transmission Feedback....

[PMcCall]

I have had my 2500 6.7 TD Laramie since mid December. On occasion I have noticed a hard downshift around the 30 MPH zone. It seems to happen once in a while. Over time there seems to be a correlation between the hard downshift and the exhaust brake being set on "auto". I noticed this on a trip this past weekend. When it happens its more of a "thunk" than any sort of grinding noise. I couldnt get it to happen when the exhaust brake was "on"

I had the new flash done last week. Is this something with the 68 transmission or could there be a problem? I have about 4500 miles on it. I checked the fluid and its OK.

Thoughts?

 

[EStarns]

Yes mine will do it too. I always use the EB and I have a down hill that wants to engage the EB before the computer normally allows it on a cold engine just as the speed gets up to 30 MPH. So I get the clunk of the converter locking up to maintain speed. It will also happen if it doesn't get locked before I have to slow for the next stop sign even on a warn engine. This happens when I have it set to 4th gear because of the roads I am on and I hate to use the brakes when the truck can do it itself. It does not do this when just in drive as nothing is locked yet. After 7 years with mine 30 is the minimum speed for lock up in 4th & 5th and 40 for 6th. I have 4.10 gears.

2007.5 2500 quad cab long box 4x4 Inferno Red, Insight guage.
89,000 still on original tires and brakes still have half their thickness. Still runs better than new.

 

[EDankievitch]

My 13 does more or less the same thing. If you use the Tow haul mode it really downshifts aggressively. It will really slow the truck down with the engine break in tow haul.

 

[mpaulson]

My 07.5 would do a nasty clunk and jerk you around as well if I let off the throttle quickly in the speed range that you are mentioning as well as below down to say 20 mph. I trained myself to let the throttle off gently in those speed ranges to avoid it. Must be a 68 RFE programming thing because I don't notice anything like this with the aisin 69 transmission in the new truck.

 

[Bob V]

I have found that the EB on, Tow/Haul on, and the brake peddle depressed will get into an aggressive downshift pattern

 

[slingshot383]

Nothing wrong, nothing going to get hurt. These transmissions are computer controlled and torque managed. With the Exhaust brake and Tow/ Haul on it will be much more aggressive. Just touching the brake enough to get the brake lights on will enhance the downshifts.