The Stovebolt Site Forums The Shop Area Driveline Rearend ratio for T5 Tranny

Guys,
I could use a little help. Here's what I have.
'52 3100 with 235 (The 235 will stay in for a while but a 350 will eventually find its way in)
Fenton dual carb intake with Roch 1 bbls
Fenton headers with dual exhaust

I have a newly rebuilt T5 tranny to install and a rearend from a '71 Nova. The rearend has 273 gears which I suspect are too low for the T5 paired with the 235. I'm thinking something closer to 355's or 342's would be better. I live in NE Georgia with rolling hills. What do you guys think would be the right range for my setup? Any help is appreciated.

The 2.73 gear is too high, it'll make the overdrive gear in the transmission pretty much useless. You'll definitely want a lower gear, maybe something around the 3.73 range, or maybe a 4.10. Tire size will also dictate what ratio you'll need. Taller tire, lower gear ratio.

Also there is variation in the O-D ratio in the T-5 trans. Like Long Box says about 3:73 with the 235 engine. When you get the 350 in it you can use 3:43 or 3:05.

The OD in the T5 I have is .72. I plan to run tires that are around 28 inches. I don't plan on doing a lot of 80 mph running but would like to be able to do 70 mph without getting the RPM's too high. Does that narrow things down more?

3.73 would be fine for that.

Thx LB. I figured I needed something over 3.42. I know I can get ring and pinion sets from Summit for about $150. 3.73 sounds good to me.

I am also using a T5 in my '55 1st series. I have a built 261 with dual carbs and dual exhaust. The original open driveline rear end has 3:90 gearing. It seems to be a good combination. Able to have fun driving around and still keep up with the traffic on the freeway.

"As a side note, a forum friend has a 67-72 truck with a T5, 250ci and a 3.42 rear. His OD gear is 0.72 and he complained to me that he has to down shift on hills because the engine bogs."

That's exactly what I thought my problem would be around my area with a 3.42 or higher. Thx Lugnutz. Thx again also for the T5 help.

That is why it is not called an automatic transmission.

To further clarify my earlier comment, my friend was complaining that his truck couldn't seem to manage even SMALL HILLS and inclines. If the gearing is correct for the engine and driving conditions, then small hills shouldn't require downshifting at normal RPMs.
Even an AT such as a 700R4 will be down shifting on small inclines if the rear diff is not properly matched with the engine HP. That's why Chevy S10 4 cylinder trucks had 0.86 OD gears and 0.72 OD gears in the 6 bangers.

Even then, the S10s with the 4 cylinders and the small V6 have 4.10 rear end gears with the overdrive option.

I could be blind but i no not see anything posted on what wheel size your running. What is the actual tire overall dia size? Stock? Smaller?

I can chime in on this as i just went thru a t5 install. Im changing my rear end now due to my smaller non stock tire size.

What is your trans code number? You sure its a .72 and not a .76? 1352-xxx?

He's got the proper setup for a 3.73 rear. See above.

wow i'm blind.

My setup has a 3.73 rear with the #145 trans (.72 od) with my smaller 15" wheels and 235/60 rubber im doing 60mph at 2200 rpm. Off the line im shifting like crazy. I mostly use 2nd right now to start. Going to change over to a 308 shortly and that should put me in a good spot for cruising and off the line.

It's all about tire diameter. Your 235/60/15 tire diameter is 26.1". The online RPM calculators show 2074 RPMs at 60 mph with a 3.73 rear and 0.72 OD gear. If you swap to a 3.08 rear then you will loose some power off the line but get better RPMs at highway speeds. Your new RPMs with the 3.08 rear will be 1713 at 60 mph.

This thread has required a commanding use of decimal places.
Very educational, though- thx.

Brad

That's just how I roll (pun intended).

My 235/60r/15 inflated to the correct pressure at standing with the tire deflection turns out to be 24.75" When rolling it might grow a bit.

I can afford to lose a fair chunk off the line. The 3.73 now puts my first at a 14.02 ratio. Taking off is second right now is a 9.08 ratio and it handles it with ease.

The 3.08 will put my first at 11.58 I don't want to go any lower than the 3.08 as i don't want my highway rpm to drop too low

Currently in 5th what farting around i can bring the rpm down to 1100 in 5th and accelerate out of that quite nicely.

Your setup would be perfect with taller wheels/tires (28"). You will get more use out of 1st gear, and 5th gear will be closer to the optimal power range of your 235.
Carl

My head is spinning!

