Innocent Fool

Can't Bleed Rear Brakes!

Have just replaced all hard & soft brake lines on the truck with new rear cyl but can't bleed the brakes. Not getting any fluid to the rear bleeders on both sides. Did a search and tried some things but so far nothing seems to work.

Here's what I've done so far in the order that I did them

- Replaced all hard & Soft Brake lines as well a new rear cyls
- Opened the bleeder on the LSPV and pumped until I got fluid and repaired any leaks
- Opened the bleeder on the rear left and pumped (a long time) but got nothing
- Went to the passenger rear and same thing. No fluid
- Went to the right front and got fluid
- Went to Left front and got fluid
- Removed the load sensing control arm from the rear axle and raised it to provide more pressure to the LSPV but no change
- Removed line going from LSPV to the rear lines and it looks like it was dry
- Pumped the brakes with the rear line removed and got no fluid at the opening where the rear line was removed
- Removed LSPV line running to the front. It had fluid but when I pumped with the line removed got no fluid (Don't know why???)
- Removed the boot and plastic guide from LSPV and it appears that the needle was stuck. Managed to free it up and re-assembled lines and LSPV
- Tried Bleeding and got the same result: Was able to bleed front but not back.
- Attached a vacuum line from the engine to the rear left bleeder and tried bleeding it under vacuum but got no fluid
- Removed the bleeders from the rear cyl and verified they were not clogged. Was able to blow through them.
- Removed the line from the LSPV to the rear and gravity bled both rear cyl thinking that it may need back pressure from the rear lines to open the valve. Got fluid from both rear cyl with gravity feed. Re-attached the rear line and still no change.
- Tried bleeding rear with the engine running to get air assist but no change
- Swapped in another used LSPV but still no change

Does anyone know how to bleed these suckers?
I am out of ideas!

1990 Pickup V6 with ABS

PS: I'm getting "some" pedal when I pump it up with the engine running but not much

wyoming9

iTrader: (1)

Do you by chance have the lines on wrong on the ABS Computer where the lines go back to the LSPV??I don`t think 1990 vehicles had ABS Brakes.

Although some did have some sort of rear antilock brakes but it has been a 17 hour day in the heat so I don`t remember the details

Did you get dirt into any of the lines??

Did you kink any of them putting them in??

Bad Master Cylinder??

While bleeding you have not let the reservoir run dry? Allowing more air to enter.

abecedarian

ABS... enough said.

You can't use "normal" bleeding procedures with ABS.
As soon as a rear bleed valve opens, the ABS blocks fluid to the rear.

wyoming9

iTrader: (1)

If you do Have ABS brakes pumping the pedal will not work your going to need a vacuum bleeder.

Innocent Fool

Thanks for the replies and advice.

I tried everything I could think of for 2 days and haven't made any headway.
Is there a procedure to vacuum bleed the ABS? Is this something I could do myself or do I have to take it to a specialized shop to have it done?

I tried hooking a vacuum line from the running engine to the rear bleeders but so far no luck

JonnyBoy

My '90 Runner had abs and I never had a problem bleeding the rear brakes when it was installed and operational. I'd say the more likely is that your LSPV is blocked inside. Happened to my '83 that didn't have abs, same symptoms you describe. Eliminated the LSPV and put in a manual prop valve, no more problems.

Innocent Fool

I've thought about deleting the lspv but it's a daily driver and I'm concerned about safety. I think the LSPV isolates the front & rear brake circuits so that if one fails the other still works. If I remove it and put in a manual valve I'm thinking I "could" loose the brakes all together. Probably not a bad option for a trail rig but as a DD I'd like the peace of mind

Still no progress

87 4x4

i dont have ABS but when i had a similar issue it was because i accidently crossed the 2 lines running back to the LSPV, takes 1 min to swap them and eliminate that as an issue

wyoming9

iTrader: (1)

What the LSPV is a valve that senses just how much weight is on the back of the vehicle.

The more weight the more brake fluid is allowed into the rear wheel cylinders.

It has nothing to do with losing your brakes that is why you have two ports on the master cylinder.

Back in the olden Days one just learned to drive knowing that your rear brakes would lock up in the rain with your empty truck.

Now we are much to stupid to learn how to apply brakes and have a feel for the road.

In answer to your question you can remove it and replace it with a manual one or just leave it off. Then just learn to brake according to how it feels

dropzone

iTrader: (6)

Dunno how ABS affects bleeding the brakes but I bet you can find the process here
http://ncttora.com/fsm/index.html

Innocent Fool

Checked the two lines going into the lspv and looks like they were crossed.
Able to bleed now.

Thanks again "87 4x4"!