The Stovebolt Site Forums The Shop Area Driveline Which 4 speed do I need?

My 3100 with a 235 1958 vintage engine. It had a column mounted shift the po converted it to a floor shift. The stick shift is not where it should be and it's a three speed at 2500 rpm we are doing 50mph. I would like to purchase a four speed stick shift transmission which would bolt up to my engine without a lot of hassle. I guess a direct swap. Which transmission would we be looking for?We don't need a granny gear nor a 70mph road speed...55-60 would be nice. Maybe another three speed? Just don't have a clue never have done this type of swap. Thanks for your help!
Steve

Sounds like it might be better to adapt one of the newer 5 speed with overdrive transmissions to your engine. Most 4 speeds are only 1 to 1 in high gear, same as the 3 speed you have now. So you'd gain nothing in top end speed verses rpm.
I'm sure someone will be along with advice on doing the T-5 conversion.

John

Thanks....was hoping it was easier. We don't want an auto trans. A guy we met told us an SM 420 would do the trick give us a bit more speed and easy to install?
Any thoughts on this idea.......
Thanks, steve

While the SM420 is a direct swap, it will not give you what you want, other than being a floor shift transmission. 4th gear is still the same 1:1 ratio as the standard 3 speed, and 1rst gear is a very deep 7.05:1. The spacing of the rest of the gears isn't very good either. A better choice would be the T5 5 speed, which will have an overdrive gear, as would the MY6 4 speed found in early '80s GM trucks (Dodge also used this trans, but I don't know if the bolt pattern is the same).

I have this transmission in my 1953, it is still 1:1 in 4th and has a granny gear in 1st. Usually use 2nd for starting out in which is 3:58 to 1, a little lower than 1st in a 3 speed transmission.
You might up the differential ratio some instead, to a 3:55. you probably have a 3:90 there now.

John

I know you said your engine is a 1958 is that the same year as the driveline. What I am getting at if you have an open driveline what I would recommend is doing a T-5 conversion instead of the SM420 4spd. tranny. There is very little modification needed and if you get a T-5 from a early s-10 you still with have the mechanical gear for the speedometer and the shifter location will be close to the original location unlike if the T-5 is from a Camaro where the shifter on the tail housing is further back.

I purchased a T-5 and it bolts directly to my clutch housing and I just need to purchase a spacer because the input shaft is just a little long. Other than drilling out the 4 mounting bolts its a good fit on my 235 motor.

Here is the way it was explained to me about changing the rear gears vrs. tranny with overdrive. If you have the 3.90:1 gears there is only one gear set made for it. A 3.38:1. Plus you have pretty much put new seals in the rear end and while your in there just better replace the bearings etc. so now you have the expense of labor , gear set, and rear axle seals. Now if you just replace the tranny you can save some money by just replacing it.

Now I talked to the rear end shop in town and they suggested in replacing the whole rear end with a newer style so if I ever decided to swap out the internals it can be done easier than with the 3.90:1 Eaton HO33 style I have.

There is many threads here you can read about the t-5 swap. plus there is a guy here that has a lot of experience that might chime in named lugnutz. here is his page http://lugnutz65chevystepside.weebly.com/

Here is what I did on mine. I am running the 225/75R-15 tires which has an overall diameter of 28.29" and fits the original 5" rim. (Sidewall Height of 6.64, Section Width of 8.86, Tire Circumference of 88.87, and Revolutions per Mile of 735.24). I have the Eaton HO33 3.90:1 original rear end with an open drive line. Borg Warner T5 5 Speed O.D. Transmission Model #1352-145 from an 1985 or 1986 S10 Engine 2.5 L4 or 2.8 V6. (1st gear 3.76 2nd gear 2.18 3rd gear 1.42 4th gear 1.00 5th gear 0.72). Mated with my rebuilt 1956 235 engine.

When I run the RPM numbers here is what I get.
70 MPH = 2335 RPM
65 MPH = 2168 RPM
60 MPH = 2001 RPM
55 MPH = 1834 RPM

Engine RPM Caculator


If you are planning to go 70 MPH or greater you may want to consider in upgrading the suspension or braking. Just a thought.

You also need to think about how you are going to use it. Daily driver, towing, going fast from stop light to stop light etc. My set up is for driving around town hitting the freeway with lower RPM's now and then with out making people mad because I am going slow on the freeway.

Just my .02 cents good luck and keep us posted.

Hey thanks for the complete information on a tranny swap. We have the Borg Warner OD transmission with the cable and mechanical solenoid. I think it's an R-13. I have the lever on the side of the case wired back as to keep it from going into neutral by itself. Therefore I use it as a 3 speed with no OD. They seem complicated when being used. The stick as I mentioned is in the wrong place. Worst of all is NOBODY wants to work on it in my area. Nada from transmission shops. They won't touch it.

Which three speed stick transmission would bolt up directly to my 235? I would just need to change the location of the hole for the stick shift. I would have the clutch replaced and the tranny bought rebuilt. I'll just keep the speed to 45-50 and enjoy the ride..Agreed
Steve

The OD trans may also be the same as the later 60-66 era trucks and others. Is it the Muncie SM318? If it is you should be able to find out how to set it up yourself; quite a few guys on the interweb running them. Also the same unit as 50's car versions, IIRC. (Why I asked if it's the SM318; not sure if trucks used them in the same era or not.) It's a planetary gear type and isn't known for being problematic, IIRC.

I think it's also pretty well agreed that you can run a pressure-oiled 235 a lot harder than 2,500RPM with no ill effects. If 50 is 2,500, then 60 should be 3,000; That's not idling or anything, but I don't think it will hurt anything to run it like that if you need to.

(I don't have any 235's to say for sure, but I haven't seen anyone that thought that was harmful-besides; trucks ran wide-open like that, anyway. I personally wind my later-generation engines up without much worry. Lot's of guys on here with 235 experience if you wanted to ask.)