TH350 to 700r4 conversion - The 1947 - Present Chevrolet & GMC Truck Message Board Network

65chevysub · 01-03-2018, 07:41 PM

Can someone point me in the right direction of the post or thread that tells what is needed to change from a TH350 to a 700r4 with overdrive? I cant seem to find anything.
I have a 65 Suburban 1/2 ton 2wd that will be getting a 350 this year. Currently have 3:73 rear gears but need new of those as well
Thank You

sixty4bigwindow · 01-03-2018, 08:10 PM

Not sure of the entire "needs list" for doing a swap like that. But under the tranny FAQ section. There is a post by 1bad62 here that has a lot of good transmission info. Hope it helps

http://67-72chevytrucks.com/vboard/s...d.php?t=390542

65chevysub · 01-03-2018, 08:47 PM

Thank you

sixty4bigwindow · 01-03-2018, 09:25 PM

Quote:

Originally Posted by 65chevysub

Thank you

No prob man! Love your burb!

**Captainfab** · 01-04-2018, 12:33 AM

There are tons of posts in the Engine and Drivetrain section all about correctly setting up the TV cable and adjusting the line pressures. As for the actual install, it is basically just moving the trans crossmember back and having the driveshaft shortened. You can either use your existing shifter or change that to your liking.

65chevysub · 01-04-2018, 09:52 AM

Quote:

Originally Posted by sixty4bigwindow

No prob man! Love your burb!

Thanks. Lot of memories with the old girl from when my dad bought it in 1976 up until now.

65chevysub · 01-04-2018, 09:54 AM

Thanks Captain. Im going to start looking ibto this swap. What gesrs would you recommend for daily driving? And could I keep them after the swap?

**PGSigns** · 01-04-2018, 11:00 AM

I have a 350 and a 700R4 in my 66 with a 373 gear. Not a bad combo. I drive it every day. If I did more long interstate runs I would put a 342 in it and still might. Running 65 it turns right about 2000 rpm. I have a 342 to go in my burb and I think it will be a good combo. That one is getting a 5.3 4L60 combo.
Jimmy

chevy_mike · 01-04-2018, 12:26 PM

3:73 and a 28"-29" tall tire is perfect. You don't want to lug the engine and ideal RPM's are in the 2100-2300 range at whatever your normal max cruise speed is. If you have EFI, you can lower the RPM range a couple hundred but on a carb, you might find worse mileage.

My old '68 C10 had 4:10's, 28" tall tires and cruising at 70 MPH, I could get 21 MPG. Downside was due to the deep first gear and the 4:10's, I would smoke the tires if I got on it too hard.

sixty4bigwindow · 01-04-2018, 03:34 PM

Quote:

Originally Posted by chevy_mike

3:73 and a 28"-29" tall tire is perfect. You don't want to lug the engine and ideal RPM's are in the 2100-2300 range at whatever your normal max cruise speed is. If you have EFI, you can lower the RPM range a couple hundred but on a carb, you might find worse mileage.

My old '68 C10 had 4:10's, 28" tall tires and cruising at 70 MPH, I could get 21 MPG. Downside was due to the deep first gear and the 4:10's, I would smoke the tires if I got on it too hard.

Like smoking the tires when you dump the gas pedal is EVER a bad thing??

65chevysub · 01-04-2018, 04:19 PM

Quote:

Originally Posted by PGSigns

I have a 350 and a 700R4 in my 66 with a 373 gear. Not a bad combo. I drive it every day. If I did more long interstate runs I would put a 342 in it and still might. Running 65 it turns right about 2000 rpm. I have a 342 to go in my burb and I think it will be a good combo. That one is getting a 5.3 4L60 combo.
Jimmy

Thanks Jimmy. Right now with a TH350 and a 283 Im turning 4000-4500 rpm at 70-75mph. Waaay to high. I will see how the 3:73's do after I get everything in and set. Id like to take it on long runs but cant ubtil I get the rpm and mileage issues fixed

**PGSigns** · 01-04-2018, 07:50 PM

First thing you need is a good tach. You would have to have a 4.56 gear with a 28" to turn 4000 at 70 mph. With a 4.11 you would be at 3500 and about 3200 with a 3.73.
Jimmy

