Still having brake overheating problems, can you rebuild a combo valve?

My friend is still having problems with his brakes overheating and locking up on him.

So far he has.

Removed and cleaned out his MC including all the valving.
Changed his flex lines.
Changed the caliper that was doing it really bad.
Welded up and filed the grooves in his knuckles.

Its a 91, 4.0 with 350kms It started with the passanger side and he replaced the caliper and after that both seem to get hot now. I think the bit of heat may just be normal but the drag on the passanger side is way too hot.

After finding out we can only get a combo valve at the dealer for $250 CAN.
Can he rebuild it? In the manual it says no but then reading on here it sounds like some people have rebuilt it.

One last thing we are thinking is maybe his hub is too tight? Its brand new and we put anti seize all over the axle shaft and nut and washer. Could it have torqued a bit higher then the reading because of that?

Thanks for any help, its driving him so crazy that he is thinking of just trading it in for something else.

Published torque values are cited for clean, DRY threads. Anti-sieze is a thread lubricant, so when using anti-sieze you should reduce the torque by 20% to 25% of the published value.

However, I doubt over-tightening would cause the hub to bind up. Are you lads certain that you have the correct hub, the correct rotor, and the correct caliper for the year of the vehicle? There are subtle differences from year to year, with differing offsets that can create problems.

As to rebuilding the proportioning valve, I just took one apart last night and it appears to me that they can get gummed up, and that the crud can be cleaned out with a few shots of brake cleaner. However, I don't think this would cause a front caliper to stock. The usual mode of "failure" (or advanced decline) of the combo valve is LOSS of braking power to the rear wheels. The valve doesn't proportion front braking, it only reduces the braking to the rear wheels under certain conditions.

Ah thanks for the info on the Anti seize, I would rather still have some on that nut cause if not it can be a real bitch to get off. Reducing the value is what I was thinking but now I have a number to work with

As for the valve, well we are just thinking if there is some crud in there not letting the fluid back up when you let off the brakes, at least now we know we can take a look inside and clean it up.

As for the right parts, I guess you never know but I don't know how to confirm besides taking it all back to the store?

He works at a local parts place but that doesn't really make it much easier cause they are assholes.

Oh this whole thing seemed to start in the spring, he put new rotors and pads on it last october and drove it all winter till april and it starting acting up so if the rotor and pads were wrong wouldn't it have been doing it then?


Also how much drag should there be on a wheel trying to spin? Cause it stops almost right after you stop trying to spin it.

Well something is really messed up, he just phoned me and he was out wheeling a bit and it locked right up, he loosed the bleeder screw to let out the pressure and that didn't do anything, then he disconnected the line and its still not letting off so its something to do with the caliper/rotor/pad/hub combo thats doing it as far as we can tell.

It sucks cause we don't know exactly what part is messed up since everything but the caliper is 5 months old and the caliper is 1 month old.

Things that have kept the calipers from retracting that I have seen are, mud packed around the piston, rusty piston well, rubber brake line seperates inside (it´s layered) acted like a valve, crushed hard line and water mixed in with the DOT 3 that turned to steam when the brakes got hot.
Other things that have caused caliper problems are the caliper sticking on the rods (doesn´t center correctly) there is an insert (sleeve) inside the rubber where the cliper rides on the rods, that gets twisted up. I usually lub the rods with a dab of silicon (grease) lubricant.
Have found junk in the orifices inside the master cylinder that has caused problems on other manufactures master cylinders.
Have read about some part listing mistakes, rotor? that has caused other people grief.
I´ve pushed the caliper piston all the way in and lubed around the piston and behind the dust seal with penetrating oil as a temp. fix to get me home. The dust seal tears easily and isn´t in any parts book, I´ve found.
One friend of mine, mixed tow types of brake fluid (or hydrolic fluid), not exactly sure what he used, but the results resembled dark grey cottage cheese.

have you guys checked the brake lines? open the bleeder valve on the caliper and see if fluid comes out. if not it's probably the brake line. the hub really shouldn't have anything to do with it. good luck

Today he blew the lines out and replaced the combo valve with one we opened up and flushed with more clean brake fluid and air.

Its still seizing up.

I'm really starting to think it must be the new pads or rotors are out of spec or something.