Allison Transmission Flashing R Or D

[mav2300]

Have 2002 Duramax/Allison 324000 miles on the allison. At idle speed when backing up it will drop out of gear

and the prindl R will flash (blink). Sometimes when going forward at idle same thing but prndl D will flash.

 

1) changed the NSBU switch - no help

2) changed the internal and external transmission filters - no help

3) have codes po0746 and po0776

 

GM Dealer thinks it might be valve body

Allison dealer checked the clutchs by computer said they are not slipping but he hasn't seen the blinking R problem and thinks its electrical

 

I would be mighty grateful if someone could say they have seen this before or could tell me what the problem is.

[mav2300]

I just noticed tonight that if I torque the engine with the brake on just before backing up, the allision stays in gear and does its job perfectly.

 

If the solenoids/valves are dirty will they get better with the new oil and filters?

 

Just changed both the internal filter and the spin-on 3 days ago. I noticed that the magnet was missing from the spin-on so I went back to allison dealer and got one & put it in.

 

Changed to Dexron VI ATF. I resisted the suggestion to put Lucas Transmission Oil treatment in.

 

Old oil was somewhat discolored but not bad. The internal filter was

really clean. Bottom of pan had that dark film material coating but nothing else.

 

If I knew it was the valve body I'd change it out. Can you change out just the solenoids?