Shifting Questions

[lorim]

I have a 1999 winnebago with the Cummins 24V Diesel & Allison Transmission. We just replaced the turbo and was out for the 3rd test drive (finally nothing blew off.. yea). We have a really big hill that the MH is technically overweight to come down it but its a great climb to test things out and it's super close if issues arise. Anyway, starting from a dead stop at the light I had my foot to the floor and it never downshifted, crested at 20 mph, not that it mattered but geeze. I feel silly asking but what gives, why wouldn't it attempt a shift? In the mid 90's I drove all sizes of school buses (old and new) up & down that big hill twice a day for eight years, never needed to shift an automatic on a good weather day.

[Skip426]

OK, starting out from a dead stop , you're in first gear .
The Allison shift pad ( I'm assuming a shift pad with a six speed Allison here ; if that's not your trans , please add info to your post) shows " 6 " as the top gear the trans will go to , when accelerating depending on the speed achieved , that you didn't mention you may have gone up a couple of gears , but the shift pad would still show 6, if the trans felt that a lower gear would over rev the engine it will not downshift .

What RPM were you turning at 20 MPH. if it was over 2,000 you were probably in the lowest gear possible without over revving the engine.
Did you drive this hill before the turbo replacement and achieve a higher speed ??
Need to compare apples to apples here , not this coach to a different vehicle.

[lorim]

I'm pretty sure it's just a 4 speed, no shift paddle just the old lever with a push button on the side for your thumb to move the lever. I've had the MH up this hill a few times with the old turbo and it didn't scream up the hill but I never really looked at my RPMs and today I was all into the boost gauge so I wasn't looking. My son said he thinks the RPM was close to 2000 but certainly not over. There's another long hill I climb a lot and thinking about it, it doesn't down shift on that one either, dogging up at probably 20 mph.

[Crasher]

At 20 mph and 2,000 rpm, what gear do you think it's in? If there is a wide ratio between 1st and 2nd gear, it might over rev the engine with a down shift at that rpm. I think you have the 275hp w/550# torque version with the Allison 643 4 speed. I had the same thing in a 99 Bounder. Try shifting manually without over revving the engine. You might have a bad sensor preventing the downshift.