Road test with the overdrive transmission

[Botietruck]

After weeks of testing and tweaking, I finally took the truck out today with the overdrive transmission installed. I ran it up to 55 mph at 4,000 rpm in 3rd gear, let off the accelerator and then pressed it back down. It smoothly shifted into overdrive and the rpm dropped to 2500. The engine was very smooth and quiet. I am very pleased with the results. I might take it on a 250 mile road trip next weekend. Can't wait to check the fuel mileage on the highway.

[Brad]

Sweeeeet! What a great feeling that must be.

[mikajo39]

Dang, that sounds nice, I still have my TH-400 with 4.11s in the rear who likes 60mph at 4200 rpm! I do! I am curious to what your fuel economy will be I would hope it'd pick up make it in to the mid-high teen area. I usually get like 14 mpg on the freeway when I drive conservatively

[Number98]

Originally Posted by mikajo39

when I drive conservatively

Good luck with that!

[faribran]

Bowtie... tell us a little about the tranny you mention.. plz

[Botietruck]

Originally Posted by faribran

Bowtie... tell us a little about the tranny you mention.. plz

It's the typical 3 speed Saginaw with a Borg Warner overdrive unit. The o/d bolts right up to the Saginaw. Now the Saginaw case with the o/d unit is drilled in two areas for the o/d application, so a standard Saginaw case will work, but it would require some mods. The unit I have came equipped with the o/d. I did not have to modify the driveshaft or the linkage.

It has an electric solenoid that engages the o/d, it has a governor that allows the unit to shift out of o/d when desired, and it has a control cable under the dash to lock it in/out of o/d. It also requires a kickdown switch mounted at the carb linkage, and it has a relay mounted on the firewall. Those are the basic components.

Once you get up to 28-30 mph, with the o/d cable pushed in (o/d engaged), you let off the gas pedal just a bit and the unit shifts into o/d by mechanical means inside the unit. It was pretty sophisticated for its day - they were used in the '40's & maybe earlier, up until 1969. That's when GM stopped putting them in trucks. There's alot of info out there on these units, but parts are somewhat hard to come by. I was very fortunate, I found mine on Ebay and it was complete. Mine is the 7-bolt side cover unit which has the synchronized 1st gear. The earlier units were not synchronized and they had the 4-bolt side cover. Here's a pic or two of mine. The first pic is the internals of the o/d unit-before I cleaned it up.

[Uwe Blab]

Thanks for the great info. I've done some research on this and didn't realize you could modify a standard Saginaw 3 speed and add the o/d solenoid. You said you found a complete setup, any idea how hard it is to find just the solenoid? I believe I have a standard 7-bolt cover Saginaw.

Also, does the overdrive only work for 3rd gear? I'd love to figure out a way to apply the same concept to 1st and 2nd and basically have a splitter transmission. I've looked at Gear Vendors but I can't find where they make one of their adaptors for a 3-speed column shift. Besides, a GV setup would cost more than what I paid for my entire truck.

By the way, terrific pictures and amazing work on that truck. It looks incredible!

[Brad]

I have one of those BW units in my garage and it's up on CL right now, but it's the earlier 4 bolt non-syncro trans. Somewhere I have files on how to adapt the OD unit to a later syncro 1st Saginaw.

[CG]

Hey congrats on the road test. You realize you have just made yourself the expert we are all gonna ask for help on these now =)

[WorkinLonghorn]

Wow,great job. Thanks for the info and the pics.
I looked up that trans in my '69 literature pack and it says OD works in all 3 gears. It's a .70 ratio.

[special-K]

Originally Posted by mikajo39

Dang, that sounds nice, I still have my TH-400 with 4.11s in the rear who likes 60mph at 4200 rpm! I do! I am curious to what your fuel economy will be I would hope it'd pick up make it in to the mid-high teen area. I usually get like 14 mpg on the freeway when I drive conservatively

His is a 6.I bet it`ll do better than that.

Botie,I have to say it again...yours is on my favorite truck list. You done good boy. You had a vision and you nailed it!