Maybe it would be a helpful exercise (for you and us) to restate what you have specifically, and what you want to accomplish.
I like specifics in list form so I can wrap my head around them.
Carl

Here's what I have:
'52 3100 with a 235, SM420, Fenton dual carb intake with Rochester 1 bbls and Fenton headers.

Here's were I'm going:
I have a newly rebuilt T5 ready to go in. I just picked up a rearend out of a 71 Nova (because it's the perfect width) that has 2.73 gears in it. Bought 3.73 ring and pinion gears to go in the RE but didn't consider that the carrier would need to be changed too since going from a 2.xx to a 3.xx. That's another $500+. I live in NE Georgia so I have a lot of hills and it would be nice not to have to downshifts all the time. That's the reason for the 3.73 choice. I plan on running tires/wheels that gif me about a 28" height.

Any other options on the carrier other than new?

Correct on the 0.72 OD gear. Forgot to add that detail

I can't help you with a source for an inexpensive carrier, but will say again, that if you go with what you have listed, you will be all smiles when you get there.
Carl

Thx Carl. Already ordered the carrier. Waiting for it to come in so I can get it all together.

I have a two part question. I have a 59 1/2 ton with a 235. I would like to put in a T5, but have been given conflicting info as to whether I can keep the original clutch or have to convert to a hydraulic clutch. Any experiences? The second question is what gear ratio works best for the stock rear end and where can I find the gears? My current rear end has a replacement 3rd member from a donor and is very low geared. 55 mph has it wound out. Also saw Tremec at a show and they suggested going with a T6. Anyone tried this?

There is a T6 in Fords and a GM/Volvo T6. Same or different I do not know.

Though Volvo class action lawsuit on the T6.

Stock clutch linkage will be fine, though you may need to change the disk to match the splines on the new transmission. IIRC, the Chevrolet Astro clutch works great with this conversion. For the rearend ratio in the stock housing, there's only 1 aftermarket choice, the 3.38, which is too high for use with the overdrive. The stock 3.90 or option 4.10 gear works great with overdrive.

You do NOT need to covert to a hydraulic clutch. I just got off the phone yesterday with a very good clutch man in Waco, TX. Here's the contact info.
Brake and Clutch Supply
407 So. 8th Street
Waco, Tx 76706
Talk to Richie
PH: 254-752-4307
FAX: 254-752-7533

That shop can custom build pretty much any clutch you might need. I mention this because the Astro van clutch discs are very hard to find. T5 transmissions come with either a 26 spline input shaft or a 14 spline input shaft. If you want to keep your factory 10 spline clutch and pressure plate, then you can swap the 14 spline shaft for a Jeep T5 input shaft. My website has all that info. I know nothing about the T6. Tremec makes nice transmissions but they are pricey and then you have to spend even more money for the mid-shift kit to get the shifter up in front of your bench seat.

Jay

Thanks for the replies. I guess this takes me to another question. I have a wide ratio Muncie 4 speed in the truck now. Would going to the 3.38 rear ended gear work ok with 1st gear on the Muncie? My debate is whether to rework the rear end or change transmissions. I want to keep the 235 either way.

Several factors will determine how the truck will drive. What is 1st gear on the Muncie? What tire diameter will you have? Since 4th gear on your Muncie is 1:1 I think the 3.38 rear might be ok, but not enough to be in a "happy place" when driving 70 MPH.

Use this RPM CALCULATOR to calculate the RPMs at any speed, but you need to know the different variables.

For an example, I'll assume you have a 28" tall tire and a 3.38 rear diff. Since the Muncie 4th gear is 1.0, your engine RPMs will be 2636 at 65 MPH with a 28" tall tire. Not ideal but you could live with that if you never plan to drive 70 MPH. At 70 MPH the RPMs would be 2839. If your Muncie has a 2.95 1st gear, I think your acceleration in 1st gear will be poor with a 3.38 rear diff. and 28" tires.

For better performance, I'd recommend getting an overdrive transmission with a 0.73 5th gear and leave the rear diff the same. If you currently have a 3.90 diff, 28" tall tires and install a 0.73 OD tranny, then RPMs would be 2221 at 65 MPH and 2391 at 70 MPH. You will have much better power in 1st gear too.

When considering a T5, you must decide what things are important. Do you absolutely need to keep your cable speedometer operational? Do you want the shifter to come up through the floor in front of the bench seat? Many options exist but not all are easy to solve (cheaply).