Gears

[terrible one]

Hey guys,

I was wondering what the easiest way was for finding out what gears I have in my rear end. Stampings? Factory chalk? What about some way of counting wheel rotations vs. input rotations?

Also, what gears were available for the 8 3/4 in '68?

[mikepmcs]

already a posted thread on here about this somewhere.  i'll try to find it.

v/r
Mike

[terrible one]

Thanks man. Sorry if this has already been discussed.

[mikepmcs]

TO
no, it's all good, i just can't think of how to do it right now, cause i'm well ahhh... it's friday night.

[Chryco Psycho]

if you do not have sure grip leave 1 wheel on the grond & count the rotations of the driveshaft to get the 1 lifted tire to do 2 full rotations
if you haqve sure grip lift both tires & count the rotation of the driveshaft to get the tires to do 1 complete revolutuion

[mikepmcs]

TO
here's a pretty good explanation and how to article.

http://www.jedi.com/obiwan/jeep/misc/gearratio.html#how

[squeakfinder]

Or, if the third member is out of the car, divide wring gear tooth count by pinion gear tooth count.

[Ghoste]

For that matter, if it's out of the car, the ratio should be stamped into the side of the ring gear someplace.

[terrible one]

I appreciate the help everyone. The third member is not out of the car or anything, and it's not a suregrip unit, so I'll go for the one wheel on the ground and counting rotations process here in a little while.

[mikepmcs]

keep us posted, i'm curious to know.  My guess is 2.7's.   and don't forget to look for a tag on the center chunk on one of the bolts too, it might still be there.

i'll look for the gear info for you let me do some pokin around.

here's a link to moparts page in the mean time.  great info and some real cool education on rear ends.  i learned alot

http://www.moparts.com/Tech/Archive/axle.html

v/r
Mike

[terrible one]

Well, as I (and mikepmcs) expected, I'm quite certain I have 2.73's. With two turns on one wheel while the other was on the ground, the input turned a little over 2.5 times.

Furthermore, there is what I would consider more play than normal between the input and the axle shafts. I can move the wheel forward and back a bit without the input moving...lots of slack.

Anyways, my back brakes are shot, and it seems as if the third member has seen better days. I was planning on pulling the rear to replace the leaf springs, shocks, and brake parts, plus to clean up the gears and all. But with these high gears I would like to swap them out for something lower, like some 3.55 or 3.91's...

[mikepmcs]

Hey you made it to old timer, congratulations.   

i'll just take a stab on the 68 gear availability and i'm sure if i'm wrong someone will correct me.

2.73, i think there might be a 2.9 one. 3.23, 3.55, 3.73, 3.91, 4.10.

I actually just stuffed a 3.23 sure grip in there from my 2.7 one legger and I notice a little difference.  I was hoping to score a 3.55 chunk and that would have been primo for me but the price was right so i went for it.  I'm not going to experiment with setting up a rear at this point but if i find another 489 case for cheap i might go for it.  here's a great read on how to set up a rear end. not on my top priority list right now though.

http://www.moparmusclemagazine.com/howto/155_0308_mopar_rear_end_gears_set_up/

3.55 should be all you need but if you want more punch out the hole 3.7 or 3.9 would be even better obviously.  depends on what you are going for.  I know Dodge Freak is real happy with 3.9's in the rear and he drives it all the time.  I just thought 3.5 would give me the best bang for my application.

v/r
Mike

[terrible one]

Yeah, I guess I'll see how things play out. Maybe once I pull the rear and inspect the current gears, etc. I can go from there. I would really love to have a lower geared suregrip chunk to put in there but they're getting pretty high. We'll see.

[mikepmcs]

as you know, they are on ebay, i got mine for $200 bucks, because the guy made a mistake in the ad and noone would bid on it.  I looked at the picture and it was obviously a SG rear but he had open differential in the ad.  I emailed him and asked/told him this so he could update his ad but by the time he did it the auction was almost over and i'm the only one who bid on it.

