The Stovebolt Site Forums The Shop Area Engine Shop 3 speed transmission open drive

I’m going to change out my closed drive 3speed transmission to 3 speed open drive transmission out of a 55 Chevy bel air.
Look at the first picture of the the transmission on my 54 Chevy truck 235 engine straight six see the first linkage pointing up,
Second picture is the 3 speed transmission off the 55 bel air the first linkage is on pointing down what is the correct way it goes thanks

If I recall correctly you can rotate the lever with a little careful filing of the shaft. That way it may match up to your truck’s shifting mechanisms. If I’m wrong someone will be along shortly to correct me. 🛠

You can use your original side cover on the later transmission to match your existing linkage. However, you need to replace the 1-R shift fork with the one from the 55 trans as the gear is wider.
Fred

You can use the side cover as mentioned above. If you're going to the trouble and expense of changing the rear end and driveshaft, you also could look for a later model fully synchronized 3 speed which can be converted to work.

You mentioned I can use a later model 3 speed synchronized transmission what year should I be looking for ?

I used a '66 Saginaw 3 speed. It was a challenge to make the levers and shift rods to work. I drove that for a while and swapped it out for a T-5. The rest is history.
I would not bother with a non-stock 3 speed. The T-5 swap is everything that they say it is and then more. Awesome swap, no question.
Carl

If swapping out with a T5 transmission I will not be able stay with 3 on a tree right? I like the 3 on a tree shifter though but if your saying I will be happier in the long run I will need to start looking for a T5 transmission you guys are the experts I’m just starting my project and want to do the right upgrades for the 54 Chevy truck I have thanks Ernie

I second the T5 swap. It makes the truck so much more enjoyable to drive.

T 5 makes stovebolts come alive !

Maybe an overdrive 3 speed like a Muncie 319 would allow you to keep the column shift? I have one I'm not using so PM me if interested. I have a T5 and am like it a lot.

Dennis

If you go the T5 route, please be careful to get one (a T5, that is) with the right gear ratios for your rear end. If you're careful you can get a T5 with gear ratios which will make your AD drive almost exactly like stock in the first 3 gears. The beauty of this is your AD truck will feel just like it did with the 3 speed but all gears will be synchronized. Then 4th will be your first overdrive and 5th will be your second overdrive. It all has to do with your final gear ratio. I've posted this several times. Please let me know if you need more information.

Isn't 4th gear 1 to 1?

What year and model (vehicle) T5 are people referring to?

One of many of the charts that I found is attached.

Isn't 4th gear 1 to 1?

Yes, but unless you use a rear end that is 4.11, your 4th gear will be like an overdrive. For example if your rear is a 3.08, your 4th gear will represent a reduction in rpm of apx 25%. Then your 5th gear (if you have a T5 with a .86 fifth) will be 2.65.

Re-post of a prior post...

We don't know what ratio of rear end you have at this point, and we don't know what transmission gearing you have. So, let's look at one option. If you can find a 3.07 or 3.08 rear end and a T5 with these gear ratios:
1st gear---4.03
2nd gear---2.37
3rd gear---1.49
4th gear---1.00
5th gear---.86
(There were lots of these out there. Mostly they were used in S10 trucks or Isuzus with either 4 or 6 cylinder engines. 1982-1984 as I recall.)

The rear end with a 3.07 or 3.08 ratio.... common in 12 bolt rear ends and some used in late 60s or early 70s pickups were the right width. Your driveshaft may or may not work...you'll have to see about that. The T5 is roughly 25 inches long from where it bolts to the bell housing to the end of it.

Ok, if you find these two combinations, here's what you'll have as your final gear ratios:
1st gear---4.03 x 3.08 = 12.41
2nd gear---2.37 x 3.08 = 7.30
3rd gear---1.49 x 3.08 = 4.59
4th gear---1.00 x 3.08 = 3.08
5th gear---.86 x 3.08 = 2.65

And these final ratios will go up/down based on the diameter of your wheels and tires.

So if you still want to be able to put 1/2 ton of "stuff" in the bed and drive like a pickup should drive, the above combination will work great for you. It is very close to the ratios the original GM engineers wanted in there, so for the first 3 speeds, you'll feel like nothing has changed except your first gear will be synchronized. There are other ways to skin the cat and I'll mention one of those in a moment. Then in 4th gear, you get your first overdrive gear (in my case it was a 25% reduction from the stock 4.11 rear that was originally in the truck). Then on nice flat or slightly hilly roads, in 5th gear you get your second overdrive gear (a 14% drop) and you'll be cruising (60 or 65 mph) at 2000 to 2200 rpm depending on your tire size, etc. With a 235 I really don't believe you want to cruise at less rpm than that. Torque maxes out around 2000 and that's a good spot for you. You don't want the six to be lugging.

