Need help with brakes on M35A2

[Sarge 69]

I have a 1971 m35a2 and the brakes won't release all the way. It only does it when it is warm outside in the winter they work fine. When the brakes stay on the brake petal is very stiff and will barley move. I have replaced the airpack on it and that did not help. When I bought it from the military the brakes did not work, their was a bad brake line and no fluid in it so I fix it and put dot5 brake fluid in it. I am not familiar with the air over hydraulic brake system that is on them so if anyone could give me some info on this matter that would be great.

 

[welldigger]

How long ago did you replace the air pak? Did you replace it with a new or used unit? Does it do it constantly during warmer weather or every now and then? Your symptoms sound like a frozen air pak. The air over hydraulic system on these trucks is very simple. Think of the air pak as the vacuum booster on your car. Except instead of using vacuum it uses the air pressure generated by the on board air. This simply boosts the braking power.

 

[Sarge 69]

I put a new one on it about 6 months ago. Some time when its warm it will not do it until you dirve it a little ways. I looked at the valve in the airpack when I put it in and it looked great. I put some air tool oil in it when I put it in to help lubricate it.

 

[doghead]

Have you looked in the bottom of your master cylinder? Are the 2 tiny holes clear(not plugged). Is it perfectly clean(no rust).

Is your master cylinder/brake rod adjusted properly?

Is your master cylinder vented properly?

You can remove the lube plug on the air chamber of the air pack, and hold your finger over it, and see if air builds with no brake pedal pressure. If it does, your air pack is leaking air into the cylinder.

 

[welldigger]

Hmm...has it been doing this since you owned the truck or did it suddenly start? Sounds like you need to go through the brake system and inspect everything. Check your master cylinder and pull each drum off and inspect the shoes and wheel cylinders. Also check or shoe adjustments.

 

[Sarge 69]

The inside of the master cylinder is clean with no rust. The brake shoes and drumes are good. They will still stay on alittle bit if you dran all the air out but not as bad as when there is air pressure.

 

[welldigger]

When your brakes hang up crack the bleeder on the air pak and see if they release.

 

[Sarge 69]

Ok will have to try

 

[Adrian A]

Make sure both holes in the master resevoir are open. There is one tiny one that releases the pressure that is famous for clogging.

 

[Sarge 69]

Ok thanks for the info

 

[Adrian A]

I rebuilt my master cylinder and actually never saw the little hole. I had to do it twice. Lessons learned. At least it was cheap to fix.