I guess the reason i say this is type in obscure stuff when you look for the chunk.  there are so many different ways to say mopar 8-3/4, 8/75, 83/4  dodge rear, etc.... you get the idea.  another thing is a lot of these guys on there call it posi!  so type in mopar posi, dodge posi, etc....

you'll be surprised on what you come up with and be patient it will come around. 


v/r
Mike

[terrible one]

Yeah, I'll keep my eyes open. What is the visible difference between a suregrip and open unit?

Also, how expensive are aftermarket gears for my current third member? I know it would still be open, but maybe that would be the best way to go?

[mikepmcs]

TO,
if you want to go that route there is 2 or more 3.55 open diff's on ebay right now for $50+
one's in pieces and one is complete.  the second ad i'm linking you to has a great picture of an open differential rear and it has the much desired 489 case..  SG are cone and clutch , and I believe the clutch type is more desired as to the ease of rebuilding parts available for this type SG unit.  I'll get you the link to the explanation of sure grip units and try to find you a picture of both types(cone and clutch)

http://cgi.ebay.com/ebaymotors/mopar-dodge-8-3-4-8-75-741-complete-3-55_W0QQcmdZViewItemQQcategoryZ33731QQihZ009QQitemZ190065689762QQrdZ1QQsspagenameZWDVW

http://cgi.ebay.com/ebaymotors/mopar-8-3-4-3-55-489-large-yoke_W0QQcmdZViewItemQQcategoryZ42606QQihZ015QQitemZ250068560832QQrdZ1QQsspagenameZWDVW

to answer your question on ring and pinion prices, they are pricey brand new, then setup cost and so on.  If it were me, i'd piece some old stuff together like,score a sg unit somewhere, a case with gears already in it.  this is the much cheaper way to go.

UPDATE.... here you go, an excellent explanation of the SG units with pictures. 

http://www.moparts.com/Tech/Archive/axle/13.html

v/r
Mike

[Bandit72]

Yeah, I'll keep my eyes open. What is the visible difference between a suregrip and open unit?

Also, how expensive are aftermarket gears for my current third member? I know it would still be open, but maybe that would be the best way to go?

keep an eye on old dodge trucks, (61-71) most of them had 8 3/4 rears with usually 3.5 gears, some sure grip some not, if you can find an ex government or military truck, almost all of them had sure grips, i got lucky and found an ex military 62 with a 3.91 sure grip, scored teh whole truck for $150 bucks 

[terrible one]

I might look into one of those 3.55 open units currently on Ebay, but I'm not going to rush. I still think there is hope for a good deal on a suregrip unit.

Thanks for all of the help everyone!

[terrible one]

Furthermore, if I ordered a 3.91, or 43-11 ring and pinion, and switched them out for my old ones, would that be all that I need to be good to go with my current chunk?

[Chryco Psycho]

you need to get gears for the specific carrier you have & I would install new brgs while you have it apart
you May need a different yolk as well depending what spline the pinions [new & old ] are

[terrible one]

you need to get gears for the specific carrier you have & I would install new brgs while you have it apart
you May need a different yolk as well depending what spline the pinions [new & old ] are

Do you know how much gears and bearings would run me? I figure it might be easier just to buy a new ring and pinion and then bearings because the price of a new chunk plus shipping would be a killer. Those things must weigh like 80 pounds. It still wouldn't be a suregrip but at least I could have the gear combo I have and put them in while I already have it apart.

[mikepmcs]

IMHO, you can get a chunk with a desired gear ratio(maybe open carrier) for less than it would cost to put together a new set. 

my.02

[d72hemi]

are the sure grip units 8 3/4 only, or did they come in other rearends (dana 60?) also?

[mikepmcs]

are the sure grip units 8 3/4 only, or did they come in other rearends (dana 60?) also?

No, yes, and yes.  believe it was called power lock in the 60.

http://www.autohobbydigest.com/dana.html

[Chryco Psycho]

the gears & brgs generally run 300-400 + the labor to set them up
powr lock in the 60s & lighter units in the 70s were Track locks / Crack locks