60-66's with 3.42 ratio's and 700R4's please chime in

[Budget63]

Hi All,

I searched, but didn't see any threads listed specifically for what I'm hoping to learn. I'm hoping to get input from people with SBC's and 700R4's in their 60-66's, that have changed their rear end ratio's over to 3.42. Preferably if they previously had 3.73 ratio's. I'm looking to do this and wanted to know if the acceleration difference between the two is that different. How about 4th gear acceleration on the freeway? MPG difference's? My motor is a stock 350 with 2.5" ram horns, and 2.25" dual exhaust with an x-pipe. Hopefully someone with a similar setup will see this and chime in. My truck doesn't have a whole lot of power obviously (being a stock 350), and I'm worried I won't like the acceleration of the higher ratio once it's all installed. Maybe it won't be noticeable? Hopefully I'm just worrying too much..

[YOLO]

That is not a huge difference in gears. I would concentrate more on your stall converter for your transmission. Maybe 2200 to 2500 if you want decent MPG and keep some power. I have a sbc 350, 700r4, and 373 with 2000 stall. I built mine for daily driving and mine is a dog off the line but has tons of power left at 80mph with very low RPM.

[Budget63]

Originally Posted by YOLO

That is not a huge difference in gears. I would concentrate more on your stall converter for your transmission. Maybe 2200 to 2500 if you want decent MPG and keep some power. I have a sbc 350, 700r4, and 373 with 2000 stall. I built mine for daily driving and mine is a dog off the line but has tons of power left at 80mph with very low RPM.

Thanks for the response. Since the transmission is currently without any issues, and I'm looking to get my truck back from the shop while spending the least amount of money possible, I just want to fix what needs to be fixed for the time being.

[YOLO]

Originally Posted by Budget63

Thanks for the response. Since the transmission is currently without any issues, and I'm looking to get my truck back from the shop while spending the least amount of money possible, I just want to fix what needs to be fixed for the time being.

New gears are more expensive that a new stall.

[Budget63]

I'm told that the rear-end is howling and that's why I'm looking at possibly changing the ratio, since the ring and pinion have to be replaced.

[YOLO]

http://67-72chevytrucks.com/vboard/s...d.php?t=743494

[Budget63]

Originally Posted by YOLO

http://67-72chevytrucks.com/vboard/s...d.php?t=743494

I came across that thread and saw the post from 63burban, and was hoping to hear more from people with that same setup.

[LostMy65]

Sorry, I have 3.73
But my truck is really wound up rather quickly with my 26" tall tires.
I swap to my winter tires that are 31" tall, and it's such a nicer drive.
My point in posting is the chart below helps me appreciate that 3.08 would be better for my low profile tires.

[Clyde65]

My set up, although different essentially is close to yours, I have a 4.8/4l60e/3.73. I went from 3.08 rears because of the beating and because the 3.73's gave me a little
Low end to tow my vintage travel trailer. I thought about getting the 3.42's but felt it was such a subtle difference, I went with the 3.73's. I can and have run at 80 and the truck ran well...as well as pushing a brick could.

Your 350 isn't gonna be a fast motor, like my lil v8 too, give it some gears to get moving and put it in its sweet range so you can enjoy it!

Good luck!

[TopFuel1966]

My combo is similar to Clyde's. I changed from a 3:70 to a 3:50 and if I had to do it over again I wouldn't have done it. Low gear acceleration is fine but it's a slug on the freeway in OD. The stock short stroke motor doesn't have enough torque at 1800 RPM for any kind of speedy acceleration without stepping down on it hard and kicking it out of OD.

[Brad54]

I've got 3.42 gears, and a 4spd manual OD... it's got the same ratios as the 700r4 (pretty sure).
In a manual truck, it's a fantastic combination.
Engine is a 290hp crate engine with small-diameter ram's horns, Edelbrock C3B (obsolete compared to the Performer), and an Edelbrock 4bbl.

235/75/15 tires are tall.
It's a fantastic combination, and I'll be repeating it on my K10 build.

-Brad

[LVPhotos]

https://www.google.com/amp/www.hotro...ion-build/amp/
Th200 better gear ratio and .67 od vs th 700 with .70
Stick with 3.73. If mpg is game your driving a brick. Even new trucks have issues with 20mpg. In reality how often are you in od?.
http://67-72chevytrucks.com/vboard/s...d.php?t=743494

[rvrfoot]

Off the line will be slower.

[Captainfab]

With a stock engine you DO NOT need a stall converter. With an OD trans and a 28" tall tire, 3.42's are a decent gear. The 3.73's would work as well but the 3.42's will drop your rpm's just a little. You said your rear gears are howling. If it is time for gears and not just bearings and seals, then 3.42 may be a consideration. However be aware that you will need a different carrier.

[Clyde65]

Good point capt on the carrier. Swap from 4 series to 3 series.

[63burban]

Stall converter will not help on the street. my Suburban will run about 2100 at 70
If you want to accelerate, a 700r4 will kick the toque converter out, downshift and haul the mail if need be. The only combination, works awesome. My buddy just installed a 350/700r4 and 3:55 rear in a 40 Ford and loves it.

[rvrfoot]

Originally Posted by 63burban

stall converter will not help on the street. My suburban will run about 2100 at 70
if you want to accelerate, a 700r4 will kick the toque converter out, downshift and haul the mail if need be. The only combination, works awesome. My buddy just installed a 350/700r4 and 3:55 rear in a 40 ford and loves it.

oh no you said the f... Word. Lol

[LEEVON]

I have had a bunch of 700R4 trucks from factory 2.41 (yes that's a thing!) to 4.10's. My favorite is 3.42. My '50 pickup has them behind a 5.3L/700R4 on 27" tires and 2500rpm converter. It rips in 1st gear and will cruise at 85mph. But I'm not sure the expense of going from 3.73 to 3.42 would be worth it.

[Budget63]

Thanks for all the replies guys. Due to the fact that the truck has a 4 series carrier, I'm sticking with 3.73's. At this point I'm planning on going with the Yukon R&P and the Summit Racing Installation Kit. Anyone running the Yukon R&P? Any noise/wear issues?

[LVPhotos]

Adams driveshaft uses these in most hard core jeeps with no issuse. As far as LSD or posi they istalled an Eaton Tru track gear driven lsd in my 12 bolt.
http://www.eaton.com/Eaton/ProductsS...trac/index.htm

http://adamsdriveshaftoffroad.com

[rvrfoot]

I am going to the rear end shop this weekend to get a price on my c10.