Help with towing

[milto]

I have a 95 3/4 ton 410 rearend, 65000 miles automatic.

Have had the truck for a year but only ran 2 tanks of fuel through it as I bought it to pull a fifth wheel we were going to buy as I neared retitriment. New fuel,air, and oil filters.



Towed it home yesterday, 30 ft fifth wheel 7700#. Started on the trip home brought it up to around 45 on the freeway then turned off the O/D light took it up to 65 at 2100 RPM pulled beautiful. Several short and long inclines, never kicked out of O/D or lost more then 150 RPM.



Off of freeway to a 55mph road with hills, shifted manually off of O/D. Could not get above 54 MPH at 2500 RPM. Throttle to the floor. turned O/D back on manually, went down to 2100 and stayed there for a few seconds and then down to 1700 RPM and ran smooth.



Should i be able to do more then 54 out of O/D. What was the double shiffting when i shifted back into O/D. Was it first the T/C locking up and then the O/D. Sure am confused as it is not what I expected from this truck. Any suggestions will be appreciated.



I have ordered gauges but DIS is having problems getting the 3 hole pillar.

 

[LSMITH]

Milto, that sounds like it is working just like it is supposed to. Dads 95 is the same way. About 55 in drive is all it will do, and 82 in OD is flat out. The double shift is the trans shifting to OD and then the TC locking up. If it will run 1700 RPM or higher in OD let it run in OD. If you get below 1700 towing in OD lock out the OD. Good luck and hope this helped.

 

[Howard Durand]

milto,



With the 7700# load and 4. 10 gears, I believe your truck is doing pretty much what it should. With my 3. 54 gears I am pretty much limited to around 60 with OD locked out pulling my 7000# trailer.



As for the double shifting, when the OD is manually enabled or disabled, the first thing the transmission does is unlock the torque converter. Following that it proceeds to shift the OD. When the OD shift is completed and the computer is happy, it then re-locks the torgue converter.



These transmissions are complex and I know there are guys on this forum that know a lot more than I do about them. Hopefully someone else will contribute to this.

Added power is not going to get you more speed unless it lets you to top out at a higher rpm.

I needed more power to allow me to stay in OD longer and not have to shift for the rolling hills and short grades you mention.



The big problem is the difference in gear ratio between 3rd and OD.

I would think that a good auxiliary gear box like US Gear or Gear Vendors have to offer would be a worthwhile addition to a truck that is dedicated to the towing job you have. Either one would greatly increase your choice of gears.

 

[Joe G.]

If your pump is defueling at 2500 then you probably can't get much more RPM even with no load. With a 12 valve engine the 410 gears are over kill. It's a different story with the 24 valve with the flatter torque curve so they run better at higher RPM. Stock 12 valvers vary a bit about the defueling point. Mine defueled at 2800.



The double shifting is because the transmission will not shift with the torque convertor clutch locked up. So when you down shift from OD with the TCC locked the first thing that happens is that the TCC lets go. Next the transmission shifts from OD to 3rd. Then the TCC locks back up again. When you have the OD locked out and unlock it to shift up, the TCC will let go, the transmission will shift from 3rd to OD, and then the TCC will lock up again. With the stock TC the RPM drop when the TCC locks up in OD is pretty dramatic.