OT but need help -1998 Tranny Question/Problem - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Old Chevy Lover · 03-09-2003, 12:43 AM

I posted in 88/98 forum, but know there aren't as many people as there are here. My 98 Ext cab 1500 350 totally stock 60,000 miles... drove it for a little over an hour straight today, not pulling a trailer, not hauling anything, in OD, and I noticed the 1-2 shift getting VERY stiff. The 2-3 shift was firm, and it quit going into OD. By the time I got home, it felt like I had a full race shift kit.. Obviously it was heating up, but does anyone know what would cause it??? After sitting and cooling off for awhile, it was fine. Didn't drive it long enough to heat up again. Was normal driving conditions, some highway, some country road driving. I do not have an extra tranny cooler on it, but it still shouldn't do this under normal conditions.. HELP. I would like to figure it out before something big happens and it costs me a whole tranny!

O'l Buck · 03-09-2003, 02:45 AM

vacuum modulator? maybe fluid level. I don't know much about automotive automatics. I used to know a lot about Allisons, but have forgotten most of that over the last 10 years and would have to look at a book to answer anything about that. I do know that if you're vacuum modulator isn't getting enough vacuum, it will shift hard.

Blazer1970 · 03-09-2003, 08:52 AM

I think those electronic controlled trannies have a limp mode where they lock out overdrive, and default to full line pressure. This is what causes the symptoms that you see (hard shifts). I am not sure what all can cause them to go into limp mode though. Did it trip a code?

*Piston* · 03-09-2003, 11:10 AM

Do you have a Check engine light on? Blazer1970 is correct, If the pcm see's a significant problem with the transmission (something that will do damage) it signals full line pressure to all shifts and disables the Convertor Clutch. You'll notice if you pull over real quick and turn the key off, start it back up and drive off... it will shift normal until the problem comes back. That is, if there is a actual problem with the trans. If you try the key trick and it still shifts harsh w/no od then its possible you have internal trans problems. Usually an overheating transmission will be very sluggish and even slip when shifting.
Since this is OBDII, you wont be able to pull codes like it needs to be. Have someone with a scanner go into the transmission section and see what the problem is. Most of the time we've seen either the ground wire from the PCM (gm has a tsb on this) or the PWM soleniod/shift soleniod/tcc soleniod.

03-09-2003, 12:43 AM	#1
Old Chevy Lover Registered User Join Date: Dec 2002 Location: Chillicothe OHIO Posts: 717	OT but need help -1998 Tranny Question/Problem I posted in 88/98 forum, but know there aren't as many people as there are here. My 98 Ext cab 1500 350 totally stock 60,000 miles... drove it for a little over an hour straight today, not pulling a trailer, not hauling anything, in OD, and I noticed the 1-2 shift getting VERY stiff. The 2-3 shift was firm, and it quit going into OD. By the time I got home, it felt like I had a full race shift kit.. Obviously it was heating up, but does anyone know what would cause it??? After sitting and cooling off for awhile, it was fine. Didn't drive it long enough to heat up again. Was normal driving conditions, some highway, some country road driving. I do not have an extra tranny cooler on it, but it still shouldn't do this under normal conditions.. HELP. I would like to figure it out before something big happens and it costs me a whole tranny! __________________ Keith 70 Chevelle Malibu SS Clone 468/Auto 72 C10 SWB 350/Auto 13 Camaro SS/RS 6.2/Auto Last edited by Old Chevy Lover; 03-09-2003 at 12:54 AM.

03-09-2003, 02:45 AM	#2
O'l Buck Recovering Truck Driver Join Date: Mar 2002 Location: Orleans, NE USA Posts: 1,883	vacuum modulator? maybe fluid level. I don't know much about automotive automatics. I used to know a lot about Allisons, but have forgotten most of that over the last 10 years and would have to look at a book to answer anything about that. I do know that if you're vacuum modulator isn't getting enough vacuum, it will shift hard. __________________ 67 K-20 350, SM465, Eaton rear, 4.56 no spin option 00 Dodge 2500 4x4, 24V cummins, 5 speed Chad South Central Nebraska

03-09-2003, 08:52 AM	#3
Blazer1970 Registered User Join Date: Dec 1999 Location: Old Mission, MI, USA Posts: 2,510	I think those electronic controlled trannies have a limp mode where they lock out overdrive, and default to full line pressure. This is what causes the symptoms that you see (hard shifts). I am not sure what all can cause them to go into limp mode though. Did it trip a code? __________________ Tim

03-09-2003, 11:10 AM	#4
Piston Account Suspended Join Date: Oct 2002 Location: Olathe, KS Posts: 2,301	Do you have a Check engine light on? Blazer1970 is correct, If the pcm see's a significant problem with the transmission (something that will do damage) it signals full line pressure to all shifts and disables the Convertor Clutch. You'll notice if you pull over real quick and turn the key off, start it back up and drive off... it will shift normal until the problem comes back. That is, if there is a actual problem with the trans. If you try the key trick and it still shifts harsh w/no od then its possible you have internal trans problems. Usually an overheating transmission will be very sluggish and even slip when shifting. Since this is OBDII, you wont be able to pull codes like it needs to be. Have someone with a scanner go into the transmission section and see what the problem is. Most of the time we've seen either the ground wire from the PCM (gm has a tsb on this) or the PWM soleniod/shift soleniod/tcc soleniod.



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