View Full Version : Acceptable spider gear play in diff?

09-20-2011, 09:57 AM
Attached are photos of my 1980 FJ40 rear diff. I'm trying to find/eliminate a shake at 55-60 mph, and popped the cover off the diff to be sure that all was well. The ring/pinion look great. But, notice the gap between the sleeve and the spider gears.

The FSM makes no mention of spider gear tolerance (runout) - it just says 'inspect spider gears and shims for wear' - it doesn't say 'use xx shims on each side to attain zz clearance".

On a stock, non-locker equipped rear end, how much slop should there be? I can move either spider gear in and out a bit more than 1/8". This seems excessive. The face of the spider gear in the other photo shows pitting, but this (from what I understand) is pretty normal. The magnetic drain plug had a small quantity of fine steel fuzz on it - no chunks. Truck has 100K miles.

I'm having the driveshaft tested today for balance, but this spider gear issue sorta side-tracked me from my vibration issue.


09-20-2011, 11:59 AM
15 views and no replies. I'm going to go out on a limb and say you're fine ;)

09-20-2011, 12:07 PM

page 24 covers the thrust washer clearance for the opposite side.

09-20-2011, 01:15 PM
Thanks! The wear pattern on the side gears (not sure if that's the correct term) looks pretty well centered. I only noticed that later, after viewing the photo. I'm referring to the gear circled in the photo attached.

Mike - thanks for the link - I found many 'lunchtime locker' write-ups last night, but none that included the measurements.

09-20-2011, 01:19 PM
Yeah you gotta realize that the only time those gears are turning is when there is a difference in speed in the two tires. So headed down the hwy, they are not moving really fast if at all really. They don't have to even be that healthy to do that job either.

I personally wouldn't worry about it unless you plan on doing lots of one wheel spinning action (like one wheel stuck in the mud while one has traction) on purpose. I don't think they look too dang bad.

Some other folks may have other opinions though.

Air Randy
09-21-2011, 04:01 PM
I don't see anything with the clearance or tooth patterns that would say you have a problem. For sure nothing that would cause a vibration at high speed.

Have you modified your suspension height or done anything else that would have changed the driveshaft angle in relation to both the pinion yoke and the TC output yoke?

09-21-2011, 04:12 PM
Steve, what did the driveshaft folks say?

09-21-2011, 04:17 PM
I had the shaft balanced yesterday ($50) and they said that it was significantly out of balance. I noticed two 1" dia. circular weights welded to it. They said that many Toyota (and for that matter, domestic) drive shafts are not well balanced from the factory. They agreed that the u-joints and spline were in good shape and not an issue.

I'm waiting on a new diff cover gasket from the dealer, which I will get today. I hope to put it all back together tonight and test-drive it. I'll be sure to update.

09-22-2011, 09:39 AM
In a fit of early-morning productivity, I got up at 5:30 this morning, cleaned the diff face and cover, installed a new cork Toyota gasket with FIP, filled the diff, and installed the drive shaft. I could already tell the balance/smoothness difference at 35-45 mph in my neighborhood. My morning commute includes I-25, and I hit 65 before I realized it. I still feel a faint shake between 55 and 60, but it probably is either a natural harmonic or tire balance. This shake is barely noticeable and is perhaps 5-10% of what I had before.

So, the balanced driveshaft made a HUGE difference, and I suspect I will have this done to my other FJ40, too, which has never been too smooth at 60+, either. The driveshaft shop guy said that he sees quite a few Toyotas (of every era) with out-of-balance shafts (but then I mentioned Chevys, and he really teed off on those!) This FJ40 shaft had no weights welded to it anywhere, which should make anyone suspicious.

Thanks for all your comments/suggestions.

09-22-2011, 09:49 AM


That's gotta feel good!

09-22-2011, 10:00 AM
I'm mostly thrilled that it's not some evil internal xfer case issue or diff problem. It feels so good that I want to remove all the drive shafts from all my trucks and have them balanced!

10-10-2011, 12:03 PM
Just saw this thread (still catching up) and wanted to chime in that the space noted in the photo is normal and a non-issue. Those spiders are driven outward and the spacer in the middle is only to keep the axles ends in their proper place. The thrust washers on the outside of the spiders are just for a bearing surface and don't matter much how thick or thin they are, very different story than the side gear thrust washers which position the c clips and axles.

10-10-2011, 06:41 PM
Thanks Jeff!