If you have a 3.55 rear end, you will do better with a T5 that has the following gear ratios:
1st gear---3.50 (x3.55 = 12.425)
2nd gear---2.14 (x3.55 = 7.597
3rd gear---1.39 (x3.55 = 4.93)
4th gear---1 (3.55)
5th gear---.73 (x3.55 = 2.59)

You can see the final gear ratios change a bit from the 3.08 scenario but stay in the same ballpark. The 5th gear ratio is a bit lower than I'd like, but a slightly smaller tire diameter would solve that if needed. The bad news is this transmission might be harder to find. As I recall this one was only used in 85 and 86 minivans with V6 engines. I think there may have been more T5s made with the 4.03 first gear scheme, but I could be wrong on that.

Or, you may be able to change your rear end gearing to 3.38 and go with one of the T5s with the 3.76 first gear...as I said different ways to get to the same spot. You just want to be very mindful of the first gear overall ratio...some would call this your SLR or Starting Line Ratio and other people might call it your takeoff ratio. With a pickup and an inline 6 I believe you need that to be at the minimum 11 or above. Otherwise when you start off there won't be anyone home under the hood and your clutch won't last long.

Important note: you may have to settle for a T5 with an electronic speedo output. Those with mechanical output are getting hard to find and costly. If you do, don't worry. There are ways to overcome this. If you look in the electrical bay section of this forum, you'll see where I (and a couple of other people) have been doing work and explaining how we're doing this. And it is possible to have the electronic speedo look pretty much like the original. So, you do have choices. Good luck no matter which direction you go.

Not a hard find.. I had to go mechanical because we could not get the electronic sender to work on my aftermarket speedo.

Ron, I hesitate to purchase nor even suggest one of those because I haven't heard a single person say the needle didn't bounce oddly at speeds below 25 mph. Plus those are expensive...especially if they don't work. A few years ago...maybe 4...I spoke to the person with Cable X or one of the makers everyone on this forum was talking about and was told "yes, that is a problem but we don't think there is a solution. Turning pulses into smooth motion at that speed is going to require more sophisticated technology than we have." That was all I needed to hear because the words "more sophisticated technology" meant to me "we paid some kid to come up with this design which didn't work well and now we need to sell it to get our money back." And this makes perfect sense to me. Mechanical to electronic? A clever high school student could figure out how to do that one. Electronic to mechanical? A complete different set of variables.

Jon,
The OP seems to be in the early stages of understanding everything involved in coming up with the best way to go for improvement of operation.
I understand the premise of what you are trying to say, but the way you presented "4th gear as your first overdrive" is technically misleading.
Yes, they are interrelated, but it might be better to discuss OD transmission function separately from rear end ratios for his benefit.
I am just envisioning the OP going somewhere and asking a guy for "one of those T-5s with 2 overdrive gears" and getting a strange look.
Carl

Ha, ha, Carl...yes, he'd get a strange look, wouldn't he? I use the term "first overdrive" because after driving the truck with a 4.11 and 3 speed for decades, going to a T5 makes 4th gear feel exactly like the old 3 speed overdrive. You recall the one that dropped your rpms by about 25~30%. Also...if you're in a hilly area and find yourself shifting from 5th to 4th a lot you can just leave it in 4th until the road flattens. A 3.08 (or in my case a 3.07) rear end is fine for the 235 with a 1 to 1 gear and 5th in this case only drops rpms by 14%. Didn't mean to add confusion. It also reminds me of a 10 speed bike I once owned. The final sprocket in the lineup didn't do as much as the other 4 did to change things.

I get you, Jon. The bottom line for me is, if one decides to go away from stock, it is a no brainer to go with a T-5. There will be no regrets. You bring up a good point about down shifting out of overdrive, especially with a 3.08 rear end, to keep the RPM in the optimal range for these virtually old tractor engines.

I resisted giving up my 3 speed on the column too. Go T5 it makes the truck so much more usable - I can't imagine going back. Jon G, 52Carl, and Lugnutz helped me so much. I have a 235, 3.27 rear, T5 with .72, with 27" tires - good combo since IA isn't real hilly.

If I were to go T5 transmission will that be a floor shifter ? What donor car or truck should I keep my eyes open for ? Now help me understand when your saying tire size 27” is that including rim and tire ?

