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3600 T5 Differential Swap #1342993 Mon Jan 20 2020 07:41 PM
Joined: Feb 2017
Posts: 24
F
Fancyt Offline OP
New Guy
I have a 52 Chevy 3600 that I replaced the original 4 speed with the T5 per Lugnutz page. He has a lot of very good info and everything went fine from the input shaft swap to making a short throw shifter. The rear end on this truck is a 10 bolt GM at 4.57. It has the full float axles and 8 lug rim which I have 245-75-16 mounted. I really need to change this out. Research says I may be able to get down to 4.1 but a 3.73 seems to be the preferred rear end. I want to keep the 3600 look of the 8 lug. So has anyone with a 3600 ever changed out their rear end and what did you use.

Re: 3600 T5 Differential Swap [Re: Fancyt] #1342995 Mon Jan 20 2020 07:46 PM
Joined: May 2001
Posts: 1,347
W
Wally / Montana Offline
Shop Shark
I replaced my 4.57 with a 4.10. A real simple swap. I don't know about a 3.73 but the 4.10 gets me going fast enough (45-50 MPH for me) at a comfortable RPM.


1948 3/4-Ton 5-Window Flatbed Chevrolet

28 Years of Daily Driving. Now with a '61 261, 848 head, Rochester Monojet carb, 4.10 rear, dual reservoir MC, Bendix up front, 235/85R16 tires, 12-volt w/alternator, electric wipers and a modern radio in the glove box.
Re: 3600 T5 Differential Swap [Re: Fancyt] #1343051 Tue Jan 21 2020 01:40 AM
Joined: Mar 2010
Posts: 8,862
5
52Carl Offline
Master Gabster
What is the ratio of 5th gear?
How tall do those tires measure?
The reason that I ask is because I too, was bitten by the Lugnutz bug.
I have a '50 3100 with a T-5 with .73 overdrive, 4.64 to 1 rear end gears, and 30 1/2 inch tires.
I could not be happier with this setup from zero through 65 MPH through all 5 shifts. (I do not want to ever go faster than 65 MPH for safety reasons. These babies do not stop on a dime and you will never win a high speed slalom course.)
Carl

Re: 3600 T5 Differential Swap [Re: Fancyt] #1343059 Tue Jan 21 2020 02:20 AM
Joined: Sep 2013
Posts: 967
M
moparguy Offline
Shop Shark
Fancyt, Carl's questions are spot on. You can go too high when making rear gear ratio changes if you have a .72/73 5th gear.

I have a .72 OD T5 with 31" tires (235/85/16) with 4.10 gears from a 67 Chevrolet C20 in my'51, 3600 with 216. It works fine as long as I'm running in flat country which is usually the case unless traveling. Well, got to add head winds to the list of when 4.10's are a bit too high. Of course all you have to do is drop down to 4th and all's well. With current gearing my truck will now run comfortably at 60-65 with a 75 mph max. But any hill or headwind and it more like 50/55 mph.

Fact is the original 4.57's were good with the .72 OD. Now if/when I get around to swapping in the 261 that's holding the floor down in a corner of the shop I think the 4.10's will be just right. And if I find a set of the hen's teeth 3.73's that were installed in a select few Eatons I'd be up to trying those. But no way with a 216 would I go with anything higher that 4.10s.

Good Luck,

RonR


1951 3600 with Clark flatbed, T5, 4.10 rear
1970 340 Duster
1990 5.0 V8 Miata (1990 Mustang Gt Drivetrain)
1951 Farmall Super A



Re: 3600 T5 Differential Swap [Re: Fancyt] #1343066 Tue Jan 21 2020 02:33 AM
Joined: Apr 2016
Posts: 77
A
ASU Offline
Shop Shark
Fancyt,

I have a 48 3600, with a 292, and T5 with 0.86 OD. I have 4.11 gears (14 bolt out of an 04 2500) and 245/70/16 tires, which are 29.5" tall. I think I would like 3.73 gears or 0.72 OD better with this set up, seems a little slow for me. It does just fine in the hills of western PA, rarely do I have to shift out of OD.

Jon

Re: 3600 T5 Differential Swap [Re: Fancyt] #1343078 Tue Jan 21 2020 04:14 AM
Joined: Feb 2017
Posts: 24
F
Fancyt Offline OP
New Guy
My tires per a tire calculator are 30.5". On a T5, direct drive is 4th gear for a 1 to 1 ratio. Using a speed calculator, http://advanced-ev.com/Calculators/TireSize/ , I find that with a 30.5" tires, 4.57 differential, and 2500 RPM, the truck will do 50 mph. In OD, 0.72, the drive ratio would be 3.29, and using this number, in 5th gear at 2500 RPM, the speed would be 69 mph. As I don't have a true speedometer setup yet and no tach, I am going to use a GPS and portable tachometer to do some testing. I don't know if 2500 RPM is too high a revolution for the 235? Plus am I correct in using the 5th gear drive ratio as .72 x 4.57 = 3.29?

Re: 3600 T5 Differential Swap [Re: Fancyt] #1343095 Tue Jan 21 2020 12:11 PM
Joined: Sep 2013
Posts: 967
M
moparguy Offline
Shop Shark
Your calc's look spot on.


1951 3600 with Clark flatbed, T5, 4.10 rear
1970 340 Duster
1990 5.0 V8 Miata (1990 Mustang Gt Drivetrain)
1951 Farmall Super A



Re: 3600 T5 Differential Swap [Re: Fancyt] #1343114 Tue Jan 21 2020 03:05 PM
Joined: Mar 2004
Posts: 4,150
M
Mike B Offline
Shop Shark
The 235 used in big trucks had governors set at almost 4000 rpm, so you running it at 2500 is probably on the bottom end of the power curve.

Mike B smile

Re: 3600 T5 Differential Swap [Re: Fancyt] #1343229 Wed Jan 22 2020 03:54 PM
Joined: Oct 2015
Posts: 183
P
panel fan Offline
Shop Shark

I have a 62 one ton panel that weighs in at 5800 lbs before bondo , a warn out 235 with a t5 with .73 o/ d and a 4.57 rear end with 30 in tires. I run the truck between 2500 rpm and 3000 and seems to be the perfect set up for Me right now. I did have a 3.90 rear end in it which dropped the rpm to the point where it wouldn't climb even a gentle grade at high way speeds with out dropping a gear so I put back the 4.57. This not only improved drivability but improved my mpg as well.
At one point a few years back I lost over drive and drove home ,a 600 mile one day trip at 60 mph and 3000 rpm for about 12 hrs that was with the 3.90 rear end,.and the truck seemed to have been running at its best on that trip. I learned on that trip that rpms are your friend.
Once I repaired the o/d I went back to the 4.57 rear as I like to travel at the 70-75 mph on the longer trips of which I do many .
I don't think over gearing it is the answer.
I had 5 different ratios for the rear end here and the 4.57 is the one that worked best with an o/d trans. There is only a couple of mph difference in high way speed between a 4.10 and a 3.90.

John


good planning is no substitute for dumb luck
Re: 3600 T5 Differential Swap [Re: Fancyt] #1343409 Fri Jan 24 2020 03:27 AM
Joined: Mar 2010
Posts: 8,862
5
52Carl Offline
Master Gabster
Setting these drivetrains up correctly for optimal performance fro 0-70 MPH is dependent on the optimal powerband RPM of the engine being used.The 235 seems to just begin to power up at 2500 RPM and hits the sweet spot at between 2800-3000 RPM. At or below 2500 RPM and they lack what it takes to accelerate up even a slight hill.

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