7 replies to this topic

[Sphinx]

Was putting in a spare transmission when I noticed that the shim behind the transmission front cover is destroyed. Any guess what caught what would cause this? Or does this indicate a bigger problem with the transmission?

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[davew]

This trans has been apart before and the rebuilder did not get the shim properly positioned when he installed the front cover. No big deal. If you have a new shim laying around put it in with a small dab of silicone to secure it to the front cover. 

 

Dave

[FTodaro]

This trans has been apart before and the rebuilder did not get the shim properly positioned when he installed the front cover. No big deal. If you have a new shim laying around put it in with a small dab of silicone to secure it to the front cover. 

 

Dave

I have seen stock transmissions come with destroyed shim. not often but have seen it.

[RWP80000]

As for cause I would surmise the input shaft outer bearing race (which this shim presses against) turned in the bearing bore.  This in turn resulted in shim turning as well, which when it encountered the unsupported portion of the front bearing retainer casting proceeded to separated from the face of the outer bearing race, catching on the leading edge of the unsupported area resulting in the "accordion" portion of the shim and resultant shim fracture.  As to what precipitated all of this would probably be either the input shaft bearing binding (contamination?) or excessive housing bearing bore clearance. 

[Sphinx]

I have seen stock transmissions come with destroyed shim. not often but have seen it.

 

From a bunch of pots on miata.net, that may very well be the case, including mine.  Mine is a junkyard trans that I got a few years ago.  Haven't needed to use it till recently.

 

When you guys replace the front seal, do you put any rtv around the paper gasket or the front seal?

[RWP80000]

"When you guys replace the front seal, do you put any rtv around the paper gasket or the front seal?"

 

The front seal doesn't need anything applied to it when installing but I do like to smear a thin film of RTV on the paper gasket.  The main thing to seal is the threads of the front bearing retainer bolts as the trans oil will wick through the threads if sealant isn't used.  Interestingly, the Mazda service manual recommends applying grease to the front bearing retainer just behind the newly installed seal.  Not quite sure what the purpose of doing this is as nothing would be in contact with the front bearing retainer in this area.  If they wanted you to lube the seal lip, they could have just said that.  It almost seams like they are trying to stop some oil leakage with a grease dam. 

[FTodaro]

I use a dab of RTV on the gasket to hold it in place. I use thread sealant, on the bolts so they do not leak. Those shims come in different thicknesses, there is quite a bit of play forward and aft on the input shaft, a thicker shim will do the trick.

[SaulSpeedwell]

I have seen stock transmissions come with destroyed shim. not often but have seen it.

+1 ... and crate transmissions, too!