M1008 Brake problem

[sht2kll]

Howdy all: A couple of weeks ago, after coming to a stop, my rear brake/brakes would drag a little. I read on this site a post that said to check the seals. A few days after noticing the problem, I apply the brakes coming to a stop and the pedal goes to the floor. Upon inspection, I find the right rear line leaking. This is a rusty M1008 from New Hampshire. I change the Rt. and Lt. line the hose and the little "C" shaped one from the proportioning valve to the hose. I rebuild the brakes. The left side was a gummy mess (leaking seal). Brakes work well, all is good... so I thought. four days ago. I am at a stop and the brake pedal felt a little squishy. I pushed harder then let off, the red brake light came on. push on brake, light goes out, let off, light comes back on. I did this a couple of times. I go to take off and the truck will not move. I floor it and overcome the brakes to get it off to the side of the road. I open the left bleeder and fluid comes squirting out. I jump in and drive home with no problem. I pull drums to see if anything is amiss. Everything is in order. The truck has not done this again, so I do not know if the right was locked up also. While replacing the lines, I played with (wiggled) the arm on the proportioning valve. could this rusty thing be causing it not to let off the pressure? Sorry for the long post. Thanks to you all for the knowledge and experiance you share. Tom

 

[dependable]

Sounds like it was a proportioning valve issue, as letting off fluid pressure freed you up. Maybe your problem is solved. Remember there are two valves. The 'rusty one with the lever' and the main valve on the cross member behind the radiator, This is the one that controls the brake light. One thing that sometimes gums them up is if there are two types of brake fluid mixed in system (DOT 3 and DOT 5).

 

[twomorestrokes]

Yes make sure you don't mix fluids. These trucks use silicone based dot 5 which is harder to find and far more expensive.

 

[sht2kll]

I am well versed with silicon. Thanks for the reinforcement of what I was thinking. Now the only problem is that I can not get a proportioning or combitantion valve. The worthless manufacturer GM, I have issuses with GM these days, has discontinued both of them and none of the parts places have them listed anymore either. I have been trying online Military Vehicle salvage and civi salvage to no avail. Next option is to eliminate the propo valve or both and graft in an aftermarket propo valve.

 

[Sharecropper]

sht2kll - I would completely purge and refresh all brake fluid to dot 5, and then make sure the rear proportioning valve is adjusted correctly. Instead of going into it here, please review post #75 in my rebuild thread http://www.steelsoldiers.com/cucv/54469-kinda-got-carried-away-8.html

Hope this helps.

 

[sht2kll]

Thanks Sharecropper. I will look at the orientatin of the valve. Although I am not sure how it would have changed just by wiggling pieces by hand. the linkage is close to 90'. When I changed the lines and hoses, I bled the brakes with DOT 5. I used about a pint and a half of fluid when I bled them. I figured that would be enough. The fluid was a nice purple color. The brakes seemed to work well for about the first week. Are the proportioning valves rebuildable? The one on my truck is rusted really bad. The brake line rusted through. That is what caused the failure. Tom

 

[Sharecropper]

Tom - My rear proportioning valve is rusty too but seems to be working properly. I'd be willing to bet there's a quantity of those things laying around boxed up somewhere. Don't believe they are rebuildable.