6 Shaker

Hi,

I just got back from a big camping trip through the mountains with the new truck and overall I'm really impressed. I just have a couple of questions.

Has anybody else noticed that while towing in tow/haul mode the truck sometimes doesn't want to shift into 6th gear on its own? I was in the mountains and when I'd crest hills and start going downhill, the truck would only shift into 6th on its own maybe 50% of the time. The rest of the time I'd have to kick the cruise off and take my foot off the gas to get it into 6th.

I could understand if this was still going up hill, but this was either flat ground or starting to go downhill before the speed would pick up enough to get the exhust brake to kick in.

Oh, this also happens on flat ground when passing others. As soon as I'd get back into my lane and to start slowing down the truck usually wouldn't go back into 6th on its own.

Is this just a quirk of the 68re, or is this just how it is with an auto towing, since I've never owned an auto truck before.

Thanks

Blake Clark

In tow haul the 68RE is designed to shift into 6th only in the right conditions as to not put more strain than necessary on the overdrive.

When Im towing heavy I rarely see 6th gear in tow/haul.

6 Shaker

Thats what I figured, but I'm not towing all that heavy. Only a bumper pull travel trailer that weighs in around 8000 lbs.

Grit Dog

I've only driven a 68RE truck a couple times, but my impression was that 5th gear was about the same as 6th on a G56 or 4th on a 48RE, and that 6th gear was really deep. To the point that I don't think I'd want it to upshift into 6th with any load behind it unless I was going very fast (faster than I'd tow a 8000#TT).
Just my uneducated opinion.

67guzzler

Ratios & RPM's @ 70 mph:

G56 Manual w/0.74 final drive ratio in 6th gear, 265/70-17 tires, 654 revs per mile @ 70 mph:
3.42 axle -- 1931 rpm at 70 mph
3.73 axle -- 2106 rpm at 70 mph
4.10 axle -- 2321 rpm at 70 mph (combination NOT available -- just for comparison)

6-Speed Automatic w/0.63 final drive ratio in 6th gear, 265/70-17 tires, 654 revs per mile @ 70 mph:
3.42 axle -- 1644 rpm at 70 mph
3.73 axle -- 1793 rpm at 70 mph
4.10 axle -- 1976 rpm at 70 mph

6 Shaker

Well the truck was at the dealer today getting a leaking transfer case repaired. Supposedly there is a flash to fix the problem with it not wanting to shift into 6th. When I get it back tomorrow, I'll post the flash number.

As for towing in 6th.... I don't see it being a problem as long as it isn't lugging. My truck on flat ground anyways has no problem handling my trailer in 6th at around 1600-1650 rpm.

Grit Dog, I had a G56 before this truck and it was a beast. I mean I never had to downshift unless traffic was in the way. This 68re is very shift happy. But I think that is just a automatic trait. It'll rev the truck like I never would have with the old manual.

ctnv

I tow across country and back every yr and the tranny is designed as stated to shift when conditions are correct. I usually use the up/down button on the shift lever to save the tranny from reving too high when down shifting. I try to anticipate a down shift and do it manually. If in very hilly or mountainous area I keep it in 5th gear and let the diesel do it's thing.

Iron Monkey

I noticed the other day that when I was pulling my truck shifted into sixth gear. I was in tow mode and it seemed like the transmission would shift into 6th at a low speed. I think this would be bad for a transmission to shift at such a low speed. I set my shifter to 5th and when I get going about 70 I shift up to sixth for Highway driving. I have 3:73 gears and my truck has 2400 miles. I guess it just needs to be broken in. I pull a gooseneck trailer with diesel welders and gang boxes. I have a miller 300 welder in the bed it weighs about 1200 pounds plus the trailer is 7,000 pounds. I would really like to put a chip on this truck but I don't want to loose my warranty.