect, they are far more prone to failure by swelling internally and restricting or blocking flow. I've seen this happen several times now and the symptoms are exactly as described. The system will force fluid through the blockage but the brake return springs cannot push it back so the brake/s remains applied on the wheel/s downstream of the faulty hose. There is no outward sign of this, the hose looks perfectly normal.
The only anomaly is that you say more than one wheel is affected but it is not impossible you have developed two faulty hoses at the same time. They were probably from the same source and installed at the same time so if they do prove to be faulty you can expect more.
If you can release all locked brakes with one bleeder, then-back to Ben.

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Re: CCKW Brakes locked up

Post by D.R.H. » Sat Jul 06, 2013 10:12 pm

My guess would go on broken return springs.
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Re: CCKW Brakes locked up

Post by motto » Sun Jul 07, 2013 12:58 am

That wouldn't explain why the fluid shoots out and the brakes release when the bleeder is opened. The return spring must be intact to cause that to occur. Something is trapping the fluid at those wheel stations. If it's only two wheels that are affected, I'd go with the hoses being the cause.

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Re: CCKW Brakes locked up

Post by Gordon_M » Sun Jul 07, 2013 1:17 am

Hoses, lines, and / or dirt Somewhere between the wheel sets and where the main line for those wheel sets leaves the rest of the brake system.

Try to identify the hose, line, or fitting first, and then pull ALL the hoses and replace the lot. Flush through, have a look at the flushed fluid, check you are not putting silicone fluid or some modern spec in a hose made for older fluid types - stuff like that.

When you get it fixed, stay cautious with the brakes for the first few hundred.
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Re: CCKW Brakes locked up

Post by Joe Gopan » Sun Jul 07, 2013 2:38 am

Does the truck have a history of both DOT 3 and DOT 5?
Am sure that a complete wheel cylinder service and check of the flexible lines will shed some light, after all, it has been years since the brakes were last done, and the truck has had little use, time does take a toll whether in use or not.
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Re: CCKW Brakes locked up

Post by Bean » Sun Jul 07, 2013 12:54 pm

Well here is a update on the brake situation.After a long day of taking things apart ,The brakes still lock up.I have found that ALL of the wheels lock up when you pump the brakes.The only way to release them is to open a bleeder screw.I removed the master cylinder check valve and got the same results.Actually,If I pump the pedal till the wheels lock and then disconnect the brake line at the master cylinder,The wheels stay locked.Now I am thinking Hydro vac.This was just newly rebuilt.But I don't believe it is a vacumn issue because the wheels will lock with the truck not running.Any ideas???????????

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Re: CCKW Brakes locked up

Post by motto » Sun Jul 07, 2013 3:39 pm

Well that changes everything entirely. As I said , If all wheels are locking up or opening one bleeder releases more than one wheel, -- back to Ben. It's now looking like a booster or master cylinder problem.

Taking in to account the 'fiddle factor', (that's the term used if a system has had work carried out on it at about the time the problem arose), the master cylinder becomes the prime suspect.

David
Last edited by motto on Sun Jul 07, 2013 8:19 pm, edited 3 times in total.

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Re: CCKW Brakes locked up

Post by motto » Sun Jul 07, 2013 8:05 pm

Whoa there!
I've just re-read your post and you've already eliminated the master cylinder yourself by disconnecting it and the brakes remaining on. The only thing left is the hydrovac which you now say was recently rebuilt. Once again the fiddle factor comes into play. First up you had better determine exactly what series it is. I believe that the series three has a check valve that must be removed for this application. Is it the one from the truck that you had rebuilt or is it an outsider?

David

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Re: CCKW Brakes locked up

Post by Bean » Mon Jul 08, 2013 1:13 am

The hydro Vac is original to the truck and is the one pictured in the TM for a 44 CCKW.It worked fine,But was leaking internally so I had it rebuilt.I believe it to be a Bendix series 2.

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Re: CCKW Brakes locked up

Post by motto » Mon Jul 08, 2013 5:07 am

That has to be a 2nd series then. It will have the hydraulic and vacuum controls all clustered on one end, plus it will have two vacuum chambers joined in the middle with a broad spacer.
The booster is designed to allow brake application with or without vacuum. Without vacuum the fluid should be able to flow through the booster in either direction but you seem to have proven that it will flow down the system and is not able to return. This has got to mean that the booster is faulty. If there was no vacuum present it is faulty in the hydraulic function. If there was any vacuum present, even residual, the fault may be in the vacuum control function. You had best talk to the people that did the rebuild and see what they have to say. Hopefully they will stand behind their product. If not you may need to sort it yourself. Ben could probably steer you in the right direction in regards to overhaul literature or there may be something on line

Just one more thing, does opening the bleeder on the booster slave cylinder release the brakes? If so the fault is definitely in the booster, if not it's downstream of the booster but before the lines split. Not far. Just trying to cover all bases.

Please keep us posted.

David.

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Re: CCKW Brakes locked up

Post by artificer » Mon Jul 08, 2013 5:54 am

Certainly not time to be pulling wheels or contemplating full brake overhauls, as we don't know what is wrong, just what is happening.
I replaced the master cylinder with a newer M35 type.It was a direct bolt in. That's when the problems started....Mine are locked up when you just sit in the garage and pump the brake pedal.
Master Cylinder:
1. & most likely....All brake hydraulic systems must have free travel clearance between the master cylinder push rod & the master cylinder piston. So first check the linkages associated with the pedal to push rod, as you have done work around this area & fitted a new master cylinder. No free travel & your symptoms fit exactly with a NOT fully returning master cylinder piston & the primary cup rubber NOT uncovering the reservoir by pass port.
Hydrovac:
2. Broken vacuum cylinder piston return spring [unlikely]
3. Broken or incorrectly installed valve diaphragm return spring
4. Sticking control valve piston
5. Swollen rubber components due to fluid contamination [master cylinder or hydrovac].
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