What is causing this gear damage?

[98gst14b]

Upon my yearly inspection of my transmission I found that my int shaft was doing this. Everything else in the trans looks great, aside from a bunch of silver oil, clearly this is where its comming from, any ideas?

 

[twicks69]

What specific gear oil is being used?? It looks like the gear tooth is getting polished and the gear is fretting. You likely do not have the proper amount of preload on the bearings and you are using a gear oil that is not protecting the gears good enough.

Disassemble the gear clusters and deburr the gears and shafts. Inspect and replace the shaft bearings and reshim the transmission for more preload on the input shaft, intermediate shaft and output shaft (fwd) /center diff (AWD).

 

[98gst14b]

Redline mt-90 would fretting be from a loose preload causing the cluster to jar over and contact the gears at an angle? That was my take. Thanks for your reply .

 

[twicks69]

Well, yes, but look closely at the gear face itself; the opposing gear is leaving impact impressions on the gear face. Your gear oil is not protecting the way it should be IF your bearing preloads are tight. If the bearing preloads are loose or you have endplay on the bearings, you are not helping anything, nor is MT90 going to protect from floppy shafts. Either way, the gear teeth faces are literally getting polished and getting scarred. Replace your bearings, and either replace the gears or debur/detail/shotpeen them to help them last a bit longer before they fail. Either way, you are looking at potential failure in the near future if you just throw it back together like it is currently.

 

[98gst14b]

Ok, so being that the only cluster that it showing damage is the intermediate should I just replace the int shaft bearings? Or do I need to replace all the bearings in the cent diff/int shaft/input shaft? Also after I replace the bearings how can I measure the preload? With solder? What is the spec? Where can I buy the shims from? Thx twicks.

 

[twicks69]

I have all the shims in stock that are available from Mitsubishi.

You are going to need to inspect all your bearings and see how they look for wear patterns. If it just requires intermediate shaft bearings, then replace the intermediate shaft bearings, but I would strongly recommend replacing the input shaft bearings at the same time, and if the center diff bearing age is unknown, replacing those as well.

As for measuring the bearing race to case gap, yes, you will need to do the solder crush tests to figure out the zero-value, then add the preload you want onto the zero-value number to get the desired shim thickness you need. If you want to figure out endplay, then you would subtract from the zero-value number to get the desired shim thickness you need.


As for stock specs, they really suck. We normally add preload to the input shaft, intermediate shaft, center differential, output pinion shaft; and keep the endplay on the front differential if it is still using standard roller bearings. You want preload on ANY tapered roller bearing.

Stock/Street Transmissions with less than 400TQ at the crank:

Input Shaft --> 0.004" - 0.007" PRELOAD
Intermediate Shaft --> 0.005" - 0.007" PRELOAD
Center Differential --> 0.005" - 0.007" PRELOAD
Output Shaft --> 0.003" - 0.005" PRELOAD
Front Differential --> 0.002" - .0067" ENDPLAY

Street/Strip Transmissions with less than 600TQ at the crank:

Input Shaft --> 0.005" - 0.007" PRELOAD
Intermediate Shaft --> 0.007" - 0.009" PRELOAD
Center Differential --> 0.005" - 0.007" PRELOAD
Output Shaft --> 0.003" - 0.005" PRELOAD
Front Differential --> 0.002" - .0067" ENDPLAY

All out RACE Transmissions that are Rebuilt/Inspected regularly with more than 600TQ at the crank:

Input Shaft --> 0.007" PRELOAD
Intermediate Shaft --> 0.008" - 0.010" PRELOAD
Center Differential --> 0.005" - 0.007" PRELOAD
Output Shaft --> 0.004" - 0.006" PRELOAD
Front Differential --> 0.002" - .0067" ENDPLAY

 

[98gst14b]

10-4, I did see a questionable race on the output shaft but none the less ill rip into it tomorrow and replace any bearing with a anything but brand new looking race. Ill order the bearings from jacks and try and get them ASAP, then ill measure and buy the shims I need from you. As for oil what would you recommend?