Happy Rear Ends
The Watson Guide to Happy Rear Ends:
Here is Craig Watson's now infamous guide. Its a compilation of numerous e-mails to
Bruce Johnson, so if its seems to jump around a little, that's why.
I did mine myself and can steer you around some of the pitfalls that I
encountered. Here's the basic procedure:
1. Number the bearing caps so that you get them back on the same
side as they came off of. I used a punch and put one mark on one cap and a
matching mark and that side of the housing. And then punched two marks on
the other cap and the other side of the housing.
2. Remove the bolt that holds the cross pin in and then pull out the
cross pin. This will let you push the axles in so that you can get the
3. Remove the axles, unbolt the caps and drop out the carrier (be
careful, its kind of heavy). Keep track of what shims are on each side (it
will change, but its nice to know in case you want to put your old gears
back in sometime).
4. Drop the driveshaft and remove the pinion nut and yoke. This will
let the pinion come out the back side.
5. Drive out the two pinion bearing races (this is best done with the
body of the car on jack stands so that the rear end is dropped as low as it
can go). The seal will come out with the front race. Wash out the housing,
and drive in the new races. Be careful not to raise any burrs anywhere.
6. Take your old pinion gear and have the rear bearing pressed off. Save
the shims under it. Take those shims and put them on the new gear and have
a new bearing pressed on. Don't reuse the old bearing. It will most likely be
damaged by removing it.
7. Slide a NEW crush sleeve on the pinion and slide it in the housing.
Slide on the front bearing, drive in the seal, and put on the yoke and nut.
Don't torque the nut yet.
8. Unbolt the old ring gear (the carrier has left handed threads for the
ring gear bolts). Look at the carrier and the new ring gear for any burrs
that won't let the ring gear seat flat on the carrier and file them off if
there are any. Put on the gear and torque the bolts to what ever the
instructions recommend. You might use some Loctite on these bolts, but
I've never had any trouble with them backing out.
9. Put the carrier back in the housing and take a guess at the side
shims (I'd start with the stock shims on each side if you can get them in
like that). Put the caps back on and torque them down. Put your
dial-indicator so that it reads perpendicular to a ring gear tooth. You
are shooting for about .008" back lash. Just rock the ring gear back and
forth and measure the amount of slop (technical term!). If the backlash is
too much, move the ring gear closer to the pinion by adjusting the side
shims or vice versa. Do this until the backlash in at whatever the gear
10. Snug up the pinion nut and using an inch-pound torque wrench,
measure the amount of torque required to rotate the gears and carrier.
Your gear instructions should give you a value to shoot for. Torque the pinion
nut until you reach this torque value. You can probably borrow the
inch-pound torque wrench from a local mechanic since you won't have much
need for one any other time.
11. Put some white grease on the ring gear and rotate the pinion in
the proper direction (so that the car would be going forward). Look at the
pattern left in the grease. It should be centered on the ring gear tooth.
Again, your instructions should give you some good info on what your looking for here.
12. If everything looks good, slide your axles back in, put in the
c-clips, slide in the cross pin (making sure the side gears are in
properly) and install the bolt that holds the cross pin in.
13. Now you're ready to button everything back up and fill it with GM lube
(the only stuff to use in my opinion and if you add a posi carrier use the
14. Follow the gear manufacturer's break-in procedure.
15. Lay rubber!!
You will need to find some way of keeping the pinion from rotating while
loosening and torqueing the pinion nut. I found an old body spoon (I guess
that's what it is!) that I wedged between two bolts in the yoke and let the
other end rest on the floor.
I was able to borrow a wide assortment of shims from the local GM
dealership and then I just had to pay for what I used when I brought the
box of shims back. I think they charged be 50 cents per shim.
I didn't put new bearings or races on the sides of the carrier, but if you
do, don't put a new bearing on an old race.
If you buy a posi carrier, make sure it matches whatever gear you'll be
using. I have a posi unit from a Camaro with 2.41 stock gears, so I had to
add a ring gear spacer to use the 3.70 gears. It hasn't been a problem
yet, but I'd rather not have the spacer.
It's really not that big a job once you know that the trick is to start with
the stock shims under the pinion bearing. The side shims are easy to
change, but the ones under the pinion bearing are a pain in the butt. If
everything goes well, you should have a quiet setup and the car will feel
like it's picked up 100 hp!
