towing in overdrive

[corvette]

hi folks, i'm new to this board, just found it this morning while surfing for info on my 1998 chevrolet diesel dually automatic transmission. i've been towing a 6000 lb. camper trailer for three years with it, not steadily, about 4 or 5 times a year as vacation permits. although i've heard your not supposed to tow in overdrive, i have been. otherwise i'm turning 2800 to 3000 rpms at 55 miles an hour. the truck has worked flawlessly all these years, when i reach a big hill it downshifts to third till i get to the top then it goes back into overdrive. the engine heats up a bit, from 190 to 210 on most hills. sometimes the big long ones it'll run up to 240 to 260 in third, but then quickly cools going down the other side. this weekend i was out with the trailer and as i climbed a hill i've climbed many times before it shifted down to third, but when i got over the hill it would not go back into overdrive. even though the engine temp. cooled it remained in third. after stopping for a while to let things cool, i drove off and the overdrive worked fine, till the next hill when it shifted down and would not come back. i was able to climb a few small hills where it shifted and returned, but it seems the big hills where it heats up were the problem. but stop and let it cool and all was well. the transmission felt tight, not like anything was slipping, and now driving around without the trailer it is fine. i asked my dealer about this and thier trans. expert told me i shouldn't be towing in overdrive at all. i explained the 55mph thing to him and then he told me i should pull it into third manually before it shifts itself and this would eliminate the problem. he told me that there's a temperature sensor on the transmission and when it gets hot it locks out the overdrive and the only way to return it is to stop and let it cool. i went to another gm dealer and inquired about this and he said he never heard of such a thing, but did recommend that i manually shift to third as needed. i just wonder if anyone out there has had such a problem or ever heard of it, and what is the proper way of towing with this truck. i've pulled a lot of car trailers and construction equipment with it and never had a problem. i guess the camper trailer is heavier than those plus i do a longer haul with it. and how about the engine temps. when towing, i thought diesels were supposed to be the way to go to tow, but i've been dissappointed with the performance of this truck. any insight you folks can give me would be highly appreciated. thanks for reading this and allowing me to post.

[99-2door]

Your tranny temp is what you need to worry about. Install a gauge and then you can see when you need to shift out of overdrive.

[jeffs98]

First of all---- What trans is in this truck?? 4L60E 4L80E???? The 4L80E is made to do some Towing in overdrive!! I would not let trans continually shift from low to high a lot though!!!! There is a trans temp. sensor and it will lock out if temp is too high and will do the same with temps too low (such as initial start up in morning) till normal operating temp. is reached!!! Hope this helps!!

[99-2door]

It's a diesel.......Its the 4L80e.

[crews]

I used to tow with my 94 Crew cab dually with a 454/ 4L80E combo, and I ALWAYS towed in O/D. I never had any problems, nor did the tranny "hunt" between gears. Of course, when i approached a steep grade, I always made sure the trans was placed in the appropriate gear prior to the point of dragging the truck down. I don't think you can beat GM O/D trans for towing applications.

Just my 2 cents.

[jeffs98]

If it is a 4L80E then you can tow in OD!! I don't know if there is a restriction on how much weight though!! I really doubt it but i will look today and chime back in and let you know!!!! I would atleast kick trans. down manually on a steep grade and then upshift after grade is achieved!! Also, not to be forgotten is the fluid and filter change!! This is very important on trans. especially a trans used for towing!!I am sure you know that but i also know how easy it is to put it off! Hope this helps!!!

[corvette]

hey guys, thanks for your replies. i will manually downshift on steep grades from now on, as per from what i hear. i'm also changing the filter and fluid, one of the first things i thought of when it happened. and the trans temp gauge, is there a fitting for it on the trans. thanks again for your replies.

[corvette]

hey, what's a good tranny temp gauge to get and how difficult is it to install. is there a fitting on the trans or do i have to tap into a line. also, would an aftermarket cooler be better than the factory, or both.

[apstguy]

Get the largest aftermarket tranny cooler and put it on there. The tranny getting too hot and locking out overdirve doesn't make sense to me though - In overdrive the tranny makes much less heat because the torque converter is locked.

[Z16]

I always pull in OD with my 350/4L60E as long as the road permits it to stay in OD. The tranny temp never gets above 130 if it stays in OD with the converter locked. Once it has to shift to 3rd, or the converter unlocks, the temp gets up to the 180-200 mark. If the tranny starts to search for gears, I shift it to 3rd. You should run a LARGE cooler in conjunction with the factory cooler if it gets cold where you live, but if you live in a warm climate, you can eliminate the factory cooler with no problems. Always use the largest cooler you can find and fit. As`well, get a good Autometer trans temp gauge. The factory programs the computer to go into limp mode when the trans temp goes above 275 degrees, but that seems way to hot for a transmission to me.

[Rickracer]

As was stated before, for towing, get the biggest, most efficient cooler you can find. Trans fluid starts to break down at anything over 280*.

[corvette]

thanks guys for all your advice. hope i can help ya's out in the future. love this post and we'll be keeping an eye on things

[see-n-things]

Yeah, I had a 350 / 480LE set up in a 98 chev p/u that would not give me 2nd gear under load. With the mountains in BC, it's kinda necessary to haul with 2nd pulling a trailer, and I would downshift manually. I had a tranny gauge and tranny cooler(after factory) installed for this purpose. I'd be shifting from 3rd down to 2nd and it would default into 1st, slowing me 20mph. When the revs came up, I would shift to 2nd,and it would jump to 3rd and the revs would drop off again. When I brought it to the dealer, the certified GM mechanic plugged in the diagnostic and cleared the codes, telling me to come back if it happened again. (they couldn't get it to repeat) When it happened again no codes came up, but I still didn't have 2nd. After 3 more documented trips to the GM dealer their computer insisted that I didn't have a problem. So with that info, I traded it in . . . and cleared my codes! ! !