**Captainfab** · 01-05-2018, 12:31 AM

This \/ \/ \/

Quote:

Originally Posted by PGSigns

First thing you need is a good tach. You would have to have a 4.56 gear with a 28" to turn 4000 at 70 mph. With a 4.11 you would be at 3500 and about 3200 with a 3.73.
Jimmy

Since a 283 is low on torque, I would go with 3.73 gears and the 700R4. You could go right to 3.42's if you plan on a lot of highway driving and do not plan on towing anything.

rvrfoot · 01-05-2018, 01:12 AM

I have a 66 c10 with a 350 motor and a 350 trans. I think i have 373 gears. When i am going 60 my motor screaming. I was told i need 308 gears.

**The Rocknrod** · 01-05-2018, 06:06 AM

This calculator is great to figure what gearing you need with your tire size.
http://www.csgnetwork.com/multirpmcalc.html

65chevysub · 01-05-2018, 08:33 PM

When you say 28"-29" tall tires, are you measuring from the ground to the top of the tire? Currently Im running 235/75r15's but will be dropping to I think a 225/75r15 which is the equivelant of the original 7.15-15

rvrfoot · 01-05-2018, 09:55 PM

Quote:

Originally Posted by 65chevysub

when you say 28"-29" tall tires, are you measuring from the ground to the top of the tire? Currently im running 235/75r15's but will be dropping to i think a 225/75r15 which is the equivelant of the original 7.15-15

yes.

65chevysub · 01-05-2018, 10:41 PM

Quote:

Originally Posted by rvrfoot

yes.

Thanks

01-03-2018, 07:41 PM	#1
65chevysub Registered User Join Date: Feb 2013 Location: Cottonwood, Arizona Posts: 1,373	TH350 to 700r4 conversion Can someone point me in the right direction of the post or thread that tells what is needed to change from a TH350 to a 700r4 with overdrive? I cant seem to find anything. I have a 65 Suburban 1/2 ton 2wd that will be getting a 350 this year. Currently have 3:73 rear gears but need new of those as well Thank You

01-03-2018, 08:10 PM	#2
sixty4bigwindow Registered User Join Date: Feb 2016 Location: BACK in Southern Oregon... Don't ask Posts: 151	Re: TH350 to 700r4 conversion Not sure of the entire "needs list" for doing a swap like that. But under the tranny FAQ section. There is a post by 1bad62 here that has a lot of good transmission info. Hope it helps http://67-72chevytrucks.com/vboard/s...d.php?t=390542 __________________ Been a crazy 2018. Moved twice, back HOME in Oregon. Now to put everything back together, including the truck... My build thread for "Rocket" - http://67-72chevytrucks.com/vboard/s...d.php?t=753023

01-03-2018, 08:47 PM	#3
65chevysub Registered User Join Date: Feb 2013 Location: Cottonwood, Arizona Posts: 1,373	Re: TH350 to 700r4 conversion Thank you

01-04-2018, 12:33 AM	#5
Captainfab 60-66 Nut Join Date: Mar 2007 Location: Coeur d'Alene, Idaho Posts: 23,246	Re: TH350 to 700r4 conversion There are tons of posts in the Engine and Drivetrain section all about correctly setting up the TV cable and adjusting the line pressures. As for the actual install, it is basically just moving the trans crossmember back and having the driveshaft shortened. You can either use your existing shifter or change that to your liking. __________________ Power Steering Box Adapter Plates For Sale HERE Power Brake Booster Adapter Brackets For Sale '63-'66 HERE and '67-'72 HERE and '60-'62 HERE and "60-'62 with clutch HERE Rear Disc Brake Brackets For Sale. Impala SS calipers HERE Camaro Calipers HERE D52 Calipers HERE 6 Lug HERE Hydroboost Mounting Plates HERE

01-04-2018, 09:54 AM	#7
65chevysub Registered User Join Date: Feb 2013 Location: Cottonwood, Arizona Posts: 1,373	Re: TH350 to 700r4 conversion Thanks Captain. Im going to start looking ibto this swap. What gesrs would you recommend for daily driving? And could I keep them after the swap?

