The GMC CCKW

I pulled the 4 rear wheel cylinders off this week. It turns out 2 appear to be original and 2 have been replaced. I say both because 2 have casting numbers (5300892) on them and have been resleeved. The other two are plain. The resleeved ones have rubber plugs with a nipple in the center. There is a metal plate that fits over the nipple and clips on to the spring. The plain ones don't have this.

According to my CCKW owners guide from VoV, I think the plain ones match the diagram and are original. The ones with casting numbers are replacements. Is this correct?

All are made by ACDelco but Napa, Carquest and even ACDelco couldn't identify the casting number. ACDelco could tell me the 5300892 was a good number (duh!) but nothing more than that. Is there a source other than VoV for rebuild kits? He is out of stock right now because I got the last one.

I was happy to see the 2 resleeved ones. Although they were stuck badly, they cleaned up very nicely with the cylinder hone. The pistons were in good shape as were the rubber cups. The other 2 were also stuck but cleaned up fairly well with the hone. I guess I will find out when I put them back on the truck.

The cylinders and caps were sandblasted (masking off the machined areas) and painted with gloss black caliper paint. I won't win any shows like that, but I will know which parts have been rebuilt. Next time I am just going to spend the money on new resleeved cylinders. This is just too much work.

I was considering pumping brake fluid through the steel lines before hooking up the hoses. Is this necessary or am I being overly cautious?

Neil

Jim Carter Antique parts has the unsleeved new wheel cylinders.

I would be wise to flush/bleed as much air out of the system before you start.

SpookyDad wrote:
I was considering pumping brake fluid through the steel lines before hooking up the hoses. Is this necessary or am I being overly cautious?

Neil

Neil

I pressure flushed my lines prior to removing to old cylinders to get any possible gunk out of the lines.

I removed the lines to each wheel cyliinder 1 at a time starting with the farthest from the master and at a very low pressure let the brake fluid run out. I then finger tight reattached each line. When all were bled I raised the pressure a little and let each seep at the wheel cylinder as I tightened the lines up. I then let is sit 48 hours and flushed again.
After this second flush the lines were reattached to the new wheel cylinders which were installed.

Some strange stuff and dark fluid came out the first time. The second was mostly clear. I would hate to have pumped that dark fluid into new wheel cylinders.

The above procedure was pulled out of a restoration book I read many years ago.

Bill

>Some strange stuff and dark fluid came out the first time. The second was mostly clear. I would hate to have pumped that dark fluid into new wheel cylinders. >

That is why just flushing the lines using the bleeders is NOT a great idea. You are now putting all that gunk and particles into the delicate wheel cylinder.

Bill has it right!

There is a post somewhere on this site with a Part# for NAPA new rear wheel cyl.
Wheel cylinder repair kit is Raybestos # 37 or equavalent.

John

I disconnect all lines + hoses and flush them with an alcohol (isopropanol or another dry cleaner) at least 2 times. Then, I dry them with air before connecting them back on the truck. Most of the time, I replace the hoses because they are cracked. Like Steve, I would hate to have old fluid or impurities in new cylinders or a restored hydrovac.
I found many different cylinders on my trucks or as army spare parts, made by lookeed, Delco, Stop, and some other manufacturer I forgot. They have different designs and cups but all are working great as long as they are correct for the cckw

Thierry.

I agree with Thierry.

When the US Army was evaluating brake systems and considering the switch to Silicone brake fluid, they found as a side line that flushing an existing system was a very important step.

The testing resulted in the development of a brake system flushing procedure that specified the use of alcohol prior to installing any new brake fluid. The Army found the same thing Neil did, there is some really ugly stuff that comes out of the system.

I can't find the report but remember that alcohol was the specified fluid for flushing.

I don't have an automotive pressure brake bleeder system, but purchased a small 1 gallon plastic garden hand spray can at the hardware store. We adapted a hose and fittings for brake filling. And use the can only for brake work. It works really well when flushing and bleeding brake systems without an assistant.

Cat Man

Yes, the insecticide sprayer works well as a pressure bleeder. You need a master cyl cap with a fitting on it or as I use, an M211 master cyl extension which has a cap with fitting.