The Stovebolt Site Forums The Shop Area Engine Shop Why not replace tranny with overdrive tranny for rpm

My son knows of a junkyard that has an overdrive tranny that he says would bolt right up to my 55.1. He says I could reduce my rpm to 2/3 of what it is right now. That would leave me with my current pulling power at the low end plus give me highway speed. I would have to shorten the drive shaft, but what do you all think? What is the down side if there is one? My current tranny needs work anyway, and this seems better than a 3.5 rear end. - Curious Scott

The old overdrives are great, and will do all that you say, but parts are getting scarce. It's kind of a gamble putting out $$ for something that can't really be checked out without at least pulling the tailhousing. The planetary gears and freewheeling clutch parts are the most likely to have problems - thus the most difficult to locate spares for. Be sure the solenoid and governor are there. Anything else, such as relay, kickdown switch or lockout cable will be a plus.

Depends on how close to original you wish to be. Have you considered installing a T5? All the details on on the Tech page by Grant Galbraith

The T5 is the better way to go in my opinion. Probably cheaper in the long run, I've turned up some s-10 T5's for $150 or less, working. It's a good tranny behind a 235 and it gives you 5 usable gears. You RPM's at 65 are very livable, 2260 with 29" tires . Look into it.

Or you can go with the 89MM. You lose a gear (4-speed) so the T5 might give you better acceleration. The 89MM was used in full-size GM pickups in the early-mid 80s.

It gives you a .73 overdrive and 3.09 first gear. There were 2 bellhousing configurations, one for Dodge and one standard Chevrolet. Finding a bellhousing for a Dodge box will likely be a hassle. But on the plus side you have the GM 10-spline input (same as Saginaws) and standard fine spline output (Saginaws, TH350 etc.). So fitting shouldn't be any more difficult that the T5. Durability should be as good, if not better.

I agree that the T5 is preferable, but a true overdrive has some nice features, like freewheeling (saves gas) and clutch-free shifting. Installation is a tradeoff. It's a bolt-in using stock clutch and throwout collar, and the standard 3-on-the tree will work. But with the T5 you don't have the issues of solenoid and governor wiring to contend with.

Just be sure you get the right T5. Some of the S10 versions have undesireable ratios - like a .86 overdrive 5th, hardly much help at all.

Thanks for all the replies. It is hard to decide, but given my mechanical abilities, and after reading the tech tips on the T-5, I think it sounds too complicated for me to use the T-5 or the 89MM. - Scott

Installing the 89mm is a snap. There was an article in Custom Classic Trucks- Feb 2001, I think, where the author showed the install. Ignore the fact the guy thought it was a Dodge trans and get Chevy 89mm and you could do it in a few hours. I put one into my 46 and I had to change to a later bellhousing to get right bolt pattern and it still was fairly easy. Just make certain no problems with the external linkages. Shifts like a dream and hugely better than orig trans.

sixpack: How can you tell which T-5 has the preferable gear ratio? Is there an external marking? How does one check out a used trans to make sure it is good? I want to make this swap in my 62, 3/4 ton 235.

Oh one more thing.... I have a bench seat and aftermarket AC in my 62 Chevy with a 3-on-the-tree. Can you anybody tell me exactly where the T-5 shifter comes out through the floor and how long the shift throw is on these transmissions? I don't want to replace my seat and AC unit.

To ID a 5 speed first go here for a visual ID then go check 5-speeds to narrow it down. You are looking for an early to mid-80s S10 trans from a V6 truck. Astro Vans are a possibilty too. Later V6 S10s will fit but have electronic spedometers.
Check out the trans by shifting through the gears to see if everything moves smoothly. Rotate the input shaft and check for any grinding or binding. You can SWAG the ratios by counting number of rotations of the output shaft vs turns of the input shaft in first thru 5th. Try to stay near your stock 1st gear ratio. Look for a .70 - .73 5th gear. There may well be a list of T5 internal ratios somewhere on the web, if you have time to wade through all the Mustang and Jeep stuff.

As far as placement of shifter...The base of the S10 shifter is 12" back from the bellhousing flange surface. Remove your floor pan cover and measure your stock tranny. The shift knob in 2nd & 4th gear is about 11" back from the shifter base with a Hurst S10 shifter - I don't know about the stock shifter.

Thanks sixpack:

Has anybody installed a T5 trans in a 62 cab style Chevy with a bench seat? Does the seat interfere?

Tab,

I have a '66 and had the same dilemma as you. I'd purchased a couple of saginaw 4-speed to replace the stock three-on-the-tree. 2 immedate issues were the location of the shifter and there was still a new ring and pinion set to be installed to make best use of the 4 speed on the interstate.

Well I found a tranny that took care of both problems. The GM 89MM. Being that it was factory equipment in full-sized bench seat GM trucks it came with the perfect shifter handle. Plus it has .73 overdrive. If you can find one it's money WELL spent. I have yet to install mine, as I'm waiting to finish my 292. chuckthetruck has some cool pics of one on his website.

-ftyler

I highly recommend the overdrive option if it is the original type Borg-Warner with freewheeling clutch. I replaced my 3 speed with this unit on my 57. It bolts right up. Furthermore the original set-up with the kickdown linkage can be greatly simplified by simply wiring the OD solenoid to a dash mounted switch. The OD can then be activated whenever needed. It's a simple and easy solution that reduces my 3.90 rear to effectively a 2.61. Compare that to the commonly available 3.36 ratio rear end set advertised for these trucks ($400, ouch!) If you have any questions, contact me and I'll be happy to help.

My wife is hopefully putting her 55 1st together this winter and is going to replace the stock three speed with a 55 three speed Borg-warner with OD that I picked up at a garage sale for $20. In front of it she will have a 55 Corvette engine with dual tattersfield and Fenton headers. I have the engine down pretty pat for her but she will need some real input when it comes to that tranny and overdrive, So Joe don't you plan on no extended vacations-LOL.
I found a site with a lot of infomation on that tranny and
O/D setup- Borg-Warner O/D
It has a lot of other great information also.

Oly,
I've seen that Borg-Warner OD page. It gives a lot of good info. I'd be happy to help you when you get ready to set it up. Good luck.