Join Our Ford Truck Forum Today

Document your Ford truck project here and inspire others! Login/Register to view the site with fewer ads.

Register Log in

rear end question

countryboytn

countryboytn

'78 Bronco owner
4,371
204
Cincinnati, Ohio
What trans do you have?

I have a 400(stock), c6, on 33's with 3.55 gears, and it sucks. I feel like I need at least 4.10's

anything over 35's, i can see needing a 4.30, and you probably could get by with 4.56's. It depends alot on what you do with the truck too: is it's a toy, show truck, dedicated mud truck, ect?
 
countryboytn

countryboytn

'78 Bronco owner
4,371
204
Cincinnati, Ohio
yeah, I don't think you wanna run 3.70's.

What's in it now? By driving it that little, you could get by with 4.56's or 4.88's, IMO. but you could go higher or lower as well, like I said... depending on what it's used for.
 
countryboytn

countryboytn

'78 Bronco owner
4,371
204
Cincinnati, Ohio
yeah i bet, and 3.70's would only make it worse. trust me on this.. I have no power with 33's and 3.55's.
 
countryboytn

countryboytn

'78 Bronco owner
4,371
204
Cincinnati, Ohio
Anytime... and I dunno how much skill you have with stuff like this, but you can get the ring and pinion for a decent price if you install it yourself. Bronco Graveyard is my go to place, but you might have your own preferred place to get stuff.
 
m78

m78

15,319
667
Virginia Beach Va.
I agree that the 355 is a bit high.
But . The 351M and the 400 don't put out much at higher RPM , and your 351m may be high mileage and low on compression, making it worse.

I would check this before compensating with lower gears.
 
LEB Ben

LEB Ben

Arrogant A-hole At-Large
34,919
1,124
outside your house
With a C6, I typically recommend 4.56's for up to 36-37" tire. 4.88's for up to a 40" tire. 5.13's for up to a 44" tire. Whatever you do, don't listen to the guy that suggested 3.70's...I'm not entirely sure they make a 3.73 set (or a 4.30) for your axle set (if they're still stock). Going with a lower gear (higher numerically) should theoretically help your mpg's bringing you back into an acceptable operating rpm range, instead of constantly having your foot through the floor.


I'd also consider what Mark had to say...the 351M I pulled out of my Bronco, didn't even register triple digit power.
 

Alvin in AZ

1,330
46
Venta de la Mesilla
UTfball68 said:
With a C6, I typically recommend 4.56's for up to 36-37" tire.
4.88's for up to a 40" tire. 5.13's for up to a 44" tire.
Click to expand...
x2

I don't know the number to tell you off hand but going to go with those.
Over on FSB this question is a -big-deal- and has been run through the
wringer so many times it's become almost pure science and little art at
this point because of so many have BTDT there. :)

Off hand the recommendation is a step past stock RPMs for a very small
or no increase in tire diameter over stock and two ratio steps past stock
RPMs for the next tire sizes up etc.

See? There's wind drag, rotational weight and then the "play factor" that
all points at "lower gears are good ;)".

Like it's been mentioned a jillion times over on FSB...
"nobody complains about the felt-power the lower gears make :)"

-----------------

I'm fixin' to follow that same advice since I went from 30.5" diameter tires
to 31.5" on my '91 Bronco 351w +ZF. That's like a half-step or less in tire
size but will go a full step on the gearing from 3.55 to 3.73.

Mine's not a city'n'trail truck it's going to be a highway queen or I'd go to
4.10 ...which is the stock gearing for an F250 with that diameter of tire.

I don't like cars! :/ Only cool thing about a 5.0 '93 Mustang GT is it's A9L
computer, IMO. ;) YMMV on that? LOL :)

Alvin in AZ
 

Ford Truck Articles

Recent Forum Posts

Top