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wvabeer · 09-24-2021, 07:16 AM

I have a 99 Dutch star 300 Cummins 3000 Alison. When the engine brake is on and I am decelerating sometimes 4th gear hits hard, but not always. Does anyone have this too?

grldst · 09-24-2021, 08:43 AM

I have a 300 Cat with 3000 Allison Freightliner chassis. Mine will do same thing occasionally, not all the time, more so when trans temps are cold.

Skip426 · 09-24-2021, 08:56 AM

Yes 99 DSDP .Cat engine 3000 series Allison , exhaust brake . Occasional harsh downshift .
I've put this down to the transmission shifting down two gears instead of just one .
Now when I crest a summit and slow to my control speed I manually shift the trans down to 5th or 4th depending on what I expect of the downhill .
If you don't manually downshift any time you touch the throttle the trans could shift back to 6th , then double downshift when the exhaust brake re-activates.
If the speed is low enough coming off exhaust brake the trans will only go to 5th , then a single gear downshift on reapplication of the exhaust brake will be much smoother that a double gear down.

BTW: I'm guessing your DS with Cummins , is on a Spartan chassis and your engine is an ICS 8.3L , and has an exhaust brake , not an " engine brake " the term for a; multi stage compression brake.

wvabeer · 09-25-2021, 07:32 AM

Ok exhaust brake. Anyway , so this is a common thing with these. I wonder if there's a remedy for this?

ArtJoyce · 09-25-2021, 09:06 AM

I have the issue on steeper grades with my 3060 allison. I had more issues when tolling a 5.1k toad, much less with a 2.8k toad. About the same time I changed the transmission fluid. I think it's rwo gears. I also start manually per downshifting.

wolfe10 · 09-25-2021, 09:13 AM

EASY-- you need to turn that one BIG "braking event" into several small ones.

At certain speeds, the transmission will drop TWO gears at the same time the exhaust brake comes on. That does make for an abrupt decel.

Instead:

Hit the Allison down arrow once, again. THEN turn on the exhaust brake. That is now 3 mini-steps.

You can not harm the transmission by selecting too low a gear-- it will not downshift until safe to do so.

Can you always anticipate slowing to allow for 3 mini-steps. No. But for 90% of them you can.

Been there done that.

Rob_M · 09-25-2021, 09:16 AM

Quote:

Originally Posted by wvabeer

Ok exhaust brake. Anyway , so this is a common thing with these. I wonder if there's a remedy for this?

Probably not. Maybe if you’re due for a trans fluid change the friction modifier in the fluid is breaking down.

And unless it is a violently hard shift it won’t hurt a thing. A firm shift is better for transmission longevity than a soft shift as any slippage during the shift process wears the friction plates. Conversely violent hard shifts can break “hard parts” (drums,gears, shafts etc).