GMCNet Proportional Valve

T

thomas r whitton

New member
Jun 15, 2015
72
0
0
Suggestions on removing the proportional valve. 
I have loosened the tubing nuts from the valve but all the nuts are frozen to the tubing.  I'm sure I would corkscrew the tubing if I try turning the nuts more than a quarter turn or so.  There is no sign of rust on the tubing or the nuts but, of course, I can't see between the parts.  How do you free the nuts loose from the tubing?  I don't relish the thought of ruining  and having to replace the brake lines.
This is a job I've never done and can use suggestions.
Tom Whitton26 foot upgraded GMCPaducah, Ky
 
Patience, Patience, Patience.

Soak the nuts and tube with Kroil, once a day for 5 days. Then give it a try.

A little heat from a propane torch before soaking and then shooting the connections with Kroil to rapidly cool them sometimes helps speed up the
process. Do not over heat them because there is brake fluid inside that can boil at somewhere over 300 degree F. Once you get one of them to move
even slightly keep soaking and move then back and forth while soaking with more Kroil.

If you do not have Kroil, get some and in the interim use PB Blaster. It will just take you longer.

You can also mix up your own using a 50/50 mix acetone and Power Steering Fluid. I just unlocked a frozen 403 engine that had been sitting of 19
years. I soaked the cylinders for about 3 weeks with this mix before it broke loose.

Patience is a virtue. Give it plenty of time to work.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
Ken's advice is spot on. chances are you may twist and brake a line. Some are shorter and easier to replace(i broke off the one going up to master
cylinder and was not bad). Otherwise you have the option of cutting and flaring and adding a union and small piece. That is not ideal.

Like ken said, lots of penetrant.
--
Jon Roche
75 palm beach
St. Cloud, MN
http://lqqkatjon.blogspot.com/
 
A crows foot 3/8 or 1/4 drive wrench and a small impact tool can send enough shock waves through the fasteners to break the nut free from the line
after judicious application of penetrant. If not, I usually use the smallest torch tip I have and heat just the nut to expand it a smidgen to get them
to separate. Same story on wheel cylinders but sometimes can't get the crows foot wrench on those. Don't forget to use a wrench on the block and put
your turning force against that instead of relying on only the block mounting.
--
Terry Kelpien

ASE Master Technician

73 Glacier 260

Smithfield, Va.
 
> A lot of folks swear by Kroil, but there was an "independent" article posted that indicated a 50/50 mix of trans fluid and acetone was the best.
> Here's a previous thread with some data: http://gmc.mybirdfeeder.net/GMCforum/index.php?t...

That is what I used to free up this 403 engine. I used it because I needed a large quantity around 1/2 gallon to fill up the cylinders. It also was
readily available locally and cheaper. I have been told that the acetone will evaporate off and leave just the oil.

We buy spray cans of Kroil around here by the case.

--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
> That is what I used to free up this 403 engine. I used it because I needed a large quantity around 1/2 gallon to fill up the cylinders. It also
> was readily available locally and cheaper. I have been told that the acetone will evaporate off and leave just the oil.
>
> We buy spray cans of Kroil around here by the case.

Ken,

The acetone does leave fast in an open can, but I keep it in a pretty tight pump oil can and it stays pretty well. But I can't carry it in the
coach.

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
Tom,
I recently replaced the proportioning valve on our GMC. The 50/50 mix of acetone and ATF (as recommended to me on this forum) worked very well for me.
What I did first was scrub the fittings and the tubing with the 50/50 mix and a toothbrush. I also purchased the vice-grip locking wrench (also
recommended here) that grabbed the fittings tighter than the flare nut wrench. After tightening the wrench on the fitting, I would tap it with a small
hammer while applying pressure to loosen the fitting. It worked successfully on all the fittings, but I did replace some of the brake lines anyway,
since I had previously purchased the stainless steel brake line kit.

valve before cleaning
http://www.gmcmhphotos.com/photos/data/7010/20170102_074927.jpg

after cleaning
http://www.gmcmhphotos.com/photos/data/7010/20171230_092718.jpg

New valve in place
http://www.gmcmhphotos.com/photos/data/7010/New_Proportioning_Valve_Installed1.jpg

--
Russell Keith,
1978 Eleganza II "Harry" 403, Danny Dunn Tranny (w/shift kit, 3.50 sprockets, Allison), Thorley, Stock Brakes w/Remote Vacuum Brake Booster, Mico
Electric Actuated brake lock, Dakota Digital Dash, 6.5kW Onan,
Dunedin, Florida
 
Russell, Ken Jim and others...
Thanks everyone for excellent advise.  Here's where I stand on the project... 
This will be the third day to spray the acetone/ATF 50-50 mix on the proportional valve fittings.  So far, I have resisted the urge to get out a wrench, hammer and torch.  I'll try a wrench tomorrow.  By the way, as far as I know, my proportional valve and brake lines are original.  Amazingly, they show zero rust.  I guess that may have something t do with keeping the coach garaged most of its life.  Russell, if you were able to free up your lines I may have a fighting chance.
I'll report whatever happens.
Thanks,
Tom Whitton26 foot updated GMCTom Whitton
 
Tom,
If you do end up busting any of the brake lines (or just want to change them), I have a complete set of stainless steel brake lines for 26 footer
available if you are interested.
--
Vadim Jitkov
'76 Glenbrook 26'
Pullman, WA
 
Tom, Get a little butane pencil torch and heat the just the nut. Then shock cool it with your penetrating oil and let it soak. The heat and uneven
shock cooling lets the oil penetrate quicker.

TSC has the torches for a couple of dollars and you fill them with butane lighter fluid.

Here is an example:

https://www.ebay.com/itm/Set-of-2-Butane-MINI-PENCIL-TORCHES-Refillable-Welding-Soldering-Jewerly-Repair/312036072984?epid=1340428883&hash=item48a6cc9e18:g:BDcAAOSw-RFaYSS8

--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
Tom, et al,

While you're at it, if you haven't already, get these:

http://www.irwin.com/tools/locking-tools/the-original-locking-wrenches

At least the 4" & 7" ones.

FAR superior to flare nut wrenches for tight nuts -- they won't spread.

Ken H.

> Tom, Get a little butane pencil torch and heat the just the nut. Then
> shock cool it with your penetrating oil and let it soak. The heat and
> uneven
> shock cooling lets the oil penetrate quicker.
>
> TSC has the torches for a couple of dollars and you fill them with butane
> lighter fluid.
>
> Here is an example:
>
> https://www.ebay.com/itm/Set-of-2-Butane-MINI-PENCIL-
> TORCHES-Refillable-Welding-Soldering-Jewerly-Repair/
> 312036072984?epid=1340428883&hash=item48a6cc9e18:g:BDcAAOSw-RFaYSS8
>
 
> Tom, et al,
>
> While you're at it, if you haven't already, get these:
>
> http://www.irwin.com/tools/locking-tools/the-original-locking-wrenches
>
> At least the 4" & 7" ones.
>
> FAR superior to flare nut wrenches for tight nuts -- they won't spread.
>
> Ken H.

As you all have to know, I love mine, but they are a little tough to get on the master cylinder lines at the combination valve. One I could just
enough to break the line loose, but not the other and I don't remember which.

With the 7", you can actually get on a line nut at a wheel cylinder with enough torque to shear the line nut and it won't slip. Not Mine, not even a
GMC, but fortunately wheel cylinders are cheap and the line had to be replaced anyway. (You know this was not a good day.)

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
You must log in or register to reply here.
GMCMI Fall 2026 Rally
Get your shine on at www.cruzingear.co

Share this page

Share this page
Top Bottom
Back