CCKW Brakes locked up

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Joe Gopan
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Re: CCKW Brakes locked up

Post by Joe Gopan » Mon Jul 08, 2013 6:20 am

It was noted that the problem exists with the Master Cylinder disconnected. The correct procedure for adjusting the CCKW master cylinder linkage is listed in TM9-801.
The fact that the truck has sat for years is good reason to do a thorough inspection and service of the complete brake system.
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Re: CCKW Brakes locked up

Post by j506 » Mon Jul 08, 2013 9:58 am

I though good useable rebuild kit for series 1 and 2 hydrovacs were long gone only series 3 were avail
Is there a possibility your rebuilder used incorrect parts?
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Re: CCKW Brakes locked up

Post by Joe Gopan » Mon Jul 08, 2013 12:04 pm

I have only seen one reference to fresh recent manufacture Series #2 Kits and that was from someone who claimed to have found it in Norway, I believe. Any existing WWII period kits have dried out components, especially the seals and are not fit for use. There were some early type 1st Series Hydrovacs (Double Ended) that were manufactured by Bendix of France and dated 1968, I bought several from SECO and installed one of those on my CCKW in 1984, it has functioned perfectly since then.
The safest Hydrovac for CCKW use would be a professionally reconditioned Series #3 BENDIX 374750. The Army had post war kits with brackets, hoses, tubing, and hardware to retrofit these and replace the earlier models. These are the way to go and result in more sensitive braking. Beware of the foreign copies of the 374750 3rd Series which are metric and will not accept Made in USA fittings.
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Re: CCKW Brakes locked up

Post by Bean » Mon Jul 08, 2013 12:33 pm

Thanks again for you help.I have adjusted the master cylinder push rod all the way in,So there is plenty of play in the pedal.And yes if I open the hydro vac bleeder when the brakes are locked,They unlock.Seems to me that the Hydro vac is holding pressure.I had it rebuilt by Rebuilders Inc in Chicago.They are a brake booster specialty co.They where referred to me by a well know CCKW parts dealer.BUT to be honest,I have had nothing but problems with them.I sent the booster to them in Febuary.They said I,d have it back in 2 weeks tops.I just got it back last week(missing all the fittings) and now apparently it doesn't work.I did contact them today and they said to send it back.I'm very frustrated with this whole thing.

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Re: CCKW Brakes locked up

Post by Joe Gopan » Mon Jul 08, 2013 1:28 pm

can you post a pic of your Hydrovac?
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Re: CCKW Brakes locked up

Post by Bean » Mon Jul 08, 2013 2:15 pm

Ben,
TM9-801 page 332

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Re: CCKW Brakes locked up

Post by Joe Gopan » Mon Jul 08, 2013 2:25 pm

Did you hook up the hydraulic lines the same as shown in the same TM9-801?
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Re: CCKW Brakes locked up

Post by Bean » Mon Jul 08, 2013 2:31 pm

Yes I followed the TM.I got the lines new pre bent From Frank a few years ago.

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Re: CCKW Brakes locked up

Post by artificer » Mon Jul 08, 2013 2:44 pm

Basic check of hyrovac....engine not running pump brake pedal hold on starting engine the pedal should go down.

It seems obvious that if you release a wheel cylinder nipple the brakes come off & you release a line @ the master cylinder they do not come off
With the hydrovac atmospheric pressure is what helps you apply the brakes but spring & vacuum is what helps you release them
You have, it appears, a mechanical issue with the hydrovac causing a hydraulic non return issue that will most likely be associated with one of the following


Hydrovac:
1. Broken vacuum cylinder piston return spring [unlikely]
1a. Atmospheric not being replaced by vacuum so brakes are held on
2. Broken or incorrectly installed valve diaphragm return spring
3. Sticking control valve piston
4. Check/by pass valve in hydrovac slave cylinder
5. Swollen rubber components due to fluid contamination

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Re: CCKW Brakes locked up

Post by Bean » Wed Jul 10, 2013 5:11 pm

OK,hydro vac is going back to the rebuilders.I hope they get it right this time :roll:

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Re: CCKW Brakes locked up UPDATE

Post by Bean » Sun Jul 14, 2013 7:53 am

Well I removed the Hydro Vac to send it back to the rebuilder.Just out of curiosity I connect the two brake lines that went to the hydro vac together. Now the brakes work fine.

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Re: CCKW Brakes locked up

Post by Joe Gopan » Sun Jul 14, 2013 8:15 am

Good decision.
Years ago, the local Bendix Authorized Service Station had a Bendix testing machine that they would use to test New, used, and rebuilt Hydrovacs. Those days are long gone as Bendix stopped supplying parts and Kits to repair Hydrovacs. Bosch is now the repair parts supplier and they do not make parts for the #1 and#2 Series Hydrovacs.
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Re: CCKW Brakes locked up

Post by Bean » Sun Jul 14, 2013 9:57 am

I do not know where this company is getting the parts to rebuild these hydrovacs.But,I did peek inside mine and it does appear to have new parts in there.Although,It was not sleeved as the rebuilder had told me,(added additional charge for machine work) :x Looks like it was just honed .

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Re: CCKW Brakes locked up

Post by Joe Gopan » Sun Jul 14, 2013 1:19 pm

In order to recondition the 1st and 2nd Series, some parts have to be reused, and that is normal.
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Re: CCKW Brakes locked up

Post by johne504 » Sun Jul 14, 2013 3:36 pm

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.
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