View Full Version : Combination Valve button?

02-16-06, 11:21 PM
Ok, with all the headaches on my rear brakes still being overachieving (yes, still, just not as bad as before), I have looked back in my older FSM's (1975 Pontiac, 1976 Olds, 1985 Olds) they ALL state that with ALL rear drum brake/front disc brake cars that in order to properly bleed the front brakes you MUST install this GM tool Jxxxxxx to push in the override button on the combination valve.

But in my 1994 FSM, on the MANUAL brake bleeding, it says nothing. But in the power brake bleeding, it DOES say to do it, but does NOT show how or where.

Anyone have any idea? I firmly believe this is my problem, this valve ALSO has a cutoff that allows for full brake pressure when one side is damaged. If you remember, I did press on the brakes when the drum wasn't on yet, and it pushed out pretty far. So I think I set the protection mode on it, and this button I think also resets it.

Either way, I want to bleed the front brakes properly, with this button pressed.

Also, I suspect this is where the Stealth Bolt Mod, or Combo Valve Mod came from for the B/D 4 Wheel Disc mods.

02-17-06, 03:04 AM
might want to just take it to get power bleed at a caddy dealer

02-17-06, 05:53 AM
I've bled many systems on these cars and the only place I've seen a problem is in the ABS modulator. If you look in the FSM, I think they mention a bleeding procedure for it. As for the reset button on the valve, the only time that should pop is when there's a huge front/rear imbalance. So why's it popping for you?

02-17-06, 12:24 PM
I pressed on the brake pedal with the left rear drum off, so I suspect it popped. But I can't find the reset.

Do I need to take the ends off the combination valve to see it? The older cars is was visible and easily pressed.

The book says to bleed the modulator by opening the valve and let it drain via a hose into a jar with fluid in it so no air can get back in. I did that, no air came out, do you do it long or short time? I had it open maybe 5 min, hard to get much out of it, it didn't flow as fast as I expected....

02-25-06, 01:12 PM
I'm gonna take the combi valve apart today and see what I can come up with. A friend feels it is the delay valve that is staying delayed and not putting full power to the front brakes ever.

When I was bleeding the front, I had my son push on the brakes and at the moment I would hear anything in back, the front pads did move. So they seem to be working in concert with each other, but it seems like full pressure isn't realized in front, so all the pressure that should be in front, goes to the rear.

If you do a quick stab of the brakes, the rear both lock up immediately. If not nailed hard, it it just a lot of rear brake power. Once on a hard stop the rear locked, ABS kicked in and I got a good feel for just how little front brake force is going on right now. It wasn't fun. And the guy in front of me probably was hoping he had a change of clothes handy....

The rears are still doing too much work...

Finally it is warming up a touch that I can do something....

02-26-06, 01:01 AM
Well, I opened up the front side of the combination valve (proportioning side I think...) and took out the insides, cleaned and reinstalled. I still had good pedal, so I drove it, it seemed a little better, but not terribly much.

So I bled the front, it seems a little bit better, but still is rear lockup happy. ABS is my only saviour.

It is like the rear brakes are getting too much pressure, like the metering is off.

Letting some air in the rear seems to be the only help.