The Stovebolt Site Forums The Shop Area Driveline Research Complete T5 Install

Lugnutz helped in building my T5 with the correct input shaft and Langdon's T5 guidelines for drivability. Also used are apps from Spicer and Tremec. My research consisted of 2 different 1985 T5 models, both from chevy S10'. Model numbers 1352-145 and 1352-146. The ring and pinion sets used in my research are as follows,
3.38, 3.55 and 3.90. My Engine a 235 and tranny have new mounts and sits at -3.5 degrees. The rear springs are new and so I will weld in the perch's at a +3.5. The result should be that the pinion and trans output shaft are now parallel. Adjustments for vibration and drivability will be made with different degree axel shims. I am not sure what degree the pinion will change under normal driving conditions. So calling all driveline aficionado's please take a look at this and let me know what you think. All opinions and corrections will be greatly appreciated. See attached.

Thank You
Red

You’re asking which rear end ratio to go with?

Only one page (the 145 tranny with the 3.38 gear) came through on your PDF. The -145 and -146 T5's have different first gear and OD ratios. So the choice in rear end is going to depend on which one you buy. You should be able to come up with a suitable combination either way.

Oh, I see your point. I will work on updating my post with all my research, I am glad you caught that.

Thanks Red

Please do let us see the other options. There's a lot involved with gear selection. It will also help to know if you plan to use your pickup as a truck or not.

Just to clarify᠁.you have not purchased a rear end, nor a transmission yet?

If so᠁.I think your best approach is to find your transmission first. Those early S10 T5s are scarce. Either one of them has ratios that can be matched with a rear end᠁to meet your needs for the truck.

There are a lot more options for suitable rear end swaps, and more availability of those options, than the T5.

Edit: Need to know the truck. I assume we’re talking about the 1950 1/2 ton in your signature?

I ask myself this question.
What speed DO I WANT TO DRIVE on the highway?
For me, I will gladly drive 65—70 mph. I’m not gonna go 75 mph and 60 mph on the highway will likely get me run over by other drivers.
Then I use an RPM calculator online to determine what my RPMs will be based on my tire diameter, speed, OD gear and rear axle gear.
An S10 T5 comes with only 2 options for OD (0.72 or 0.86). I do the RPM calculation for both OD gears to see which one puts my RPMs in a comfortable range for engine power.
IMO, a healthy inline 6 likes to run in the 2200-2600 RPM range but doesn’t lug the engine if RPMs drop to 2000 every now and then if traffic slows in front of me.
So my goal is to pick a combination of rear gear, OD gear and tire size so my RPMs are optimal at THE SPEED I WANT TO DRIVE.

If you already have a T5 and know the OD gear, then play with different tire sizes and rear axle gears until you find the right combo.

For most older Chevy trucks, the 0.72 gear will work well if the rear gear is 3.55 or numerically higher as long as highway driving doesn’t have a lot of hills.

I drive my stock 216, 3 spd, 4.11 all the time on the highway at 55-60. Did it today in the rain during rush hour. No hard decisions or mathematics required.

There is no way!! I am driving this old truck above 70 miles an hour and that's got be pretty scary. I agree with the 2200-2600 rpm range my friend Lugnutz referred too. My graph for a 1954, 235 from GM Heritage shows the cross for horsepower and torque dead in the middle of 2200-2600 rpm power range, that's why I used 2500 rpm for my research. My selection of tranny and gear is based on the information from Langdon's T-5 guidelines. He suggested a
1st gear overall driveline ratio of 12.1 for say a pleasant driving experience. This info is still available on line. I like the 1985 S10 1352-145 with a 3.38 gear. That still allows me to run 64 MPH at 2100 rpm with more room left. Hopefully there are no math errors as it's getting late. Please see attached. As always comments, and corrections are appreciated.

Thanks Red
81 MPH LOL

PS See if you can find the stump puller.

**EDIT**
Since posting my comments below, I realized I entered the wrong tire size for the RPM calculations. I have edited the photo to now show the correct tire diameter of 26.5 inches.

Red,
I’m gonna recommend 0.72 overdrive with a 3.55 or numerically higher rear axle. I’m thinking you are trying to optimize both 1st gear and 5th gear. That’s not bad thinking but the 3.55 with a 0.72 is just about perfect and first gear won’t be bad. I drive a 4.03 first gear with a 3.73 axle and it’s fine. A quick shift and it’s a thing of the past. Plus, I’m comparing that 4.03 first gear to my other T5 which has a 2.95 first gear matched with a 3.73 axle. The difference is minimal.
See photo.

