The Stovebolt Site Forums The Shop Area Engine Shop 308 rear with t5

Anyone tried using a 308 rear end with a t5 swap? I got the t5 with mechanical speedo. hooked up and everthing looks good. I have a 10 bolt 308 rear end out of a 4x4 (6 lug). I have a 235 six.
Thanks in advance

john46, that's what I have and it works quite well. There's plenty of 1st gear pull off the line (sounds like it's a drag racer - nope) and I shift into OD at around 45 mph the same speed a 4L60E locks up. Most here will say a 3:08 is too tall and a lot of that will depend on your tire size too but I can cruise on level ground and even slight hills at 55 or 60 without lugging the 235 at all, it's no big deal to drop it back into 4th if you need more grunt to pull a steep hill.

Great looking truck waldo53!
I have P215/75R16 tires. I believe they are 27" tall. what did you use for a shifter on your T5?

Don't really want to cause any major controversy but not ALL T5's will work with a 3.08. S10 T5's come in basically 2 configurations.....the .86 OD model with a 4.03 1st gear that will work with a 3.08. This transmission is normally found behind the 4 cylinder S10 engine. As Waldo pointed out...you shift out of 1st gear VERY quickly.

The second S10 T5 is the .72 OD from behind the 2.8/4.3L V6's with a 3.76 1st gear that WILL NOT work as a 5 speed with a 3.08 R&P. REPEAT...WILL NOT WORK AS A 5 SPEED WITH A 3.08 R&P with a 27-28" rear tire. As proof I have an 88 IROC-Z 3.08 posi/disc that I was told would work, collecting dust in my shop.

The 235 makes it's power between 1600 and 2400 RPM's. I've found over the past 8000 miles, that the engine is happiest in the 1800-2200 rpm range. After the pricey 3.08 debacle, I settled on a 3.42 89 Camaro diff which works great. Cruise at 70 mph is at 2000 rpms, there's plenty of throttle/mph left and you can drop down to 45 mph in traffic and accelerate without a downshift. First gear is short and you can cruise in town in 4th gear at 35 mph with no lugging. If you lived in an area with long hills you might even want to run the numbers on a 3.73. It would let you cruise at 55-65 mph at 1800-2000 rpms which might prove to be more comfortable in your truck. The 3.73 62" wide Camaro diffs aren't as common as the 3.08's and the 3.42's.

You didn't mention which T5 you have.....it'll make a BIG difference in whether your 3.08 diff will work as a 5 speed or limit you to the first 4 gears. To identify your specific mechanical speedo T5 you need to have a small tag with numbers that start 1352-xxx-xxx. The numbers cast into the case will not identify the ratio. If you're really lucky, you'll have a paper barcode label on the top cover that will let you ID your ratio. If you have neither.....send me a PM and I'll fill you in on how you can quickly/easily determine the ratio.

I hope this helps you sort out a few things with your T5 swap. Without a doubt it's the best upgrade you can make in a Bolt. Being able to cruise at highway speeds effortlessly, makes the modification worth the effort.

Dave

I have a 3.08 posi out of a 93 caprice under my 55 2nd.series truck. It has a 261 engine and a T-5. My T-5 has a 3.50 first gear and a .78 5th. I think it is just right.

Me too! Have a 3:08 rear and a T-5 with a pretty low 1st gear 4.something(sorry can't find my T-5 file just now) and od is around .76 or so. If I could do it all again would be better with a 3:50 rear but it's done now and on our long flat CA roads it's fine. With the '46 and older trucks and the pretty narrow cab the T-5 is the ticket, no shift linkage to make fit etc. I had a Saginaw 4 speed before and it was great but the T-5 is just so nice.

I too would be interested in what people are using for a shifter. I think that B&M used to make 2 part numbers for the S-10 but you have to find one in somebody's excess stock as they appear to have ceased production.

I found a guy on e-bay who sells a shifter for the S10 T5.
It is listed as an S10 base. Its $99.00+shipping. zrchris shifters & knobs