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1946 2 Ton 2 Speed Rear
#1171805 Thu Jun 30 2016 01:36 AM
Joined: Jan 2015
Posts: 1,038
32vld Offline OP
Shop Shark
If there is no vacuum sent to the read end does the truck stay in high speed gear of 6.03 or does it stay in the low speed gear of 7.98?

Last edited by 32vld; Thu Jun 30 2016 01:36 AM.
Re: 1946 2 Ton 2 Speed Rear
32vld #1171841 Thu Jun 30 2016 04:39 AM
Joined: Dec 2012
Posts: 208
Shop Shark
The 2-speed used in '46 was a mechanical shift unit with a short lever just about under the driver's right thigh. There is no vacuum involved. I have one here in a parts truck I bought with the idea of putting it in my farm truck, but haven't gotten to it yet. If you want, I could send you some pictures.

Re: 1946 2 Ton 2 Speed Rear
32vld #1171860 Thu Jun 30 2016 12:57 PM
Joined: Nov 2000
Posts: 1,296
Camp Commandant
The 2 spd in my '46 is vacuum operated. Jeffery, I would think that if the vacuum part of the system is not operating at this time that rear would be in what ever position it was last shifted into before it lost vacuum. But, if you wanted to get it in high and drive it as is, I suppose you could manually shift it. Here is a bit of info from the 2 spd tech tip ( )

"Obviously the biggest thing different about the Advance Design and other older 2-speed rear axles is the vacuum shift unit itself. The easiest way to check the operation of the two speed (especially if the driveshaft is disconnected or the axle is out of the truck)is to use a vacuum source to shift the axle from one range to another while turning the pinion yoke by hand. You can feel the unit shift. A small hand operated vacuum pump is useful. On some units, the vacuum diaphragm can be removed and the unit shifted mechanically."

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Re: 1946 2 Ton 2 Speed Rear
32vld #1171878 Thu Jun 30 2016 03:23 PM
Joined: Nov 2005
Posts: 5,738
3B Offline
Master Gabster
Hy 32vld and guys, on my 46 300 series GMC with Eaton two speed, when there is no vacuum the rear axle shifts to low speed range. There is a sign embossed into the shifting control in the cab which says "Park In Low",hope that helps.

Moderated by  69Cuda, Grigg 

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