91 brake bleeding

[Dime]

Brake pedal had been getting progressively spongy, and I finally have some time to change the fluid. I've been doing some search and have found mixed answers as to the method for bleeding the brakes. Some say the ABS needs to be attenteded to on some years while others don't.

Is there anything more to bleeding a 91 other than bleeding at the calipers, is the orders ps rear, ds rear, ps front, ds front, and about how much fluid should I expect to need?

Thanks

[secondchance]

I don't know the answer to any special procedure for ABS. I have a 94 and I hooked up a vacuum bleeder (kind that hooks up to a compressor) and bled it, while adding to the reservoir, until dark color of the brake fluid turned clear. Used same sequence you described.

[Hib Halverson]

The bleeding sequence on a 91 is a bit different.

right front
right rear
left rear
left front

To flush the system, I usually start by sucking the old fluid out of the reservoirs with a Mityvac just until the reservoirs are dry but there is a little brake fluid left at the very bottom where the master cylinder inlets are located.

Then I fill the two reservoirs with fresh fluid.

Then I bleed per the FSM starting with the right front until clean fluid comes out. I do the other three the same way.

Then I force the ABS to self test by starting the car and driving forward until I hear the ABS self test. Then I shut off the ign. turn it back on and drive forward again until I hear the ABS self test.

Lastly, I go back and bleed all four one more time.

[secondchance]

Hib,

What would be proper sequence for 94? Is ABS actuation and bleeding necessary for 94 also?

[WVZR-1]

Not to confuse the thread, it would be wise since the procedure is different for the various years to just check the FSM, Hib's comments for the '91 are directly from the '91 FSM and the sequence posted by the OP is not correct for the car in his SIG, '92+ is RR, LR, RF & LF and it's stated that way in the FSM.

The '92+ cars with ASR also has a "prime pipe" and the FSM I'm quite sure for all years mentions that for a complete system bleed you start there. Hib's follow-up after ABS self test is I believe a personal preference and I've seen guys actually create an ABS event and do it the second time.

[Hib Halverson]

The ABS self-test IS an "ABS event". The service manual explains what takes place during the self test and, as long as the ABS EBCM is not faulty, the easiest way to rid the module of old fluid is to flush the system, enable a couple of self tests then bleed the system a second time.

You also can force "ABS events" with the car on jacks if you have a TECH1A or a MasterTech along with a GM chassis software.

My earlier post was, indeed specific to 90/91. As WVZR-1 says, with the 92-up cars the procedure is different and must begin with the ABS prime pipe. 92-95 methodology is also discussed in the Service Manuals for those years.