I like your thinking, the 3.55 was my second choice with a .72 fifth gear. The good news is I have both gears, a 3.38, 3.55, I'm going to try both with a 26.5" tire. Test, Tinker, have a cold one while watching the game. Life is good. Maybe you know by what degree the rear axel moves under normal driving conditions. With everything neutral or parallel in the drive line. That would give me starting point with shimming the perches after I weld them in.

Thanks Red
1950 5 window.

Wait!
STOP! User error! My bad.
I used the wrong tire sorry when I entered information for the RPM calculator.
You will be using a 26.5” diameter tire and I had entered 24.5” diameter.
The RPMs drop a little bit. See photo.

Red,
As far as first gear goes, you have the choice of 4.03 or 3.75. If you do the math, you will see that there is an insignificant difference in how the vehicle will drive in first gear. To compare the gears, I pick a shift point that feels comfortable for normal driving. I usually shift to another gear anywhere from 2000 RPMs up to 3000 RPMs. So for this example I picked 2400 RPMs.

If you compare how fast your truck will be going if you shift at 2400 RPMs, you will see that 4.03 is only 1 mph difference than 3.76. This also holds true if you compare 3.38 and 3.55 rear axle gears.
Using the arbitrary number of 2400 RPMs as your shift point for comparison, you will shift into second gear anywhere from 13 mph up to 15 mph.

It is of course up to you, but I'd try to get my overall 1st gear ratio as close to 12 as possible. Please look at all the first gear ratios GM engineers used with the millions of straight six pickups they made...all were in the range of 12. Also...please keep in mind your fifth gear overall ratio ought to be as close to a minimum of 2.80 as possible for a 235. Mine with a 3.07, a .86 fifth gear and the tire diameter I have is 2.78 and there are times I need another .05 to .10. Even an additional number that small will make a difference to a stock 235.

When I say that please consider: if you had bought a Bel-Air in 1959 with a 3 speed with overdrive, you would have had 26 inch tires, a 3.70 rear end and in overdrive your overall ratio would have been 2.59. That's on the edge of workee/no-workee for a stock 235 and extra weight matters. A friend had a station wagon set up this way. With him and his wife, they could just barely use overdrive in third. With 4 or 5 people in the car, using o/d made it feel like they were driving up a very long steep hill. If you had bought a pickup in 1959 and had the dealership install a 3 speed with overdrive, you would have gotten a 4.11 rear end and your overall would have been .7 x 4.11 or 2.877. You can drive that all day long with stuff in the bed at 60 ~ 65 mph. I know the rpm calculators will tell you all sorts of neat things but if that ratio is too small when you shift into fifth gear it may feel like nobody is home under your hood.

You asked about pinion movement. I'd add 1 degree to the rear end measurement in order to get the most life out of your u-joints. Good luck!

Jon G is absolutely right.
I tell folks to multiply 1st gear X rear axle. Target number is 9 - 12 but 11 or 12 is best for a truck.
For 5th you want 2.8 - 3.
Folks with a 3.08 rear axle see no need for OD but they usually lack power in 1st gear.

Ok Think I am starting to see the light! I have been overly focused on 5th gear rather that the overall drivability. After review of the comments, the closest I can get to the above recommendations are using a 1352-145 T5 and 3.55 gear set. That gives me a drivability score of 13.3 and 2.6. 4th gear at 57 mph and 5th gear of 79 mph approximately. 1352-145, 1352-146 T5's. Gear sets 3.08,3.38,3.55,373 and 3.90. where used in deciding. Around town driving, so 4th gear is perfect and 5th as needed. comments and corrects are always appreciated. Please see attached, sorry for the chicken scratch.

Thanks Red

Perhaps we just use different terminology, but your reference to 5th gear at 79 MPH has me confused. Why are we discussing 79MPH?
You said you would never drive it that fast.
So answer this please.
What speed is comfortable for you on the highway?
If the answer is 65MPH, then the RPMs will be 2107 with a 0.72 OD gear. That’s barely acceptable for a 235. Then again, you live where roads are flat. The 0.86 OD gear would be a better choice with RPMs at 2516. That way you could use OD from 60MPH and up.

I've had my '51 Burb at 80+, for quite some time, without realizing it. I guess it just cruised that smoothly that I didn't notice until I read what the GPS was seeing. Stock height, radials, 5.7L with a 700R4, sloppy steering box. Since that event, I'll regularly cruise it at high speeds when I feel like. You don't know what these vehicles will do or what needs to be addressed on them, until you (smartly) take them up to their limits and maybe a little beyond.

