742 gears

[70daytonaclone]

HI all I have looked this up on the web but no luck maybe  some one can help. I bought a 70 b body and it had this 742 housing, pinion and rinng gear on the open carrier.d I would like to know the ratio. on the ring gear is the following #80-7301-1....the pinion has the number80-8301-1. both are followed by a 1 <> 4....the <> is a double diamond. any help would be greatly appreiated. thanks Stephen

[Shakey]

There were numerous numbers on mine.  There was a 7 digit Mopar part # and the ratio was stamped on there as well.

There is a way of calculating it by counting the teeth on the ring and the pinion, but I don't know the formula.  I'm recall it being simple but...

[beedees]

Divide the no. of teeth on the ring gear by the no. of teeth on the pinion.

[mikepmcs]

in Mike's pic above that 3.23 id's the gear ratio.  Is the chunk still in the rear end housing or do you have it out of the car?

you can id the ratio buy using the tire spin method pretty easily if you have the wheels on it.

you said you have an open rear so, curious to know how you know that for sure??  Anyway, open rear gear id you need to lift one wheel off the ground and mark the driveshaft with something you can visibly see like yellow paint or something.  Spin the wheel once and count the number of times the driveshaft spins.  x that by 2 and you have your approximate gear ratio or spin the tire twice and count the driveshaft turns and you have your gear ratio(ex. 2 spins of the tire yields 2 and 3/4 turns of the driveshaft = 2.76 rear end.  3 and 1/4 turns of the driveshaft = 3.23 and so on)

The one spin of the tire method would be 1 tire turn = 1 and 1/3 spin of the driveshaft x 2= approximately  2.76 rear end, etc.....


Now if you have a Sure Grip rear end.  Both tires need to be in the air and both spin in the same direction.  same thing, spin the tire, count the driveshaft turns and you should have the approximate gear ratio.


v/r
Mike

[mikepmcs]

ok just read it again and it appears you have the rear end out, my bad.  Info for the future though in case anyone needs it.

Man , I need to pay more attention, too early yet I guess.

v/r
Mike

[70daytonaclone]

Hi again I will have to count the teeth as this is out and apart rolling around in the trunk. it is not a factory part. those are all the numbers that are there. bare case, pinion out and loose, ring gear on a open carrier. I believe they are Dana with the double diamond on the ring gear but those numbers don't seem to work on various sites. thanks for the help Charger Folks!

[70daytonaclone]

I counted 10 teeth on the pinion and 41 teeth on the ring gear. does that make it a 4.10 set?  why would any one put aftermarket 410's on an open carrier? thanks Stephen

[daves68]

Yes Stephen, that sounds like a 4:10 gearset. Why anyone would do that is a mystery. The car would just sit there toasting 1 tire. Outside possibility it originally came from a truck application. Good gears for your car on the road would be 3:55. You still need a suregrip unit in there though.
Daves68

[70daytonaclone]

I agree thanks Dave

[LargerCharger383]

I just estimated mine by making a mark with a crayon at the end of the shaft/front of housing, spun the wheels 1 revolution, and counting how many times the marks passed each other.  just a quick way to get a ballpark estimate

[RD]

I just estimated mine by making a mark with a crayon at the end of the shaft/front of housing, spun the wheels 1 revolution, and counting how many times the marks passed each other.  just a quick way to get a ballpark estimate

unless it is an open rearend, in that case you have to spin the tire twice to identify the correct ratio

[LargerCharger383]

I just estimated mine by making a mark with a crayon at the end of the shaft/front of housing, spun the wheels 1 revolution, and counting how many times the marks passed each other.  just a quick way to get a ballpark estimate

unless it is an open rearend, in that case you have to spin the tire twice to identify the correct ratio

yeah, my car was open when i got it