Adapting a column shift to a 5 speed overdrive transmission would be an engineering nightmare! There's an RPM calculator formula somewhere in the tech tips section that allows you to plug in such variables as tire height (the 27" figure quoted), rear axle ratio, transmission overdrive ratio, etc. and figure out your engine RPM at a particular road speed. As a ballpark guesstimate, running a stovebolt engine much below 1800-2000 RPM in top gear on the highway will cause massive losses in fuel economy because the engine is lugged down below its comfortable torque range and the power valve in the carburetor will open up. Simply lowering the highway RPM doesn't always translate to a fuel economy or performance advantage. Make things work on paper before you start swapping parts!
Jerry

Jerry, I’m not trying to make the truck for racing mainly going on a cruise on the weekend.
Other option on transmission I have been looking at is a 3 speed manual transmission with over drive but looking at the cost of it all going open drive line swapping out rear for gear ratio to be 3.90 will it be better to just up grade gears in the rear end to 3.90 stock ?

The 3.90 gears don't fit the closed driveline rear end. The simplest conversion to get better highway speed with a minimum of modification would be to install the 3.55:1 rear end gears sold by Mother Trucker, who is a member on this site. A rear end bearing and shim kit will also be required, as well as the new ring & pinion gears. That keeps the closed driveline and your original transmission in place. The gear swap is not cheap, and will probably require the assistance of someone familiar with setting up rear end gears properly (few shops and even fewer hobbyists do) but the result is an original-appearing truck that's better able to keep up with traffic. Just be sure the brakes and steering are in good shape to be able to handle the increased top speed safely. The cost of the gear swap will probably be less than making the switch to an open driveline, different transmission, and rear axle change.
Jerry

This^^^^^ is the best advice possible for those of you wishing to go highway speeds.

I did the open drive conversion and have over 100,000 miles on my set up. My truck is a '49 with a '56 235, '69 3sp+od, 1949 rear axle housing, 1949 axles, '57 3.90 differential (plugs right in), and of course an open driveshaft made to fit. On a recent 1000 mile+ round trip I averaged 17.8 mpg.

The overdrive transmission has paid for itself by the increase in fuel mileage. About 5 years ago I installed a vacuum gauge and that has changed my shifting patterns dramatically. Formerly, I would put Overdrive to use whenever I had speed excessive of say, 60 mph. Since installation of the vacuum gauge I pay attention to optimum vacuum and NOT MY PERCEIVED SENSE OF ENGINE EFFICIENCY. I am now relying on real time data of optimal torque range as stated by HRL's post above.

Cosmo- - - -one question- - - -how did you deal with the pivoting rear spring mounts on the torque tube rear axle housing? Some people weld them, but with the rubber pivot bushings integral with those mounts, I've heard horror stories about broken welds, etc. I believe the best possible approach would be to eliminate the pivoting mounts and substitute rigid ones in their place.
Jerry

"...I believe the best possible approach would be to eliminate the pivoting mounts and substitute rigid ones in their place." HRL

Exactly what I did. The bonus with the rigid saddles is that you can now space the rear wheels in the exact center of the wheel wells. I have a 1955-1962 3.90 axle with Bendix brakes and natural saddles in the garage for future use. I wonder if I will have to shim them for proper Engine/Drive Shaft/Differential geometry.

For those of you that care for a great APP for your phones consider the TREMEC TOOL BOX. It is very user friendly and contains four very helpful 'drawers' that contain the following information:


Driveline Angle Finder

Vehicle Speed Calculator

RPM Calculator

Tire Size Calculator

Here's a little story about adjusting wheelbase- - - - - -when I ran the crew on a dirt track car in California, the minimum wheelbase for the class we ran (Northern California Sportsman) was 106". We ran a piece of channel iron as a spring mount with several holes in it, and partway through the season we would move the rear axle forward a bit. With open wheels and rub bars between the front and rear wheels there was no fender opening to be concerned with, and by the end of the season just about everybody at the track was running a wheelbase close to 102"! I had a couple of shorter driveshafts made up, as shortening the wheelbase for better cornering would make the slip yoke bottom out in the transmission. A shorter wheelbase made for much better handling in the turns.
Jerry

Maybe a bit late to the conversation but here's my two cents.
I had a 48 years ago with a 3 speed. It was worn out and would stick in second gear until you came to a complete stop. I was cutting and hauling firewood (3 trips per cord) so skipping second gear wasn't an option.
In those days (1970) there were dozens of those transmissions in the wrecking yards but they all had the same parts worn out. I don't remember if new parts were unavailable but they might as well have been because I had not money for that. So I patched together enough parts that weren't completely worn out to come up with a transmission that wouldn't stick in second gear. This was a trial and error deal and I got very good at R&R ing the transmission. Any how I have long believed that the 3-speed was the pickup's weak point. That and worn out vacuum wiper motors. A T5 seems like a dream come true.