steep downhill grades & auto trans

[HWright]

I've heard that long down hill grades can burn up an auto transmission if the lower gears are used for breaking . Is this true?

 

[Bill Stockard]

I've heard that long down hill grades can burn up an auto transmission if the lower gears are used for breaking . Is this true?

I've been downshifting automatic transmissions for additional engine braking on long steep grades for over 30 years towing trailers all over the lower 48 in Chevys, Fords, and Dodges, both gasoline and diesel powered. I've driven some of my vehicles nearly 300K miles and have yet to have an automatic transmission problem.



I service my automatics regularly at 20-25K miles using OEM filters and fluid.



Bill

 

[bombero]

Apsolutely , you can burn it up easily. Had a friend of mine do it with a new Ford going into Death Valley from the west entrance. When you shift down into a lower gear the trans fluid in the torque converter starts slowing down, trying to hold the vehicle/weight back. It will feel like everything is OK until the fluid start squirting out the dip stick and probably the front and rear seals. Can cause a nice fire!!

 

[keimmmo]

I too have downshifted my automatics for years without a problem. My '92 has over 325,000 miles on it and the '01. 5 has over 100,000. I have a trans temp gauge on the '01. 5. Downshifting DOES generate heat! But, if you have a guage and do not excede safe temps I fail to see that it will cause damage.



Steve

 

[MMathewson]

What really is the best way to go down a steep hill (7% grade for 6 miles) with the 48re and no exhaust brake with a 6000# trailer? Obviously switch it into Tow/Haul mode, but that only helps some. 2nd gear helps more, but then you are limited to 45-50 mph. Tow/Haul mode, let it accelerate, use the service brake. Sure wish there was an exhaust brake that was approved.

 

[Bill Stockard]

What really is the best way to go down a steep hill (7% grade for 6 miles) with the 48re and no exhaust brake with a 6000# trailer? Obviously switch it into Tow/Haul mode, but that only helps some. 2nd gear helps more, but then you are limited to 45-50 mph. Tow/Haul mode, let it accelerate, use the service brake. Sure wish there was an exhaust brake that was approved.

I have found that the 48RE in my '03 will keep the torque converter locked at engine RPM above about 1,800 when manually shifted to 2nd gear before going over the top of the grade. The truck's 4. 10 ratio axle allows a slower speed when keeping the RPM to around 2,000 on the down hill grades. The locked torque converter in 2nd gear with the engine braking holds back pretty well. It would help if D-C had programmed the torque converter to lockup on deceleration and to stay locked up to a lower RPM.



Bill

 

[Beast2B]

Does the tow/haul mode keep the TC locked on decel? THAT'S the key to keeping the temp down. Many of the aftermarket controllers do just that, whereas the stock trucks unlock any time the service brakes are touched...

 

[Road9]

steep down grades &auto trans

I have 95 with auto tow 5th over 10,000#;would not leave home without E brake. Trans. mods. aftermarket TC, mystery switch,ect. . Shift to 3rd{D} @top of 6 or7 % grade lock TC clutch & never use service brakes until you round turn & see the log tr. or car pulls out! Best $$$ you can spend if you tow in the mt. west. As others have said add gauge ,Watch trans. temp. if you down shift & don't have TC clutch locked. Enjoy your CTD,Rd9.

 

[cwsoules]

Before I had my DTT mods to my transmission I used my cruise control. I would try to top the hill in 3rd gear at the desired down hill speed in cruise control. I found that my 10. 4K 5th wheel trailer would push my truck down hill. If the hill was 6% or less the cruise control kept my transmission locked and I got engine braking. If the grade exceeded 6% the truck and trailer combination would accellerate down hill, the cruise control would unlock the transmission, the engine rpm would drop to idle and it would be brakes only to the bottom of the hill. My exhaust brake was part of my DTT modifications and I would not be without it.