Brake issue, ideas welcome

[Prospect62]

My M1009 appears to have been sitting for some time when I got my hands on it. Before I tore into it, I took it for a short (1/2 mile) shakedown run and quickly realized I had a caliper sticking (driver front). Got hot to the point of smoke rolling out and me being unable to touch anything around that wheel for over an hour due to the heat. When I got home, as I pulled into the driveway, the brake pedal suddenly went to the floor and I lost almost all braking capability. I did get the rear passenger side to lock up if I really mashed the pedal.

Quick inspection revealed no outward signs of brake fluid leaking anywhere. Never had a pedal go right to the floor before and not had a leak somewhere, so I am stumped.

With the truck off, the pedal still feels spongy after several pumps. I am currently doing the entire front end (calipers and pads, hub/rotors, bearings, seals, ball joints, u-joints, etc). I have a vacuum bleeder and I will bleed when done.

I was just wonder what might have failed causing me to lose the pedal but with no leaks. Proportioning valve? Master cylinder? Did I boil the fluid? What do you guys think?

 

[dougco1]

My M1009 appears to have been sitting for some time when I got my hands on it. Before I tore into it, I took it for a short (1/2 mile) shakedown run and quickly realized I had a caliper sticking (driver front). Got hot to the point of smoke rolling out and me being unable to touch anything around that wheel for over an hour due to the heat. When I got home, as I pulled into the driveway, the brake pedal suddenly went to the floor and I lost almost all braking capability. I did get the rear passenger side to lock up if I really mashed the pedal.

Quick inspection revealed no outward signs of brake fluid leaking anywhere. Never had a pedal go right to the floor before and not had a leak somewhere, so I am stumped.

With the truck off, the pedal still feels spongy after several pumps. I am currently doing the entire front end (calipers and pads, hub/rotors, bearings, seals, ball joints, u-joints, etc). I have a vacuum bleeder and I will bleed when done.

I was just wonder what might have failed causing me to lose the pedal but with no leaks. Proportioning valve? Master cylinder? Did I boil the fluid? What do you guys think?

I should have offered to sell you my M1009

 

[Prospect62]

Yeah I got a real money pit here. Thank goodness parts are cheap but man it's adding up. Very dishonest Facebook seller.

 

[Curtisje]

I'm no brake expert but if it were me I would:
Replace both front calipers, pads & rotors.
Replace front wheel bearings.
Check and replace rear brake pads, hubs and bearings as needed.
Bleed out all old brake fluid.

I think your pedal went to the floor because of the heat in that brake. Brake fluid does have a boiling point; 400 for DOT 3, 450 for DOT 4, 500 for DOT 5. Once it boils you loose your brakes.

That heat could also have affected your wheel bearing. At keast clean it up, check it and if the bearing and race are good repack with grease and put her bavk together.

Good luck. You'll get it figured out.

 

[Prospect62]

Found a pinhole leak in the hydroboost line, what I assume is a low pressure line?
Not too sure if that would cause a pedal to sink. Brake fluid is an entirely different circuit. Either way this must now be repaired as well.

 

[Barrman]

Low pressure Hydro boost hydraulic leak won’ do the pedal drop like you had. I agree about boiling fluid.

I would also suggest brake hose replacement.

 

[MarcusOReallyus]

I think your pedal went to the floor because of the heat in that brake. Brake fluid does have a boiling point; 400 for DOT 3, 450 for DOT 4, 500 for DOT 5. Once it boils you loose your brakes.

Exactly. Boiled = turned into a gas. Having any kind of gas in their is the same as having air in their. That means no brakes.

But it's 'lose your brakes'. "Loose" rhymes with goose, or moose, or juice, which is weird, but that's English!


And yeah, if it got that hot, lots of things got trashed, or at least compromised. You don't want to mess with brakes
.

 

[LT67]

I'm no brake expert but if it were me I would:
Replace both front calipers, pads & rotors.
Replace front wheel bearings.
Check and replace rear brake pads, hubs and bearings as needed.
Bleed out all old brake fluid.

I think your pedal went to the floor because of the heat in that brake. Brake fluid does have a boiling point; 400 for DOT 3, 450 for DOT 4, 500 for DOT 5. Once it boils you loose your brakes.

That heat could also have affected your wheel bearing. At keast clean it up, check it and if the bearing and race are good repack with grease and put her bavk together.

Good luck. You'll get it figured out.

^^what he said...

Just to be on the safe side, flush out all of the old brake fluid and clean the lines. Ya never know if someone may have mixed DOT 3 with DOT 5 fluid...

 

[Prospect62]

Good advice. Everything in the front end is getting replaced, I will do my best at flushing, replacing with DOT5 and bleeding. Then I’ll see what the rears look like.
I was mainly curious about the proportioning valve and if I “tripped” it because I’d rather not mess with that. Seems like boiled fluid was a very good possibility.

 

[MarcusOReallyus]

I will do my best at flushing, replacing with DOT5 and bleeding.

IIRC, the military published a 'how to' on flushing the brake system. I think they used isopropyl alcohol to wash it out. Not your basic drug store rubbing alcohol - that's mostly water. You can get 95% on Amazon.

