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Old 06-20-2016, 06:57 PM   #1
angelobackwards
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Swap TH350--->700R4????

FIRST BUILD (attempt)

In the process of doing suspension work for a 58 Apache on a 77 C10 frame. Been thinking of swapping the TH350 for a 700R4. From what I've read and looked up I have a 3.73 gear ratio, (I found this by following info on a YouTube video, https://m.youtube.com/watch?v=fB0jrucjlxg I marked a line in the drive line and wheel to count revolutions. I spun the tire two complete rotations and the driveline rotated 3.73 times. Please me know if this sounds correct to you) Is this rear end good for either trans, or if I stick with the 350 should I get a different rear end. Tires won't be too big because of the wider track width of the frame. Thinking of running 225/50/16 Front and 235/50/16 rears. Any advice would be greatly appreciated.

Angelo S
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Old 06-20-2016, 11:22 PM   #2
Captainfab
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Re: Swap TH350--->700R4????

A 700R4 typically works well with the 3.73's. However with those short tires a 3.42 gear might be better. If you were to stay with a TH350, I would switch to a 3.07 rear gear. The 3.73's will also work with the Th350, but your highway rpms are going to be up there.
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Old 06-20-2016, 11:59 PM   #3
angelobackwards
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Re: Swap TH350--->700R4????

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Originally Posted by Captainfab View Post
A 700R4 typically works well with the 3.73's. However with those short tires a 3.42 gear might be better. If you were to stay with a TH350, I would switch to a 3.07 rear gear. The 3.73's will also work with the Th350, but your highway rpms are going to be up there.
Thanks for the advice. What size tires you think I wld work better if I were to stick with the 3.73? Thanks again
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Old 06-21-2016, 11:18 PM   #4
Captainfab
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Re: Swap TH350--->700R4????

With 3.73's and the TH350, I would run at least a 235/75R16. On my '68 C10 with a SM465 and 3.73's I was running a 235/85R16. I don't have a working speedo, but at aprox 55-60mph the engine is turning about 2250.

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Thanks for the advice. What size tires you think I wld work better if I were to stick with the 3.73? Thanks again
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Old 06-22-2016, 08:18 AM   #5
fleetsidelarry
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Re: Swap TH350--->700R4????

what the others said.

if you want, you can play around with some calculators to get ideas:

this one needs tire diameter and transmission gear ratio-- http://www.wallaceracing.com/calcmph.php

for the tire diameter (if you want to see what a different tire does)
http://www.wallaceracing.com/tire-aspect-calc.php

for the 350 TH the trans gear is 1.0, for the 700r4 it is .7 in OD

depends on what sort of driving you intend to do. the 3.73 gives the best acceleration but if you get out on the highway much you might not like it with the 350. I have a 700r with a 3.07. I leave it in D (3rd) around town (tires are 275/60r15)
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Last edited by fleetsidelarry; 06-22-2016 at 08:34 AM.
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Old 06-22-2016, 07:01 PM   #6
angelobackwards
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Thanks for all the info guys appreciate it. Will mostly be in town driving cruising in the weekend maybe the occasional day trip out of town. I'm hoping to get some sheet metal hung this wknd to see what will actually fit! Appreciate the tips and info guys.


Quote:
Originally Posted by fleetsidelarry View Post
what the others said.

if you want, you can play around with some calculators to get ideas:

this one needs tire diameter and transmission gear ratio-- http://www.wallaceracing.com/calcmph.php

for the tire diameter (if you want to see what a different tire does)
http://www.wallaceracing.com/tire-aspect-calc.php

for the 350 TH the trans gear is 1.0, for the 700r4 it is .7 in OD

depends on what sort of driving you intend to do. the 3.73 gives the best acceleration but if you get out on the highway much you might not like it with the 350. I have a 700r with a 3.07. I leave it in D (3rd) around town (tires are 275/60r15)
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Old 06-21-2016, 02:51 PM   #7
Clyde65
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Re: Swap TH350--->700R4????

I'm running a 4l60e which is the same as your 700 but electronic. I run 3.73's with 275/60/15 BFG tires. I am around 2000rpm at 75mph. I also have gotten 21MPG too!
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