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!957 Corporate GMC 2 speed Parts #1308016 Sun Apr 21 2019 03:11 PM
Joined: Jan 2019
Posts: 13
D
Davie Boy Offline OP
New Guy
I need 2 speed parts for a ton and a half big bolt truck. Just the 2 speed box and wire harness and any internal parts for the 2 speed, not the entire rear end. This is a GM corporate, not an Eaton. Will buy all or any or parts. Or information were to get some would be great too. Thanks guys.

Re: !957 Corporate GMC 2 speed Parts [Re: Davie Boy] #1308224 Tue Apr 23 2019 04:43 AM
Joined: Mar 2004
Posts: 3,811
M
Mike B Online
Shop Shark
Davie,

The Corporate 2-speeds are Vacuum shifted, not electric.

Is your current rear a single or 2-speed? I don't believe you can swap carriers and make a single speed into a 2-speed, you need to swap the entire rear.

Since it's vacuum, I assume you need the vacuum lines with check valves that attach to the firewall and drop down to the cable activated vacuum switch that's mounted on the side of the transmission cover.

You'll also need the 2-speed speedometer adapter that mounts to the back of the speedometer housing...it keeps the speedometer in calibration when you change from Hi to Lo range.

Mike B smile

Re: !957 Corporate GMC 2 speed Parts [Re: Davie Boy] #1308408 Wed Apr 24 2019 05:19 PM
Joined: Sep 2018
Posts: 25
N
Noonan Offline
Wrench Fetcher
Just this past weekend I picked up a rear axle from a 1957 GMC 3 ton. It has the electrically activated 2 speed rear.

The reason I bought this was in hopes of swapping 2 speed actuator parts between the rear from the 57 3 ton and my 55 Chevrolet 2 ton.

Here is what I have found.

the 57 Gmc 3 ton uses the eaton 2 speed rear. 6 bolt pattern

the 55 Chev 2 ton uses the Corporate 2 speed. 10/5 bolt pattern.

The housings are different shapes where the u bolt saddles bolt down.

I haven`t pulled the drums yet to see if any of the brake components are similar.

Check out the pics

Attached Files
55 2 ton.2.jpg (640.47 KB, 84 downloads)
57 3ton.2.jpg (663.93 KB, 84 downloads)
55 2 ton.1.jpg (721.7 KB, 84 downloads)
57 3ton.jpg (627.93 KB, 84 downloads)
Re: !957 Corporate GMC 2 speed Parts [Re: Davie Boy] #1308479 Thu Apr 25 2019 02:32 AM
Joined: Mar 2004
Posts: 3,811
M
Mike B Online
Shop Shark
To the best of my knowledge none of the parts are interchangeable between GM and Eaton rears.

Also, if you see an electric actuator on a 2-speed rear axle it's a good bet it's NOT a GM Corporate rear.

Mike B smile

Re: !957 Corporate GMC 2 speed Parts [Re: Davie Boy] #1308731 Sat Apr 27 2019 03:16 PM
Joined: Jan 2019
Posts: 13
D
Davie Boy Offline OP
New Guy
Well thank all of you for your thoughts. But I have a 1957 -1959 GMC Manual and it is called a Corporate rear end and it is an electric 2 speed rear end. This truck was purchased brand new by my grand father and has not been modified at all. I have been able to purchase a NOS electric motor drive screw and block and the switch. If you have access to an older service or parts book it will show it. On page 88 section two there is an exploded pars view of the electric 2 speed parts. One of these days I will learn how to post a picture. Thank you all for your input. smile

Re: !957 Corporate GMC 2 speed Parts [Re: Davie Boy] #1311027 Fri May 17 2019 11:54 PM
Joined: Jan 2019
Posts: 13
D
Davie Boy Offline OP
New Guy
Here are the pictures.

Attached Files
thumbnail.jpg (64.76 KB, 38 downloads)
thumbnail2.jpg (55.49 KB, 38 downloads)
Re: !957 Corporate GMC 2 speed Parts [Re: Mike B] #1311028 Fri May 17 2019 11:55 PM
Joined: Jan 2019
Posts: 13
D
Davie Boy Offline OP
New Guy
Mike B, please see attached

Attached Files
thumbnail2.jpg (55.49 KB, 34 downloads)
thumbnail.jpg (64.76 KB, 34 downloads)
Re: !957 Corporate GMC 2 speed Parts [Re: Davie Boy] #1311123 Sun May 19 2019 03:05 AM
Joined: Mar 2004
Posts: 3,811
M
Mike B Online
Shop Shark
Davie Boy,

Based on your information it looks like I need to retract everything I told you! The Corporate Rear used by Chevrolet NEVER had an Electric Shift Motor, they were always Vacuum (at least up to 1967...that's the newest Chevrolet Parts Book I have). When Chevrolet used electric shift it was always pared with the Eaton Rear's.

So, now we know GMC did things different!

I will be of little help from here on out because I don't have any GMC parts book to reference. You'll need to find a late 50's or early 60's GMC Parts Book (which will cover your '57) so you can get the original parts numbers to start your search.

Sorry for confusing things, but it looks like we all just learned something new, which is a good thing!

Mike B smile

Re: !957 Corporate GMC 2 speed Parts [Re: Davie Boy] #1311795 Fri May 24 2019 02:50 PM
Joined: Jan 2019
Posts: 13
D
Davie Boy Offline OP
New Guy
Yes it is a good thing.. I really do appreciate your help and interest. And as a matter of fact I do have the reprint GMC parts book for that year of truck. I shall dig into the numbers at a later date. Got to go to work:)


Moderated by  John Milliman, Tiny 

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