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Topic: [SuperCrvgroup] Dura max won’t downshift (Read 1234 times) previous topic - next topic
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[SuperCrvgroup] Dura max won’t downshift

Yahoo Message Number: 16773
Do either of you use the OD switch on dash just in front of where you grab the shifter arm?

Best
Ron Hall

Re: [SuperCrvgroup] Dura max won’t downshift

Reply #1 –
Yahoo Message Number: 16774
If I thought that I would need a down shift sooner than the trans would make that decision, I would force a down shift by momentarily turning off and back on the overdrive switch. That would keep the engine from getting into a lugging situation.

Re: [SuperCrvgroup] Dura max won’t downshift

Reply #2 –
Yahoo Message Number: 16775
It comes out of OD automatically far before any wanted downshift but yes, sometimes I use the that toggle switch to take it out of OD earlier or if the climb makes it come in and out annoyingly on the hill.


Re: [SuperCrvgroup] Dura max won’t downshift

Reply #5 –
Yahoo Message Number: 16781
I never let it get that low. Was in a hilly area pulling my explorer. It went back to downshifting normally the next day.


Re: [SuperCrvgroup] Dura max won’t downshif t

Reply #6 –
Yahoo Message Number: 17156
Ron, have you seen any advice when you should use that overdrive button and when not too? We drive the smokies a lot with the 34ss towing a wranger. Recently there was a oil leak that happend behind the turbo that was allowing smoke to come in and set off the smoke alarms. I tend to leave the OD on at all times and I am now wondering if thats a bad idea in those mountains which blew that gasket... Any advice on what people do would be great!

thanks!

Carl

Re: [SuperCrvgroup] Dura max won’t downshif t

Reply #7 –
Yahoo Message Number: 17157
We also have the 34SS pulling a CRV and we love it.

The OD usually kicks off on a hill between 55 and 60. But sometimes I turn it off if there are a lot of hills in a row. For a long, hard pull where the mph drops to 40 or 45 I'll shift down and take some pressure off the throttle.

One time out of Vantage Westbound on I90 I left it to the cruise control full throttle and the tranny got pretty hot (10-15 mile climb). Never got below 50, but we did use a bit of oil. I don't want it to ever get that hot again. I'm not in that big of a hurry.


Re: [SuperCrvgroup] Dura max won’t downshif t

Reply #8 –
Yahoo Message Number: 17162
Same thing with mine... Never moves off of 160 degrees. 2007 and later units have rhe 6 speed with synthetic fluid and a larger cooler. Allison factiry rep informed me that, no matter what the conditions you may never see 200 degrees. Thought there was something wrong with the guage, too. Bought one of those IR temp guns and crawled under the rig several times to check the true temp at the transmission pan. Guage was completely correct in every instance. Guess Im one of the fortunate ones that never has to worry about it. Do watch the EGT guage on hard pulls... Try to keep it below about 1250 degrees.. GM says temps as high as 1350 deg are ok for very short periods of time.
Thats my experience over the last 5 years of travel..
Dave

Re: [SuperCrvgroup] Dura max won’t downshif t

Reply #9 –
Yahoo Message Number: 17163
As you all are aware the medium duty in 06 and the first half of 07 were delivered with 5 speeds. Those transmissions were actually 6 speeds but dormant. All the medium duty transmissions were serviced from the factory with Transsyn synthetic fluid as well. If you have one of those transmissions the 6th speed can be turned on by reprogramming the TCM with a bin # from any medium duty last half of 07 08. Not sure about later transmissions that may have different internals. I had number 6 turned on in mine and realized only slightly better milage but a much quieter operation. The trans temp was always normal. If I felt that I needed to force a shift down I simply flipped the OD switch off and back on. Worked very well.

[SuperCrvgroup] Dura max won’t downshift

Reply #10 –
Yahoo Message Number: 16783
Yup thats what I did whenever something unusual showed. Including ABS and transmission. It was nice to have a chassis disconnect switch under the hood.

Best
Ron Hall