93 Jimmy Transmission Problems

I was hoping I might find a Jimmy or Blazer expert out there. I have a 93 S-15 Jimmy, 4.3 Vortec, 4WD that I am starting to have tranny problems with. It's an automatic with 150,000 miles. I have also scanned for codes and it's not pulling any.
When the trans is cold(first few miles ) the trans shifts fine. However, after it warms up, it does not want to shift from first to second. It either winds up to about 3000 RPM and then drops in hard with a clunk, or I can let off the gas, let the rev's down, in which case it drops in smoothly. It is only from first to second, every other gear is fine. The fluid level is fine and does not smell burnt.
I have been told several differnt things by several different "experts". I've heard possibly the vacuum modulator, possibly the valve body, or possibly the bands are out of adjustment.
Unfortunetly, the mechanics I have relationships with aren't willing to tackle this big a job and have had no refferals to suggest other than the dealerships all 3 of which I've spoken to have told me I should just replace the tranny due to the fact it has 150,000 miles on the clock. And when I asked about prices on rebuilts they tried to steer my away from those saying you're better of with a new because the prices end up being about the same due to double the labor to rebuild my current one. These last two suggestions have really got my hackles up and don't feel I can trust them. I think they're trying to take me for a ride.
If anyone has had similar problems or any suggestions I would love to hear them. I am kind of up in the air as to what to try first and would greatly appreciate any advice I can get. Thanks in advance for your help.

Have you EVER had you transmission serviced with new fluid and a new filter?

Have you EVER had you transmission serviced with new fluid and a new filter?

I'm embarrased to say no. When I bought it it had 45,000 miles on it and had never been serviced according to the previous owner. After asking around I was told to leave it alone unless I had a problem with it. The thinking being the new fluid would eat at the established varnish around the seals and possibly cause seal failure. I only planned on keeping it a couple years and decided to leave it alone. One thing lead to another, and 100,000 miles later here I am. The fluid does not smell burned and still looks clean and just slightly discolored.

I'm embarrased to say no. When I bought it it had 45,000 miles on it and had never been serviced according to the previous owner. After asking around I was told to leave it alone unless I had a problem with it. The thinking being the new fluid would eat at the established varnish around the seals and possibly cause seal failure. I only planned on keeping it a couple years and decided to leave it alone. One thing lead to another, and 100,000 miles later here I am. The fluid does not smell burned and still looks clean and just slightly discolored.

The "don't change it theory" is a complete myth. Transmissions today need their lubicants changed.

I would suggest doing it with a new filter.

Chances are the filter is clogged up and is hindering the fluid flow needed for proper shifting.

The "don't change it theory" is a complete myth. Transmissions today need their lubicants changed.

I would suggest doing it with a new filter.

Chances are the filter is clogged up and is hindering the fluid flow needed for proper shifting.

Hi Blazer,

I appreciate your help and hate to question you, but are you sure about that being a myth. I have heard it from several mechanics and I believe I even read it in a Chiltons Manual. Are you a mechanic yourself?
Like I said, I really appreciate your help and I'm sure new fluid and filter would help, but I hate to do it at the expense of the seals. I don't mind dropping the pan and doing it, I just don't want to cause a potential leak. Also, if it was fluid and filter, wouldn't it affect the tranny in all shifts, not just first to second?
By the way I checked out your site, that's a great looking rig you have there. I have 2 questions. One, I have installed a dynaflow muffler on mine and was considering a cold air intake. Did you feel after your muffler change that the cold air added noticable improvement? Also, I noticed it looks like you have your woofer box setup with the speakers facing the rear gate. I have double 12's myself but face them toward the front of the truck. Do you think facing back gives better tone?
Thanks again for all your help.

