Hard shifting HD

[agoody68]

I have a 2001 GMC 2500HD 4X4 6.0L AUTOMATIC EXTENDED CAB LONG BOX. I CAN DRIVE IT AROUND TOWN ALL DAY AND THE TRANNY SHIFTS GREAT. ONCE I GET IT OUT ON THE HWY FOR LONGER THAT 30 MIN THE NEXT TIME I COME TO A STOP AND THEN TAKE OFF THE TRANNY SLAMS INTO SECOND, THEN THIRD, THEN O/D. THE TRANNY TEMP NEVER GOES OVER 200 DEGREES. IT DOESN'T MATTER IF I DRIVE IT IN DRIVE OR O/D IT STILL DOES IT. ANY SUGGESTION WOULD BE GOOD. THANKS

[ctfan]

When was the last time that the tranny fluid and filter were changed? That might be something to have checked/changed. You could also try some ot the Lucas or Sea Foam tranny products.

 

William

[agoody68]

When was the last time that the tranny fluid and filter were changed? That might be something to have checked/changed. You could also try some ot the Lucas or Sea Foam tranny products.

 

William

 

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I just had both the fluid, and the filter changed about 1500 miles ago. That was the first thing I tried to fix the problem. I'll have to try the See Foam product. I hadn't thought of that, thanks

[mmmikkke]

I have a 2001 GMC 2500HD 4X4 6.0L AUTOMATIC EXTENDED CAB LONG BOX.  I CAN DRIVE IT AROUND TOWN ALL DAY AND THE TRANNY SHIFTS GREAT.  ONCE I GET IT OUT ON THE HWY FOR LONGER THAT 30 MIN THE NEXT TIME I COME TO A STOP AND THEN TAKE OFF THE TRANNY SLAMS INTO SECOND, THEN THIRD, THEN O/D.  THE TRANNY TEMP NEVER GOES OVER 200 DEGREES. IT DOESN'T MATTER IF I DRIVE IT IN DRIVE OR O/D IT STILL DOES IT.  ANY SUGGESTION WOULD BE GOOD.  THANKS

 

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I'd check the dipstick with the trans fully warmed up, both after driving around town, shifting smoothly, and then after driving on the highway, with the rough shifts happening.

 

I'd look for foam in the fluid that's showing on the dipstick when it's shifting smoothly and/or when it's doing the rough shifts. Also I'd note if there is any difference in fluid level.

 

Is the trans temp the same for both rough and smooth shifting periods?

 

I wonder if you could have an obstruction in your coolant lines or in the trans cooler itself. Guys who *want* firm shifts usually start by raising the pressure in the trans. Maybe an obstruction in the coolant lines (or elsewhere in the trans) is raising the pressure only after long drives in one gear.

 

Also, how long does it take to "settle down" after getting off the highway and driving around town. The shifts eventually smooth out, I'd guess. Is that correct? If so, how long does it take...5 minutes? Does the trans temp change during this time?

[polarisboy]

Sounds like you have a shift solenoid hanging up. My 99 1/2 tond did that a couple of times. Shifted so hard you would think it was going to break something!! If you service the tranny, you might want to replace the solenoids, they're only about $25 each.

[agoody68]

Sounds like you have a shift solenoid hanging up. My 99 1/2 tond did that a couple of times. Shifted so hard you would think it was going to break something!! If you service the tranny, you might want to replace the solenoids, they're only about $25 each.

 

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I'll check for the foam. The temp isn't ever different whether in town or hwy. It doesn't ever stop doing it unless I shut it down for a long period of time, like several hours.

[mmmikkke]

I defer to the suggestion on the solenoids, but, with that being said, that 2 or 3 hour time span would be about right for fluid aereation to dissipate. So I'd still check for that, but it's sounding like polarisboy's suggestion about the shift solenoids is worth following up on also.

[agoody68]

Ok, after driving a little more on the HWY, it is only doing it after I drive in O/D. It doesn't do it after driving it in drive. So, it is icealated to a problem only in O/D. Like I said the tranny tenmp never exceedes 200 degrees.

[chevhot]

The shift solenoids DO NOT control shift feel the EPC solenoid controls shift feel

if the computer see a problem it sets the EPC to max line PSI more than most likely you have a converter clutch slip and the ecm is setting max EPC psi you need to have it scaned and watch converter clutch slip it should be 100 to -100 if any higher than 100 it will set EPC to max line PSI

[agoody68]

I will check that. If it is higher than 100, do I need a converter ? Thanks for the info.

[chevhot]

more than most likely you will what trans do you have 4L60E or the 4L80E

if you have the 4L60E the lockup control vavle in the vavle body wears out and you need to ream the bore or replace the vavle body

good luck

[renolaw]

my 8.1/allison does the same thing-- but usually only after being in 4 high, then back to 2 high... it really slams hard...

 

?????

 

mb

[chevhot]

what year is yours and did you reprogram the computer?

[agoody68]

what year is yours and did you reprogram the computer?

 

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Mine is a 2001GMC 2500HD 4X4 EXT CAB LB. No I have not reprogramed the computer.