jumper

I pulled a bumper tow brick at 16,500 lbs gross GCVW (plus me) back and forth over the I-5 Grapevine to southern California last weekend. Axle weights were 4,240, 4,360, and 7,900 respectively for the front, rear and trailer. With the 35" tires and 3.73 gears I could run 55-60 MPH up the hill in 3rd at 1,200 degrees EGT with no appreciable transmission temp impact. I've got a BD valve body and a double deep transmission pan.

About half way up the southbound side I had to slow to about 40 MPH for truck traffic. The TC unlocked and I was nearly done, almost having to slow down and let her drop to second and plod along with the semis. I was just able to get my speed back up to allow the TC to lock up again. It took a dance with the throttle to manage EGTs while watching the transmission (pan) temp climb past 200 before I finally got my speed up and the TC locked up again. Clearly the oil temp coming out of the torque converter was higher than 200.

What do you guys with automatics do that tow even just this heavy? Do I need a new TC built for towing, is a TC lockup switch the only needed solution, or something else? I don't want to be in this situation again.

grantx5

I hear you. Don't pull that much weight but my Sunnybrook does come in around 7200-7500#. Just about the time I think all is well, the tranny shifts into OD and, uh-oh, there goes the temps.

I have read, not tried, about shifting into 2nd once the TC is locked. Some say the 48re will then stay locked until you shift to D or slow down a bunch.

What I do is double-click the T/H button when it shifts to OD. The tranny rethinks things and kicks out of OD into 3rd, then locks the TC. Not a very good work-around but I have been successful in keeping it out of OD for long periods of time (up hill).

There is flash that will turn off the T/H feature and change it to an OD on/off toggle. What I don't like about that is losing T/H.

There is an after-market fix from BD Power that will add OD on/off to the '05 48re. This allows you to keep T/H while adding OD on/off. Pretty neat feature, I'm just too cheap to buy one.

jumper

Thanks, in my case I was comfortably pulling hard in third up the hill with the TC locked but when I slowed down the TC unlocked but remained in third gear. Perhaps had I downshifted to second I could have roared up the RPMs and perhaps have gotten to a speed at which the TC would have locked immediately when shifting back to third. I didn't think to try that and instead milked the speed back up while heating the transmission.

I didn't have a problem with OD other than I wish I'd had a gear between third and OD so I could have run higher RPMs at 60 MPH when cruising the flatlands. As it was I only got to 1,600 RPM at 63 MPH. I didn't want to run faster than 65 on the flatlands.

grantx5

Yea, it would be nice to move the shift points out a bit.

Russ Roth

Mine is an '01 so I know the shift logic is different but I think a lockup switch would have been helpful. You would have likely had to shift down to second to be able to pull it in lockup. I don't know if BD valve bodies are set up to shift locked or not. You better ask them before you do it. I can with my Dunrite and do it all the time. If they tell you not to shift locked you can time the unlock with the shift to make some good gains and then relock it. I have played with mine and it works pretty good that way. I shift mine locked when towing about 12,000 gross with no issues. I even lock it up in first gear and 4 wheel drive sometimes. I don't shift out of first locked under a lot of power though.

IMHO, there is no downside to the lockup switch as long as you use it properly. Gives you more options.

LFD2037

I have the opposite problem. In tow/haul when the TC locks up & the engine is lugging, the EGT's climb really fast. So you have to ask yourself, do you want your tranny temps to climb high or do you want your EGT's to climb high? Just something to think about!

Raspy

jumper,

If you insist on keeping it locked, the TC switch is the answer. But, it is a very bad idea to let it shift while manually locked! What a slam! With an aftermarket TC, a bombed Cummins and a shift while locked under heavyload, it's broken shaft time. I use my switch all the time and am always wishing I had a stick when I'm in the mountains.

When towing heavy, RPM is your friend. I slipped my stock TC while towing and even now can slip something when in OD. I used to tow at 1600 RPM but realized after gauges that the EGT was way up there compared to 2500 RPM.

Now to preserve my tranny and to keep the valves cool it's RPM for me if I'm really pulling something. Oh what I'd give for two more gears!

As far as 200 degrees or a bit more in the pan, oh well. I don't think that's really a big deal. If you are going to push the truck toward it's limit with higher than stock power there has to be some down side, especially with and antique tranny that was designed for gas engines over 40 years ago and that has been built just strong enough for stock power.

Just last night I went over the Sonora pass with a 4000 pound trailer and maybe 2000 pounds of stuff. On and off the throttle constantly for hairpin turns and very steep. I've found it's not the speed of the other traffic that matters so much as the happy zone for the truck. Find that best compromize where the Cummins is in it's power band, the tranny is locked in a good gear, and all is well.

John

Russ Roth

My Dunrite shifts very smooth under full power and pulling my TT. Tony even advertises they can be shifted locked. Quote from his ad in a Diesel Power magazine I have in front of me.

"The shifts are so smooth you can manually shift up or down, even when the torque converter is locked up."

I can say that not all of them are smooth as butter but the ones that count when pulling under load are. Certain shifts are a little rough at part throttle or on compression but if you are paying attention, figure out how it works, when and under what conditions, you can work around it just fine.

Truth is if you let it shift itself you would swear it's a stock valve body.

Gary Emerald

isn't there a lever on the column?

pronstar

On my 2007, if left in "D" while going up a steep hill at 40mph or so in second gear, the TC won't lock and my tranny temps rise.

But when I pull the lever down to "2" the TC locks, and the tranny temps go right down.

slickwillie

ive maxed my tranny temp gauge more times than i care to remember while pulling a trailer weighting over 35k lbs. smarty was on beta 4.4 and i was getting after it. i change the fluid and keep driving it. my temps go above 200 daily. and since the ambient temps are on the rise, i can see it with higher tranny temps

LFD2037

The highest mine has ever gotten to is 176 & that's when I was trying to back a 9K lb. 5th wheel in reverse & kinda sank down in the mud.

TriSum

The converter lock-up switch is the way to go. I have a switch, converter and valve body, stock trans other than that. Sometimes it's a little tricky on the shifts if your using cruise control, but you'll figure it out.

It works great, and I tow HEAVY. I went across the scales last night at 4040, 9620, 17200 #'s (front, rear, trailer) and no problems.

As stated above, RPM is your friend when towing heavy. You can't lug the engine. It will run all day at 2500 rpm, don't be afraid to pull it down a gear.

David

paulrecore

I have a few questions on when and the best way to use the lockup switch. I am towing a large 5th wheel trailer and just want to get there with no damage to tranny.

1) Starting out. After accelerating and it shifts into second and do about 30 MPH flip the switch to lockup? Do I back off of on the gas pedal or hold it steady?

2) Cursing along and in overdrive doing about 62 mph. Now coming to a hill that you could normal go over in overdrive but after getting half way up you need to take it out of overdrive (traffic). Just push the button to turn off overdrive and leave the switch in lockup or turn the lockup switch off then turn overdrive off or???

3) Cursing along and in overdrive doing about 62 mph. Hill coming up drop out of overdrive (per #2 above). Now in third and lockup switch on. Need to turn lockup switch off, what is the best way??? Just turn it off, let up on gas first or??

4) Going up a hill in second or third and would like to lock up the TQ. Can I just flip the switch when under power or do I need to let off the gas first or???

Beatle

I would also like to here what people are doing. I have the same questions as Paulrecore. Can someone chime in and answer these great questions.