Banjo Rear axle gears

[Rusty A]

Hi All, just need some advise on rear axle ratio's. I have a 46 Ford Kustom running a SBC with a stock 3spd gear box and rear axle (640 x 15 rear tyres)...here's the problem, the rear axle ratio is 4.11 meaning a max speed of about 55mph :eek: and really...really crap MPG. I know there are replacement gears available, but I'm not sure wether to go for 3.54's or the 3.25. I'm not looking for blistering performance, but I also don't want to end up with a "slug". I also want to retain the banjo, so please no advise just to swap the axle out.
Any advise would be appreciated
Thanks
Rusty A

[weemark]

rusty the common swap seems to be to 3.54s - this is what I swapped mine out to - can only think thats because most of the ford vendors (macs, job lot, dick spadaro etc) only go as high as 3.54s - think its only speedway who do 3.25s - ford also offered 3.54s as a std ratio.

never really tried it yet but hoping for better mpg and a better driving speed, like you my top speed seemed to be about 55-60mph but hopefully will be able to sit at 70mph on the motorway now.

[kapri]

You'll be able to use this to calculate what you need.

http://www.darkside.ca/tool.asp

3.54 will make approx 3 mph per 1000 rpm difference ( in top 1:1) , 3.25 is about 4.5 mph.

[gotzy]

Go here - http://www.locost7.info/gearcalc.php - and down load the calculator, put in your gearbox ratios, tyre size and it will give you all the info you need to make an informed decision. You don't need to put in max power and it will give you rpms every 5 mph in all gears.

3.54 will give you 125 at 5300 rpm with a 28" tyre and a 1:1 final whilst the 3.25 will give you 135 with the same setup. 70 would be 2700 rpm with the 3.25 and 2970 with the 3.54's.

I'd go the 3.25s and your transmission will be happier in my opinion and it will still be fun.

[weemark]

just realised you say you have a sbc in it, would have expected way more than 55mph out of it even with 4.11s - that isnt only because of the rear axle ratio - I would consider changing out the 3spd ford box in it as that aint helping either.

[kapri]

6x40x15's are about 26.5 / 26.75 tall so the figures will be lower than above. About 1 /1.25 mph / 1000 so 5.5 / 6.875 less respectively at 5500 rpm.

[kapri]

With 4.1 and 26.5 tyres I'd expect about 19 mph/1000 rpm so flat out in 3rd should be about 105mph .. Top gear in most modern boxes is 1:1 direct drive so it's sounding more like you're not getting 3rd gear at all ( which is obviously impossible in a manual )??

Have you got a tach on the motor ?

[weemark]

kev thats all I got with my roadster as well, 55mph, with 4.11s and 6.50s which are just under 30" tall.. certainly i had a flattie in the car at the time but engine nearly flat out by the time it got there.

[kapri]

It's the revs that are different though Mark surely , how much does a flatty rev to 3.5 / 4k tops ?

[Rusty A]

Great, thanks fellas. Like Gotzy suggests, I'm leaning towards the 3.25's. I was just concerned that it would end up gently "gathering speed" rather than accelerating :D if you know what I mean....

Thanks again for your advise and the links

[weemark]

It's the revs that are different though Mark surely , how much does a flatty rev to 3.5 / 4k tops ?

yep would have thought about 4k, not got a tach on it so dont know..

[Rusty A]

With 4.1 and 26.5 tyres I'd expect about 19 mph/1000 rpm so flat out in 3rd should be about 105mph .. Top gear in most modern boxes is 1:1 direct drive so it's sounding more like you're not getting 3rd gear at all ( which is obviously impossible in a manual )??

Have you got a tach on the motor ?

No, no tach on the motor, I guess I could push the motor harder, but it really would be pushing it, and that doesnt make for a relaxing drive when on a run. I guess the gearbox isn't helping the situation either, but I would rather keep that in place too.

[hotroddickie]

I would go with the 3.25's with a small block.
Most 70's 80's small block cars had taller gears than that stock and went all right.
It will also mean your gearbox will be under less strain.
You will have plenty of torque and easy 70 cruising.
Rich

[rem]

If you are buying new gears it might be worth having a browse through the early V8 forum on Fordbarn, as I think there has been discussion about them on there: I think it is something do do with the quality of fit or something (they're made in Italy, not the USA, which might be part of the problem :))

[rottencorsair]

While we're talking 3 speed boxes and the like. Anyone got one their tripping over and want to let go cheap? P.M me if thats the case.

[Brizey]

a 46 Ford Kustom running a SBC with a stock 3spd gear box and rear axle (640 x 15 rear tyres)...here's the problem, the rear axle ratio is 4.11 meaning a max speed of about 55mph :eek: and really...really crap MPG.
I would expect a lot more top speed than that, Dean.
When I last ran my roadster at the drags it had a mildly hopped flatty, a 46 trans and 4.11 rearend, and was topping the quarter at 87mph. I know my roadster is lighter than your car, but on a motorway you should still be getting way more than you do with a small block, as suggested by Mark.
Even a stock `32 was capable of 75mph!.
Are you certain you have 4.11 gears. Other gears available (and fitted by Ford) years ago, were.
3.54
3.78
4.11
4.44
4.55
You could possibly have one of the lower ratios.
Normally, but not always, the ratio was stamped on top of the central banjo rib (just above the pinion) in the form of 2 no`s. The first no. is the pinion teeth, the second no. is the ring gear teeth.
Another possibility is the trans, or even the gear sets, could be from a truck, with horrendously low ratios.
I remember years ago, Bernie Chodosh broke 3 transmissions in his coupe and one replacement trans was a model A truck box which netted a princely 35 mph top speed. Needless to say, it didn't stay in there very long... :o

[Rusty A]

Thanks fellas...I really appreciate all of your comments and advise. As I say, I feel I'm really pushing it along to go over 55...it would go quicker but it feels like I'm thrashing it :( which is ok in short bursts, but not on trip down the motorway...and MPG is bad enough at 55

Thanks again all

Deano

[rem]

While we're talking 3 speed boxes and the like. Anyone got one their tripping over and want to let go cheap? P.M me if thats the case.

Russ Pepper (39coupe) was selling a handful on here recently for about £190 each, which is pretty reasonable over here, although I have seen Pilot ones cheaper.