2.92 open to 4.10 or 4.56 sure grip

[lordofrc]

Ive got a 67 b body and i want to put significantly lower gears in the back because i have an overdrive and i want to launch. What all would i need to do to convert it and by any chance would anyone have something for sale???

 

[addict4christ]

I have a very good almost new gears set up for racing and never used... 742 casing with 4:88 suregrip gears..... $500.00 plus shipping

 

[racedodge]

first you have to know what 8 3/4 case you have, 741, 742, or 489... each require a different set of pinion gears due to their design. secondly, if you are to do it yourself what you will need are based upon the case you have. With that being said, I need a little more information to determine what you need and the process to do it as I do not want to type up 2 different processes.

 

[Cranky]

Being a 67 B body, and possibly a V8 car, it's an 8 3/4 but yeah, what is the case number. The number will be on the driver's side and low on the 3rd member. All the cases interchange and so do the SureGrip units but the carrier bearing fit will be smaller on the earlier carriers iirc.

 

[waygun]

When calculating the final drive,keep in mind the tire size also factors into the equation.
If you have a 27.5 inch tall tire,with OD 3.55's will be best for off the line launch and civil highway driving.28 or 29 ionch tall tires go 4.10.
Even with OD,IMO,4.88 are for the track and still make the engine rev even in OD--depending on the OD ratio chosen.
Just an example.
Sure the 741 pumpkin has a smaller pinion,but it does not make it the weakest.
Still stronger compared to some Phord/Chebbie rear diffs.

 

[lordofrc]

I believe mine has a 741 case but i would have to double check. I dont mind having somewhat too low gears because i have an overdrive. are the axle shafts different for the different gears. I have a case pre-built and the 2.92 gears do not fit the 3.91 sure grip i have. i would like to have everything just bolt in

 

[67 B-body]

Take up addict on his offer if shipping isn't too bad. You'll realy know you have a set of gears though!!!!!! OD wont soak all of that up!
I wonder why no one is mentioning 4.30:1 ratio??? 4.10 to 4.88 is a huge leap...
If you have the coin,,, I would buy an Auburn setup and a new ring / pinion and have it setup with 4.30's. This would probably give you what your looking for "best of both worlds" scenario.

 

[lordofrc]

if i bought those gears would my axle shafts slide right in? i dont mind having that low of gears cause this isnt exactly a daily driver.

 

[racedodge]

if i bought those gears would my axle shafts slide right in? i dont mind having that low of gears cause this isnt exactly a daily driver.

yes they would if that gear set was designed for 30 spline axles. Hopefully he will chime in. I think 4.88 is not the way to go even with your OD, but to each their own.

 

[lordofrc]

that does seem extremely low. i will have to search around for 4.30'sm they seem a little more appropriate for the application.

 

[Sweet5ltr]

With a 28" tall tire I would personally run a 4.10 gear set out of the two selections.
An example of the RPM's you would be turning during normal street driving are (833-4 SPEED, 1:1);
2,000RPM/40MPH
2,500RPM/50MPH
3,000RPM/60MPH
3,500RPM/70MPH
It is always best to be more conservative with gearing. a 4.88 ratio is complete overkill, unless you combination is strictly an 1/8th mile contender or you're running 31" slicks.

If you are running a 26" tire, then a 4.10 gear would be very similar to a 4.30 gear set with a 28" tire.
A 4.10 gear with a 28" tire is similar to a 3.91 gear with a 26" tire.

Any reason on the install of a "sure-grip" LSD over a locking style differential?

 

[moparmarks]

I'd run a 28" tire like said w/ 4.10 or 3.91 gears. I've drivin OD cars w/ 4.88, 4.56 4.10 3.91 3.55 gears. Like said too, even with OD you'll feel those 4.88's.
Your 67B problably has a 741 case.

 

[1badgtx]

I did a gear change in my 67 gtx this summer...I went from a 3.55 sure grip to 4.10 with a spool...Just trying to get a better time at the track...It auctually slowed me down...But it made me more consistant...Took home 120 bucks...Came in second place in the quickest loser,,,Got beat by a girl in a pink dodge dart!!!At least it was,nt a chevy!!!!
Petty Blue 67 gtx

 

[mopar367]

i have a 741 case. open differential. it has 4.89:1 gears. ready to drop in but its not a sure grip. if your still interested?

 

[daredevil]

Axle spline count wont change. Splines are in the suregrip or carrier.Ring and pinions have no splines.

 

[daredevil]

Being a 67 B body, and possibly a V8 car, it's an 8 3/4 but yeah, what is the case number. The number will be on the driver's side and low on the 3rd member. All the cases interchange and so do the SureGrip units but the carrier bearing fit will be smaller on the earlier carriers iirc.

I have 8 different carriers 66 and up and the caps are all the same. They are 741 742 and 489s.the ones you are talking about are pre 64 I believe.Maybe 487?

 

[daredevil]

i have a 741 case. open differential. it has 4.89:1 gears. ready to drop in but its not a sure grip. if your still interested?

Whats that out of a dump truck? thats way low for an open rear.

 

[mopar367]

what is the difference with the pre 64 cases? they are 741 aren't they?

 

[696pack]

Since the OP is relatively new here and we (at least I know nothing about the car he has) I think a crucial question has been overlooked.

What do you have for an overdrive? Manual trans or automatic? If manual is it an overdrive trans? Is it a Gear Vendor type overdrive unit? If it is an overdrive trans I HOPE it is not the Chrysler original equipment one built years ago as in the 4 speed OD trans. If that is what you have you need to forget about using it as it will likely explode with drag strip use.

 

[lordofrc]

I have a torqueflite with a gear vendors. I dont know much about rear axles. What are the pros and cons on a sure grip versus a locking type. What would be best for my streetable 440 that i could do well on the strip but still be able to drive to school and stuff occassionally.