The Stovebolt Site Forums The Shop Area Driveline Old Truck Guys - Gotta Love 'em

Met the nicest guy yesterday. I've been picking Fred Schlump's brain on the forum about an OD transmission for the Bubba Truck ('66 C10 LB 4.1L SM318) for about a year - he's in Seal Beach, I'm currently in NorCal. The truck started popping out of 3rd gear on the trip to San Diego this week, so I gave Fred a call on my way back up. At the drop of a hat he spent a couple of hours giving me a "hands on" lesson about gearbox innards, took me for a ride in his very clean 3100 to demonstrate how an OD functions and went over the Bubba Truck and gave me some pointers (I'm a recovering VW guy and still learning about American iron). Then he made some calls and hooked me up with Jim Hamlin, who had a solid trans for a reasonable price that I could take with me and drop into the truck until we find the time to do that overdrive. Old Truck Guys - gotta love 'em. Thanks Fred!

The overdrive is a wonderful way to get highway speeds without a lot of trouble. A dear friend of mine, the late John Erb told me all about it and once I tried it, I was sold too. Its a shame they are so rare and hard to find. It bolts right up and its especially nice if you have 3 on the tree already. There cant be enough praise for those that came before us. John forgot more than I will ever know about these trucks. I spent a lot of time working with him and learning from him but as with everything else, time is not on our side!

BTW - Fred is rfs56trk on the 'Bolt.

The overdrive section is almost bulletproof, but the front section has the same vulnerabilities as the SM318. I have a 67 or so Saginaw that I picked up at a swap meet and the guy didn't know what he had, but it requires tinkering with the linkage. I drove a Borg Warner OD in a 56 Blue Oval from the time I got out of high school. I Hurst Mystery shifter took its toll on input shafts and cluster gears. But it was a fun car to drive. It would paint the street black for half a block in direct with a 3.89 rear and I still have a ticket to prove it would go 120 in OD. My wife drove the car for 9 years getting groceries and hauling kids. She never did have. I have a T89 BW OD which was the toughest one they built. It is out of a Blue Oval, but it could be modified to fit a GM. I swear by overdrives ever since I bought my first one in 1962.

For the guys who have access to some machine tools, the Laycock overdrive that was used on Volvo, Jaguar, Austin-Healey, Triumph, and other European cars is exactly the same unit Gear Vendors is selling as an add-on overdrive. It's got a self-contained hydraulic pump driven from the output shaft of the transmission it bolts to, and it's possible to machine an input shaft that incorporates that cam, add an input flange, and make the Laycock unit a stand-alone, divorced overdrive similar to a transfer case. All it takes is an electric signal from a toggle switch to engage/disengage it. Those OD units are available on Ebay for pretty reasonable prices on a regular basis.
Jerry

My buddy picked up a Laycock/Gear Vendors OD unit from ebay a couple of years ago for about $700 with shipping. It came with an adaptor for a Ford gear box. However he wanted to use it with an SM420. We went to the Gear Vendors shop and got the necessary adaptor, a shaft, and I believe some electrical components. The additional parts came to almost $900 and they don't give any discounts. It worked fine in the truck but kind of pricy in my view. A driveshaft mod was also required which was about $150.
As Jerry states the key would be to have some machine tools to make some of this stuff it could be more reasonable.
Fred

I've got the remains of a trashed 67 Volvo transmission out in the barn, and I'm about to take a cutoff wheel to the shaft that plugs into the overdrive, then make the necessary parts to convert it to a stand-alone unit on a separate crossmember immediately behind a 3 or 4 speed GM transmission. It's "Machine shop 101" to make the stuff to convert it to a divorced OD unit!
Jerry