Rear Brake Proportion Valve question

[dieselbegreat]

Folks:
I'm dealing with rusted brake lines -- you know, trying to replace only what's needed and everything else snaps or strips when you touch it. :mad: This is another reason why I now try to use anti-seize lube on everything!!

Question: Can I bypass the variable rear Brake Proportioning Valve? The fittings are stripped and won't come out, rendering the valve useless. Where is the cheapest place to get one (used is good) if needed? Thanks.

P.S.: If I may say so, don't ever get Ziebart rust treatment! The paint-like coating they spray on cracks and seals moisture in which never dries out. The result has to be worse than if you'd used nothing and just washed your truck underneath. (I'm talking layers of painted rust coming off.) I understand the best rust treatment is Krown and Rust Check, both of which are only in Canada sorry to say. The coating is a thin creeping tar-like substance which needs reapplication yearly for best results.

[dieselcrawler]

I sure wouldn't try to bypass the proportioning valve, you'll end up with your brakes locking up on one end or the other, before the other end. I think you can get new replacement ones from LMC truck, don't have the phone # in front of me, but have seen a link to it elsewhere on this page... (anyone got that link handy?)
If your old fittings are simply just froze up, my advice is soak them with penitrating oil, (my favorite is PB Blaster, works great) spray all fittings sevral times, let it sit over night, and do it again then next day. Then get your best, newest, sharpest set of Vice Grips, and take 'em to what's left of the brake line fittings in your prop. valve. They should come out, it's always worked for me... if there's not enough of the fitting to grab with the Vice Grips, well, then, you might be shopping for another valve. If you check out a junk yard, make sure you get one from a truck that has the same front and rearends, with the same brakes, as diffrent size calipers and wheel cyl. will affect your brake performance. Another note, you most likely will need adaptors to go from the standard size line fittings to the fittings on the prop. valve, as they are diffrent... Good luck...
Greg

[88 K30]

I think dieselbegreat is referring to the load-sensing proportioning valve above the rear axle? If by-passed, it should not really have any impact on lock-up characteristics, but will cause lower braking power with heavy loads in the rear.

The PB blaster and vise grips are the only realy choice. I've usually had good luck with them. Only once or twice have I actually twisted the line off.... :(

In any case, I would not bypass either one. I've never looked into replacing one of the rear units, but LMC may have them. NAPA or another chain may possibly have them too. Actually, you may want to check NAPA first anyway, because I've gotten parts from LMC that came still wrapped in their original NAPA packages....

[Kadzban]

I replaced all the brake lines on my truck with new pre bent ones from www.classictube.com (http://www.classictube.com) and threw that load sensing thing out. They are knowledgeable at classic tube and asked if I was going to be using it. He said most people throw it away. The newer trucks don't use them. The only difference I noticed is now the rears lock up sooner unloaded. No big deal though.

[NH2112]

I've always had really good luck using a propane torch to heat the fitting red-hot then quenching it with water and using the Vise-Grips. Concentrate the heat and the water on the fitting as much as possible, and as much as possible avoid heating the wheel cylinder, valve, slave cylinder, etc.

[dieselbegreat]

K30, you are correct about the load sensing proportioning valve which only modulates the available line pressure depending somewhat on how much weight is in the back. Kadzban confirms this because now his rear brakes are at full available line pressure and may tend to lock up with the truck unloaded. I'll try to save the valve by soaking in PB Blaster overnight and hope that does it. Hope I won't need the torch.

Thanks for all the info.

[dieselcrawler]

Good luck with saving it... hope it works out. At first I was thinking of the valve up front, didn't think of the one at the rear. The only one I've ever seen is on my K-30, do they put them on others, K-10, 20's? Subs? All the other trucks I've had/worked on didn't have one at the rear, unless it was a one ton.
Till next time,
Greg

[Kadzban]

The only trucks I've seen with one of with them where HD 3/4 tons with no emissions and TH400's and 1 tons. But I've never really looked at subs much. Older body style trucks only. I don't think any newer post 88 trucks have them.

[dieselbegreat]

Just so you know, PB Blaster (avail at Auto Zone) is wonderful stuff! I sprayed some on and whacked it with a hammer several times. A couple hours later I sprayed some more and hammered real tight 6 pt. metric sockets right onto the fittings, set it on the ground, attached a wrench and stomped on it -- saved the valve which would have cost over $50 from Dal! Next time I'll just spray some on before I even get started.

[dieselcrawler]

Awesome, Glad to hear that the 'Blaster worked for ya... I've been sold on it for a few years, my ol' man still trys to get me to try other stuff, some more expencive, but I'll stick with the PB... nothing quite like it out there.
Happy Holidays!
Greg

[rke1]

BTW, just as a point of interest my '82 C20 does not have the valve but my, '85 sub GMC 2500 does.

It also has adjustable linkage which I have never been able to find out how to adjust.

[EWC]

The valve has a plastic gauge arm , that is put in place of the metal linkage arm , and has an end that goes into the hole that is cast into the body of the valve . There are three different arms that are used based on the rear spring options for the truck . I had all three at one time and would rotate the valve and then pull the arm off and reattach the metal linkage .

[dieselbegreat]

You can just keep turning the shaft by hand any direction all you want. The plastic linkage is pressed onto the splined shaft on the valve. I think the valve is self-adjusting because, as the chassis travels up and down and the linkage rotates the shaft, it seems to automatically center itself in its adjustment range.

[ 12-22-2003, 02:32 PM: Message edited by: dieselbegreat ]