The T-5 Tranny - The easy way
Here's how I put together a T5 transmission for my '51 GMC with no machine work and no worries about clutch disc / spline matching. I started with a '84 F-body (Camaro / Firebird) 5-speed. Later versions had electronic speedometer drive, which can be used but require a $300 adapter to work with a mechanical speedometer. The tranny I used was probably for a car equipped with a V6. It has the following ratios:
|1st 2nd 3rd 4th 5th|
|2.95 1.94 1.34 1.00 .73|
These ratios are very nice for street use with a rear axle ratio of 3.90 or 4.11. They are an improvement on the S10 version of the T5, some of which had a 4.03 first gear and .85 overdrive in fifth gear. F-body cars with the above ratios came with a 3.45 rear axle. There is another version for 305 V8 engine cars which has the same ratios except for a .63 5th gear. The V8's used a 3.08 rear.
This T5 has an input shaft and bellhousing bolt pattern which are correct for any early truck (mine is a '51 GMC). The only difference is that the holes to mount the trans to the bellhousing need to be enlaged to 1/2" . The input shaft has 26 splines which is a common count for most any late GM clutch disc. So far so good. The major problem is location of the shifter. F-body cars all have bucket seats and the shifter is located at the rear of the tailshaft housing. If your old truck has bucket seats, it will probably work as is, but I like to use that space for miscellaneous junk in a little console with a cupholder. Sooo...
I was fortunate to find an S10 T5 that was sold as "parts only". On teardown, it had bad synchros and pieces of metal throughout, so it was truly good for parts only. The part I was after was the tailshaft housing. The S10 has a shifter location suited for a truck - about in the center of the floor. And T5's being designed for maximum parts interchange, the tailshaft housings are interchangeable. This can be done with NO disassembly other than removing the tailshafts and side cover/shift fork/rail assemblies - you don't have to get into the transmission itself. So - voila! Swap the tailshaft housings and other parts mentioned and we're good to go!
Pictured above are the side covers, shift forks, and shifter rail from the Camaro (L) and S10 transmissions. These have to be swapped along with the tailshaft housings. Use the shift forks that show the least wear.
Whoops....major problem here. The speedometer drive gear is in a different location. On the S10 trans, it's a bit forward of the shifter housing. On the Camaro trans it's well forward. I've heard that some mainshafts had both locations machined, but on mine, no such luck. So, it's gotta move if I want to use the speedometer. "Gee officer, I really don't know how fast I was going - you see, I just put two transmissions together and now my speedometer don't work"....Yeah, right!
So here's what I did. Notice the shiny spot in the picture above? that's where the speedo gear was in the Camaro tranny. There is a little hole drilled in that area, for the retaining clip that holds the gear in place. I carefully measured the S10 shaft for the location of that hole and drilled one the same size, in the Camaro shaft. What's not apparent in the picture is that the shiny area is actually a slightly larger diameter than the rest of the shaft. When you slide the gear over this area, its a fairly tight fit and the little retaining clip is held tightly in place. I my case the difference in diameter was .055". So I made a shim out of .026" stock (remember you have to split the difference) which wraps around the shaft to make it the proper diameter. It doesn't go all the way around, just enough to make the gear a tight fit. I epoxied this shim onto the shaft (using a couple of hose clamps to hold it in place overnight) and tapped the gear and clip into place.
Some background on the T5...originally produced by Borg Warner Gear Division, all T5's are now known as "Tremec" and are manufactured by Transmission Technologies Corp. An excellent repair / disassembly manual is available for the T5 at minimal cost by calling (800) 401-9866. Here is a page from that manual:
Not shown in the above diagram is the side cover and shift fork assembly (photo 1). You will have to use the entire thing from the S10 box, because the shifter shaft (23) must be the correct length for the S10 tailhousing.
Here's an "Aw, S**t !" to avoid. Removal of the tailshaft extension requires driving a roll pin out of the shifter shaft, into the offset lever (14 on diagram). There is a drilled passageway there to hold it. As soon as you get the tailshaft off, drive this pin all the way out and put it aside where it won't get lost. It's all to easy to re-install the offset lever with the pin still in there...and you won't realize it's there until you try to drive in a new one. Of course, this will be AFTER you have re-installed the tail housing with gasket cement, torqued the bolts, etc, at which point you must remove everything and do it all over again.
Jack Halton / Inliners International May 2001