The Stovebolt Site Forums The Parking Lot Big Bolts 2 speed rear diff. question. (video)

I just picked up a 2 speed rear differential as a replacement for my 1966 C60. It's operated by vacuum. I'm not sure how to hook that up, any advice. Or, could I replace that with an electronic version?

Please see the video below...



Thanks!

An electric actuator should bolt right in where the original vacuum actuator is now.
Are you changing over from a single speed rear to a 2 speed, Or are you changing to another 2 speed with higher gears?
The 2 speed wont allow you to go any faster unless its high gear is geared higher than your original.
Nice looking truck by the way!

Thanks for commenting Jeff! I'm switching from a single speed rear to a 2 speed.

You may have to add a speedometer adapter to the back of the speedo head, this will keep the speedo accurate while in 2 spd low.

Are the electronic actuators available at a parts store or is this something I'm hunting for?

Im not sure if the parts stores can get them, they are available. They may still be available from GM
A lot of the 2 spds use the same actuators.
If you wait for Spanky , or Crenwelge to chime in , I know they have that answer for you.

Thanks again Jeff, I really appreciate it! Oh, I'll keep that speedo adapter in mind as well......

If we dont hear anything, I do know a guy I can ask. he has my gear case out of my 2spd right now, installing all new bearings for me.
I should have that back this week.
I think where you didnt have a 2 spd, the electric is the simplest way to go.

That would be great! Any help would be appreciated. As you can probably tell, this is my first attempt at a truck this size, LOL...I've always had pick-ups......

Lookin'GOOD!! Sent you a P.M.

Thanks wetwilly5757. I have replied to your PM. I most definitely will be in future contact!

Nice truck. The vacuum hookup is pretty simple, look in the book or dealer for similar truck. The 2 speed you got looks good, however, the truck probably will not go any faster, ratios are slow and slower. Looks like not much room for a brownie, don't know what trans. you have now, however, NV-4500 would help top speed or an OD auto.

Thanks Ed for the advice. I was told that the '67 Chevy this came out of traveled 65 on the highway. I'm going to install it and see what happens. If it doesn't work, on to the next solution, LOL....

I think that you said that your single speed was a 7.20:1 or something? I think most 2 speeds were 6.40/8.72:1 from what I've read. Figuring that, at 65MPH the two speed truck with 9.00-20 @ 520RPM would be turning 3,600RPM. 7.20:1 gives 58MPH @ the same 3,600RPM. It's a 12.5% reduction. An option I'd look into for an additional overdrive would be an old auxiliary or "brownie" trans. With a .85 OD brownie and the 6.40 gears you'd only be turning 2,800RPM @ 60MPH and a little over 3,000RPM@65MPH, plus even more gears if you use the truck as a truck.

I hope I'm not out-of-line here,but on the "Parts for sale",(about a year ago??),Marvin Ribbich had several Clark 5-speed O.D.'s,and Brown-Lipe auxy. trannys for sale,since none would fit his '46 1-1/2-ton panel. Floor clearance issues. Maybe you could send him a P.M.,and see what happens. I bought some wheel cylinders from him,and he's very knowledegable,and nice to deal with. Hope this helps.

I'm not sure Chevrolet ever made "electric shift" for their rears. All of the 2-speed electric rears I've ever seen installed in Chevrolets were made by Eaton and they don't interchange with GM vacuum rears.

Wire brush the front of the center section of the rear to find the stamped numbers...the ratio should be there. It would be a shame to go to all of the trouble of replacing the rear only to find out you didn't gain anything. The guy you bought the rear from may have kept his foot on the floor or been going down hill to maintain 65 mph.

Mike B

Chevy used a 15,000 2 speed rear in their 60 series during 60's until the 70's which had vacuum shift. Their 70 and 80 series used an Eaton 18k 2 speed which could be either electric shift or air shift. The air and electric shift were interchangeable. And these shifters were interchangeable from the 40's until the 80's when they went to an electronic shifter. Dana made a kit to retrofit the earlier electric to the later electronic shift. This is a service manual for the Eaton shifters. http://www2.dana.com/pdf/AXSM-0029.pdf

I know the earlier corporate 2 speeds were vacuum and nothing would fit from an Eaton. I don't think the later corporate will accept an electric shifter either. The shifters for Eaton are all the same whether they came from a Ford, IH or Chev except that from the mid 50's back the motors were 6 volt and the later ones had 12 volt. All I would know to do is take a shift unit from any old electric shift axle and try it. But I really doubt if it will fit. If you take the 2 bolts holding the shifter on and photograph what kind of shift fork sticks out of the carrier housing, I can probably tell by looking at it if an Eaton shifter will work.

If it won't run over 45, you aren't stepping on the gas hard enough. A 292 6 is rated at 4000 RPM a 327 is rated at 4400 RPM.

WOW! Thanks much folks for all this information. I really do appreciate it. 66Sub, WetWilly, Mike B, and Crenwelge, this is all great info. You guys are steering me down the right path It doesn't bother me to stay with the vacuum shift unit as long as I can get it to work and find all of the components, LOL....I'm thinking of going down that path. Crenwelge, I'll try to get a picture of the shift forks as soon as I can. Also, I'm going to order the 1966 and 1967 Service manual supplement tonight! This rear diff. came off of a 1967 Chevy C60 that was part of my Wife's family fleet of water trucks back then. Apparently this truck would do 60 to 65 mph, although I don't know what tranny was in the truck. Thanks again, and anymore info. would be greatly appreciated...

Hello, I may be interested in your single speed rear end that you are removing. Please tell me more about what you have. Maybe you could send me a PM. Thanks.

My 1958 GMC LCF 370 Has factory electric 2 speed and the actuator connected to the speedometer. It's a corporation GM rear end. It also has the factory 2 speed switch in the gear shift knob. Someone had changed it to the red push-pull button. But I disassembled the gear shift knob and reworked the switch in it. Then removed the red button.