slreno1217

i had some brake lins rust through and lost all fluid to rear and front brakes.
well got the lines replaced and cannot get the rear brakes to bleed, i knbow i am supposed to work from the farthest brake forward but couldnt get the rears to bleed for nothing..

got the fronts done fine, but i was told there is some knind of pin in the master cylender that is some kind of saftey precaution when the lines lose fluid it keeps one set of the brakes from losing all fluid.. andone know what this might be and how to reset it so i can get fluid to the rear lines?

forgot to mention its a 1989 chevy scottsdale 2500.

slreno1217

no replies at all hmmm?

2000CAYukon

I have the factory manuals for 1990 at home. I will look at the books tonight and post what I find.

//2000CAYukon

2000CAYukon

I am sorry that I could not get to this last night (my wife was not feeling well). I will take a look tonight.

Sorry,
2000CAYukon

slreno1217

ok thanks alot bud
this is driving me nuttz! i have been driving with front brakes only..

2000CAYukon

Just remember that I am on the West Coast so it will be late (after 9PM PDT) before I can post but I promise to look this up tonight!

//2000CAYukon

MT-2500

There is a equalizer/portioning valve where front and rear brakes lines run threw with a pin in it that shuts one end off if one end loses
pressure. It may have a small rubber boot on it.
Look under master cylinder for a valve that the front and rear brakes lines go threw.
If the pin is way out push it in a little and try it. If it is all of the way in you may not be able to pull it out.
If that is the case open a bleeder valve or a line to the other end at the equalizer valve and step on the brake pedel and see if the valve trips back the other way and lets you bleed the rear.
A pressure bleeder works better and also they make a special tool to hold the pin centered for bleeding.
Good luck and 2000CAYukon may be able to help you to.
MT

__________________
Remember proper testing gives us the answer to many problems.
MT

2000CAYukon

Well I don't know how much help I am going to be.

The 90 Factory manual talks about bleeding the Isolation/Dump Valve but it does not talk about moving the pin; however, it does show the special tool when pressure bleeding.

In the section titled "Combination Valve" it talks about Bypass feature which assures pressure to the rears if the front fails and visa versa. When this occurs the brake light is illuminated. It says, "the only way the warning lamp can be turned off is to repair the malfunction and apply a pedal force required to develop about 3102 kPa (450 PSI)." So it sounds like you really need to stomp on the brake pedel!

On mine the bleeder valve for the Isolation/Dump Valve had a rubber seal over it (pointing towards the front of the vehicle). It is not your typical bleeder screw. More flat than the ones on the caliper. It also looks like there is a rubber seal on the back side so that must be the rear end of the pin/valve.

Bleeding directions for the isolation/dump valve are: press and hold brake pedal, open valve, release brake pedal. Repeat as necessary.

I would also crack the rear line of the master cylinder to make sure there is no air in that line.

If you follow the rear brake line of the master it will lead you to the isolation/dump valve.

I sure hope this helps!

//2000CAYukon