R180 differential runout questions

[djwarner]

I posted this on the ClassicZcarClub forum but I think I will get some additional input by posting it here.

 

My R180 has 180K miles on it and has the developed the usual whine between 45-55 mph that changes pitch between driving and coasting.

The manual says this is an indication of excessive runout between the pinion gear and drive gear. I have previously replaced the wheel bearings all round and have been impressed with the change in ride.

When I first got the vehicle 18 months ago, the side seals showed evidence of leakage and one half shaft was installed backwards. After the mechanics replaced the forward differential mount, side seals and re-installed the half shafts, I noticed a clunk when shifting from driving to coasting and vice versa. The u-joints were okay but there was a noticeable amount of free play (read runout) in the differential.

After my success with the wheel bearings and I have read through the FSM several times in anticipation of replacing the bearing in the differential. I have learned several things:

A. It appears that the shims on the pinion shaft serve to establish preload on the pinion bearings and to establish the correct height of the pinion gear to the side shafts. The preload is required to minimize the axial movement of the pinion shaft. The correction to the height is needed due to variation in the various machined dimensions of both the pinion shaft and housing.

B. The left/right position of the differential case assembly is established by shims installed under the side bearing retainers. These shims establish the preload of the side bearings and the clearance between the drive gear and pinion gear. The variation in clearance of the drive gear and pinion gear determines its runout. These shims come in various thicknesses from 0.2mm to 0.5mm. Again these shims account for variations in machined dimensions including bearing heights. The various machine dimensions are stamped on the parts to determined which shims are to be used.

C. The shims in A. correct heel or toe contact errors in between the pinion gear and drive gear.

D. The shims in B. establish the clearance between the pinion gear and drive gear. This is a major contributor to runout.

E. Page PD-8 of the FSM manual says to inspect the pinion and drive gears for surface defects and runout in excess of 0.08mm and to replace the pinion and drive gears as a set if needed.

F. Pages PD-12-13 describe checkout after re-assembly and specify drive gear/ pinion gear runout of 0.1mm to 0.2mm - This is greater than the allowed runout in E. ?!?

G. Correction for excessive runout or improper preload under F. is to adjust the shim thicknesses under B. by trial and error. The side bearing preload value is less on re-used bearings to account for wear and may require adjusting shim thickenesses.

The various shims are sold in sets of 10 - if you can find them. The pinion/drive gear matched sets are rare and can cost more the a used differential. The side bearings are relatively cheap. Pinion bearings are expensive.

Considering the above, I have the following questions:

1. If the pinion gear preload is acceptable and no axial runout found, would you consider changing the side bearings only?
2. Since one half shaft was installed backwards, what are the odds that the left and right side bearing retainers and or shims were inadvertently swapped resulting in a shift in the differential carrier assembly and an excessive runout?
3. Assuming bearing heights should be pretty consistent, would you consider changing bearings and re-using the same shims?
4. Has anyone replaced bearings without swapping the pinion/drive gear set and what was the result?

I am also open to the opinions of our more experienced members.

 

 

 

[JMortensen]

Re the clunk: http://forums.hybridz.org/topic/105207-the-dreaded-diff-clunk/

 

"Runout" is usually a problem when the carrier or the ring gear isn't true. If runout were a problem, I'd think you'd have a womp-womp-womp noise, not a whine, because the ring gear would get closer and farther away from the pinion. Runout in the pinion would be if the head of it was bent and I think that would be quite a bit less likely to find. A runout issue is also not something that is likely to happen after years of driving quietly. Runout is an assembly or machining error IME.

 

I could see if the bearings are really worn how the backlash could change, but in my mind that isn't runout, it's slop in the bearing. 

 

With respect to your questions:

1. Yes. You can change carrier bearings without messing with the pinion bearings.

2. Next to nil, and unless the carrier shims are within a couple thousandths, this would have caused major problems a long time ago.

3. Yes. Shims shouldn't change if you use the same bearings, because the new bearings should be the same size as the old ones.

4. I changed the bearings an an R200, the result was that my wallet was $500 lighter and I didn't gain anything from it, but I somehow convinced myself that I needed to change them since the diff came out of a junkyard.

