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Won't shift past 3rd gear. But only some days.

14K views 31 replies 5 participants last post by  g0t0pless 
#1 ·
I drive 44 miles round trip to/from work. Every now and then, and only part of the way, my van won't shift up to overdrive. Before this happened, there were no strange leaks, smoke, or noises. It just decided one day it wasn't going to shift past 3rd.

It will shift in Reverse, Park, 1st and 2nd just fine. Even manually shifting down to 2nd and 1st works just fine.

Any ideas?

It's a stock 95 Astro, with the stock automatic 4L60 (I assume) transmission.
 
#3 ·
Astroplane said:
You are saying the 2-3 shift is OK but no OD?
Actually, it seems to start out in 2nd or 3rd as well. It DOES shift, but maybe it only goes from 2nd to 3rd? It so hard to tell bcause it only does it sometimes.

OK, if i had to narrow it down to a specific detailed description, I would say this:

Normally it shifts just fine, but...
when it acts up, it starts in 2nd gear then only shifts up to 3rd gear.
 
#6 ·
g0t0pless said:
Normally it shifts just fine, but...
when it acts up, it starts in 2nd gear then only shifts up to 3rd gear.
Have this van scanned for trans codes. Currently, this qualifies as an intermittent. Probably a sticking shift solenoid on its' way out. I wouldn't drop the pan until we have a little more info.
 
#8 ·
Even if there are no codes, live data will allow you to diagnose with a greater deal of certainty. If you want to proceed without diagnosis: Drop pan, inspect fluid/pan/magnet. Replace shift solenoids A and B AND solenoid o-rings. Make sure wiring connections to new solenoids are secure. If internal wiring harness insulation shows signs of rub through or cracking, replace wire harness. Clean pan/magnet. Replace filter/gasket/fluid.
 
#9 ·
Astroplane said:
Even if there are no codes, live data will allow you to diagnose with a greater deal of certainty. If you want to proceed without diagnosis: Drop pan, inspect fluid/pan/magnet. Replace shift solenoids A and B AND solenoid o-rings. Make sure wiring connections to new solenoids are secure. If internal wiring harness insulation shows signs of rub through or cracking, replace wire harness. Clean pan/magnet. Replace filter/gasket/fluid.
You can get live data from OBD I?
 
#10 ·
On GM, we have live engine data all the way back to '81. OBD 1 has nothing to do with it. A good scanner is the key. A reputable diagnostic shop, whether dealer or independent, will have the needed tool. Do you remember a code or a questionable reading on the temp sensor?
 
#11 ·
OK, here's some specifics on the shifting problems:

I drove all the way to work with no problems.
On the way home, about 3 miles from my home, it started to act up. I was pulling away from a stop sign, and when it shifted from 1st to 2nd, it shifted just a bit hard er than usual. It shifted from 2nd to 3rd just fine, but stayed in 3rd. So I slowed down, manually shifted down to 2nd, and it shifted. I then slowed down more and tried to shift down to 1st. It just stayed in 2nd.

So I completely stopped, shifted back into OD and got on the gas a little. It started out in 2nd, shifted to 3rd, and stayed in 3rd.

I made my way to Wal-Mart for some grocery shopping instead of stopping home first. I was on Wal-Mart for about an hour.

I got back in the van, and it shifted just fine all the way home, a distance of about 8 miles.

So, its almost as if my transmission is heating up after a while and it starts acting up.

If I need to replace the solenoids, can someone give me a part number or something to ask for at the parts store?
 
#18 ·
I swapped out both old shift solenoids with new ones. Put in a new pan gasket and filter, and filler it up with some PennzOil high milegae transmission fluid. So far so good.

I'll tell you waht though, replacing those solenoids was easy as hell.
 
#20 ·
This sounds like my problem as well:

3rd gear starts, can manually shift through all gears. When car has been turned off for a bit, then back on it will run normally.

Speed Sensor (VSS) dropoff w/ Hi-stall converter. The rpms are too high, but Speed Sensor (VSS) is showing no movement. Happens after a tire burning take-off. Doesn't store a code, will not throw a CEL.

Reprogram PCM for Speed Sensor (VSS) dropoff.

How do I reprogam the PCM?
 
#21 ·
I'm not sure... so don't quote me on this...

But I did read in another topic in the forums somewhere that the TPS has something to do with bad shifts... I don't know if replacing it will help you or not... But it is only 30 or 35 bucks for a 95 tps last I checked :/

It's the only help I can offer.
 
#24 ·
The symptom fits except for the hi-stall converter. I don't fully understand what a PCM flash would do to fix this on a stock van. I think there is a system voltage connection that goes open when hot. Got a digital meter?
 
#26 ·
I had a similar situation a few month back. It would shift fine, but every once in awhile it would act up and not want to shift. Now the kicker was that my gearshift indicator on the column would flash on and off. No check engine light either and no Code. My trans guy said he didnt think there was any thing wrong with the trans, so he did a little pocking around and found the electronic part of the ignition switch , the square part under the switch itself on the column, was not sending a signal/power to the trans all the time. So the trans wouldnt get any power and it would go into "Limp Home Mode" 3rd only, as he called it. He replaced the switch and it shifts like new.
 
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