I'm as happy as a clam, or a pig in poop, or whatever else is happy. With the help of member DougH6100 I transplanted a 2 speed differential from a doner truck he bought. My truck is a '57 5700 LCF, his doner is a '56 6100, mine originally was a single speed rear end, now with the 2 speed my truck can run at a more relaxed rpm at 60 mph/3700 rpm. Prior to the transplant I was topped out at 50 mph/4000 rpm. No welding/drilling/grinding or other major fabrication required, I used his original vacuum shift valve and cable/knob, I ran 3/8" copper tubing from the transmission mounted valve back to the rear axle, tee'd into my vacuum at a factory tee, added a vacuum reservoir. The system works very well, it gave me incentive to finish cleaning and painting the rear hubs, along with chrome lug nut covers from I-80 truck stop. I'll have to post some pics.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
Congratulations on a successful transplant. 3700 is still a high RPM for cruise. If you anticipate long cruise trips, an OD transmission such as NP-540 series, Clark with an O in the MN, Advance Adapters, I believe, makes an OD unit that bolts in front of main trans. These and most similar units bolt right in with shortening of the driveshaft required.
Ed
Last edited by EdPruss; 08/25/20239:34 PM.
'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires. '47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle. '54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed. '55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.
Did you get all the vacuum lines, fresh air lines and fittings off of the 6400 including the speedometer speed controller?
Here a few pages from the FAM showing how all the parts go together if you need them. Mike, I did not use the original steel lines from the '56, I ran new copper to the rear. I tee'd into the vacuum side on the right frame rail where the factory supplied a 1/2" inverted flair tee and a hole in the frame rail, I added a vacuum reservoir tank at that location and ran 1/2" and 3/8" over to the shift valve on the tranny, exhaust air is tee'd into the exhaust on the firewall. Surprisingly the speedo is only off by 3mph in high range according to GPS. It's close enough with the big 10R-22.5 rear tires. I might try to get the speedo adapter at some point. Ed, the 3700 rpm is of course a little higher than preferred but the 283 V8 is pretty short stroke so it'll survive. I don't plan on any long trips, maybe up to DougH6100's place to let him drive it, that's about 40 miles from me.
Mike B
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
Yes, the original check valve is still in place on the firewall, since I am using the original steel tubing and rebuilt Hydro-Vac I decided to add some reserve vacuum. On the right frame rail near the rear of the cab is a tee in the vacuum line, the leg of the tee lines up with a factory hole in the frame rail, I removed the inverted flare plug and extended that vacuum to a reservoir on the outside of the frame under the right step. A second tee that I added allowed me to run a vacuum line to the transmission mounted 2 speed shift valve. The complete vacuum side of the plumbing is downstream of the check valve.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
Congratulations on a successful transplant. 3700 is still a high RPM for cruise. If you anticipate long cruise trips, an OD transmission such as NP-540 series, Clark with an O in the MN, Advance Adapters, I believe, makes an OD unit that bolts in front of main trans. These and most similar units bolt right in with shortening of the driveshaft required.
Ed
The Advance Adapter Overdrive (Ranger Torque Splitter) is no longer available. They work great though! I had an older cast iron one, and ran it for a few years but, the countershaft and needle bearings are shot so, I pulled it out.(of course, it used non-std parts and they are no longer available!).. I sure miss it! One of these days, I will find another one, or maybe have mine fixed to bring it back to life!
Congrats on getting the rear end swapped out! I run mine at 3800-4K for 8-10 hour trips quite often. Yes, it is noisy, but doable... and yes, it will suck down the gas at that speed! (My 6400 has a 350 in it)
~ Victor 1941 3/4-Ton Pickup (in process). Read about it in the DITY Gallery 1955 Grumman Kurbside "Doughboy" 235/3 on tree w/ OD 1957 3100 - moved on 1959 C4500 Short Bus "Magic Bus" - moved on 1959 G3800 1 Ton Dually "Chief" - moved on 1958 C4400 Viking "Thor" ~ moved on to fellow Bolter
At least you have 22.5" wheels and taller tires, that should knock a few hundred RPMs down on the highway. Curious, are those original 22.5" wheels, or aftermarket?
When I bought the truck it came with 7 wheels and mounted tires, all 22.5" tubeless wheels, 3 different sizes of tires. I then kept an eye out for new rubber, found the Michelin on Craigslist near home, those are smaller in order to clear the front fenders. The rears are virgin Firestone steer tires from a school bus fleet,10R-22.5. I had some of the wheels sandblasted and then primed and painted them at home. When I found the bus tires at a truck tire shop they offered to blast and powder coat the other wheels. As far as I know, all the wheels are original, they are/were in the same condition.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