I was heading toward the stock shim on the stock pinion, but that's where it
wound up at and later on I read an article saying to start with the stock shim
because it would be right almost all the time.
I wish I had read that article before I tore down the rear-end 7 times!
I bought the Ratech install kit, but it's basically just a few shims, a seal and a
crush sleeve. You could probably buy them individually as cheap or cheaper.
I'd check on finding a shim deal like I have here with the GM dealership.
You can re-use your front bearing and race if they are in good shape. This
bearing is a very light press fit and won't be damaged by removing the
pinion from it. It will stay in place along with the front race as long as
the front seal is in place. The problem is whether you can get the rear
race driven out with the front race in place. I guess you could remove the
front seal, take out the front bearing, drive out the front race, drive out
the rear race, drive back in both races, put the front bearing back in, and
install the new front seal. By the way, you will need something to beat on
while you drive out the pinion gear so that you don't screw up the snout of
the pinion gear. I had an extra pinion nut that I used and its beat all to
hell, so be careful.
So basically you'd need side shims, new front seal, crush sleeve, gear lube
and posi-additive. The Ratech kit doesn't come with much of a selection of shims,
so you'd probably be money ahead to buy all the stuff separately unless the kit
is really cheap and that's all it comes with. I can't remember exactly what came
in my kit.
So I guess I'd check the prices on the stuff and compare that to the kit price.
The carrier bearings are pressed onto the carrier and will be replaced when
you put in the posi unit. I'd spin the with my fingers in the axle holes
and feel for any roughness and wiggle them to feel for excess play. I
think carrier bearings last quite a long time. Usually it's your pinion
bearings that start whining since they see a more of a cyclic loading.
Oh, one more hint. The ring gear has left handed threads.
If you've got access to an impact wrench, things will go much easier for
you. The pinion nut is self locking and the ring gear bolts are torqued
pretty tight and it's hard to keep from turning the whole thing with a wrench.
As for measuring back lash, the dial indicator will generally be pointing
toward the front of the car. You will rock the ring gear back and forth
and measure how much it will move from one extreme to the other. You are
shooting for .008". You need to get the dial indicator positioned as close
to perpendicular to the face of the gear (where the pinion gear teeth contact)
as possible. Is this a better explanation?
As for the shims, its kind of a shooting match. Who knows what you'll
need. The stock side shims are a good place to start, but you'll probably
need a wide assortment in order to get .008" backlash. Did you check with
the any of the local dealerships to see if they have a shim assortment to
borrow and bring back what you don't use? If not, you'll probably need to
order a shim assortment from Summit or Jeg's, I guess.
The GM posi additive is a small bottle. Put one bottle worth in the case
first and then fill the rest of the way with genuine GM lube. The genuine
GM stuff is the only stuff that will go in my rear-end so I highly recommend
it to you. You won't need to add any until you change the lube again,
unless your seals leaks a bunch and you are adding lube all the time.
Basically if the posi grabs in a slow tight corner, you need more additive.
Here's a tip on getting the bearing race out. Use a long punch and the biggest
hammer you can swing with one hand. There's not very much room to swing it,
so you need as much mass as you can get. You won't need to disturb the front bearing
race to drive out the big race. I wasn't sure until I took my rear apart, but it's
not a problem. I didn't even have to take out the front seal.
The 6-8 in-lbs. (sounds about right for used bearings) is measured while
turning the pinion gear with the carrier and ring gear in the housing.
Just try to turn the torque wrench at a steady pace so you aren't
accelerating or decelerating it. It takes a lot more torque than that to
tighten down the pinion nut. Its hard to do without an impact wrench.
But you have to sneak up on it so that you don't over compress the crush sleeve.
The best way I've found of torquing the pinion nut (except for an impact) is to
bolt in a very strong shaft into one of the u-joint saddles using the u-joint strap
and then torqueing the pinion nut with a strong ratchet and a floor jack.
A long cheater bar will just flex.
Just a final note, the crush sleeve is kind of hard to find unless you happen to
know that a '88 (and probably many other years) Chevy pickup with the 8.5" 10-bolt
uses the same crush sleeve as a 8.5 10-bolt that are in most of our beloved 70's Chevys.
Your local GM dealership will have one.