|Author: Jay Kopycinski July 2001||
In the early truck years, Toyota used a cast iron (solid) spacer between the front and rear pinion bearings in the axle third member. In later years, Toyota switched to using a mild steel crush sleeve that is collapsed during the pinion setup to adjust the pinion bearing preload. This was supposedly done to facilitate faster assembly line times without sacrificing longevity or reliability of the third member.
A number of people have claimed that the crush sleeve style assembly is much weaker and prone to damage during any severe impact with a rock or other hard object. But.....I've yet to see any careful explanation as to the possible difference between a crush sleeve and solid spacer. I have only heard observation and some loose speculation as to the vulnerability of the crush sleeve.
Here I will look a little deeper into the differences and hopefully state some theories based on logic and reasonable mechanical intuition.
|Toyota Pinion Assembly|
First, let's take a quick look at how a typical Toyota pinion assembly stacks up. The assembly consists of the pinion itself, pinion shim(s), rear tapered roller bearing and race, a crush sleeve or spacer, front roller bearing and race, driveshaft flange, flange washer and pinion nut. There is also a pinion seal and oil slinger washer, but these are not significant to our strength discussion here.
For a more detailed look on how to assemble and setup Toyota gears
Toyota Gear Swap Tech
If I have an assembly with the third member housing, races, bearings, flange nut, etc. all clamped together.....what does the crush sleeve do for the assembly after the preload has been set?
As far as I can see.....nothing.
With the whole assembly clamped tight, the only "play" left should be that which is produced by bearing wear over time. This should be very little. Any such play due to bearing wear will be present whether a crush sleeve or solid spacer was used in the assembly.
Now, suppose the third member flange gets banged on a rock. Theoretically, the crush sleeve could crush further by the amount of freeplay now in the bearings and any "flex" in the whole assembly. So, now the crush sleeve is loose in the assembly. Does it really matter?
I don't think so because after any third member has been run for more than a few hundred miles, bearings will break in and preload will basically drop to zero. There is no need for anything to maintain a bearing preload within the assembly. The slight snugness initially imparted to the pinion nut is now gone, but IF it has been properly staked in place, all should be fine and the nut should not loosen.
I have heard of cases where pinion assemblies have developed play in them, but the pinion nut has not moved from its staked position. This could very well be due to the pinion bearing races not being fully seated within the housing during assembly. The races usually fit tightly and it is important to insure they are completely seated or the pinion stack will loosen over time.
If a pinion nut is not properly staked, it can loosen and cause all sorts of problems, including allowing the pinion to shift inward toward the differential carrier assembly. If looseness progresses, the pinion could contact the carrier and produce gear tooth marks on it.
Pinion setup is commonly misunderstood, and the idea of a "crush" sleeve is perceived as a weak link in the assembly. I have heard so many people talk about "banging it on a rock and crushing it more" but this does not make much sense to me. I have yet to hear anyone present a solid chain of facts to substantiate their claims that the crush sleeve setup is flawed.
I prefer to use factory Toyota crush sleeves that appear seamless and are about 0.078" thick. I do not like the welded seam aftermarket ones and have seen them as thin as about 0.050" thick.
One advantage to using a solid spacer is that it makes pinion seal replacement easier. Just remove the nut, flange, etc., then reinstall and retorque to spec and you're done. However, you can also replace a pinion seal on a third member with a crush sleeve if you simply return the nut to its original position. You won't be able to reliably restake the nut in the notch, but you can always tack weld the nut to the pinion end. I think tack welding is the best all around staking method anyway.
|Solid Spacer Reliability|
Now let me attempt to highlight some ideas on why the solid spacer may be more reliable. Marlin Czajkowski and I had a little chat recently and I brought up this subject wanting his insight on the technical aspect. He too agreed that once the crush sleeve has been used to set preload, it serves no further purpose and later "crushing it further" by some means would have no effect on the pinion setup or reliability.
However, he did mention that he feels that there is a very slight rocking in the bearing assembly once the preload drops to zero after break-in. Having the pinion, bearings, and the complete stack as firm as possible may provide better stability in the assembly. (I know this is hard to explain.) He feels that over time, as the assembly gains a little play, that having the solid spacer helps with the alignment of all the parts and provides some increase in reliability. He does prefer to install solid spacers on hard core third members, but says they are a bit more difficult to do and take more time to install.
Also, the pinion nut should not back off AT ALL if it is properly staked, AND even if the crush sleeve were to somehow crush further the assembly stack should not experience increased play as a result.
Marlin did mention where he thinks increased play in the assembly comes from. He mentioned that the pinion flange is relatively softer than all the other pieces in the assembly stack. He feels that over time (and beating on rocks) that the forces on the flange displace the metal and basically mushroom it out, causing the axial dimension under the pinion nut to decrease. THIS would cause play in the assembly, even without the pinion nut moving. Theoretically, this could grow enough to allow the pinion pattern to move around and cause gear wear problems.
If you have other thoughts or ideas contrary to what I have presented here, please email me.
Thanks for reading!
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