86 Suburban R20 strange linkage ?

[Artie in Miami]

AS I am working to remove the old fuel tank, I noticed a strange linkage over the rear end that looks like it has something to do with rear hydraulic brakes ?? Rear brake lines stop at one end of the linkage...then continue from rear of linkage to wheel cylinders. WTF is this about ? Some type of booster for rear brakes ? This baby has a 411 rear end and is set up for heavy towing (oil cooler and towing package). Anyone else ever see this...came this way from factory...not added on.

[kwmech]

Can you throw a pic in here of it. Sounds like it may be a no load anti skid deal

[Keith Seymore]

Yes - it is a height sensing valve that limits the rear braking in an unladen condition.

Loading the vehicle causes the rear ended to go down, trip the valve open and allow full line pressure to the rear brakes.

Think of it as a primitive mechanical antilock braking system.

[Artie in Miami]

Wow...I guess that is part of the 1986 super towing package...this truck is a beast and would probably have enough torque to tow my house ! I am willing to bet that is why I had trouble bleeding the rear brakes when I put the new master cylinder and front calipers/hoses in ! How can I determine if that rear brake linkage system is still working ?

[Keith Seymore]

Originally Posted by Artie in Miami

Wow...I guess that is part of the 1986 super towing package...

Nope. Every '86 C20 Suburban gets one (and a bunch of other trucks, too).

https://www.gmheritagecenter.com/doc...t-Suburban.pdf

Originally Posted by Artie in Miami

I am willing to bet that is why I had trouble bleeding the rear brakes when I put the new master cylinder and front calipers/hoses in ! How can I determine if that rear brake linkage system is still working ?

Could be. Undo the linkage and swing the lever up, to see if the valve moves freely and allows fluid to flow.

Or - just remove it entirely. It was basically a test beater to pass FMVSS brake testing.

K

[Keith Seymore]

Originally Posted by Keith Seymore

https://www.gmheritagecenter.com/doc...t-Suburban.pdf


K

Here's the '85 version, which is basically the same and is (thankfully) not printed sideways.

https://www.gmheritagecenter.com/doc...t-Suburban.pdf

K

[Artie in Miami]

Keith....thanks for the idea ! And also for the really interesting charts (I saved them to my computer !!) I have a feeling that system is not working...since I could not bleed the back brakes very well. While I am working on the fuel tank replacement, I will check out that brake system and probably disconnect it ! I replaced the master cyl, calipers and hoses (front) because the front brakes were locked...all the time it was just bad hoses that go to the calipers. I should have checked that first !
The rust problem was not the fuel tank...interior of tank is clean...it is the steel 3/8" fuel line that goes from sending unit to fuel pump...probably a nightmare to replace and will keep me under the truck for weeks !! The only saving grace is that the '86 C20 does not need to be jacked up to crawl under ! I will be putting many miles on the creeper !