Transmission / rear end set up
 

Hey guys - sorry for what is most likely a duplicate of a duplicate of a duplicate post. I've been searching around on here, but there are SO MANY posts!!! I love reading through the posts, but not when I'm on a mission for something specific.... LOL

'65 LWB
283 V8 :: PS / PB / elect ign
350 auto with towing shift kit :: I think it's a TH?
3:73 rear end :: guessing
Engine and trans rebuilt ~ 3 years / 3,000 miles ago

Last owner used it on the farm sparingly for his horses. I don't tow anything, but I bought the truck to USE it. I haul lumber and furniture and mulch and stuff with it. She ain't a show truck and I have no plans of hot-rodding it.

Problem is I can't drive it on the highway for long at all. It SCREAMS at 70 mph. This is what I need to remedy. (That and I get maybe 8-9 MPG.)

What's my best option?
- Change the rear end? (to what?)
- Go to a 700R4?
- Do both?

Thanks in advance for the input - you guys are the best!

Re: Transmission / rear end set up
 

Overdrive or slow down. 3:08 will still be 3000 at 70. How tall a tire because a simple tire change can help. A 28"+ tire works well with 3.73 gears

Re: Transmission / rear end set up
 

I am having the same problem.The rear end shop told me the 308 or 325 will be good.

Re: Transmission / rear end set up
 

It looks like the sweet spot is 26 to 30 inch tires with 373.The speed limit is 65.

Re: Transmission / rear end set up
 

I run a 295/45/18 (28.42") about stock height, and 3.73 gears but the od drops 800-900 rpms @75. So in 1:1 4th gear 2900 to 3000 rpm

Re: Transmission / rear end set up
 

So in a 350 we need overdrive Or a 308 rear end gear.

Re: Transmission / rear end set up
 

Or a taller tire

Re: Transmission / rear end set up
 

Hey guys - thanks for the comments.....

Average highway speed limit out here is 65. <-- That's my goal. My days of street racing are long behind me.

Taller tires are out. These are as big as I want to go. I'm running 235/75R15s with a total height of about 27.5-28".

If the truck *does* have the 3.73 rear end, I guess I really should be okay. If it has the optional 3.07 or 4.11, I'm borderline. Reckon I just need to pull the cover off and count teeth to be sure.

I've got a guy who can do a rebuilt 700R4 and gear swap (he recommended 3.08) for about $2500.

Thanks again!

Re: Transmission / rear end set up
 

I have a 700R4 with 3.08 rear in my truck running 275/60/15 tires which I believe is about 28" tall. It tach's about 2200 rpm at 75MPH. I do have a BB, I really have not done a MPG average but from what I did it was at low end 12 MPG. Running a Q-Jet carb.

Re: Transmission / rear end set up
 

I just fixed this exact issue. I have a stock rear end with 373 gears. The transmission was a T350, 27.5 inch tires and unknown cam. I could not go faster than 60-65 without my tachometer pinging out of the gauge. I ordered a 700r4, 2000 stall (daily driver) from Animal Performance in FL. I can now drive 80mph at a very low RPM and have a lot of power to play with. My truck is not a performer and somewhat slow off the line. If I ordered again my stall would have been 2200 to 2500 but I am very happy with it.

Re: Transmission / rear end set up
 

Stock 700r4 and 3:42 gears if that's an option for you, great all around set up. That is actually Chevy's Z71 set up and works great. I have this combo in three vehicles. My 56 Chevy gets 22mpg with a 305 and Edelbrock carb.

Re: Transmission / rear end set up
 

I've got a 4spd manual trans in mine, with 3.42 gears in the Dana 44; OD is .73:1, and the rest of the gears are the same as the TH350.

235/75/15 tires.

Honks down the highway perfectly at any speed you'd like, gets off the line at the stop light just fine.

VERY happy with that gear combo.
I'll be duplicating it in my '62 K10.

-Brad

Re: Transmission / rear end set up
 

Heres another calculator with od at .70,
3.73 with od should be 2200rpm right in sweet spot
https://www.ringpinion.com/calculators/Calc_RPM.aspx

Re: Transmission / rear end set up
 

If you do the 700r4 you can leave the 373 rear end. If you do the rear end 308 or 325 will be good.

Re: Transmission / rear end set up
 

Man, I thought I had added a post and forgot about it. This is the exact issue I'm having. Hopefully I will get better power and mileage next year when I put in a 350. Should I stay with my 3:73's with the 350, and TH350? I know my truck weighs a ton and I don't expect to take off like a rocket, just a little more power and better mileage.

Re: Transmission / rear end set up
 

I believe that for a straight forward, economical drivetrain it's hard to beat the reliability of a 350/TH350 combo mated to a 3.08. I know it's not glamorous but it's cost effective and it'll get you everywhere you ever want to go.

Re: Transmission / rear end set up
 

That is what i am shooting for.

Re: Transmission / rear end set up
 

Agreed.
-Brad

Re: Transmission / rear end set up
 

With an non-overdrive trans, a 3.07 gear is a good choice for highway driving. With an overdrive trans a 3.42 or 3.73 gear is best.

Re: Transmission / rear end set up
 

I went with a 3.42 rear gear while using a 200R4 trans so my tire size hopefully will about 27 inches and should keep her in the sweet spot at 70 MPH. Getting off the line should be awesome. :)
It could happen.

Re: Transmission / rear end set up
 

I will keep my 350 and just do my rear end gears.

Re: Transmission / rear end set up
 

Until you drive a 700r4 in an older vehicle you will never understand what it does for driveability.

Re: Transmission / rear end set up
 

You can still find five lug 3.08's on squarbodies in PickN'Pull. It's getting harder, but you still can. As for the 700r4, I have ridden in 2 differnt trucks which had them, but I guess they were poorly done because they just seemed to bumble around shifting oddly alternating from 3rd to 4th. Then 2 more guys I know fried theirs with the cable being botched up at the throttle. I'm sure they are fine when done properly but since I operate on the K.I.S.S principal, I pretty much wrote 'em off already.

Re: Transmission / rear end set up
 

I have 6 lug with nice rims. I heard if the 700r4 is not hooked right it will toast the trans.

Re: Transmission / rear end set up
 

https://www.google.com/amp/www.hotro...ion-build/amp/
The th 200 offers better gear ratios and .67 od vs .70 th700