Auto transmission Down-shifting

[JRG]

IF SOMEONE WERE TOWING A GROSS WEIGHT OF 14000# AND NO EHAUST BRAKE, WOULD IT BE HARMFULL TO BRING THE AUTO transmission DOWN TO 2nd WHILE STAYING IN THE PROPER RPM RANGE?



JRG

 

[red1ton]

I think you will find that it is more a matter of no braking from the engine when you take your foot off the pedal. The problem is the tansmission unlocks and lets the engine spin freely. You can see this when the tach goes to the idle RPM when you let off the pedal.



The exhaust brake system provides back pressure for the engine while the transmission is held in a locked up condition. This is what provides the braking.

 

[Boldt's Wagon]

Go ahead and shift down, thats what the owner's manual says to do. On 8 or 9 % grades shift into 1st (you have to be below 15 mph for the transmission to manually shift into 1st).



Use of 2nd gear will not hurt the transmission because the maximum drag you can get from the engine is about 70 HP at 2700-2800 rpm. 70 hp is nothing compared to 220+ hp you can run thru it the other direction.



It gives some small increase to operate the air conditioner even if it is cool out (another 3-4 HP).



With the engine at 2500 to 3000 rpm braking in 2nd or 1st, the transmission pump is operating at 2700 to 3300 rpm and providing maximum transmission fluid flow.



I have put hundreds of miles on while engine braking in 2nd and 1st. My transmission temp is below 150 in 2nd, I have seen 180 on a long 9% grade in 1st. I installed front brake pads at 50,000 miles and 30,000 miles was towing in the mountains.



My GVW is 18,000. If you are towing 14,000 you might consider a DTT upgrade and exhaust brake. The 70 braking HP you get without an exhaust brake is marginal for stopping 21,000+ lbs.