48RE question

[kklemme]

I am a new member to Tdr this is my first thread. I have a 04. 5' 3500, swb, 4 wheel drive, 4:10 gears. I haul a 9' Arctic Fox cabover camper 3500 lbs. dry. My question is, when I am descending a steep mountain grade with the camper I will sometimes put it down in to first gear in towhaul. When I get to the flat after putting it in drive the transmission dumps into 4th gear. I stop the truck take off and again it immediatly goes into the highest gear. I have 3,000 miles left on the transmission warranty. Also where do I find service bullitens on the website. Thanks.

 

[cerberusiam]

Are you saying even though TH is still on its going into OD?



That should not happen. Now, if you turn TH off it will.



Are you sure its going to OD and not just the TC locking in drive?



Running in first like that is going to generate a fair amount of heat and the trans will want to shift in OD and lock the TC to cool things down. Thats possibly what is happening.

 

[BHanna]

It sounds like you're not driving nice paved roads and you're trying to go pretty slow. Have you tried using low range? I get a lot more engine braking that way (which is to say I get a little). Also the trans can get into a higher gear and lock the TC so it generates less heat.

 

[kklemme]

That is correct, even in tow haul it still goes into overdrive. It takes a few minuets to cool down then the transmission shifts correctly.

 

[HBarlow]

Your torque converter doesn't lock in low range so it's slipping and generating considerable heat on a long slow downgrade like you described. Using second gear will provide some torque converter lockup and generate less heat.

 

[kklemme]

Thanks for the response's. That helps out alot.

 

[cerberusiam]

That is correct, even in tow haul it still goes into overdrive. It takes a few minuets to cool down then the transmission shifts correctly.

Hmmmm... . granted the OD shift is purely computer controlled, but, this is the first time I have heard of a trans shifting in OD with the TH engaged.



Thats just not a normal condition and I would question if that is the correct operation. If anything it should shift to drive and lock the TC, not OD.



After it cools down in a couple minutes does it shift back to drive?

 

[Pawpaw]

Hmmmm... . granted the OD shift is purely computer controlled, but, this is the first time I have heard of a trans shifting in OD with the TH engaged.



Thats just not a normal condition and I would question if that is the correct operation. If anything it should shift to drive and lock the TC, not OD.

Depends on what year the truck is. At some point ('06?), the tow/haul button gained two functions. A single-tap put it in one mode, while a double-tap put it in another.



One mode had it work like my '04. It adjusted the shift points and locked out overdrive.



The other mode adjusted the shift points and TQ lockup, but still allows overdrive.



At least, that's what I think I remember reading on here.



Bob

 

[cerberusiam]

Depends on what year the truck is.

If you had read the OP's original post you would see it is 04. 5, not an 04 and not an 06. It doesn't depend on the year of truck or anything else, when OD is locked out it should stay locked out.



TH in in an 04. 5 was an OD lockout just like everything since 1991. I have had 4 trucks in that year range and NONE of them would upshift to OD with the TH or OD Off engaged. At least I never found a situation where if things were functionally correctly that would happen.



Since I have not had an 04. 5 and have not done exactly the same thing the OP did, it is impossible to say for certain it can't happen. I can say with certainty it is very unusual that it would happen.



If that is truly what is happening its a rare anomaly or a problem developing.

 

[Pawpaw]

Well, I did go back & look at his post, but still missed that it was an '04. 5. I plead old-timers disease! :-laf



You are 100% correct. This does sound like a real problem developing, or the transmission is getting too hot, so the computer decides to use overdrive anyway to cool things down.



I really don't know. I'm not a transmission guy, nor do I play one on TV.



Bob

 

[B.G. Smith]

If you had read the OP's original post you would see it is 04. 5, not an 04 and not an 06. It doesn't depend on the year of truck or anything else, when OD is locked out it should stay locked out.



TH in in an 04. 5 was an OD lockout just like everything since 1991. I have had 4 trucks in that year range and NONE of them would upshift to OD with the TH or OD Off engaged. At least I never found a situation where if things were functionally correctly that would happen.



Since I have not had an 04. 5 and have not done exactly the same thing the OP did, it is impossible to say for certain it can't happen. I can say with certainty it is very unusual that it would happen.



If that is truly what is happening its a rare anomaly or a problem developing.

Can't comment on other year models but as stated by someone above, TH on the 06 DOES not lock out OD. Push the button a second time, also stated above and OD is locked out. Not arguing, just stating a fact. bg

 

[KLauber]

Get that transmission checked!!

Your torque converter doesn't lock in low range so it's slipping and generating considerable heat on a long slow downgrade like you described. Using second gear will provide some torque converter lockup and generate less heat.

I changed to a triple disc TC for towing and hauling heavy loads, it can lock up in each gear (except for first of course). But I am not driving such steep grades as he does, so maybe the trans is acting correctly to dissipate the heat as several have theorized. But we can all agree to take it in for a checkup before that warranty expires!!



Ken

 

[bheiting]

I'm no transmission mechanic, but it sounds like the trans is trying to keep the
torque converter from slipping to reduce heat before it burns itself up. Does your
trans fluid smell burned? With a 3500+ lb camper, I wouldn't leave the driveway
without pyrometer, boost, and trans temp gauges.