4.88 gears daily driver?

[ibbuckin]

Hello! I have a 72 Bronco 302 600 edlebrock headers three speed cam 4" lift on 33" tires. I eventually want to replace my 28 spline ford 9 with the 31 spline and put 4.88 gears in all(possibly arb locker in rear) and run 35" tires disc breaks all around.my question is will I be able to drive this on the highway? (This is not my primary vehicle)I drive mostly around 40 mph in town to beach but if I had to would like to be able to go 60mph.also would my best bet would be to wait and get new axels with the 4.88 gears AND disc breaks since I want to replace the stock 9 with a later 31 spline 9? Would I have to make shaft mods? I know thats like ten questions at once but im kinda new to this and im trying to save time and money while I have everything apart.Thx guys this forum has been really helpful to me

 

[Mountain Ram]

Are you running a newer transmission with overdrive??

Assuming you have either a typical Bronco trans (C4, 3 speed, 4 speed)- In my opinion... the 4.88s are going to be too low for highway use. I have 36" tires with 4.56 gears and 65-70 is tops. I also have an F250 on 35s with 4.88s as a tow rig. It does good on the highway, but has an overdrive transmission.

TD

 

[Myllo73]

I had 4.56 gears w/ 35" tires on a daily driver with a C4 and I wasn't happy with how it was on the highway. Nice offroad and going uphills, but without an overdrive it wasn't fun. That's my opinion on it. As for the rest I'm not sure, I know there are different ways to have a disc brakes on the 9" and it depends on if you want an ebrake still or how much you want to spend. If you aren't hard on the throttle the shafts will be ok.

 

[rob wilson]

Currently running a NP435 (1:1 final drive) with 4.56 gears and 35's. I sure wouldn't want to go any higher on the gears and have to spend any time on the interstate. At 65 MPH, I'm turning about 2900 RPM. My opinion would be that 4.88's are limited to in town and offroad.

Here is a link that'll give you good numbers to compare with different driveline options.

http://www.grimmjeeper.com/gears.html

 

[ibbuckin]

Yeah its stock three speed so im not sure but ratio is 3.55? Would that be enough to run 35's with 4" lift?

 

[Broncobowsher]

I had 4.88s and 33's. It was great on the highway. But it had to have an overdrive to do so. I was running a .70 OD in a 4R70W. When it kicked down into 3rd (1:1 like most any other non-overdrive transmission) it was a screamer. 6000 RPM was good for about 100 MPH.

Without an overdrive 4.11 gears and 33's are a great combo. That still turned a good bit of RPM on the highway but was livable. For 35's that would be a 4.30 gear is comperable.

I would not do 4.88s and 35s without an overdrive for a rig that will see any highway miles.

 

[stock1970]

i have 35s, c4, 31spline, 4.88s, 351w, arb front and rear and run down the highway at 65mph 3200 rpm.. It seems everyone has forgotten that in the 70s cars ran 3k rmp at 65mph.. .. now granted i get 10 mpg on the highway.. and I am going up to 37s soon and that is why i have 4.88s.. I think 4.56 with 35s would be your best bet.. if that is all the bigger you are going..

 

[fetorino]

Just getting ready to gear mine

Yeah its stock three speed so im not sure but ratio is 3.55? Would that be enough to run 35's with 4" lift?

No. It will work it won't work well. In the short term it won't cost you anything to try but it will add wear and tear on your clutch and beat up your little 302.

i have 35s, c4, 31spline, 4.88s, 351w, arb front and rear and run down the highway at 65mph 3200 rpm.. It seems everyone has forgotten that in the 70s cars ran 3k rmp at 65mph.. .. now granted i get 10 mpg on the highway.. and I am going up to 37s soon and that is why i have 4.88s.. I think 4.56 with 35s would be your best bet.. if that is all the bigger you are going..

I'd agree with this if your are not going to go with an overdirve trans.

A stock or mild 302 needs to be spinning some rpm to be in the torque curve to push the brick through the air with 35s. 4.56 will put you right where Ford engineered the motor to run with the stock gearing and tires. 4.88 will help you if most of your driving is offroad but you will be buzzing a few more rpm when on the fwy.

Gearing is a bunch of $$ so best to think it through. Answer the following:

What tire size for sure, 35s, no bigger no smaller?
What transmission, do you envision going to an od or maybe a NP with lower first gear?
31 spl are really a must JMO especially if you are buying carriers, gears, ect.
Why are you going rear discs? Depending on the disc set up your axle choice will be different. Different brakes require different axles due to the offset. You don't want to buy axles twice do you?
11" drums either the truck skinnys 1.75" or the later 76-77 style work well and as an emergency brake actually do work vs the disc which will be a parking brake only.

Measure twice cut once applies here also if you ask me. Think it all through before spending all that $$ on gearing. Everything has to match up to perform well.

 

[Broncobowsher]

And when you think you have the ideal ratio figured out...
Start with just the rear axle. Go for a drive and see if you like it. The 9" is an easy axle to swap ratios in. If you don't like the gear, get another ratio and try it. At this point you are only out a little time, a little gear oil, and a crush sleeve. you can sell the other ratio and take a little loss there.

Once you get the rear axle the ratio you like for the highway get the front done to match. Now you can use 4WD again. Doing it this way will give you a chance to test drive the ratio(s) without spending the money to set up multiple axle ratios just for a short highway trip.

 

[broncnaz]

4.88 gears and 35in tires with no OD. Id say 60 mph on the hiway is very doeable engine will only be turning around 2850 RPM at 65mph about 3000 RPM. Basically vs 4.56 gears you only turn about 200 rpm more with the 4.88's not a big jump in RPM's. Anymore than that and you'll really have the engine screaming. 302's dont mind turning some RPM's but most have there power in the 2200-3000 RPM range.

 

[addicted]

Im planning on running 4.11s with 35s and an NP435. But Im also going to be running a 351W. Im hoping the extra torque will even out with around town grunt and lower highway rpms. I guess we'll see. With a 302 I would shoot for 4.56s since they are happy spinning a little higher in the rpm range. But thats just my humble opinion.

 

[fetorino]

NP435 has a lower first gear also

Im planning on running 4.11s with 35s and an NP435. But Im also going to be running a 351W. Im hoping the extra torque will even out with around town grunt and lower highway rpms. I guess we'll see. With a 302 I would shoot for 4.56s since they are happy spinning a little higher in the rpm range. But thats just my humble opinion.

doesn't it?

 

[ibbuckin]

Broncnaz how you like that np435? Has a granny low right? I want that too

 

[ibbuckin]

Thx guys for your input.I def have alot to think about

 

[addicted]

Yes. Np435 has a super low, non syncronized, first gear. So low in fact that alot of people dont use first gear in normal daily driving. Only for very low speed four wheeling and crawling. However, final drive is 1:1, just like a standard 3 speed.

 

[broncnaz]

Broncnaz how you like that np435? Has a granny low right? I want that too

Best tranny I've had in so far yes first gear is super low 6.69-1 hardly use low range in the t case unless its really rough. and with 3.50 gears and 33in tires you get kind of a free OD. For my setup it works great. Also 2nd gear is slightly lower than the stock 3 speeds 1st gear. Many people dont like it because of slow shifting well to me I'm driving a truck anyways not a sports car and I'm so used to it that I dont notice it. I've had it in since 1986.