Diff shimming Walkthru with pics and step by step.

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Diff shimming Walkthru with pics and step by step.

Post by SLAYERDUDE » Mon Jan 16, 2012 1:37 am

This is how I shimmed out my Savage XL diffs, but it should be very similar for any Savage.
This should also work on just about any other diff, there are other places to use shims on different vehicles to get the same result.
Some vehicles you would install shims behind the outer race of the bearings, between the pinion and bearing, etc..

If you have the 2 spider gear setup you should install this while you are in there- http://www.hpiracing.com/products/en/87193/

If you have the plastic diff I would get one of these as well-

I got the XL new and it came with shims in a bag.
Z892 is the HPI PN# for the diff shims.
So if you got it used or didn't come with the shims there is the PN# and a link.
http://www3.towerhobbies.com/cgi-bin/WT ... EARCH=z892

First take off the plastic clips that hold the bumper bars in the bulkhead.
I have a pair of needlenose pliers between the 2 shocks to pull the clips.

Clip removed.

Pull the bumper out of the holes.

Next remove the 2 screws on the bottom that are closest to the bumper.
These screws go into the diff case as well.

Now you can access the front screws in the diff case.
2 above the upper hinge pins.
And 2 below the alum brace that the upper hinge pins go thru.
If you are doing the rear - the turnbuckles need to be removed first.
I have a worn one and just put a washer to hold the plastic end on.

Order some turnbuckle ends. P/N # 85050 - comes with 4 on a tree and a whole bunch of other parts for $6
The turnbuckle ends WILL stretch out after a good crash or cartwheels!!!
This is a weak link and I like it that way.

Here's the turnbuckle ball end with the washer to hold on the worn end (arrow)
And the diff shims that should have come in the parts bags with the truck. (circle)
Diff case screw locations.
Case removed
Red arrows are 4 screws that hold the diff case in. (Besides the 2 on the bottom.) 6 screws total.
Green arrows are the hinge pin holes.

Diff without case half.
To pull the diff out you will need to get the dogbones out.
2 options.

1 Remove more suspention parts to take dogbones out.

2 Wiggle it...just a little bit.
Get the diff pulled out partially and let the suspention hang.
You should be able to push the dogbone into the wheel area just enough to slip the dogbone out of the diff cup.
It's not easy, but it will come out this way.
Or you can remove the upper hinge pins and the upper A-arm will give more room.

Diff and dogbones out.
Diff cleaned and Z164 30K heavy diff grease.

Next you need to remove the 4 screws in the back of the 43 tooth ring gear. (bevel gear)
Photo shown is with just 2 screws holding it together just for shimming.
This is best done by holding the diff on the table.
Down flat on the cup so you can push straight down towards the table with the screwdriver.
The screws are loctited in and take some effort to remove.
Be careful not to strip the screws.
I had to push down hard to keep from stripping the heads.

Now remove the spider gears after separating the diff from the ring gear.

Spider gears removed.
Keep them together until you clean and reassemble.
Now you can remove the diff shafts.
There is a pin going thru each of the shafts holding them in the ring, and the other in the cup.
Remove the # 87193 gears from the shafts.
Then remove the pins and the shafts will slide out.
I use needlenose in the diff cup to get the pin out of the shaft and to reinstall.
(No room for man hands in there)

Now I discard the paper gasket and clean the parts.
(I had no replacement gasket, so I just put a thin film of RTV on the cleaned diff cup before final attatchment of the ring gear)
Not using the gasket may lose some tolerance, but does not seem to be an issue.

There is a large washer that the retaining pins ride against from the last step.

Washer shown with pin and diff shaft.
(washers will be stuck to the insides with grease you will see them when you clean out the inside of diff)

Keep track of these and all other parts and put the 2 sides apart from each other.
This way they will go back in the same spot and keep the same wear pattern.

Now put the ring gear onto the empty diff cup and put 2 screws opposite each other and tighten it up..

Next set the empty diff back in the truck and check the play.
Hold the driveshaft under the truck at the pinion on the backside of the diff.
Check the play by holding the pinion still and wiggle (rotate up and down, not side to side) the ring gear to see if there's slop between the gears.
There probably is.
Now take the diff back out and take the bearing off of the ring gear side and install another shim.

Shims located between the bearing and diff. (red arrow)
(More shims on the gear side will bring the ring and pinion closer together.)
There should already be 1 shim from the factory on each side of the diff.
The manual shows on page 32 2 shims on each side, I tried that and it didn't feel right. Also, it doesen't come that way so....
Put the bearing back on.
Now that you have 2 shims on the ring gear side and 1 shim on the other side.
You can put the diff back in and check the play.
It should be minimal, if any.
A hair of play between the gears is okay, too tight and possible binding is not.
On full size diffs there is a "gear lash" spec that you measure with a dial indicator.
All the 1/1 diffs I have worked on had a hair of play. (not tight or no play)
The grease between the gears gives some "cushion" and takes up the minor slack and promotes lubrication between the ring and pinion.
If it's not right, you will have to keep changing the number of shims on each side to get the desired play.

Both my diffs shimmed the same.
2 shims on the ring gear side and 1 shim on the other side.

Don't forget to loctite the 4 screws on the ring gear.

You will need grease to put back in.
So if you don't have any, check the LHS and they should have something.
The Z164 grease is 30,000 weight.
I still use this on the ring and pinion.
I have changed the grease in the diff where the spider gears are sealed in.
What I used is something I had on hand.
Thick automotive clear silicone brake caliper lube.
The thicker the grease or fluid you use the less "give" there is between the wheels on that axle.

You can use whatever you want to try, but HPI recomends the 30K #Z164.



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