Tranny Shifting At Too High Rpm

95S15 · May 1, 2010

I own a 1995 GMC S15 (4.3L-Z code). I've had her since new. Just turned 321,000 miles. I've babied it since day 1. Oil changes every 5,000 with synthetic blend. Does not burn or drip a drop of oil. All original drive train still. Full tune-up every 50K miles (cap, rotor, plugs, wires, pcv, fuel & air filters.

The issue...It is now shifting at a much higher rpm than it has for the last 15 years. I actually must lift off the gas a bit so it shifts at an acceptable rpm. She use to get all the shifts in below 2,000rpm, now it shifts at 2,400 at least and if I give her a little more than my usually putt-putt throttle she'll sometimes go to 3,000 rpms. It will even hang-out in the non-lockout at 55mph and 2,000rpm sometimes before dropping down finally to 1,500rpms.

The tranny was completely rebuilt. The tech (my best friend) said it was in AMAZING shape for so many miles but I had a full rebuild done anyway.

What tells the tranny to shift and when? What could be the source of my shifting woes?

Thank you in advance,

Scott

jro909 · May 1, 2010

sounds like its mildly slipping...on another note if you give it a little extra throttle it will shift at a higher rpm...lol going to get a colorado or canyon in the future?

Nytemare · May 1, 2010

I own a 1995 GMC S15 (4.3L-Z code). I've had her since new. Just turned 321,000 miles. I've babied it since day 1. Oil changes every 5,000 with synthetic blend. Does not burn or drip a drop of oil. All original drive train still. Full tune-up every 50K miles (cap, rotor, plugs, wires, pcv, fuel & air filters.

The issue...It is now shifting at a much higher rpm than it has for the last 15 years. I actually must lift off the gas a bit so it shifts at an acceptable rpm. She use to get all the shifts in below 2,000rpm, now it shifts at 2,400 at least and if I give her a little more than my usually putt-putt throttle she'll sometimes go to 3,000 rpms. It will even hang-out in the non-lockout at 55mph and 2,000rpm sometimes before dropping down finally to 1,500rpms.

The tranny was completely rebuilt. The tech (my best friend) said it was in AMAZING shape for so many miles but I had a full rebuild done anyway.

What tells the tranny to shift and when? What could be the source of my shifting woes?

Thank you in advance,

Scott

Solenoids tell it to shift.

Did you replace your torque converter when you rebuild the trans...its clutches may be gone too.

95S15 · May 2, 2010

sounds like its mildly slipping...on another note if you give it a little extra throttle it will shift at a higher rpm...lol going to get a colorado or canyon in the future?

Thanks for the reply,

It's not slipping at all. Never did. Just shifts at a higher RPM. The tranny was just rebuilt literally a week ago. I'd like it to last at least 1 more year before looking at a replacement actually. And I'm going full size when I do.

95S15 · May 2, 2010

Scott

Solenoids tell it to shift.

Did you replace your torque converter when you rebuild the trans...its clutches may be gone too.

Thank you for the reply,

Not slipping at all. Never has. My buddy is ridiculously thorough with his work. If he susupected the TC he would have said something. It definitely feels like whatever tells the tranny to shift is the problem. Where are the solenoids located and would the computer have anything to do with it?

Nytemare · May 2, 2010

Scott

Solenoids tell it to shift.

Did you replace your torque converter when you rebuild the trans...its clutches may be gone too.

Thank you for the reply,

Not slipping at all. Never has. My buddy is ridiculously thorough with his work. If he susupected the TC he would have said something. It definitely feels like whatever tells the tranny to shift is the problem. Where are the solenoids located and would the computer have anything to do with it?

The solenoids are in the trans...

The ECM tells the solenoids to do they're thing given throttle position etc... But its not like the solid state computer that controls your truck just degrades over time.

Dirty Mass air flow sensor could do it, as could the Throttle position sensor.

I would normally ask for lights...but the OBD1 system leaves something to be desired for trouble shooting. But anyways...do you have a Check Engine light on?

Hows the fluid level, smell and color

95S15 · May 14, 2010

The solenoids are in the trans...

The ECM tells the solenoids to do they're thing given throttle position etc... But its not like the solid state computer that controls your truck just degrades over time.

Dirty Mass air flow sensor could do it, as could the Throttle position sensor.

I would normally ask for lights...but the OBD1 system leaves something to be desired for trouble shooting. But anyways...do you have a Check Engine light on?

Hows the fluid level, smell and color

Torque Converter is brand new. The entire tranny was rebuilt a couple weeks ago. I was also thinking the TPS might have something to do with it too. The only time the Check Engine Light has ever been on was while driving at 60mph for about 10 minutes both ways on a 2 hour trip awhile back. It has not been back on for months now. Fluid is perfect. I dumped a can of GM's 44K and it didn't make a difference. I'll replace the TPS and see what happens. Thanks.

Nytemare · May 14, 2010

Dont need to change anything...a light would be on if there was something wrong with the sensor...

But you may have a bit of build up on it...a good cleaning may do wonders.

EDIT:

Do you have a 4L60E trans or a 4L60 trans.....If you have the 4L60...thats the non electronic version...you have a TV cable, and this is one of the symptoms of improper TV adjustment.

I'm not sure when blazers got the 60E....I know full size trucks got them in 94

gmtech4 · May 16, 2010

non electric is a 700R4 Aiden

94s have a 60 E

Nytemare · May 16, 2010

non electric is a 700R4 Aiden

94s have a 60 E

That's what I was thinking....

There you go...adjust your TV cable...oh and your trans is a 700r4/4l60.....they're the same trans...this is the year when GM went to a different nomenclature.