Differential gear setup advice

[jlcustomz]

I,m considering swapping my 373 gears in my 7.5" 79' rear which came with 2.73 's to 4.56 gears early next year.Less than 10,ooo miles on rebuild with eaton posi unit, so considering getting only what I need, not complete rebuild. I actually cheated & let someone set this one up since I had the money then ,now I don't. Have swapped some 20 years ago & did ok, still have some prussion blue laying around.Might still have a dial indicator at work.

I f anybody wants to give me some solid 7.5" specific advice on setup, I,d appreciate it. My turn to ask for advice. Knowledge is power, or in this case, reliable power.

[Keyser Sose]

richmond gear has a set-up kit for like $80, and a great tech line. check them out.

[JJLT1]

with the low miles,, bearings should be good
if its a 3 series carrier??
get the thick 4.56 gears for the 3 series,, crush sleeve,, and just a shim kit,, and pinion seal..
one of those fancy, heavy duty diff covers with the bearing cap preload look really kool.. never had one..

the gear pattern is all visual,, .006-.010 on the backlash,,
dont forget the sideload on the carrier bearings,, cant remember the "rule of thumb" for that??? .002-.003???

not really solid 7.5" specific advice on setup,, but it works on other 10-12 bolt rears,, best i can do..goodluck.. dont forget the breakin

http://richmondgear.com/ringandpinion.pdf
http://www.differentials.com/technic...n-instructions
http://www.drivetrain.com/parts_cata...tructions.html

[Zerberfert]

I would replace the axle seals just to be safe. On the carrier bearing preload, when you spin your carrier with no pinion and axles installed it should spin less than one complete turn but more than 1/4. I know that's not real specific but that's what I was told and it worked for me. Good luck.

[ccc]

you are looking for 4 in lb pinion drag and 6 to 8 thou. backlash at 10 it will howl. on aftermarket gears the pinion depth is marked on the gear. i use lubraplate white greese to check pattern. look for contact patern to be centered in the tooth not at either end.i have a old pinion bearing that i honed out to set the pinion depth. if the patern is too close to the outside diameter of the ring gear you need a thicker pinion shim and if too close to the inside diameter of the ring gear you need less pinion shim.replace ALL seals and any bearing that isnt smooth and quiet.

[464elky]

Removing the inner pinion and carrier bearings without damaging them makes it not worth the effort as the price of new bearings is not that much. The time and trouble vs risk says just get 4 new bearings and races. JMO

[JJLT1]

x2 on replaceing that inner pinion bearing at least,, ment to say that,, get 2

and on the honed out pinion bearing,, so much easy-er..

[jojothetattooboy]

I agree! The honed out pinion bearings are great for set-up. If you can find a decent set of used gears, it isn't a bad option, especially if they are factory GM. Pinion depth important. There are several "acceptable" patterns when you do your final pattern check. Yukon Gear has info on their site on the patterns. Take pictures of the patterns as you go for future reference when changing shims. This helps me as I progress and you can compare if you want to reverse something. .... If you jump in it and drive down the road and it howls....you can always take it back apart and try again! I doubt that it will.......

I went from a 3:08 to a 3:42 and it was quite a step....a 3:73 would be quite noticeable!

[zach01s]

i wouldnt go anything past a 3.73 on a non overdrive transmission,

i have 4.11 gears with a 700r4 and to do 55-60 mph im right around the 2000-2100 rpm range. 75 mph interstate speeds put me around 2500-2600 rpm. 4.56 gears might make your car a little less set up for highway, but if it only ever sees in town driving its not too bad.

i noticed a little mileage increase going from 3.42 to 3.73 and going to 4.11 it didnt seem to change my mileage at all.

acceleration wise im pleased, with regular street tires i can just mash the gas the both will squeal and come loose. with the mickey thompson street legal slicks im running now, they dont slip on a take off, but it doesent take much to get them to slip and come loose.

all that aside, before you go together with it, your best idea is to find someone with a pinion depth tool and borrow it, without measuring the correct depth youll never know how many shims youll need under the pinion bearing to get the right depth. even if youre usingf used gears, and they were set up correctly theres no way to know if they have the right number of shims if you put the gears in a different differential.

when finding the right shims you can as stated above hone the inner races of used pinion bearings, so theyll slip on and off easily and ignore the crush sleeve untill you get the depth set correctly.

next time i tear into my diff im replacing the cover to one like this:

[jlcustomz]

Guess I didn,t mention in this post that I just went to 28" tall rear tires & have a t /56 trans with a .50 ratio 6th gear. Half of 4.56 is 2.28 final drive. Haven't looked up the formula again yet, but with 28" tires in 6th gear, a 4.56 ratio doesn,t sound so silly.

[Keyser Sose]

next joe will tell us "if you loved me I wouldn't have to tell you!"

[Lenny Carey]

Keyser , Don`t give the boy any more ideas . Next thing you know he will be doing something wild , crazy and impossible like replacing his front grill , lights and fenders with a 2010 Camaro set up . Good thing he is more sensible than that !

[bugsyc]

I have a stock 85 with the 305....I 'm reading the posts and it seems the car came with 2.something rear end gears..I'd like to put the 3.73 gears in...What size do I need???I see 7,7.5 and 8 inch....Which 3.73 gears do I need...Also,an installation kit,which one????Thanks

[JJLT1]

welcome Bugs

after 25 yrs it pays to look first,, and see if someone upgraded it before,,
you could have a posi or different gears than whats on the code on the axle housing..
but most came with 2.41s in a 7.5" rear,, and options up to 3.08 IIRC.

that means it has a 2 series carrier,, normally that means 2.41 to 3.08 ratios,, but
now days you can buy thick gear sets and put 3 series carrier gears on a 2 series carrier..
a 3 series carrier normally means 3.08 to 4.11 ratios..IIRC

if its a stock setup?? youll need a 3.73 thick gear set and a kit for a 7.5" chevy..
heres a summit search.. theres lots of choises out there..
http://www.summitracing.com/search/p...rrier-series/2
http://www.summitracing.com/search/p...mino/year/1985

[gmtony55]

Hey JJ, I have same situation as Bugs, I have an 83 with 305, I am all stock right now and have a small block 400 to build and still have not made my mind up on transmission, I usually let the lack of money lead me where I can afford to go. I have a friend that will build my a trans from a core when I am ready. Now for the question..do you think I should get gears as you suggested to bugs or should I be looking for a 8.5 donor rearend..sometimes I can find cheaper with donor vehicles. I ultimely want a daily driver with a little pep, not a racecar...Anyone feel free to give advice..thanks