RPMs drops down too fast similar as engine brake is on (DD60 14L)

Could the engine fan be on at the time the RPMs drop fast. If you have a manual override switch for it, turn the fan on and see if it is what you are experiencing.

 

maybe drive w engine brake off; use brake as needed. I drove a
Cascadia that wouldn't shift for crap w the brake on.

 

either the fan has cycled on or the air compressor just loaded. On my Detroit, if I'd been working it and thought the fan might come on mid-shift, I would manually turn the fan on and then I'd know to shift a little quicker.

 

I'm an old timer, have not been out there in a while. Once had similar problem with a KW with a Cummings, it was the O-ring on the throttle shaft. And old mechanic found the problem at Headstreams Fuel Stop at Quartzsite, AZ, of course he and the fuel stop is now gone.

 

S60, with the vvg turbo...its the turbo actuator, period. If you let off the gas easy and slowly, then change, I bet it doesn't do it.
No easy fix for it, as the actuator is part of the turbo on some models. If it's separate, you can change it out though. The noise is coming from the air filter housing, as it spits it back through there. Sounds like the Jakes on low.

Martin

 

Hi OHB, while I can't help the OP with his problem, years ago when I drove a R model Mack with a 6 speed, I used to shift with the "dynatard" on all the time, especially in the 1st couple of gears, as with a heavy load, without it on, the road speed would drop off faster than the rev's and the rev's for the next gear would be too low, and it would lug the motor (below 1300 rpm)

 

One other thing: If your truck doesn't have a manual fan switch so you can engage the fan prior to a shift, all you really need to do is back out of it prior to the shift itself. The sensors in the engine will register the loss of boost and a corresponding lack of cooling from the air going through the engine and almost immediately engage the fan. You can then initiate your shift knowing the fan is engaged and adjust your timing accordingly (shift a bit quicker).