Brake Bleeding

[dinghyboy]

I have to replace the rear shoes and wheel cylinders. The existing brake fluid is a nasty brown color so it is probably time to change it. The truck is a 92 with the stock compensating valve at the rear under the bed. I've seen all sorts of comments on here about how this can be tricky to bleed the brakes and get it right.

 

Can someone give me a failsafe way to keep the original distribution block (at the front) and rear compensating valve and bleed the brakes properly.

 

Thanks

 

Gavin

[skidoo_j]

disconnect the rod that controls the height valve to the axle.   Tie the lever so that it sits about 30-45* upward.   

Connect your bleed hose (vacuum pump is easiest) to passenger rear start bleeding.  

 

Bleed until clean fluid. Close bleeder.

 

 

Connect a catch can to passenger front Bleeder.  Open bleed port on the front brake . While leaving partially open

Lower the prop valve lever to just below level.  Bleed the passenger rear again by pumping the pedal. 

Keeping the front bleeder open should allow the front distblock to let fluid flow through the "fail safe line".  You may have to play with how "open" the front port needs to be, so be sure you've got a catch can/bottle on the front bleeder too. 

 

Hint if you're able to do this with out the parking brake set you'll know if fluid is flowing through the "fail safe" line if the brake warning light comes on during bleed.  So use blocks to secure the truck,  and have the key in the on position during that part.  

 

bleed until clean.   

 

close front valve you'd left open and then bleed the drivers rear with the prop valve lever at upward angle.   

 

once clean at rear bleed passenger front   then driver front  

 

 

Be sure during all process that neither bowl of fluid goes empty.   I usually scrub the master's bowls and use a syringe to empty them before i start.   THen put clean fluid in it.   The smaller bowl feeds the rears.  

 

 

And most basic basic bleeding procedure with two people:

Person one:  Press and hold pedal

Person Two:   Opens Bleed port

Person one:  continues to press until hits floor.  And states "Floor"

Person Two:  Closes Bleed Port.  States  "Closed".

Person One:  Releases pedal.

 

Repeat until clean.  

 

If person one lets up on pedal while bleed port is open it will suck air back into the brake,  this is why some people will bleed into a bottle of fluid with the hose in fluid so if it does get sucked back up it's fluid and not air.  

 

I did mine by myself using just one of the vacuum hand pumps and was able to shut off the main rear line enough that the vacuum was strong enough to pull the fluid through the "fail safe" line with out opening the front bleeder.   It was all about just finding the spot where the height valve let the least fluid through the main line.  I could tell it was successful because i was getting nothing but clean fluid,  then started to get more and more vacuum built up as i messed with the lever, then all the sudden vacuum was released and i got all sorts of nasty again, so I kept the lever in that spot and just bled until clean.   

 

 

edit:  excerpt from the FSM:

 

 

 

After bleeding the brake calipers and cylinders the rear brake by-pass line must also be bled.

Open a front caliper bleed fitting and depress the brake pedal to the floor. This will shuttle the by-pass differential valve and allow fluid to flow through the by-pass line. The brake warning light on the instrument panel will illuminate when the ignition key is in the ON position. This signals the shuttling of the valve.

Re-Bleed the rear brake cylinders with the front caliper bleed fitting open.

After re-bleeding the rear brake cylinders the entire system must be bled again.

Bleed the brake calipers and cylinders in the following sequence:

1st -- Right rear

2nd -- Left rear

3rd -- Right front

4th -- Left front

[dinghyboy]

Thanks Skidoo. Those are excellent instructions.

[Pete M]

bump

[Eagle]

From FSM:

 

After bleeding the brake calipers and cylinders the rear brake by-pass line must also be bled.

Open a front caliper bleed fitting and depress the brake pedal to the floor. This will shuttle the by-pass differential valve and allow fluid to flow through the by-pass line. The brake warning light on the instrument panel will illuminate when the ignition key is in the ON position. This signals the shuttling of the valve.

Re-Bleed the rear brake cylinders with the front caliper bleed fitting open.

After re-bleeding the rear brake cylinders the entire system must be bled again.

Bleed the brake calipers and cylinders in the following sequence:

1st -- Right rear

2nd -- Left rear

3rd -- Right front

4th -- Left front