Hi Blazer,

I appreciate your help and hate to question you, but are you sure about that being a myth. I have heard it from several mechanics and I believe I even read it in a Chiltons Manual. Are you a mechanic yourself?
Like I said, I really appreciate your help and I'm sure new fluid and filter would help, but I hate to do it at the expense of the seals. I don't mind dropping the pan and doing it, I just don't want to cause a potential leak. Also, if it was fluid and filter, wouldn't it affect the tranny in all shifts, not just first to second?
By the way I checked out your site, that's a great looking rig you have there. I have 2 questions. One, I have installed a dynaflow muffler on mine and was considering a cold air intake. Did you feel after your muffler change that the cold air added noticable improvement? Also, I noticed it looks like you have your woofer box setup with the speakers facing the rear gate. I have double 12's myself but face them toward the front of the truck. Do you think facing back gives better tone?
Thanks again for all your help.

The new fluids do not hurt seals, they actually will swell them up better and seal better.

I just checked my chilton's manual and no where does it say to keep the fluid in the transmission if you haven't changed it properly.

Get it changed bud, it won't hurt it. Also, Best to have someone flush and refill it. The transmission pan only hold a fraction of the fluid in the whole tranny aka torque convertor carries alot etc....

Best to have a complete flush done at a local jiffy lube, and then take it home, frop the pan, replace the filter and the small amount of fluid lost during the pan drop and drive on knowing everything is back to normal, or at least, properly protected.

On to the CAI, yes, I noticed a throttle performance improvement. Throttle pickup is a lot snappier than with the stock setup and the truck does perform better at higher rpms where the stock box would be severly hindering the needed airflow.

Onto the subwoofer box, I have the box facing the back and have the woffers in reverse phase pushing back into the vented box. Sounds AWESOME.

The new fluids do not hurt seals, they actually will swell them up better and seal better.

I just checked my chilton's manual and no where does it say to keep the fluid in the transmission if you haven't changed it properly.

Get it changed bud, it won't hurt it. Also, Best to have someone flush and refill it. The transmission pan only hold a fraction of the fluid in the whole tranny aka torque convertor carries alot etc....

Best to have a complete flush done at a local jiffy lube, and then take it home, frop the pan, replace the filter and the small amount of fluid lost during the pan drop and drive on knowing everything is back to normal, or at least, properly protected.

On to the CAI, yes, I noticed a throttle performance improvement. Throttle pickup is a lot snappier than with the stock setup and the truck does perform better at higher rpms where the stock box would be severly hindering the needed airflow.

Onto the subwoofer box, I have the box facing the back and have the woffers in reverse phase pushing back into the vented box. Sounds AWESOME.

I appreciate you checking your Chilton's for me, not sure where I read that.
I believe your right that it couldn't hurt and the flush is a good idea as well. I hope to get that taken care of in the next few days and will update you with my progress. One question, I know your's is the newer body style as opposed to mine but do you know on a 93 if you have to remove the frame crossmember in order to drop the pan or can you slide it off over the top of it?
One other thing, does the reverse phase on your woof's increase base, or what is the reason for that? I've seen it done before, but wasn't sure as to why.
Thanks again for all your help bro, I'll let you know what happens.

I appreciate you checking your Chilton's for me, not sure where I read that.
I believe your right that it couldn't hurt and the flush is a good idea as well. I hope to get that taken care of in the next few days and will update you with my progress. One question, I know your's is the newer body style as opposed to mine but do you know on a 93 if you have to remove the frame crossmember in order to drop the pan or can you slide it off over the top of it?
One other thing, does the reverse phase on your woof's increase base, or what is the reason for that? I've seen it done before, but wasn't sure as to why.
Thanks again for all your help bro, I'll let you know what happens.

Hmmm...

I don't know about the crossmember, mine has the complete skid plate package but be prepared to remove it and support the tailshaft with a jack if you do.

Now onto the subwoofers, I have them mounted normally with the back of the woofer inserted into the box itself. I used to run it in normal phase when I had the box sealed, but when I vented it by drilling 3inch holes and inserting a 13 inch long section of PCV pipe for tuning, I had to reverse phase the subwoofers to get the proper tuned range and take advantage of the vented enclosure. The sound difference is amazing.