[WorkinLonghorn]

Wow,great job. Thanks for the info and the pics.
I looked up that trans in my '69 literature pack and it says OD works in all 3 gears. It's a .70 ratio.

Here's what GM said in it's Data Book given to dealers in 1969;

"Optional 3-Speed Overdrive Transmission
The 3-speed overdrive transmission provides better fuel economy,lower noise level and longer engine life by cutting down engine RPM.It is also fully synchronized in all 3 forward speeds for ease of operation.The overdrive may be manually locked out by a hand control or disengaged by depressing the accelerator pedal. This transmission is available only on C-10 models with the 4.11 rear axle ratio. The gear shift is located on the steering column."

[Uwe Blab]

WorkinLonghorn, thanks for the excerpt. Although if the unit does not engage until 28-30 mph, I'm not sure how it would work for 1st gear. Actually 28-30 is topping out 2nd gear for my transmission.

"...yours is on my favorite truck list..." x2

[Botietruck]

Thanks for the comments guys, but let me clarify a couple points here.

The front transmission case is the same on both the standard and the overdrive unit, with the exception of 2 holes drilled in the rear of the case. One hole is for the reverse lockout rod in the o/d unit, and the other is the oil drain hole in the bottom of the case. The complete rear extension housing is totally different than the standard Sag. extension housing and if you notice in the pic, the solenoid (the round canister on the side of the unit) is bolted to an adapter plate between the trans. case and the o/d housing, or rear extension housing.
So, When I mentioned that the trans. is the same, I was referring to the front case. The rear is a completely different set up. If you want to learn more about these beasts, Google "The Old Burb" website and they show a complete teardown of these units.

Also on the "Old Burb Site" there is an article that addresses split shifting these things, and it shows how to wire it up to make it work like a six speed. I was really not interested in doing that, I just wanted that 4th gear, but I wanted to keep the column shift. I guess it's kind of a nostalgic thing.

Just another short, well, not so short story.
When I was looking for the kickdown switch, I discovered that Cole-Hersee in Boston MA manufactured it. I had my local supplier call them and try to order one. Well, they were completely out of stock and would only accept a minimum order of 850 switches.
My friend asked them for the names of the last 2 buyers of these switches. He got the names & phone numbers and I started calling. I ended up making about 12 phone calls and the end buyers of those switches were in Portland OR & Seattle WA. One was a I/H Scout restoration shop and the other was a Packard Club. Both places sold me the switches and that is how I ended up with 2 of them. It literally took all day to track these guys down by phone, but it was rewarding to finally find them.

[Uwe Blab]

"Google "The Old Burb" website and they show a complete teardown of these units." I think this may be the article you're referring to?...

http://www.classictruckshop.com/club...5n/rebuild.htm

"Also on the "Old Burb Site" there is an article that addresses split shifting these things..." And this is the other article?...

http://www.classictruckshop.com/club...over/drive.htm

I'm like you though, I'd rather not have the extra lever modifications...
http://www.classictruckshop.com/club...rdrive_box.jpg

But rather have a column shift and a stock o/d lever and still get the splitter flexibility. Probably what I'm after isn't possible (i.e. if I want a splitter I have to go with a floor shifter or an automatic).

Thanks again Botie for the info, and for all the great pics of your truck.

[special-K]

When old & obsolete becomes a great new idea...
...You folks with all the old stuff still laying in junkyards better keep a watch out for these units and get it all.

[BluTrukker]

So do you have a phone number for the switches? How about a source for the governer and soleniod. I haven't been able to come up with anything on these. Also is there a spec for adjusting the switches so the linkage will contact them properly? Mine don't work, yours does, I want to be like you.

[WorkinLonghorn]

Uwe Blab wrote;

WorkinLonghorn, thanks for the excerpt. Although if the unit does not engage until 28-30 mph, I'm not sure how it would work for 1st gear. Actually 28-30 is topping out 2nd gear for my transmission.

Good point,but I'm not sure when/if the O/D disengages once the speed decreases below those figures.
If it's anything like the O/D in the '41 Packard I was driving last week,it stays in play even in 1st and second unless disengaged by the driver.