1995 Lumina 3.1L LS - Lost 4th Gear - I know it is common but pls read. Thx.

[blk95lumina]

Hello,
1995 Lumina 3.1L LS

Just this morning when backing out to leave for work, the brake pedal went nearly all the way to the floor in combination w/ a "swish" sound as I pushed it to shift from Park to Reverse. I then shifted to Neutral and could feel the brakes loosing vacuum and had to push the pedal down further, and the idle also briefly revved up to ~1200 RPM. A couple weeks ago I replaced the front brakes along w/ new calipers and lines, so I put the car in park and checked the brake fluid level and it was at the same level as when I topped it off after the brake job. I got back in and drove down the road and the brakes continued to function properly as the day before without any feeling of losing vacuum, so I thought all was good.

However, as I approached 45mph, it would no longer shift to 4th gear. I have read several past threads on here and other forums, and I understand 3/4 going out is a common problem. That said, I was hoping that based on my experiences described above that someone can possibly help provide insight as to whether this most likely indicates an internal transmission problem requiring it to be pulled or something less evasive.

Thanks for your help.

[blk95lumina]

So after further driving and closer observation, it seems the problem was Not a missing 4th but rather it was not locking when cruising in 4th. However, I just drove it around and now it is locking. Guess I just assumed it was not hitting 4th b/c I did not see that last little drop in RPM when cruising.

My theory now is that a leaky brake booster may be affecting the shift modulator and causing the shift RPMs and lockup to be just slightly higher than I am accustomed to.

Is this possible or am I headed down the wrong path?

Thanks.

[Blue Bowtie]

Could be a modulator issue, a brake pedal switch issue, problems with the center stop lamp, TCC solenoid, or other things. The fact that is is not totally dead (functioning intermittently) is a good thing,

Changing trans oil to Dexron VI might help.

[Schurkey]

Screw the transmission. FIX THE BRAKES.

There is NO reason for the pedal to drop suddenly unless there's a leak. The leak could be external--fluid dripping off of something. The leak could be internal--fluid bypassing a seal in the master cylinder, for example. There'd be no drips and no loss of fluid in the reservoir with an internal leak.

Master cylinders can leak internally, and be intermittent--they may bypass fluid around a seal occasionally.

Whatever the problem is--master cylinder, ABS system, etc--you need to address the brakes FIRST. It won't matter if the trans has fourth gear or lockup if the car is totaled in a collision because the brakes failed.

[Blue Bowtie]

Shurkey - Did I miss something? I don't read anywhere that the OP mentioned a pedal drop or brake loss, just a possible leak at/in the power booster. I presumed it was a vacuum leak. I guess we need clarification.

[Schurkey]

Originally Posted by Blue Bowtie

Shurkey - Did I miss something? I don't read anywhere that the OP mentioned a pedal drop or brake loss, just a possible leak at/in the power booster. I presumed it was a vacuum leak. I guess we need clarification.

Originally Posted by blk95lumina

the brake pedal went nearly all the way to the floor in combination w/ a "swish" sound

^^^ That.

[Tech II]

Brake leaks don't get better, so I doubt it's a line, wheel cylinder, caliper.....

Chances are it's the M/C......I would be looking for a fluid leak at the back end of the M/C leaving a trail down the booster..

[Blue Bowtie]

Oh, I certainly DID miss something!

By all means, address the brake hydraulic problem first, then the trans issue (if it still exists).

[blk95lumina]

Yup, I'm pretty sure it is both an internal leak on the M/C and a leaky booster. It is intermittent but is most noticeable when first starting up. After you press the brakes a few times it works better, probably just means the seals start to half way work. I can actually hear air sucking if I hold the pedal just right.

That said, I want to replace both the master cylinder and booster.

Transmission has been shifting great, so seems it was just a fluke for now.

I'll start a new thread.

[blk95lumina]

Been a while but better late than never.
Overdrive would still come and go after replacing the brake booster and master cylinder (which needed to be replaced anyway).



The trans issue was solved by simply replacing the brake light switch and cruise control switch, both located on the brake pedal underneath the dash. Not sure which one was causing the problem but given the parts are cheap and easy to replace I did both at the same time.


Has been over a year now and the trans has not acted up since.