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Brake Pedal goes to floor! Rear ABS?? I've researched for over a month!!
I'll keep it short and to the point
I'm no stranger to these trucks/4runners. I've owned them for 30 years, just picked up a 90 Pickup v6 4x4 w/REAR ABS. Previous owner said he replaced power steering pump (this comes up later). When I met up with the guy to check out the truck i immediately noticed the brake pedal went to the floor. Brakes will grab but only at the very end of the stroke (at the floor). Not much braking power but enough to drive around surface roads if needed. I thought it was an easy fix, over a month later and no progress. This happens when the truck is RUNNING and i have brake booster power. Pedal feels as it should with truck off.
What i have done.
1. Replaced master cylinder with Aisin one from Rock Auto. Bench bled properly
2. Found wet wheel cylinders, replaced also with Aisin from Rock Auto
3. Adjusted shoes for slight drag, they were free spinning pretty good before the adjustment (parking brake will grab with 3-5 clicks)
4. Replaced LSPV with a cheapo, factory LSPV had no signs of leaking. Also adjusted linkage for LSPV to factory spec (truck is NOT lifted or lowered)
5. Flushed and bled about 4-5 32oz bottles through the truck per factory steps in FSM including LSPV (using vacuum bleeder, 2 person method, gravity method)
Now after all this i started researching, this truck has ABS. I read in the FSM if any part of the power steering system is opened the ABS actuator needs to be bled. So i remember the previous owner said he replaced the PS pump. Ok i look up the procedure, it states as seen in attachment.
6. I bled the power steering, got some air out of it
7. bled the system with engine running then with it off (2 person method, gravity method)
8. Now that i do not have the SST required in the FSM i took 12v straight to the solenoid on the brake actuator. I had my son hold down the brake and i momentarily held 12v to it for 3 seconds and repeated 5-6 times. He did not release the pedal during this time. I could hear the solenoid clicking
9. Proceeded to bleed the entire system again as stated above
Still NOTHING!
10. Had my son hold down the brake pedal and i opened the two brake lines at the ABS actuator to bleed
11. Inspected front calipers and cleaned and lubed slide pins
12. Jacked up rear axle and put in gear, watched tires spin then pushed on the brakes.....tires keep spinning!
I'm almost positive its the rear axle
13. Called all the local dealers, no one has the SST anymore. Some even suggested they might not even take it in for troubleshooting
14. Found a junkyard unit (have not installed yet)
15. Bypassed the ABS actuator by taking the input line through a flex line and connecting to the output line, completely bypassing the ABS actuator.
16. Re-bled the rear axle..........STILL NOTHING!!!!
I'm at a complete loss, i've been working on these trucks for almost 30 years. I've never had this problem before! Sorry for the long post just want to be detailed.
I am new to the Toyota truck systems but not mechanicals in general. Sounds like if this were a little bit older car you could simply adjust the length of the rod that actuates the MC piston...is that what the 'SST' does, electronically somehow? I'll go fetch my FSM, watch, and learn
I am new to the Toyota truck systems but not mechanicals in general. Sounds like if this were a little bit older car you could simply adjust the length of the rod that actuates the MC piston...is that what the 'SST' does, electronically somehow? I'll go fetch my FSM, watch, and learn
No the SST simply actuates the ABS actuator to release any trapped air for bleeding. I've thought about adjust the rod but i don't think it's been tampered with. I think there is a measurement i can check in the FSM to make sure its within spec before i mess with it.
If you can find anything i've missed i would greatly appreciate that!!!
looks like there is an adjustable push rod inside the booster, but you have to pull the booster to check it. Not sure if you want to go down that rabbit hole, but it's a possibility. I'm sure you could take the measurement without the SST mentioned.
I would imagine if you could watch the fluid in the MC while someone presses the brake pedal, and if you see movement as soon as they start pressing it, this adjustment is not the issue. But when you say the brakes don't work until you get to the end of pedal travel, it was my first thought.
Ive also seen in a couple of recent threads that the aftermarket LSPV are junk, just FYI -Jeff **NOTE this page is from the 86 FSM**
Last edited by hurricanes; 05-03-2023 at 08:51 AM.
05-02-2023, 07:53 PM
