1st test drive - didn't make it home!!

[nosto]

Finally got the whole truck in primer, worked out all the leaks in the bags, and for the first trip on the road in 18 months, I was heading to the local custom muffler shop to get an exhaust system.

Never made it!

On the 55mph highway for 3 miles, truck started slowing, and slowing..... then saw smoke. Pulled into a gas station with all 4 brakes locked, zero pedal travel.

I did a search on "locked brakes" and most of the suggestions point to the prop valve as the most likely source of the problem.

BTW; Brake system is original rear drums, with all new parts, hoses and lines. Front discs are from a '77 C-10(with power brakes). I DO NOT have the power brakes (the booster was missing from the junker, and I don't really like power, anyhow.)

Questions:
Is the prop from a power system the same as for a non-power system?
Do I just need to 'reset' it by holding the pin/button in while I press the pedal?

On a brighter note: the rear fuel tank and fender filler neck mod can take fuel as fast as they can pump it......

Thanks,

[Blue68]

AHHH, this sounds like a case of the brake lines too close to a heat source, like the exhaust. This assuming they un-locked after sitting for a while. Steering doesn't affect the prop valve, only the disc-drum or drum-drum or disc-disc combo matters.

So, what kind of fuel tank and filler setup do you have? Got pics?

[nosto]

Hey, Blue68, thanks for the reply. I'm still sitting here waiting for the brakes to cool down so I can crawl home. The brake lines and exhaust are in the same location as they were when I got the truck 1 1/2 years ago; I haven't changed anything there....Hmmmm

My question wasn't phrased too well, what I meant is: Is the prop valve from a power BRAKE system the same as one from a non-power brake system.

The fuel tank is the poly Blazer type I got from one of the fine vendors on this board. The fuel filler door and neck is from a Mazda 323 and is patched into the side of my fender. Here's a pic I posted a few weeks ago.

[Blue68]

Yes, it will be the same. Its role in life is to ensure a 70/30 split (or so) between front and rear pressure. It's up to you to provide pressure if you don't have a booster.

Good luck on the crawl.

[ckenwright]

I know of a guy who changed his front end out to get disk brakes. When he installed them he never put in the proportioning valve and he says it still stops alot better than it did with the drums and he is using manual brakes. I think he should have the prop valve to get full use out of his rear brakes though. You can always remove the part to see if that is the problem before you go buy a new one, but I would not go very fast or go anywhere that there is much traffic before I got the problem solved.

[tommie]

are you sure that the front calipers aren't sticking?

stay off the freeway untill you figure out the problem...

tommie

[Blue68]

He said all 4 brakes locked. The proportioning valve only trips and locks "out" the front or rear circuit so that they don't get fluid, in case of ruptured line you still have brakes.

[tommie]

how could you tell when driving that all 4 brakes locked up?

and not just the front or rear?

i have never seen a proportioning valve cause all 4 wheels to gradually lock up.

the most common thing i have seen lock up all 4 wheels when hot then release them when cold was contaminated brake fluid, usually it seems to have power steering fluid in it.

just telling you
what i have seen from experience.

tommie

[tom hand]

If all four brakes are locked up I would be willing to bet it is a problem with the master cylinder. The brake system is too seperated for it to be anything else. I would first suspect a defective m/c or somthing in your pedal linkage that is not letting it return

[nosto]

Took another test run after dinner, same lack of forward progress after a few miles, but I made it home this time. Jacked up front, both wheels... locked tight....jacked up rear...they spun nicely. Hey, I THOUGHT all four were locked, oh well.

Then Tom Hand wrote...

...or somthing in your pedal linkage that is not letting it return

Ah, Hah...
Went through the '67 Service Manual for more clues, and ran into the section that says...."make sure there's 1/8" freeplay on the brake pedal at the MC rod". Mine was 0" freeplay, more like 1/2" pressing into the MC all the time. When I switched to a '77 MC, I didn't bother to readjust the rod. Needless to say, that was the problem.

Backed the rod out 1/8" and drove 10 miles with no brake problems.

Now, on to the next problem..... the backward wiper motor!

Thanks for all your input on this, folks!

[69 Short Fleet]

You just gotta love that avatar!!! (LMAO)!!!!

[nosto]

If you like unusual flamed items, there's a few more of those at

Fins & Flames

[krue]

Let me know what you do to fix your wiper!

[71GMC_3/4T]

My guess on the wiper motor is that you got the crank 180* out of phase on the motor.

[speesh]

hey thats a cool site! I like the manta rays.........

[slogo]

that's a bummer on the brakes hope you get it figured out.