Rebuild Differential?

[SRH916]

I am completely new to working on anything with gears, and would like to take the cover off of my differential to find the gear ratio. What all would I need, and need to do to check this without any harm done?

Thanks in advance.

[larry may]

Look at the lable glued to the glove box door. Rear ration may be there if the label is still intact. Otherwise remove the rear cover. count the pinion gear teeth and the ring gear teeth. Divide the lesser number in to the larger number . should get you the ratio of your gears. Clean up the mating surfaces apply a bead of rtv. and put the cover back on. If this is a posi trac add a bottle of positrac lube along with the 80/90 weight, Am sure one of the wizzards here will chime in and letcha know what I forgot. Have fun........

[SRH916]

I have looked at the sticker for what seems like hours and still havent seen anything that says the gear ratio... I must be missing something... I have also looked all over the tubing trying to find the stamped numbers, cleaning everything. Nowhere to be found. Of course there is s*** caked all over it... This is my last resort... I really don't want to, but I guess I'm going to have to.

[Thumpin455]

Put the rear up on jack stands, put the trans in neutral, put a mark on one of the tires. Mark one of the ujoint bolts, then spin the tire one full revolution and count the number of times the Ujoint bolt goes by. If it turns 3 3/4 times then you have 3.73 gears, if its right around 4 times, its 4.10, if its 4 1/2 then you have 4.56.. just make sure both wheels are off the ground and turning. if they turn the same direction all the time, then its a posi/locking/limited slip diff.

[SRH916]

Originally Posted by Thumpin455

Put the rear up on jack stands, put the trans in neutral, put a mark on one of the tires. Mark one of the ujoint bolts, then spin the tire one full revolution and count the number of times the Ujoint bolt goes by. If it turns 3 3/4 times then you have 3.73 gears, if its right around 4 times, its 4.10, if its 4 1/2 then you have 4.56.. just make sure both wheels are off the ground and turning. if they turn the same direction all the time, then its a posi/locking/limited slip diff.

Thanks Thumpin455, my friend said to do something like that, but he never gave me the details. I think I will do that instead of messing around with the internals.

[Luvlegs]

Pulling the rear cover is a piece of cake and you probably should consider it for no other reason than changing out the possibly 30+ year old lube that's in there. I didn't want to do it and put it off forever - once I did it, I kicked myself for not doing it sooner. Put a pan under the pumpkin to catch the old lube (stinks to high heaven) (even the new stuff stinks), take the cover off without bending it (originals are pretty solid) - You can read on the gears the actual ratio, then, clean it out. Clean the gasket surfaces and put your cover back on. On the front of the hogs head (pas. side I believe) take out the fill plug - I used the end of an old 1/2" extension and a pipe wrench. Refill it to the correct level and you should be good to go for several years or better. If I can find the pic, I'll post where to look for the ratio. Do it and you'll be glad you did.

[Luvlegs]

Here's a pic

[Thumpin455]

Being an ASE certified master technician, I am all for preventive maintenance. Changing the gear lube every 10k mile or around there is a good idea. However I do realize not everyone is knowledgeable or experienced in working on vehicles. That is why I give the easy button often, a simple way to check things and have a rough idea. Its what I do in a junk yard to find out what is what before I buy a part.

Also its winter time right now, and most people dont want to lay on the ground and work on a vehicle when its in functioning condition. I know I dont, and I have a heated shop to put it in.

That being said, I agree with Luvlegs that it isnt difficult to change the fluid and check the gear ratio. Its just not the only way to figure it out.

[James McClure]

SRH and everyone else for that matter. GM didn't put rear axel ratio's on option labels, only the option number(s). Some of you all have the right idea, count teeth and devide. GM has made this easier. You can't see it in the pic luvlegs sent in but it is there in the string of numbers you see stamped into the edge of the ring gear. What your looking for is 2, 2 number stamps seperated by a ( colon? and should be just after what looks like a part number. It will look like this 15:41. 15 being the # of teeth on the pinion and 41 being the number of teeth on the ring gear. Now divide 41 by 15 and you get 2:73. Easy right? Sometimes GM actually does something that makes sense, LOL
The photo luvlegs sent in is of a 3/4 ton lite rear, non posi. It was blown at one time and rebuilt. You can see pinion gear marks on the carrier assembly.
Now back to SRH. If you have never been in a rear end (especially any of the posi types) I would suggest you don't mess with it. If you don't have any noise comming out of the rear end it's ok, just change the fluid, add the additive if it's posi, and be done with it. If you want adventure go ahead and rebuild it, but be forewarned it's not as easy as it sounds to do it correctly. You will need some special tools. Dial indicator for backlash and run out measurements, inch pound torque wrench for pinion gear preload checks and a press to replace inner pinion bearing and carrier bearings and a good vernier caliper to measure shims. Usually you can re use the shims though IF you are staying with the existing ratio. GET A MANUAL!!! and read it before you start. Keep us posted OK? jim