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HR1993 · 10-12-2022, 07:28 AM

I have a 36' - 1993 HR Imperial rig

It has a Cummins diesel engine with Allison MD3060 transmission.

First we lost the speedometer and now the odometer has failed.

I attached a schematic that shows the speedometer circuit and there are 2 components that may be the issue; 'Speed Generator' & 'Speed Control Amplifier'.

I have located the 'Speed Control Amplifier'. It has the Ford logo on it.

I cannot locate the 'Speed Generator'. I spoke with my local Allison distributor and they said it is not fed from the transmission.

Any help that can be offered in locating the 'Speed Generator' as well as troubleshooting assistance would be greatly appreciated. THANKS!

153stars · 10-12-2022, 08:22 AM

3060 and 4060 have output speed sensor at driveshaft side. If that's what feeds amplifier I'm not sure.

Skip426 · 10-12-2022, 08:39 AM

Welcome to iRV2 .

Sorry your first post is about problems .
I cannot help with diagnosing your system ; but ; I will comment .

The speedo quit first but the odometer still recorded miles driven ; then the system speed sensor was still operating .
Now the odometer has quit too .
I believe your issue is in the speedo head .

Did the Allison shop mention what transmission control system your coach has ?
WTEC II by any chance ?
My 99 Freightliner chassis ( Freightliner bought up Oshkosh) with a 3060 has WTEC III and shares output speed sensor info from the transmission to the dash and speedo . But my chassis was the first year of the dash gauge package so my diagnostic pdf would be of no use to you.
I'll look over the document you posted and see if I can be of any real help .

EDIT: The wiring page you've posted shows nothing about transmission controls ; do you have another page for the transmission ?

johnhicks · 10-12-2022, 09:46 AM

If you're not having transmission issues your output speed sensor is ok. Years ago I had to have the speedo head replaced, no reading.

HR1993 · 10-14-2022, 01:04 PM

First of all, thanks so much for the quick replies and input everyone!

Using those tips I did more diagnostic work and found the OSS (Output Speed Sensor on the back end of the tranny.

I temporarily removed it and got the as-expected result...transmission would go into drive and reverse, but would not shift out of 1st gear. This tells me the OSS is good.

So today I have removed the speedometer and sent the attached pics to R.T. Grimm Co. in Camp Hill, Pa. These folks were highly recommended by one of my local parts guys (and they returned my message in less than 5 minutes!) I just spoke with them and they said my unit is self-contained and not repairable. They indicated that when they fail they must be replaced but TR Grimm does not deal in replacement units.

Does anyone have any idea if there is any bench testing that can be done to determine if it is bad? If not, my only option would be to try and find a new one.

Again, thanks for the help folks

153stars · 10-15-2022, 10:52 AM

Oh crap looks a lot like mine that also went out. Maybe some inquiry to VDO.
Pretty sure seen used. Speedos on NRV supply.
https://www.nwrvsupply.com/search/Speedometer