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!957 Corporate GMC 2 speed Parts #1308016
Sun Apr 21 2019 03:11 PM
Sun Apr 21 2019 03:11 PM
D
Davie Boy  Offline OP
New Guy
Joined: Jan 2019
Posts: 13
Ione Oregon
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
Tue Apr 23 2019 04:43 AM
M
Mike B  Offline
Shop Shark
Joined: Mar 2004
Posts: 3,706
Hughesville, MD
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
Wed Apr 24 2019 05:19 PM
N
Noonan  Offline
New Guy
Joined: Sep 2018
Posts: 21
Northern Saskatchewan, Canada
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 (80 downloads)
57 3ton.2.jpg (80 downloads)
55 2 ton.1.jpg (80 downloads)
57 3ton.jpg (80 downloads)
Re: !957 Corporate GMC 2 speed Parts [Re: Davie Boy] #1308479
Thu Apr 25 2019 02:32 AM
Thu Apr 25 2019 02:32 AM
M
Mike B  Offline
Shop Shark
Joined: Mar 2004
Posts: 3,706
Hughesville, MD
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
Sat Apr 27 2019 03:16 PM
D
Davie Boy  Offline OP
New Guy
Joined: Jan 2019
Posts: 13
Ione Oregon
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
Fri May 17 2019 11:54 PM
D
Davie Boy  Offline OP
New Guy
Joined: Jan 2019
Posts: 13
Ione Oregon
Here are the pictures.

Attached Files
thumbnail.jpg (31 downloads)
thumbnail2.jpg (31 downloads)
Re: !957 Corporate GMC 2 speed Parts [Re: Mike B] #1311028
Fri May 17 2019 11:55 PM
Fri May 17 2019 11:55 PM
D
Davie Boy  Offline OP
New Guy
Joined: Jan 2019
Posts: 13
Ione Oregon
Mike B, please see attached

Attached Files
thumbnail2.jpg (30 downloads)
thumbnail.jpg (30 downloads)
Re: !957 Corporate GMC 2 speed Parts [Re: Davie Boy] #1311123
Sun May 19 2019 03:05 AM
Sun May 19 2019 03:05 AM
M
Mike B  Offline
Shop Shark
Joined: Mar 2004
Posts: 3,706
Hughesville, MD
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
Fri May 24 2019 02:50 PM
D
Davie Boy  Offline OP
New Guy
Joined: Jan 2019
Posts: 13
Ione Oregon
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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