Spongy brakes after new master cylinder

[mechanist]

Replaced master cylinder yesterday and bled system. Bench bled MC prior to installation.

I now have brakes so no more pumping, downshifting and e-braking .

New related issue - brakes are now spongy and soft - how do I get them up again to the stiffness I experienced before the job. The FSM references using a type of gauge I can't find anywhere to set the push pin on the booster. How do you set this without this gauge? Where do you get one?

Is there another solution? What am I missing?

 

[Delancy]

The SST to engage the abs pump.

After the first five "search is your friend" replies, there'll be a lot of others regarding bleeding procedure, lspv, and a rift of other bullchit that factors some, but the real problem is the air that's now trapped in the ABS circuit, that can't be evacuated without engaging the pump, which is only possible with SST (that most dealers don't have) or by crazy driving.

 

[mechanist]

Well crap that is a problem. I was really hoping for option 6 in the FSM and a work around for the push rod gauge. I've got my front diff out at the moment w/c-diff locked thus ABS disengaged.

Are you talking about SST 09990-00150 - ABS actuator checker? What do you mean by "crazy driving"?

 

[Delancy]

Getting the ABS pump to engage like it would in a hard brake/traction loss condition.

I've never heard an ABS pump engage on any 80, but some claim they do.

 

[bloc]

Leave your CDL engaged but unhook the switch so the ECU doesn't know it is. Find big gravel parking lot or road. Lock tires to ABS delight.

 

[Delancy]

For posterity, I replaced master and booster yesterday, too.

Having fought the dearly departed Fo' Fiffy's brakes, finally narrowing the culprit to the ABS circuit, I did it differently and it's a helluva lot better than I've been able to produce before.

Bench bled master, gravity bled at the front line at master (rear seemed to be closed until depressed 1/4-3/8"), then bled at the fronts entrance to the abs pump.

Pulled loop out of rear,and bled at the first junction below master, before it splits to abs pump.

The most successful I've been if pedal rigidity is the barometer.

 

[mechanist]

Thanks @Delancy

Somebody needs to make a YouTube video of that.

 

[Delancy]

Thanks @Delancy

Somebody needs to make a YouTube video of that.

It be removed instantly if I held a starring role, since I speak an entire explicit language when wrenching, especially from a floorboard or when cramming size 16 hands in a space that's tight for a size 2.

Between the cursing and D'English, no one would come away with much more than sympathy for those with anger management issues.

 

[mechanist]

Ok didn't have the abs tool so asked for help from a local shop. They drove it, said they actuated the abs with something they have, and then bled it. I asked if perhaps I got a bad MC and they said it's good. Then they came back and said the brakes are fine and that the way they feel is normal.

But it's not. It still feels as though the master cylinder is out and I'm pushing the brakes almost all the way down before I feel them grab at each stop. This shop specializes in brakes so I'm at a loss.

Any other way to trouble shoot? Should I be measuring free play or anything like that? Could the booster be bad? Or perhaps rear calipers? How can I prove or disprove the brakes are not the way they should be?

 

[madisonr34]

If your booster is bad, you will have a had time pressing the brake pedal down as the booster uses engine vacuum to assist the brakes. I recently bled the brakes in my lx450 because I had to push the pedal to the ground for the brakes to work like yours. What I used to bleed my brakes was a MITYVAC hand vacuum pump. I bought mine from Oriley's for $60. Took about 1hr and now my brakes work great. My brake pedal has about roughly a 1/2 inch of play

If you have air in your ABS pump, Ive read the only way to get it out is to have the Dealership cycle the ABS pump using a dealer specific only tool then bleed the brakes after.

 

[Delancy]

Dealers may have the actuator, since used in a few Toyota's of the era, but lack the harnesses specific to the 1FZ....as well the desire to acquire.

I never tried, but from an old thread participated on, when chasing this monkey a few years ago.

Reviving an old thread, but I just used a version of the method SUMOTOY proposed and it worked great. I just replaced all my calipers and lines and allowed the master to go dry in the process so I had a ton of air in the system. I bench bled the master and bled the lines by pumping the brakes but they were still really spongy.

To get the remaining air I jumped both ABS relays to provide power to the solenoids and the pump. Then I disconnected the gray and black connectors at the ABS unit. Finally I used a wire to ground each of the solenoids at the gray connector on the abs unit and plugged the black connector back in repeatedly to activate the system.

I then bled the system again and got a significant amount more air and a much much firmer pedal. Most of the air came out of the LSPV, though some came out of both front calipers too. Not sure how this compares to actually activating the ABS on the road, but it worked for me.

 

[mechanist]

Thank you @Delancy for digging that up! I'll give that a try.

 

[Delancy]

I didn't, so you're on your own.

Betting @DARKNESS would provide additional support, though.

 

[mod5csi]

I agree it is probably air in the system.

But something worth checking is your pushrod from the booster to the MC. It took me a day of fiddling with that pushrod to get the feel that I wanted. I measured and set the pushrod, but it still felt like the brakes were engaging after more pedal movement than before. Page BR-20 in the 1996 FSM, page 353 of the PDF.