I was using Tremec Speed calculator which required a particular RPM so I selected 2500 RPM across all calculations as a standard, and the variables are MPH. I changed to Tremec RPM calculator and the speed was a constant with RPM as the variable. (79 mph was just a result of a fixed 2500 RPM calculations used across all research, and a result for the 3.55 and .72 measurement.) I agree with your 3.55 and .72 gear at 65 MPH being 2107 RPM. Using the 3.55 gear with a .76 gear and fixed speed at 65 MPH the RPM is 2,224, perfect. Seems like we are headed the same place just took two different approaches. As always comments and corrections are appreciated. Including my grammar LOL. Oh and the good news is I have a 3.55 gear set.

Thanks Red

1985-145 S10, T5 with Axel Ratio of 3.55

Red,
There is no 0.76.gear. I didn’t go back in check your calculations, but the only two gears for overdrive are 0.72 and 0.86.

That's wild check out the info I used By Jack H. and John M. Inliners.org, at best this is frustrating. Unless they had a typo.

Thanks Red

Red for what is it worth, here is what I did:

It was important to me to preserve the first three gears as close as possible to what the GM engineers had decided. I had the 3.07 12 bolt rear end already. So, I went with the T5 with the 4.03 first gear chain. Second, Lugnutz had a .86 fifth gear he was willing to swap for the fifth gear in there. That was really helpful.

The tale of the tape is this:
AD truck (stock as it came from the factory)

1st gear was 2.94 x 4.11 = 12.08 final ratio
2nd gear was 1.68 x 4.11 = 6.90 final ratio
3rd gear was 1.00 x 4.11 = 4.11 final ratio

The T5 I used:
1st gear is 4.03 x 3.07 = 12.37 final ratio
2nd gear is 2.37 x 3.07 = 7.28 final ratio
3rd gear is 1.49 x 3.07 = 4.34 final ratio
4th gear is 1.00 x 3.07 = 3.07 final ratio
5th gear is .86 x 3.07 = 2.64 final ratio
(the diameter of my tires will alter these a bit. The final 5th gear ratio will actually be 2.78)

You can see the first three gears are very close to the OEM final ratios. So it feels just like the old AD truck always did. Then when I shift into 4th the rpms drop by 25% (from what they would have been with the 4.11 rear end) and then in fifth they drop another 14% from that point. Would it be better if I had a 3.38 rear end? It would make 5th gear a little more responsive, but it would make first gear less pleasant (almost 14, which is awfully strong in Dallas traffic). I'd be shifting out of first enough that I'd get really tired of it all. And starting in second gear would be...2.37 x 3.38 = 8.01 which really won't work with a 235. It is always a see-saw. Even with a 12 bolt rear end there are only so many gear ratio possibilities. You have to decide what is the best balancing point for you. Good luck!

I can get close to that with a 3.38 and a 1352-145 tranny, that is if my research data is correct from Inliners.org. The math is good (Hopefully) it's only the available published data that seems to be questionable. See the attached PDF in my previous post form Inliners.org I may just half to try some different gears.

1st 3.76 .x 3.38 = 12.708 final ratio
2nd 2.18 x 3.38 = 7.360 final ratio
3rd 1.42 x 3.38 = 4.799 final ratio
4th 1.00 x 3.38 = 3.380 final ratio
5th 0.72 x 3.38 = 2.433 final ratio

Thanks Red

Red,
Spending money is easy.
Making sure you don’t waste money is hard sometimes. It takes time and some research.
The charts are often WRONG. However, you can easily know 100% for sure what each gear is in just 5 minutes in any T5 WITHOUT SPENDING A DIME.
Do what I show in this video.
LINK TO VIDEO
You’d hate to get it wrong just because some chart has a typo.

Get er done Red!!!!

Thanks everyone, I will surely check out the YouTube video. I need to rebuild both T5’s anyway, the 145 and 146. While I’m at it I’ll just count teeth and apply some math for the drive and driven gear’s. Funny thing about Inliners chart. They mention the .76 three times for the S10, and .73 twice for the mini vans. They have an email address listed on their chart info page too please notify them of possible mistakes. So I did, ask some questions. And thanks for the tip on the axel by adding 1 degree. Time for some more research. Busy in retirement.


Red

You might see if you could swap the fifth gear for the .86 gear. Lugnutz will know, and I think the answer is yes...he did it in mine. A .86 fifth with the 3.38 rear end would be good. At 60 you'd probably be around 2200 rpm and that's where your torque line begins to slide downhill.

Good advice I will check with him. And thanks for all the help. Now on to locating a 1955 the 1962 rear end assembly.

Red