My truck lives with a trailer behind it and I always turn overdrive off when under 50 mph and turn it off to help slow the truck and trailer down when coming off the interstate. About a month ago when I turned od off to take a exit truck did not decel. Just shifts to 3rd and engine goes to idle even at highway speeds. Truck still tows fine. No trans codes no flashing od light. Trans was rebuilt at 163,000 miles have 183,000 now. I'm stumped to what it could be.

 

It is the coast clutch not applying. That could be caused by several things. Here's something to try that will let me narrow down where the problem lies. At 40 MPH coasting put the shift handle in the 2 position. Does it have engine braking or does the engine go to idle?

 

Yes it has the engine brake in 2.

 

Then you're lucky. Your coast clutch is still working, the trans does NOT have to come out to fix this.

The first thing to do would to check for codes. That may show what the problem is. It is going to be either a wiring issue to the coast clutch solenoid, a bad coast clutch solenoid, or a stuck valve in the valve body.

Since it has engine braking in second it proves that the coast clutch is working because the clutch is applied without the solenoid when the shift handle is in 2.

 

Will I damage the trans further by not fixing it and countinue to drive. Just trying to hold off for a year or 2 till I can afford a bts. Didn't want to rebuild this one at local shop but it was half the price of a bts.

 

No, it won't hurt anything. If you need engine braking use 2. It might be something as simple as a damaged wire. If it is wiring a brand new BTS will have the same issue.

 

Well I say bts cause I know this one is going to go out.

 

Thank god it's not something more serious. I can't afford to put this truck back in the shop. It's been off the road too much this year. Need it on the road as much as possible. Had 2 rear ends go out this year and 1 transmission.