Using the engine for braking - Diesel Forum

joez301 · 07-07-2001, 07:53 PM

Hey all,
Just got back from a week camping near Mt. St. Hellens. Anyway I was driving on some back roads and on one there was a long step down grade. So I put my truck (v10 4x4 auto) into 1st so I would ride the breaks. It keeped my speed down which is what I wanted. But every once in a while the engine would rev up to 1500-2000 then come back down to 500-800. Has anyone else have this happen to them? Is this normal? I am use to driving like this with a manual trans. and the engine would rev up and stay there. Not jump up and down like this.

Joe

Dr Matt · 07-09-2001, 01:33 AM

The engine will not work as a brake at low speeds very well. The computer is telling the tranny to disengage to let the truck coast and thereby improve milage. If you start at greater speeds you can get this to work by downshifting and then using the throttle to get the engine up to vehicle speed. Compression will slow the truck down & it will work better than if you do not get the tranny locked up. This way the computer sort of figures out you are compression braking and cooperates better. This may not be a technically accurate description but it works.

snomoman · 07-10-2001, 11:21 PM

I do this often when towing my 5th wheel in the hills and have never had a problem or the situation that you described. It works like a manual tranny in a sense. I also blip the throttle as I downshift so that the engine revs match the transmission speed, thus making the whole shift smoother.
Works great.