CCKW Brakes locked up

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artificer
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Re: CCKW Brakes locked up

Post by artificer » Sun Jul 14, 2013 3:44 pm

You are correct....but in this case the master cylinder line was released & the brakes still stayed on.
This indicated the issue to be hydro-vac related.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.


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Re: CCKW Brakes locked up

Post by Joe Gopan » Sun Jul 14, 2013 3:50 pm

johne504 wrote:I had this happen to my cckw and it was a check valve in the master cylinder that wasn't allowing the fluid to "bleed back" into the master cylinder resivour, therefore holding pressure to the hydrovac. I believe some master cylinders come with a check valves, and without.
___________________________________________________________________________________________
There is only one instance on a CCKW with a Hydrovac that requires that the Master Cylinder Check Valve be removed, and that is on a CCKW with the Type #3 Hydrovac. The Type #1 and Type #2 Hydrovac installation requires Master Cylinders with the Check Valve in place.
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Re: CCKW Brakes locked up

Post by Bean » Sun Jul 14, 2013 4:02 pm

Ben is correct,I removed the check valve in my master cylinder to give it a try.The master cylinder would not build pressure without it.

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Re: CCKW Brakes locked up

Post by artificer » Sun Jul 14, 2013 4:13 pm

The master cylinder would not build pressure without it [check valve]
The check valve has NOTHING to do with building pressure in a brake system....
A master cylinder check valve holds a very small residual pressure in the brake lines.
This may not be needed with a hydro-vac fitted with a check valve doing the same thing.
If used when not needed the small hydraulic pressure left inside the hydro-vac hydraulic cylinder may cause the hydro-vac to not release or release properly.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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Re: CCKW Brakes locked up

Post by motto » Sun Jul 14, 2013 8:27 pm

Bean is talking about what actually happened, his personal experience. There's no need to beat him down artificer. Ben's got a fair grip on the subject to. Who do you think you are using that tone?

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Re: CCKW Brakes locked up

Post by artificer » Sun Jul 14, 2013 9:00 pm

John without a big stick or any tone other than normal wrote:The check valve has NOTHING to do with building pressure in a brake system....
Can't have others thinking 'removing the check valve in a master cylinder will cause it not build pressure' because that thinking is not correct & won't help anyone diagnose brake or hydro-vac problem/issues.
The following is not my art but shows operation & if followed will show where 'hold on' issue/s come from
1. Issues with the hydro-vac hydraulic piston not fully returning or check valve [shown in diagram]
2. The atmospheric valve will maintain atmospheric pressure on the diaphragm thus
3. Not releasing atmospheric pressure from the chamber which is assisting application.
3a. Hydraulic brake pressure must be fully released [which is why the first IA was to check pedal free travel] to fully re-assert the big spring on the diaphragm to stop any hydro vac assist

If master cylinder line release of fluid did not unlock brakes indicates a hydro-vac issue & if releasing the forward hydro-vac bleader releases brakes, guess what?
Image

There are some different types of hydro-vacs:
1 Dual diaphragm with triangular plates on each end with connecting rods holding together the assembly
2 Dual diaphragm with J hooks instead of triangular plates
3 Single diaphragm with J hooks

the operating principles are much the same so if I'm wrong in explaining why certain things are not relevant & how to diagnose please let others & myself know where I went wrong .
Let us know by addressing the issue & not the person trying to be helpful.

BTW the diaphragm rod to piston in the hydro-vac must also have free travel as do master-vacs on cars & light trucks.
That or dirt from the master cylinder are very possible culprits.
Vacuum check valve good & in place?
http://www.bepco.biz/Catalogs/VacHydCat ... OOTING.pdf
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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Re: CCKW Brakes locked up

Post by motto » Sun Jul 14, 2013 11:49 pm

Experience beats theory John, what actually happens in real life. We've all PUMPED UP a pedal that went to the floor on the first application. Obviously what's happening is the fluid downstream of the master cylinder is being added to on each stroke. This is only possible if the fluid can't all rush back into the cylinder as the piston moves rearwards. That is where the check valve comes in. It may be there for another reason entirely and the ability to pump up a pedal only a side effect but Bean is telling us that 'Without it the cylinder would not build pressure'. The fellow is not an idiot. Nuf said.

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Re: CCKW Brakes locked up

Post by artificer » Mon Jul 15, 2013 12:18 am

David wrote:This is only possible if the fluid can't all rush back into the cylinder as the piston moves rearwards. That is where the check valve comes in....
Not so but exactly the opposite & indicates little to no understanding of brakes.

Actually all the fluid & there isn't that much, does rush back causing the check valve to lift off it's seat so as to let nearly all of the fluid thru the slave [if the check valve is there] as quick as possible & back to the master cylinder reservoir [if M/C has check, lifts off seat there]....if it doesn't the hydro-vac doesn't release
David wrote:Experience beats theory John
Sure does.
Some have considerably more than others pretend to have & knowing the theory certainly helps avoid shotgunning.
Diagnosis is something that saves money, headaches & doesn't include guessing & parts changing un-necessarily.

