Switched to synthetic, hard downshifting

[smlranger]

We had the allison serviced at the FCSC in Gaffney recently and changed the Dexron to the full synthetic Mobil Delvac. On the trip home and on a recent short (less than 100 miles) trip, the downshifts are bone jarring. Fluid level is OK.

Anyone else experience this on a change from Dexron to synthetic?

[DriVer]

Quote:

Originally Posted by smlranger Anyone else experience this on a change from Dexron to synthetic?

Gary, Perhaps the clutches are grabbing better and are not slipping - not sure but I would run it for a few more hundred miles to see if the situation persists. You can always call FCCC and ask them, I'm sure they will have seen this before.

[Mike Canter]

Do you normally drive with a toad and not have it this time since it was a short trip? If so then that can make the difference. The Allison transmission adapts to how it is being driven andmakes changes can take a short time to reprogram itself. If it keeps doing it try disconnecting the chassis battery for about five minutes to wipe out the memory and let it adapt again from scratch.

[Midniteoyl]

Agree... Disconnect the battery for at least 10 mins, then take it for a short 10-15 mile drive that has several starts and stops.

[smlranger]

I was towing the toad. Also, did the battery disconnect. I had to replace the Vehicle Data Computer (getting false low air alarms) so chassis batteries were disconnected for couple of hours.

I will drive it again and see if it clears up.

[Mike Canter]

Well thats the reason in reverse. It can take two or three days for the transmission to build a synopsis of the way you drive and set the program. Give it a little time and see what happens.

[Mike Canter]

Go to page 55 and read about Adapting Shifts
http://www.allisontransmission.com/s...t=OM3349EN.pdf

[Martind4]

When I attended Camp Freightliner this spring, I mentioned to Mike Cody that I had occasional hard shift problems and he also recommended that I try the adaptive shift programming. I looked at the procedure, assumed that I needed to have the toad attached, and then wondered where I could safely drive the rig through all the combinations.

Any ideas about a safe place to try it?

[txdutt]

double check your fluid level as well, can't hurt to verify

[allisontec]

Take it to your Allison Distributor to have your shifts reset to fast adapt.This is a common problem when changing to synthetic fluid.They may do it for free,it is a 5 minute process.

[smlranger]

Quote:

Originally Posted by allisontec Take it to your Allison Distributor to have your shifts reset to fast adapt.This is a common problem when changing to synthetic fluid.They may do it for free,it is a 5 minute process.

Thanks for the tip. In my area, I believe the only Allison shop is the Western Branch Diesel shop. Every motorhome I have ever seen there sits on their lot for days. I hope I could get in-out quickly if I make an appointment.

[allisontec]

WBD is a pretty good shop.I worked at the Charleston WV shop for 24yrs.They should be able to set up an appointment for you.Just tell them you would like to have your shifts reset to fast adapt mode.Like I said it will take longer to hook up the laptop than to actually set the shifts.

[DriVer]

Quote:

Originally Posted by allisontec WBD is a pretty good shop.I worked at the Charleston WV shop for 24yrs.They should be able to set up an appointment for you.Just tell them you would like to have your shifts reset to fast adapt mode.Like I said it will take longer to hook up the laptop than to actually set the shifts.

Could you please expand on your comments about why upgrading to Transynd would require the transmission to be re-programmed? Thank you.

When I upgraded to the Ultrapower Grade Brake, I was shipped a re-programmed TCM. On the initial test drive with a friend, I was startled by a sudden downshift which actually clunked into 1st gear coming to a stop. We both looked at one another and winced and just continued on. During the rest of the test drive the downshifts to 1st were clean with no further clunks. I believe at that point that the TCM adapted to its new environment and companion ECM. Today the tranny works fine and the after market grade brake works really well.

[allisontec]

This shift adapt is not required on every unit that is upgraded,it is my opinion that units with worn out fluid that are changed over to Transynd are the ones that may need to be reset.I would think the ECU would take longer to adapt to the new fluid.It would take a while to explain this process,the ECU will eventually smooth out the shifts,just saying it will happen much faster with fast adapt.The ECU on your tranny is constantly adapting as you drive it .It will actually change the way it shifts according to the way it is driven.Drive it hard and it will shift firmer,drive it easy and it will shift smoother.