Rear Diff Pinion Shaft Spacer 0 Clearance Question (1 Viewer)

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

Joined
Mar 30, 2015
Threads
29
Messages
242
Location
Pennsylvania
Hello, my pinon is spacer 29.8" and fits perfectly with no discernable space on either side. Unable to fit the minimum fuelers gauge .0024" on either side. I can remove it with my fingers and a dental pick so it does not appear to be binding anything. Is it ok to leave this way? The FSM min standard .060mm/.0024" seems very thin. I have a fuelers gauge at .002 and it's paper thin but im unable to insert it between the spacer on either side. So, I'm wondering if it really matters that mine is touching or could I get it milled. Also, is the FSM min standard measurement .060mm/.0024" just for one side? Or is it .060mm/.0024" for each side or axel end?
Just curious if less is better in this case and I shouldn't worry about it.
Lastly, does it hurt the temper of the steel to mill it again?
Thanks,
Dave
IMG-3711.jpg
 
Last edited:
A couple of things: first please either state what you're working on in the subject line or first line of your posts, or (better still) put a description of your model, year and any non-OEM stats in your sig line. It really helps everyone reading your posts help you.

I assume this is a 1977 FJ40 with the standard semi float 4.11 rear end (from your other posts). Short answer: yes, the minimum clearance stated is per side.

So the way the spacer works is to set the distance between the side (aka differential) gears by moving the pinion (aka spider) gears closer together or farther apart. There has to be clearance between the ends of the driveshafts and the pinion spacer. The amount of clearance is determined largely by the tolerance stackup between all the parts (carrier housing, driveshaft flange-to-C-lip groove distance, etc); strictly from the differential perspective, it doesn't really matter what it is, as long as it's there, the shaft ends won't wear against the spacer body.

However, from a fit-up perspective, it does matter, and that's why there's a tolerance for the spacer length. If it's too long, the gears won't mesh when you clip the side gears onto the driveshafts, and if it's too short, the spider gears won't have any support. I doubt it's hard; if you need it shorter, cut it. Even if it was hard, cut it cool and it'll be OK.

The best way to find out what length you need is to assemble the differential without the spacer, but with the C-clips on the driveshafts. Pull the spiders together, as best you can, and measure the distance between the faces. A snap gauge is ideal for this.

Unless someone has been in there swapping out parts, you should have the correct length; as I said, it's set by the dimensions of all the parts bolted together from the hub to the diff centerline.

The image below is from the 1980 Chassis and Body manual (36044E) (but the dimensions and procedure are the same for the 1977 model year; I checked them against my paper copy):
1669676678449.png
 
Last edited:
I should also note that is is important that you not use the thrust washers to get the thrust clearance. The thrust washers are used to set the gear backlash between the side gears and the single pinion gear (the one that's meshes with the ring gear). Once that backlash is set, then, and only then, do you worry about the spider gear clearance.

1669679225656.png
 
Purely for the sake of idle curiosity, what's the goal you're trying to achieve? Why did you open the diff?
 
Keep in mind various thickness c-clips are also an option to get the cross-shaft spacer to axle shaft thrust clearance within spec.
 
^^^^^^this^^^^^^^ is a good option along with possibly thinner side gear washers. I think they offer spider thrust washers in different thicknesses too. This whole scenario seems odd to me. I've never seen the axle to be so tight against the center block. There's usually quite a bit of movement between the spiders and the case and the center block. Are all these parts, side gears, thrust washers and spiders original to the diff case?
 
^^^^^^this^^^^^^^ is a good option along with possibly thinner side gear washers. I think they offer spider thrust washers in different thicknesses too. This whole scenario seems odd to me. I've never seen the axle to be so tight against the center block. There's usually quite a bit of movement between the spiders and the case and the center block. Are all these parts, side gears, thrust washers and spiders original to the diff case?

The do, we (Cruiser Outfitters) stock them in a variety of thicknesses:

1669684335244.png


We also stock a c-clip assortment pack, part# RACLIPKIT
 
^^^^^^this^^^^^^^ is a good option along with possibly thinner side gear washers. I think they offer spider thrust washers in different thicknesses too. This whole scenario seems odd to me. I've never seen the axle to be so tight against the center block. There's usually quite a bit of movement between the spiders and the case and the center block. Are all these parts, side gears, thrust washers and spiders original to the diff case?
You can't do this, for the reason I stated above. The thrust washers set the backlash, not the clearance between the shaft ends and the spider gear spacers.

If you change teh thrust washers thickness, you change the backlash, too.
 
Thanks for all who have provided input. This is an fj40 79/2. Semi float rear differential. Swapped out the OEM that PO blew up. Bought this one off mudd and the only thing I used from my old diff was the spacer. Keep in mind when that the minimum standard distance is .0024” that is very thin. We know what happens when the spacer is too loose. And the axel shaft ends slam back and forth into the spacer and c clip. Prob will get the machine shop to mill .0012 off each side.
 
Keep in mind various thickness c-clips are also an option to get the cross-shaft spacer to axle shaft thrust clearance within spec.
Various thickness c clips. I will measure mine tonight. What sizes?If I can make up the distance with c clips , I may just try that instead of milling
 
Malleus, the thrust washers behind the spider gears have nothing to do with pinion to ring backlash.
Yes there are different thickness C clips, If that center block slides in and out I'd run it.
 

Users who are viewing this thread

Back
Top Bottom