01-04-2018, 11:00 AM	#8
PGSigns Senior Member Join Date: Jan 2011 Location: Hayes Va Posts: 4,569	Re: TH350 to 700r4 conversion I have a 350 and a 700R4 in my 66 with a 373 gear. Not a bad combo. I drive it every day. If I did more long interstate runs I would put a 342 in it and still might. Running 65 it turns right about 2000 rpm. I have a 342 to go in my burb and I think it will be a good combo. That one is getting a 5.3 4L60 combo. Jimmy __________________ 60 to 66 Chevy and GMC window decals http://67-72chevytrucks.com/vboard/s...d.php?t=661131 Good friends, good food and a hotrod what else do you need? 1966 BBW long fleet Daily driver 1965 BBW short fleet Sold and going to a good home 1965 Suburban 2003 3500 Duramax 2005 Ultra Classic

01-04-2018, 12:26 PM	#9
chevy_mike Never Ending Projects Join Date: Jul 2006 Location: San Diego, CA Posts: 3,836	Re: TH350 to 700r4 conversion 3:73 and a 28"-29" tall tire is perfect. You don't want to lug the engine and ideal RPM's are in the 2100-2300 range at whatever your normal max cruise speed is. If you have EFI, you can lower the RPM range a couple hundred but on a carb, you might find worse mileage. My old '68 C10 had 4:10's, 28" tall tires and cruising at 70 MPH, I could get 21 MPG. Downside was due to the deep first gear and the 4:10's, I would smoke the tires if I got on it too hard. __________________ . 1965 C10 Panel, Tiki Express http://www.67-72chevytrucks.com/vboa...d.php?t=506580 SOLD 1968 Chevy C10, Long, Fleetside, Hot Rod Hauler http://67-72chevytrucks.com/vboard/s...d.php?t=313233 SOLD 1965 Chevy C10, Long, Fleetside, Hot Rod C10 http://67-72chevytrucks.com/vboard/s...d.php?t=415702 SOLD We were given two ears and one mouth for a reason... listen twice as much and speak half as often...

01-04-2018, 07:50 PM	#12
PGSigns Senior Member Join Date: Jan 2011 Location: Hayes Va Posts: 4,569	Re: TH350 to 700r4 conversion First thing you need is a good tach. You would have to have a 4.56 gear with a 28" to turn 4000 at 70 mph. With a 4.11 you would be at 3500 and about 3200 with a 3.73. Jimmy __________________ 60 to 66 Chevy and GMC window decals http://67-72chevytrucks.com/vboard/s...d.php?t=661131 Good friends, good food and a hotrod what else do you need? 1966 BBW long fleet Daily driver 1965 BBW short fleet Sold and going to a good home 1965 Suburban 2003 3500 Duramax 2005 Ultra Classic

01-05-2018, 01:12 AM	#14
rvrfoot Registered User Join Date: Oct 2016 Location: san bernardino ca Posts: 1,611	Re: TH350 to 700r4 conversion I have a 66 c10 with a 350 motor and a 350 trans. I think i have 373 gears. When i am going 60 my motor screaming. I was told i need 308 gears.

01-05-2018, 06:06 AM	#15
The Rocknrod Moderator Join Date: Aug 2011 Location: China Spring, TX Posts: 7,280	Re: TH350 to 700r4 conversion This calculator is great to figure what gearing you need with your tire size. http://www.csgnetwork.com/multirpmcalc.html __________________ Master Chief, US Navy, Retired 1964 C10 Step-side Short Bed - In Progress 2009 2500HD Duramax LTZ 1948 GMC Panel 1956 Big Window Stepside 1953 5 Window Chevy Stepside 1932 Coupe New Seat Foam for Bench Seats? Last edited by The Rocknrod; 01-05-2018 at 06:12 AM.

01-05-2018, 08:33 PM	#16
65chevysub Registered User Join Date: Feb 2013 Location: Cottonwood, Arizona Posts: 1,373	Re: TH350 to 700r4 conversion When you say 28"-29" tall tires, are you measuring from the ground to the top of the tire? Currently Im running 235/75r15's but will be dropping to I think a 225/75r15 which is the equivelant of the original 7.15-15

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