I don't know if that procedure is on the web site here, but if it is, it's probably in the TM section.

 

[Mullaney]

Exactly. Boiled = turned into a gas. Having any kind of gas in their is the same as having air in their. That means no brakes.

But it's 'lose your brakes'. "Loose" rhymes with goose, or moose, or juice, which is weird, but that's English!


And yeah, if it got that hot, lots of things got trashed, or at least compromised. You don't want to mess with brakes
.

.
Yes Sir. The English language has a lot of pitfalls There and Their and They're. Lot of others too: Fair and Fare, Die and Dye, For and Four and that is just a few. I wonder how much our military might have used the subtleties of our language to eliminate potential enemies.

As far as alcohol is concerned, Isopropanol 99% is the way to go if you have a choice. We buy it in 55 gallon drums and without gloves, it will turn your hands to a white flaky mess. It sucks all the oil out of your skin...

 

[LT67]

Good advice. Everything in the front end is getting replaced, I will do my best at flushing, replacing with DOT5 and bleeding. Then I’ll see what the rears look like.
I was mainly curious about the proportioning valve and if I “tripped” it because I’d rather not mess with that. Seems like boiled fluid was a very good possibility.

DOT3 will work very well. Just not mixed with DOT5....

 

[cucvrus]

What I do on every resurrected vehicle that I get is replace everything brake and seal related. Now we are talking just brakes at this point. Brakes are very very important of course. But getting all new pads, shoes, calipers, hoses, wheel cylinders, axle seals and all clean fluid is very important. I have seen the crud and contaminated fluids in a brake system many times. But I would not even question changing out the bell shaped rear drums and the front rotor at this point to do the job top notch. It costs a bit more but in the end it is done right and it will stop straight and true. Every time. Crawl under that vehicle and closely examine every inch of the metal brake lines. Look for compression fittings and poor splices. Some leaks are minute and the fluid can soak into dirt and rust under the vehicle before it forms a drop and falls to the ground. I even seen larger leaks just travel on the frame flange and stay up there. Check everything closely. Even to the point if the metal lines look crispy/rusty it time to change them. If you see shabby work under there eliminate it with good quality replacement parts. Compression fittings are not for brake systems. Double flares are needed at every connection. Except no other. Good Luck and report back. Doing it right the first time cost more but safety out weighs the expense.

 

[cucvrus]

This guy saved 25% on his brake job. Don't take the short inexpensive end of braking system on any vehicle. Make sure they are there when you need them. Good Luck.

 

[rtk]

This guy saved 25% on his brake job. Don't take the short inexpensive end of braking system on any vehicle. Make sure they are there when you need them. Good Luck.

I bet that left a mark !!!!!!!

 

[Mullaney]

This guy saved 25% on his brake job. Don't take the short inexpensive end of braking system on any vehicle. Make sure they are there when you need them. Good Luck.

.
'Tis a scratch.
Nothing but a mere flesh wound!

A little bit of sanding and a spot of bond-o will bring her back...

 

[Recovry4x4]

Brake components are cheap for the CUCV trucks, that's a plus. Now, regardless of why the pedal went to the floor and caused a minimal brake issue, another issue has been created and will need addressed. For years and years that master cylinder piston has been travelling about the same amount of travel in the bore and as such, has likely kept that bore clean in those areas. Now suddenly, the piston and seals have been pushed into an area known to build up crud and such, maybe even some rust. This can destroy the cups. I would not trust that master cylinder as far as I could spit it. Considering the minimal costs involved, I would replace the master, calipers, wheel cylinders, all 3 rubber hoses and for a few dollars more, all the steel line from the proportioning valve to the rear. My bet is all that would be less than $200 and would be done right. I cringe when I see folks pumping brakes and letting the pedal fall to the floor. Fixed way too many master cylinders to do things that way.

 

[MarcusOReallyus]

.
Yes Sir. The English language has a lot of pitfalls

Not to be confused with pratfalls!

 

[Prospect62]

I am changing everything mentioned with the exception of the hardlines from the proportioning valve back. Unless I find a leak. They look remarkably clean and rust free so far. As stated, brake parts are cheap. I'll report back on my results.

 

[TedO]

What I do on every resurrected vehicle that I get is replace everything brake and seal related. Now we are talking just brakes at this point. Brakes are very very important of course. But getting all new pads, shoes, calipers, hoses, wheel cylinders, axle seals and all clean fluid is very important. I have seen the crud and contaminated fluids in a brake system many times. But I would not even question changing out the bell shaped rear drums and the front rotor at this point to do the job top notch. It costs a bit more but in the end it is done right and it will stop straight and true. Every time. Crawl under that vehicle and closely examine every inch of the metal brake lines. Look for compression fittings and poor splices. Some leaks are minute and the fluid can soak into dirt and rust under the vehicle before it forms a drop and falls to the ground. I even seen larger leaks just travel on the frame flange and stay up there. Check everything closely. Even to the point if the metal lines look crispy/rusty it time to change them. If you see shabby work under there eliminate it with good quality replacement parts. Compression fittings are not for brake systems. Double flares are needed at every connection. Except no other. Good Luck and report back. Doing it right the first time cost more but safety out weighs the expense.