The only reason I bothered was that others may learn something.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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Re: CCKW Brakes locked up

Post by Bean » Mon Jul 15, 2013 1:26 am

Well,This is getting a bit out of hand.I started this post just to try and fix a issue I was having with my truck.Now,I am no mechanic,I am a carpenter,But I am not a Idiot either.I 've been restoring military trucks and jeeps for many years as a HOBBY.Isn't that what we are all on here about???? This is what I meant about the check valve.With it installed the pedal will build pressure within a few pumps.Without it you could pump for a long while before it would build just a little.I am no brake expert,But that tells me (going with common sense here) that the check valve helps to hold pressure in the lines causing pressure to build more rapidly.Thanks to all for the help.

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Re: CCKW Brakes locked up

Post by johne504 » Sat Aug 03, 2013 5:25 pm

Ok, I was getting my cckw ready for the parade yesterday and my brakes would lock up, sometimes for quite a while. I installed a newer double diaphram hydrovas in it last year. It seamed like it never really worked right, it lacked the power brake at times. Anyway, to make a long story short, I realized that the hose to the filter was kinked, not allowing the hydrovac to suck in air when the vacumme assist was working. It also caused the hydrovac to not release the brakes also. I thought this might be something to check with your problem. A plugged air filter for the hydrovac could cause similiar problems with your truck. Just a idea, thought this info might help someone... I unkinked the hose and now I have power brakes and they release quickly..
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Re: CCKW Brakes locked up

Post by Joe Gopan » Mon Aug 05, 2013 8:25 pm

If you do not make out with the hydrovac rebuild, I will have a nice 1st Series available soon that was dated 1968. I am installing a 3rd Series Kit on my CCKW.
2011 MVPA PIONEER AWARD - MVPA #1064
HONOR GRAD-WHEELED VEHICLE MECHANIC SCHOOL 1960 - US ARMY ORDNANCE SCHOOL(MACHINIST) ABERDEEN PG 1962 - O-1 BIRD DOG CREWCHIEF - 300,000+TROUBLE FREE M-38A1 MILES
LIFE MEMBER AM LEGION-40/8-DAV
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COL. BRUNO BROOKS (ARMY MOTORS) IS MY HERO

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Re: CCKW Brakes locked up

Post by Bean » Tue Aug 06, 2013 3:18 pm

Thanks for all of the replys.The Hydrovac is back at the rebuilders.And I must say If any of you are planning to have your Hydrovacs rebuilt do not use Rebuilders Enterprises in Chicago Il.I am not one to trash a company ,and I am very patient.But this is getting way out of line.First they tell me it would be done in two weeks tops.That was in Febuary. Then they lost it for five months( It went to Guawda Mala) and sent me the wrong one in its place.When I finally got it back it did not work.They said during rebuilding it was sent to a machine shop to be sleeved and this was a extra cost.Well,When I got it,It was not sleeved at all,Just honed out.And all of the interior parts are what I installed 8 years ago!!!I sent it back( at my expense) 4 weeks ago and it still hasn't been looked at.All in all it has cost me $430.00 for the rebuild $34.00 to return the wrong one and $55.00 to return mine because it doesnt work.Not to mention my truck is unusable now for going on 8 months.The salesman I call Bill(Every week) just blows me off as if I am bothering him.Worst experience in my 30 years of restoring military trucks..

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Re: CCKW Brakes locked up

Post by Joe Gopan » Sun Jan 21, 2018 8:22 am

CCKW owners, many of you are new o the CCKW and are not aware of this. The Series 1 (Double Ended) and Series 2 (Single Ended) OEM Hydrovacs require the Check Valve to be located in the Master Cylinder. The 3Rd Series Bendix Part No. 374450 "Short Fat" is the latest upgrade and has the Check Valve located in the Hydrovac, it requires the removal of the Check valve located in the Master Cylinder. If the Check valve is left in the Master Cylinder on this installation, the brakes will not release when the pedal is let up. The 3rd Series is a Post WWII upgrade from around 1948. Not all trucks got the upgrade. It cane as a kit with new brackets, hose, etc..
2011 MVPA PIONEER AWARD - MVPA #1064
HONOR GRAD-WHEELED VEHICLE MECHANIC SCHOOL 1960 - US ARMY ORDNANCE SCHOOL(MACHINIST) ABERDEEN PG 1962 - O-1 BIRD DOG CREWCHIEF - 300,000+TROUBLE FREE M-38A1 MILES
LIFE MEMBER AM LEGION-40/8-DAV
7 MIL SPEC MAINTAINED MV'S
COL. BRUNO BROOKS (ARMY MOTORS) IS MY HERO


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