14 FF Ratio ?

[fatdog]

So since I did the 700/241 swap on the 72K5 the 3.73 gears and 35's aren't cutting it when the converter locks up....way too low RPM...even when just motoring down the road @ 65MPH. So yesterday I went looking around and found a 14 FF rear and a 44 8 lug front axle. Not a matched pair. Front has 4:09 gears and I think the rear has 4:10's. The FF came out of a mid 70's ambulance so it has the 70" wms I'm looking for. But, it has been sitting for some time and the drums are froze up. Not a big deal because I'll run rear discs. But I'd like to know the ratio before I drag it home. I pulled the cover and can't see any markings on the ring, but the pinion has a 41/10 marking on it. Would this indicate it is indeed a 4:10 ratio? I think so, but all the info I've found from searches indicates the ring has the info on it, hopefully, some of you more familiar with the diff will know for sure.

The FF also appears to be a factory posi of some type, I'm not that familiar with them. I know you can't do a Detroit on this housing, but I'm hoping to run it as is if the gears match the front. It should be fine for what I do with it. Thanks

 

[4X4HIGH]

Yes that would be a 4.10 gear. The markings are always on both the ring and pinion gear (that i've seen anyways). With your set-up you would be best suited with 4.56 gearing. My rig is 700/241/35's/4.56's and it almost isn't enough gearing as it will want to "hunt" between 3-4 when climbing a very slight hill. I think at some point i'm going to 5.13's and be done.

 

[4xcrazy]

agreed, 4.10's will work, i'm using them currently too, and they do just as 4x4high says, they tend to hunt between 3-4 when on slight grades, but they do work better than a 3.73 definately.

unless you can find a military diff for cheap, or someone around you is selling a different geared rear diff, i would probably grab the 4.10 gears and plan on swapping/building to fit your needs as funds allow.

that's the plan i have

 

[nsxxtreme]

Yes that would be a 4.10 gear. The markings are always on both the ring and pinion gear (that i've seen anyways). With your set-up you would be best suited with 4.56 gearing. My rig is 700/241/35's/4.56's and it almost isn't enough gearing as it will want to "hunt" between 3-4 when climbing a very slight hill. I think at some point i'm going to 5.13's and be done.

Agree....If your just driving around town and never intend to tow 4.56 work great. If you intend to tow any kind of wieght 5.13 is the way to go. Although I have an NP208 transfer case I don't know the gearing difference between that and the NP241.

 

[sweetk30]

http://coloradok5.com/forums/showthread.php?t=151608

 

[fatdog]

Thanks for the link and the opinions to go with 4:56 gears. I'm convinced it would be better also. I did look around some more and did find a 14FF and 60 pair with 4:56 gears, but he wants $1500 and I'm not gonna pay that much. Maybe I'll look some more but I probably will go with the 4:10 14FF and 44 front because I can get them both for $150. I'd rather have the 70" WMS of the van housing anyway.

One more thing...I'm currently running a SYE kit on the 241 with a CV shaft. When I set it up I used 6* shims but my diff was still shy from being inline with the shaft by 5*. The shaft is 20* and the diff is 15* I'm getting some vibes at around 65 MPH and wondering if this might be why. So when I set up the 14 FF how close should I be with these angles? Furthermore, what's the best way to make sure I get the angles correct when I weld on the new spring pads? Thanks for any tips.

 

[4X4HIGH]

The rear pinion should be 2* down from being inline with the driveshaft when using a SYE (this accounts for the slight bit of axle wrap under normal driving conditions making it inline with the shaft while driving).

 

[sweetk30]

1tons with 4.56 for 1500 is around normal price. prob from a mill truck. if so prob has detoit in the rear and thats 450 new.

and if you buy gears / install kits / labor / small parts and regear a set of axles you will be over 1500 bucks. and if carrier is needed for the gear swap there is more money out. and if it has the locker and you did one there the 450 out .

add it up thats a great deal in the end.