97 Lumina Brake Mastercylinder change

[jimbob0077]

I have a 1997 Chevy Lumina LS. With ABS brakes. The brakes have been somewhat spongy for years. This fall I bled the front calibers, rear wheel cylinders and ABS modulator using a vacuum bleeder. This has given the best pedal feel so far but it still is no where near the feel of my 2003 Impala. It is +6 degrees outside so I’m getting ready to work on this as soon as the weather gets better. I will try to bleed the brakes once more and if the pedal isn’t good, I would like to change the master cylinder. My Haynes manual does not have a procedure for ABS, only cars without. Can’t seem to get a reliable source of information that shows me how to change the master cylinder (with ABS). Rockauto sells it as a separate unit, and the local Chevy parts guy says that it can be changed. However Auto Zone’s web site and my own eyes show it has to be changed as an ABS assembly of mastercylinder, modulator and motor pack. Don’t see how you can get to the bolts to remove the master cylinder unless you remove the motor pack from the assembly. Has anyone done this job? If so, does anyone have a procedure for it? Any help would be greatly appreciated. Will try to attach pictures.

[rkvons]

I would change my master cylinder if the brake pedal slowly goes down to the floor when I'm sitting at a stop. Spongy brakes are due to air in the line, or, maybe your rubber hoses at the four corners are soft and expand a little when you step on the brakes. Do you have any leaks?

[jimbob0077]

No leaks. Have bled the ABS Modulator, back bleeder then front. Then RR,LF,LR,RF. Then I bled the ABS Modulator again. That did improve the pedal feel and improved the height of the pedal. The only other thing that I could try would be to tap on everything when I bleed and jackup the rear of the car as the master cylinder seems to be a little higher toward the front of the car. This car has been somewhat like this for at least 8 years. Like your idea about checking the front hoses for swelling. I will not work in the garage until it warms up a bit.

[ryanusrey2012]

Originally Posted by jimbob0077

I have a 1997 Chevy Lumina LS. With ABS brakes. The brakes have been somewhat spongy for years. This fall I bled the front calibers, rear wheel cylinders and ABS modulator using a vacuum bleeder. This has given the best pedal feel so far but it still is no where near the feel of my 2003 Impala. It is +6 degrees outside so I’m getting ready to work on this as soon as the weather gets better. I will try to bleed the brakes once more and if the pedal isn’t good, I would like to change the master cylinder. My Haynes manual does not have a procedure for ABS, only cars without. Can’t seem to get a reliable source of information that shows me how to change the master cylinder (with ABS). Rockauto sells it as a separate unit, and the local Chevy parts guy says that it can be changed. However Auto Zone’s web site and my own eyes show it has to be changed as an ABS assembly of mastercylinder, modulator and motor pack. Don’t see how you can get to the bolts to remove the master cylinder unless you remove the motor pack from the assembly. Has anyone done this job? If so, does anyone have a procedure for it? Any help would be greatly appreciated. Will try to attach pictures.

I understand you are comparing your brake pedal feel to an entiraly different vehicle in this instance so I just wanted to put this out here that you may not have any problem because pedal feel is different on every vehicle it is probably normal for your car to feel a little spongy

[jimbob0077]

I would agree that my 97 lumina and the 03 Impala will not have the same pedal feel. However, I found out (by someone pulling in front of me) that if I push the pedal all the way to the floor, it becomes much harder and higher for as long as a month. Just want the master cylinder procedure for backup.

[Schurkey]

Is this vehicle like older Luminas, where if you don't use the park brake now and then, the rear disc calipers don't self-adjust, and the pedal becomes low?

Check the owner's manual and/or service manual. If in doubt, engage and release the park brake--hard--a dozen times and see what happens.

[ryanusrey2012]

Originally Posted by jimbob0077

I would agree that my 97 lumina and the 03 Impala will not have the same pedal feel. However, I found out (by someone pulling in front of me) that if I push the pedal all the way to the floor, it becomes much harder and higher for as long as a month. Just want the master cylinder procedure for backup.

is the pedal getting higher and harder to press because that can also be your power booster or a vacuum leak. But yea bench bleed your master and keep us posted

[jimbob0077]

Actually this car has rear drums. I believe I tried the parking brake thing, no help then, but I could try it again. I went to a library in another city near me and found the procedure for changing the master cylinder. Have to remove the M/C and ABS modulator as an assembly. It is currently 6 degrees above zero in MN. Brakes good enough for now. Will start working on them when the temp rises above 45 degrees. I'm getting old. Will repost, if anyone is interested in the outcome. The car has 140,000 miles. If the transmission go's before now and the summer, she is going to auto heaven.

[Tech II]

When you seperate the M/C from the modulator, you have to replace the two tubes that join them together....

