The Stovebolt Site Forums The Shop Area Engine Shop New project needs an overdrive tranny.........

Hi all, I picked up a '70 GMC swb 1/2 ton. Has a 250 L6. Was strongly considering a 700r4 swap, but would like to stay with a manual if it isnt to cost prohibitive. Was thinking a T5 would be nice, but cant seem to find any info. I DID try the search function here, but as usual I cant seem to get very far with that. Anybody got a link to some info, or some other suggestions, they would be appreciated. TIA

I just got a 55-58 overdrive 3 speed on Ebay. There were a few on there while I was bidding. From the other guys on here, it is a great way to go. Also I hear alot of good news about the T5 from the S10's.

This is just my biased opinion, but I think the GEAR VENDORS O.D. is the way to go. You get to keep your original tranny and low geared rear, and then you get the ability to overdrive each gear. It is the ultimate way to go for towing AND cruising, since you don't lose any low end grunt. I'm assuming you have an sm420 or sm465 tranny? Almost forgot, it's also expensive, but I'd do it again in a heartbeat.

Everything I have heard about Gearvendors has been nothing but good praise. I was considering it myself and ended up getting the tranny, I guess I wanted period correct. I hear they are also tough as nails and will last forever!

I struggled with it not being period correct but have justified it in my mind since it is mated with the original tranny. I also have radial tires, God forbid. Oh yeah, did I say I can cruise on the freeway at 75 mph at 2600 rpm and still have a granny gear w/3:90 posi?

I guess I'm looking for info on the T5 swap into a '67-'72 vintage truck. I cannot seem to find any here, or anywhere else for that matter. I seem to recall there was an issue with the shifter ending up in the middle of the bench seat. The BW R10 three speed overdrive I have in my '61 Apache is fine, and is period correct for the truck, but it just isnt my real cup of tea for a daily driver. If I were going to spend on a gear vendors unit, it would go behind one of my diesels. I wont be doing any towing or heavy hauling with this truck, I have other vehicles for that stuff. Just trying to make a reliable, good mpg daily grocery getter, without getting too far away from the original look and feel of the truck. It is the most unmolested example of a GMC I've ever found,(the "date of manufacture" tag is still on the drivers door edge) and got it for less than a replacement cab was gonna cost for my '68. This is a 1/2 ton short P/U. It has the standard issue light duty three speed Saginaw with column shifter.

My plans for it right now, in addition to an OD tranny are..
Flowtech headers, as the original exhaust mani is cracked, and costs almost the same to replace as the stock mani. Will add the intake mani heat from Langdon's.

An HEI ignition

Freshly remmaned 1bbl Rottenchester "M" carb

New Balancer, and seals, water pump, hoses, general cleanup of the motor, etc.

Ceramic brake setup on front end (keeping the drums)

Body and paint(original red/white scheme) in the spring.
Pics are at www.picturetrail.com/yachtcare

If anyone out there has done the T5 swap into one of these, I'm looking for pictures, and how you handled the hydraulic clutch setup. What had to happen to get the shifter to fit in the right place, and any other advice or problems that were encountered.
Thanks for the input.

Keeping my 3.90 is the big thing for me. If I need to tow or pull something a 3.00 whatever won't do it. Thats why I wanted an OD so I didn't have to swap my rearend. Cruising on the highways now, I pass people going up hills because I just got give it a little gas and it will climb without me needing to down shift.

I,ve done 2 t-5 swaps & they work great. I put one in a 55-2. Sold it & bought a 58 & put one in it. I have 350 v-8s in them & the trans have held up good. Behind a 6 it would be no problem. There should be plenty of info in the past posts. It has been discussed many times. There is also some info in the tech tips section. If you get one from a S-10 pickup the shifter will be in the middle of the floor. The ones that come out in the middle of the seat are from Camero,s. They are plentiful & cheap, especially if you get it from a pull it yourself lot.

I replaced the sm420 in my 63 C20 with a GM RPO MY6 GM equivalent of New Proecess A-833. Chrysler used it in everything up to the D200 truck and behind everything from the slant six to the Hemi. Forth gear is an overdrive (.76). I've got a rebuilt 292 still pretty much stock, 4.10 Detroit Locker, first gear is great, second gear is almost freeway speed. The drive shaft had to be shortened, but the shifter ended up right in front of the seat.

Larry

There's information I can use. Thanks!



I'm sure there is, and that it has. It is those posts that I cannot find. I did a search on how to correctly do a search, and, well, you know what I came up with

BTW, I'm assuming the truck has 3.73 rear gears, as that is what was standard fare on these. I'll know for sure in a couple weeks when I open it up to change the gear lube back there.

Right now I'm off to the tech tips section......

Why not look for a saginaw 3sp with o/d, factory made them I have one for my truck. would bolt right in no problems.

As stated in a post above, I have the three speed OD in my '61 Apache. It is a nice deal, but the lack of easy replacement parts, and typically when you buy the tranny you don't get all the factory parts. This means you have a setup that (I, at least) have to "fiddle" with from time to time to keep it operating correctly. I don't mind "fiddling" with the '61 as it isnt a daily driver for me. The GMC will be, and will be the only driver I have for a period of a year or so upcoming. Fuel economy, easy repair, reliability the key issues here. The more research I do, the more I'm being turned toward the dark side, and just slapping a 700r4 to it.