742 case with 3.91 gear - Manufacturer Recommendations

[Heat-Med]

Hi all,

I have a 68' Coronet RT with a 3-speed auto. I am looking at upgrading my 3.21 sure grip to a 3.91 ratio. I have been looking on line to find a third member, but there really is not a lot out there. I am thinking about just going new, so that I know what I have. I am looking for a recommendation of what manufacturer to go with or stay away from. I am hoping to get something that I can just bolt into my existing axel and not have to mess around with switching other things. Ideally, finding another 742 case with 3.91 would be my desired pathway. Note: I mostly travel in town, or a maximum of 45 mph. Any advise would be appreciated. Thank you in advance. And, I am looking to put BF Goodrich P27560R15 tires on the rear tires, fyi.

Guy

 

[Jerry Hall]

You have all the right stuff in your car now, except the gear set you want. I suggest you buy a bearing and gasket set and a 3.91 gear set for your 742 case from a reputable supplier like Dr. Diff, and have someone set it up for you to reinstall. If you don't know anyone that does this locally, I'm sure Dr. Diff can handle the whole job for you.

 

[Heat-Med]

You have all the right stuff in your car now, except the gear set you want. I suggest you buy a bearing and gasket set and a 3.91 gear set for your 742 case from a reputable supplier like Dr. Diff, and have someone set it up for you to reinstall. If you don't know anyone that does this locally, I'm sure Dr. Diff can handle the whole job for you.

Thanks for the suggestion. I am looking to be able to swap my 3.21 back in if I want to go on a cruise at some point. Having a second member gives me the most versatility.

 

[F4R/T]

Timken bearings are my favorite.. I believe Cass at Dr. Diff is one of the go to guys around here. Gears — idk I have old Richmond's that were good for me or oem gears.

 

[Heat-Med]

Timken bearings are my favorite.. I believe Cass at Dr. Diff is one of the go to guys around here.

I am in southeast Wisconsin. I will have to look of Dr. Diff. Thanks

 

[dadsbee]

3.23 to 1

 

[Heat-Med]

3.23 to 1

Working on that. Just one more year of work and then the uninhibited fun begins. Just lining things up!!

 

[70bigblockdodge]

3.91s suck.
Especially getting passed by a old lady in a KIA on the way to church.

 

[Heat-Med]

3.91s suck.
Especially getting passed by a old lady in a KIA on the way to church.

I am thinking they will be find around town, rarely go over 45 mph. As well, with the taller tires, that should make it more tolerable. The close runner up was 3.55s

 

[F4R/T]

Just make sure your convertor isn’t slipping all the time.. otherwise stuff gets too hot.

 

[gtx6970]

Go with Dr Diff,
Avoid Randys Ring and Pinion

 

[gkent]

to swap my 3.21 back in if I want to go on a cruise at some point. Having a second member gives me the most versatility.

LOL !!! You'll never do that !

 

[Heat-Med]

LOL !!! You'll never do that !

I am thinking you are correct, haha. I intend on putting the 3.91s in and that is probably where it will stay. We were thinking of doing a 2500 stall behind the mildly built 440. For convenience though it would be nice to have a direct swap out.

 

[Jerry Hall]

As far as swap out is concerned 741, 742, and 489 are direct swaps in the 8 3/4 housings as long as everything is stock.

 

[Heat-Med]

As far as swap out is concerned 741, 742, and 489 are direct swaps in the 8 3/4 housings as long as everything is stock.

I will just have to verify my yoke/shaft units are the same size I believe.

 

[Jerry Hall]

I have what you want, but I'm not going to turn this into a for sale ad. Shipping would probably kill any kind of deal anyway.

 

[70bigblockdodge]

I am thinking they will be find around town, rarely go over 45 mph. As well, with the taller tires, that should make it more tolerable. The close runner up was 3.55s

In the '80s 4.10s were pretty miserable. Nowadays 4400-4500 rpm to get passed by almost everyone is annoying.

 

[Bee1971]

3.91s suck.
Especially getting passed by an old lady in a KIA on the way to church.

How does that happen - Lord doesn’t like 3:91 s ?

 

[70bigblockdodge]

How does that happen - Lord doesn’t like 3:91 s ?

I don't think he likes them either.

 

[Heat-Med]

In the '80s 4.10s were pretty miserable. Nowadays 4400-4500 rpm to get passed by almost everyone is annoying.

Haha, good thing for me in the city 3.91s with a 440 behind it should not have to hard of a time keeping up with people.