Master Cylinder Bad?

[GunInstructordotcom]

My 1970 M35A2C had been sitting for about 3-4 years now. I fixed the hydraulic head problem that was causing the lack of use. Now I turn to the brake system and discover no brake fluid in the master cylinder. There was a black paste on the bottom of the reservoir. I cleaned out the paste with some giant q-tips I have for gun cleaning. I filled it back up with Dot 5. Looking from the bottom, the entire master cylinder is wet with brake fluid and there was a drip coming off the bottom. My guess is I need a new master cylinder. This one was on the truck when I purchased it in 2001 from a dealer in Idaho. He obtained it from a government surplus sale, so the master cylinder has some mileage and age on it. Is it safe for me to assume I need to replace it?

 

[NY Tom]

There may be a rebuild kit out there.

When I did the brake system I was able to find a replacement for a reasonable price.

 

[SCSG-G4]

The deuce brake master cylinder is a standard design, used in the GMC medium duty trucks from 1937 to 1959 (single cylinder), just like the M-37 brake master cylinder rebuild kit is the same as the 1936 Packard. BTW, the Packard rebuild kit is NAPA part number ONE as Ferro pointed out on another post.

 

[glcaines]

I would definitely go ahead and replace it or rebuild it. The brakes are the most import part of a deuce.

 

[WillWagner]

If you are versed on repairing, that is the most cost effective thing to do. Before you go buy a kit, pull it and tear it down. Pass a hone through it to see if the bore has pits in the bottom of it. No pits, rebuild it. If it is pitted, you'll need a new one.

If it is a rebuildable cylinder, stay away from the Chinese rubber parts, buy genuine Bendix or Raybestos parts. There are only 3 rubber parts inside, the cup, V seal and the check valve washer. Most of the time the washer can be reused but if there is gunk in the bore, the cup and seal will be ruined.

 

[cattlerepairman]

Maybe this thread helps:

My Master Cylinder Rebuild with Photos

So here I am again but now with my Master Cylinder rebuild. After my Airpack rebuild the brakes were allot better but I was loosing pressure in the pedal while it was being held down. If you are interested you can see the Airpack rebuild here...

www.steelsoldiers.com

 

[GunInstructordotcom]

There may be a rebuild kit out there.

When I did the brake system I was able to find a replacement for a reasonable price.

I found NOS for $100 delivered. Now I have to tackle the dreaded fourth bolt. Garrett's video is quite helpful. I can't figure out what that black residue is which was in the bottom of the reservoir. By the way, I found my missing copper lid gasket lying on the boot. Apparently, I had been running it without the gasket for some time.

 

[GunInstructordotcom]

Maybe this thread helps:

My Master Cylinder Rebuild with Photos

So here I am again but now with my Master Cylinder rebuild. After my Airpack rebuild the brakes were allot better but I was loosing pressure in the pedal while it was being held down. If you are interested you can see the Airpack rebuild here...

www.steelsoldiers.com

Thanks for that link. I missed that thread while doing my research.

 

[NY Tom]

The bolt is not that bad...compared to working on a Porsche...

 

[GunInstructordotcom]

The bolt is not that bad...compared to working on a Porsche...

Or putting headers on a 289 Mustang where you have to pry the tubes to align the bolt holes, in tight quarters while hunched over the fender. A wise experienced mechanic told me years ago that, if you can extend your ratchet outside the tight work area, things go much smoother. I invested in some long extensions, 1/2" and 3/8", and they have been valuable at times.

 

[GunInstructordotcom]

Thank you for all the advice. I'll update the thread when my master cylinder arrives and I give it a go.

 

[cattlerepairman]

The bolt is not that bad...compared to working on a Porsche...

I just did spark plugs and coils on a 996. It was super easy with my three child-sized hands, foot-long fingers and jointless bendability. Grrrrrrrrr.

 

[WillWagner]

The bolt is not that bad...compared to working on a Porsche...

Or the #8 spark plug on a 5.7LS in a Tahoe or any GM truck for that matter!

 

[GunInstructordotcom]

So everyone agrees I should leave the difficult fourth bolt off when I install the new master cylinder? Or should I give it a try?

 

[NY Tom]

Give it a try. I got it back on.

 

[WillWagner]

It really isn't hard. Put it back where you found it.

 

[cattlerepairman]

As a related and totally thread-highjacking rant, I find it increasingly difficult next to impossible to source the automotive fine thread bolts and nuts I need for the truck. Everyone around here only seems to stock coarse thread and I do not really want to order 200 of every single frigging bolt size I need when I try to order them in.....rant over!!!!
Also "having an item in stock" is rapidly becoming a phrase from the bygone olden days.....

 

[NY Tom]

As a related and totally thread-highjacking rant, I find it increasingly difficult next to impossible to source the automotive fine thread bolts and nuts I need for the truck. Everyone around here only seems to stock coarse thread and I do not really want to order 200 of every single frigging bolt size I need when I try to order them in.....rant over!!!!
Also "having an item in stock" is rapidly becoming a phrase from the bygone olden days.....

Depending on the location I sometimes have luck with ACE. Otherwise I am stuck ordering from McMaster.

But you are right. Hard to find things on the shelf these days and people behind the counter to help you with what you can't find yourself.

 

[GunInstructordotcom]

Depending on the location I sometimes have luck with ACE. Otherwise I am stuck ordering from McMaster.

But you are right. Hard to find things on the shelf these days and people behind the counter to help you with what you can't find yourself.

Don't forget the prices. Always going up, sometimes monthly. Thank you, Brandon.

 

[GunInstructordotcom]

Well this is funny. After watching Garrett's video again, I checked if my deuce has the fourth bolt on the brake master cylinder. It does not. Some mechanic decades ago, probably in the military, did not re-attach the fourth bolt. Well, that makes my life a bit easier come Saturday's installation of my new master cylinder.