The Stovebolt Site Forums The Shop Area Driveline T5 Borg Warner Gear Swap

Hello All,

I have been following the threads on the T5 and was discussing a swap with a friend of mine and he gave me a 1352-033 T5 out of an S10. This has the 4.03 1st gear and the 0.86 OD. I was hoping on getting a little bit higher of a 1st and OD, namely the 3.761st and .73OD, but for free you can't really argue.

I was wondering if anybody knows if I can swap the 1st and overdrive and keep the rest of the gear set, or am I going to have to buy an entire gear set for a T5 if I really want to this?

The tranny is going behing a 235 in my 53 half-ton which has the open driveline pumpkin already installed and geared at 3.90. I actually am more concerned with 1st being too low and having to start in 2nd, which might be too high at 2.35. The OD isn't as much as I would want but with 30in tires and a 3.90 I think I could do 70 at about 2450 RPM, which I think is okay for a 235. What are your guys thoughts?

Thanks in advance,
54Monster

I understand you can change the o-drive gears in the rear of the trans real easily. I imagine to change the 1st gear you would probably have to change practically everything.
I think you could start in 2nd most of the time & have 1st for a granny if you need it. I would want more o-drive then that.

Changing 1st gear would require more than I think it would be worth. .86 in front of a 3.90 would allow you to go just about as fast as the 235 could break the wind. If the trans is good, I would put it in and run it. If you already have 3.90, you would already have the open drive shaft, so installing it wouldn't be that major of a deal. I would put it in and try it. If you think the engine has enough power to make you go faster, you can always put in a faster OD. I think a .70 OD is the ideal.

which rear end did you use and what was involved with the installation?

I have the original rear end with a third member out of a 60 chevy half ton. The swap is pretty easy actually, and is shown in good detail over on oldgmctrucks.com although they are showing a third member swap for an eaton ho72, but the process is the same. The hardest thing for me was finding a donor at a junk yard since most people around here don't junk those year trucks to often and aren;t ready to have you part them out if you do find one. Basically the entire ring and pinion set pops out as a unit and is replaced by the same thing only that your set up with an open driveshaft, thus allowing for "newer" transmissions to be installed

54Monster

From what I remember about your year truck, a T-5 swap would entail shortening the drive shaft and you would be ready to go. I think the T-5 bolts to your bellhousing (you might need an adapter) and your master cylinder and emergency brake is not attached to the transmission as it is in the older Chevs and GMC's, so you should be able to bolt it in and reattach a shortened drive shaft. In light of all of that, I would go for it and if it doesn't perform like you want it to, get a 3.76 1st gear / .72 OD and swap. It wouldn't take any time at all to swap the two and you would probably be able to sell the lower geared T-5 with no problems.

Hi Guys,

I think that you're right, I'm going to bolt her up the bell housing and shorten the driveshaft and give her a try. I ran some numbers and the 4.03 low first with a 3.90 gives a final drive ratio of 15.7 to 1 and a 3.58 to 1 (sm420 2nd) with a 4.56 as in my 3/4 ton final drive ratio is 16.33 to 1 (so even lower, but almost the same). So I think that starting in first should be just fine. I'm not so concerned with the overdrive, because I should still be able to do 70 at ~2450 rpm which should be an improvement over stock. I probably would be pushiong 70 as I tend to drive slow in my regular truck anyways, so the improvement in rpm at 55-60 should do me quite well, especially since the T5 was a gift. Heck I even got the slip yoke from my buddy so I'm ready to go.

Thanks a bunch,
54Monster

Hello Guys,

I was wondering does anybody have a p/n for the 14 spline vega disk required for use with the T5? I looked on Napa and AutoZone and both places carry a disk, but they both are 10 spline.

Thanks,
54Monster

O'Reilly, Part number RCF4201 it's like 9 7/8 or something very close. Also If you have a 9 Inch Clutch you can use an RCF4190 I believe, It's just under 9 and has the correct splines.

I use the clutch disc from an 83-84 2.8L v6 Firebird. Doesn't require any modification to the clutch disc. I've outlined the process in detail on page 5 of my Webshots "Shoebox" album. I've also used the RCF-4201. Both came from NAPA.

As for your gear ratios.....you're correct.....the 4.03 is going to have you short shifting but the .86/3.90 would have you turning about 2200 @60 mph with plenty of throttle/rpms left in reserve and the ability to drop down towards 45 mph without a downshift. The .72 T5 isn't that much of an improvement in regard to the short 1st gear.

As for the driveshaft.....I've found that the driveshaft from a S10 T5 shortbed pickup can be used without modification by moving the spring pad 5/8" to the rear...which centers the rear wheels in the bed wheel well. Hope this helps.

Dave

the Astro transmission had the better gearing.

On a side note, i just noticed there are 9 active threads on the same or similar T5 topic.

Re: Gearing......I've never been much of a fan of the .86 T5 because of the very short 1st gear. Having run the .72 T5 with the 3.76 low gear, 28" tall rear tire, I've found in over 13K miles that you are shifting out of low gear half-way through an intersection. However, crunching your numbers and looking at the upper gears I think your truck might be really happy with the 30", .86 OD, 3.90 combo if most of your driving is in 60 mph range.

FYI:

http://csgnetwork.com/multirpmcalc.html

In setting up my gearing I calculated that I would be doing most of my cruising at 70 mph and geared my 54 truck to run at 2000 rpms. Problem is that at 70 mph@2000 rpms I'm just getting into the sweet area of the torque curve. Increasing my ground speed to 75-80 mph ( 2216-2364 rpms) brings my vacuum up appreciably but puts me in danger of catching a fat speeding ticket.

My problem was over-estimating my "normal" cruising speed. In reality most of my cruising buddies like to putz along at 60 mph which has me even lower in the torque curve and not letting my engine breath efficiently. Crunching your numbers you'd be turning 1878@50 mph, 2254@60 and 2630@70 mph.....which would let you drop down to 40 mph in 5th gear without a downshift and would let you run at a legal 70 mph@2630 which wouldn't be excessive for a healthy 235. Granted the 4.03 would have you short shifting out of low very quickly but the 3.76 1st gear transmission wouldn't be that much of an improvement.

I think that Crenwelge's advice to go with the .86 box would work out for you in the long run. Hope this helps.

Dave

Astro trans gearsets 3.50, 2.14, 1.39, 1.00, 0.73
F-body gearsets 2.95, 1.94, 1.34, 1.00, .73

a few people have mixed / matched gear sets for cruising in town and highway.

Since 5th is the easiest gear set to change, you have the options between .72 and .86 for 5th.