[jimbob0077]

Answering Tech 2: I have researched everything on how to change the master cylinder except how to release the spring tension between the modulator and the drive pack. The mitchell manual has a warning that you should use a scan tool to select (Gear Tension Relief) function, so you won't injure yourself when you separate the motor pack from the modulator. So the three gears on the Drive Pack are spring loaded. The scan tool will run the motors backwards a little, to relieve the tension. Would be nice if someone out there has done it without the scan tool. Someone surely has tried it.

[jimbob0077]

Finally got tired of dealing with this brake issue. Here is what I did. Hope this helps someone with an old car.

Lumina 163K miles. Intermittent soft spongy pedal.
Master Cylinder replacement.
Ran front end of car up on ramps and installed jack stands under the rear end. Removed cruise control electric plug and moved cruise box out of the way for access. Removed electric plugs from ABS and master cylinder (the unit). Put plastic sheet under unit. Applied piece of masking tape to cover ABS motor electric receptacle. Removed brake lines from ABS module and plugged holes with rubber stoppers (1/2inch X 5/16inch) from Home depot. Removed unit from brake booster. Removed tape and placed sandwich bag over motor receptacle and secured with rubber band. Turned unit upside down and emptied reservoir. Laid unit on its side and removed unit bottom cover using #25 torx bit. Removed 2 screws from motor drive #30 torx bit. Laying a doubled up rag against exposed gears, removed motor drive. Gears are spring loaded so remove motor in one fluid motion so as not to damage aluminum gears. Locked 2 vertical sticks in shop vise and mounted ABS/MS between them using 2 small c-clamps. Remove 2 banjo bolts using 3/8, 12 point socket. You can now remove ABS module down and away from M/S. Mount new M/S to sticks. Install bleed kit that came with new M/S in the 2 upper threaded holes and install new transfer tubes that should have come with new M/S in the 2 lower holes. Connect clear plastic tubing to 2 lower transfer tubes. Run all tubing into reservoir (4 tubes) and bleed M/S. It took me about 50 strokes to get clear fluid. Take care not to roll one of the O-rings on reassembly of ABS module to M/S. With ABS-M/S unit on its side, looking at gears, turn all three gears counter clockwise gently to stop. Install motor drive and cover. Install unit in car. Don’t touch ignition or brake pedal, I bled ABS module, rear bleeder first, then forward bleeder and both front wheels Started car and made sure ABS and brake light where off. Try to bleed wheels, RR,LF,LR,LF. If you can’t bleed rear wheels. Drive car down the road at about 15 MPH. Then you should be able to bleed all 4 wheels. Note: I pressure bled my car with a bleeder I made @ 7 to 10 psi. Used the old M/S reservoir cap rubber gasket with reservoir adapter. You can do the above bleeding using the pedal, according to the Mitchell manual I found at the local library. By the way, I had to do this twice, as I had rolled one of the upper O-rings mating the ABS to M/S. Took a while to figure out where it was leaking. Had to use alcohol and an air gun to find it.

[Blue Bowtie]

Thank you for the informative update. This may prove useful to someone in the future.

[Tech II]

Was there noticeable braking improvement?

[jeffcoslacker]

I'm off to work, can't read all the replies. Wanted to say that Luminas and others of this design with rear drum have problems staying adjusted and the crap pedal feel and weak braking usually comes from back there, in my experience.

I have 220,000 miles on my '97 and still have meat on the OE brake shoes. Sometimes I wonder if they do anything at all.

I clean and adjust them once a year or so, lube the contact points on the backing plate, clean and lube the adjuster, etc. It feels great for a while, but slowly goes back to being how most of them are...kinda soft pedal feel (compared to other cars) and braking performance that I can only describe as "adequate".

The normal state of these brakes is such that when sitting still, I can push the pedal hard and put it into the floor. That's not ideal, in my mind, but is what I've come to expect from W-body cars with drum rear....

[jimbob0077]

To be honest, the pedal wasn't that much better. I was kind of stumped until I called a mechanic regarding the problem. I felt, maybe the booster was at fault. He immediately discounted that, saying it had to be a caliber hanging up or a problem with the rear brakes. My notes said I had cleaned and adjusted the rear brakes less than 2 years ago. So I didn't think they could be at fault. I took the rear drums off and couldn't believe how dirty they were and of course out of adjustment. Researched lubricants, noted that I shouldn't have been using silicone on everything. Should be using Molybdenum base grease. At least, they say metal to metal. Sanded drums and shoes. Now they are much improved, not anywhere as good as my 03 Impala but the best they have been in six years. The master cylinder, for me, was part of the problem. I'm still not satisfied. They are still a little soft until they are pumped a couple of times. Then they are acceptable. The only thing left is brake hoses that I will check at some point when I find a helper. Can't believe there is any air in the system, as I pressure bled it. Noted there is a correlation between the parking brake pedal and the rear brake adjustment. On my car, after rear adjustment the parking brake engages in the first 2 clicks of depression. Much higher than before.