 

I would suggest that you buy another used diff in good condition. It will be a lot cheaper than rebuilding the one you have. If you want to change bearings, I'd suggest you pull the thing apart and just look at the bearings and races and change the ones that have scored or pitted bearings or races. I think the likely cause of your problem is pinion bearings.

 

Here is another resource for noises:

http://www.ringpinion.com/TechnicalHelp/ContentFrame.aspx?FilePath=~%2fContent%2fHowTo%2fGeneralInfo%2f%2fDiagnosing_Noise_(Part_1).inc

 

http://www.ringpinion.com/TechnicalHelp/ContentFrame.aspx?FilePath=~%2fContent%2fHowTo%2fGeneralInfo%2f%2fDiagnosing_Noise_(Part_2).inc

[djwarner]

Thanks for the input, John. Your description of runout occurs when the axis of the drive gear is out of square with the axis of the side bearings. This is one type of runout. Another type of runout is radial runout where the axis of the drive gear is parallel to the axis of the side bearings but not coincident.  Radial runout presents itself as the drive gear running eccentric.

 

The runout I'm referring to is described in the FSM is when the pinion gear teeth are not fully engaging the teeth of the drive gear because the drive gear is offset from its desired position. Because the flanks of the teeth are not flat, this allows excessive freeplay when shifting from the drive side of the teeth to the coast side.

 

Besides scarcity of used 3.54 R180's, after 40 years, just how many used "serviceable" R180's are you apt to find? My suspicions of improper maintenance are based on the fact since getting the Z, for every item I've worked on that was worn or broken, I've found at least one item that suffered from a mechanic's hand.

Edited March 26, 2014 by djwarner

[NewZed]

This is one type of runout. Another type of runout is radial runout where the axis of the drive gear is parallel to the axis of the side bearings but not coincident.  Radial runout presents itself as the drive gear running eccentric.

 

Wouldn't this show in the wear pattern of the teeth?  If not worn in already, it should show up on the bench with some marking and turning.  No measurement tools needed except a good eye.

[JMortensen]

Thanks for the input, John. Your description of runout occurs when the axis of the drive gear is out of square with the axis of the side bearings. This is one type of runout. Another type of runout is radial runout where the axis of the drive gear is parallel to the axis of the side bearings but not coincident.  Radial runout presents itself as the drive gear running eccentric.

 

The runout I'm referring to is described in the FSM is when the pinion gear teeth are not fully engaging the teeth of the drive gear because the drive gear is offset from its desired position. Because the flanks of the teeth are not flat, this allows excessive freeplay when shifting from the drive side of the teeth to the coast side.

Sounds like you're referring to bearing slop, and the pinion pushing the ring gear away as you accelerate. I guess they're calling that runout, but I think you'd have a hard time measuring it unless you put a prybar in there and pried one way and then the other and measured.

 

I know you can get a late model Subaru R180 with 3.54s, you'd have to switch over to the screw in buttons as described in the big diff FAQ post. I would think that since the 3.54s came in the automatics they'd be the less heavily used option, and I'd definitely take a shot on a $50 diff to see if that fixed it before going through all the hassles and expense of replacing bearings. 

Edited March 26, 2014 by JMortensen

[NewZed]

The 3.54 R180 was used up to 1983, at least.  Copied the 1983 specs. from the FSM.  Only 31 years old!  I see them around occasionally in the wrecking yards.  They cost about $90 around here.

[djwarner]

I tried to use the nomenclature in the FSM. They show measuring the free play by mounting a magnetic base on the rear of the case and applying a drop indicator to the flank of a tooth on the drive gear.

 

They indicate the side bearings have a preload that reduces as the bearings wear in. I suspect the side bearings have worn excessively because the differential is relatively quiet until it comes up to operating temperature. I figure there is some preload left but since the outer case is larger than the differential carrier it has more thermal expansion that releases the preload as it warms up. 

[m1ghtymaxXx]

I won't comment on the symptoms, but as far as replacing the carrier bearings, it's pretty straightforward. I put the carrier in the freezer warmed the bearing in the oven to 200 degrees F. One side literally dropped into place, the other required a slight bit of coaxing with a hammer and appropriately sized socket. I replaced mine as I was installing a chinese LSD so a re-shimming was necessary. Since I don't own a dial gauge or collection of shims I paid a driveline shop $150 to shim, check backlash and wipe pattern.