# 1991 Allison Trans. speed sensor



## jerryboo

Hello,
I have a 1991 Beaver on a Gillig Chassis. It has a 4 speed Allison Transmission.  The speedometer recently went dead and I looked at the manual and then looked at the output for the speedometer . There was a plastic / bakealite/ composet/ type of fitting that screwed into the transmission and then there is a "signal Generator screwed to that.  The plastic part has two small wires coming from it and the fitting that screwed into the transmission was broken, so needless to say-- it doesn't work any longer.  Needless to say-- the cruise control does not work now either.
would anyone know where I can get that part ??? Gillig does not have that part.
Thank you very much.
jerry


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## dbarton291

RE: 1991 Allison Trans. speed sensor



> jerryboo - 1/13/2009  4:53 PM
> 
> Hello,
> I have a 1991 Beaver on a Gillig Chassis. It has a 4 speed Allison Transmission.  The speedometer recently went dead and I looked at the manual and then looked at the output for the speedometer . There was a plastic / bakealite/ composet/ type of fitting that screwed into the transmission and then there is a "signal Generator screwed to that.  The plastic part has two small wires coming from it and the fitting that screwed into the transmission was broken, so needless to say-- it doesn't work any longer.  Needless to say-- the cruise control does not work now either.
> would anyone know where I can get that part ??? Gillig does not have that part.
> Thank you very much.
> jerry



It's not an Allison part, but I might be able to find some info on it.  To start, we need to know which Allison transmission it is.  Read the model number and assembly number off the tag on the right rear of the trans and post them, please.

I'll do some checking on known support equipment.


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## jerryboo

Re: 1991 Allison Trans. speed sensor

Thanks for any help you may have  My Trans is a  MT643  With a SN of 2410433181,,, My Cat engine is a 3116
I am going to try and take a photo of the sensor.
I talked with Gillig and they do not have the foggiest idea of what the part even looks like.-- go figure.

PLEASE HELP !!!! LOL !
jerry


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## dbarton291

Re: 1991 Allison Trans. speed sensor



> jerryboo - 1/14/2009  9:17 AM
> 
> Thanks for any help you may have  My Trans is a  MT643  With a SN of 2410433181,,, My Cat engine is a 3116
> I am going to try and take a photo of the sensor.
> I talked with Gillig and they do not have the foggiest idea of what the part even looks like.-- go figure.
> 
> PLEASE HELP !!!! LOL !
> jerry



What is the assembly number (A/N)?  That will tell me which speedo drive gear is in there.

If you don't see it, consider this:

The transmission is provided with a
spiral worm gear on the output shaft to drive a speedometer
gear. If the speedometer drive is not used, the
plastic shipping plug must be removed and replaced with
P/N 6839091 speedo plug available from Allison P.D.C

MT 600 speedometer drive provisions are:
(1) A 16 tooth tone wheel for use with a magnetic
pickup and electronic speedometers. A "side
looking" magnetic pickup which installs directly into
the speedometer boss is available from:
Airpax Instruments: P/N 70082-1000-021 (Single Coil)
P/N 70082-1000-022 (Dual Coil)

The above is what I think you have.  Without the A/N, I can't be 100% sure.

If not, you have:
(2) A helical worm gear ("drive gear") for a mechanical
speedometer drive. The customer-supplied mating
component is a helical "driven gear." To attain
proper speed input to the speedometer head, several
drive/driven gear combinations are available. 

The signal generator referenced, which is what you likely have, is available from:

Airpax Instruments Division
Philips Technologies
150 Knotter Drive
Cheshire, CT 06410
Phone: (800) 643-0643
Fax: (203) 271-6100
www.airpaxsensors.com

What's frustrating is, Gillig most likely installed the signal generator at their plant when the vehicle was built.  The transmissions came from Allison with a plug in that hole.


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