Community Forums

mhughes · 09-30-2018, 10:05 AM

After driving through the mountains of Montana and Yellowstone last spring transmission shifting became very erratic. Extremely hard down shifts and flare between gears.

As I approached home, about 800 miles later, shifting got better but far from normal. Decided to change filters. The drained Transynd was far from clear having a slight muddy appearance and an efflorescent sheen. Mileage was 65k. Bought used so I don't know if any prior service had been done.

On the next trip shifting improved greatly after about 800 miles but still an occasional flare and hard shift. Noticed a "groan" or "grunt' between 2nd and 3rd. Fairly pronounced.

Took the coach to the Allison dealer in Coburg who connected a laptop and test drove for about 30 minutes. No codes. Fluid level OK. Did correlate the groan to the torque convert lock up event. Tech suggested a new TCU but had none in stock. Since heading to Salt Lake anyway and they have an Allison distributor there I decided to have another shop take a look.

Salt Lake replaced the TCU, verified fluid levels and test drove another 20 minutes. Tech reported that they didn't notice much change in behavior. Suggested that for another $2k they would pull the control valve assembly and inspect it. As for the groan they said they were not sure of the cause and that torque converter failures were uncommon unless it was a trash truck. Opted to let the issue get worse and headed off to South Dakota.

Groan hasn't changed but shifting gradually got back to normal with only one or two hard shifts and flares.

Any comments or suggestions would be greatly appreciated.

Trans model 3000MH
Mileage now at 67K

Skip426 · 09-30-2018, 11:33 AM

Any chance the noise could be external of the transmission ?

Lock up; particularly in the lower gears, where RPM and engine torque are at their highest ; puts added load on engine/trans mounts , and you could have the motor mount brackets contacting the frame ; bottoming out the mount ; transferring engine vibration to the whole coach.

If you've had harsh shifting issues for a while , the mounts may have sustained some damage.

mhughes · 09-30-2018, 11:49 AM

The noise occurs only during torque converter lockup event between 2nd and 3rd gears. Heavy or light throttle. Never occurs at any other time or gear.

In Coburg the Freightliner/Allison dealer spend more than an hour on the hoist examining the rear suspension and motor mounts. No issues found other than a slight adjustment of ride height.

mhughes · 10-01-2018, 09:51 AM

Another odd issue. May or may not be related to current problems. Starter has begun to grind gears. This happens about every 3rd or 4th time I start the engine. Engine usually starts on the second or third try.