MTFCA Forum

Just purchased a new 12 tooth pinion gear. The taper bore is .021 larger on the small ID causing a very loose wobbly fit on the original drive shaft taper. The ID of the large end of the bore is the is the same as the originals. The two originals I compared it to have full contact on the taper. The thickness along the bore is .970 on the new and .950 on the old gears
Am I missing something here ? should I try and return it for an exchange ?
Any advice appreciated.
Will
https://photos.app.goo.gl/qaD2d5x4fBA7wZdX6

https://photos.app.goo.gl/3GpJdhVwL7Z7zu9g6

https://photos.app.goo.gl/VjUSDebEF1kaN2hJ8

https://photos.app.goo.gl/mu8UaCe1MTVLt8hL7

Yes, absolutely return it! Probably should have contacted Chaffin's before the forum and they would have put things right already.

Tried calling, no answer. Will try again tomorrow.

That’s a good gut check measurement, but not an adequate method to pass/fail a component. That dimension could have fairly dramatic changes due to a number of variables. But if you have a good driveline taper and there is not a good self locking “feel” to the taper... you may well have a problem

My suggestion would be to take this topic up with the vendor, and let them investigate a possible quality control issue with the entire lot. I’m sure they will will be more than happy to honor any non-conformant products

Yes, I will give them a jingle tomorrow. The driveshaft is NOS with about 500 easy miles on it.

Willie,

Please return the gear and we will investigate your concern. Thank you for bringing it to our attention.

Willie, WE have sold hundreds of these gears without one complaint. I measured one here, 0.755 in on the small end and 1.00 in on the large end. Perfect fit on the taper of a new Drive Shaft. However, a better test is to drive the gear on by tightening the nut a little, just snug. The problem should go away. The fit is deceiving if you don't set the gear on the shaft. However, send the gear back and we will check it. Glen

From the pictures, it appears that the inside face of the new gear may be a bit inset, or thinner, compared to the old gears. If this is the case, then I would expect the smaller ID of the new gear to measure larger as it is further up the taper. The test for this would be to measure the thickness of the old gears vs the new gear and I will bet that you will find that the new gear is a bit thinner, but that the faces of the teeth will fall exactly where they need to.

The expectation from the limited info given thus far would indicate a completely different taper and I don't believe that at all. None of these kinds of parts are one-offs and if a batch is run, for better or worse, they'll be for all intents and purposes, identical.

In any event, give Chaffins the opportunity to check it, and quit airing your issues in public. We all occasionally get the bum part here and there and I have yet in 20 years in the hobby failed to get satisfaction from a vendor. BTW, I called them twice today. Once the line was busy. Try harder. I did.

Scott_conger, thank you for your advice.

It looks to me like the bearing inner sleeve on the drive shaft is preventing the gear from seating on the taper. Push the sleeve on a little further by tightening the gear down with the nut and there's your dinner. Nothing wrong with the gear.

Willie thinks the taper in the gear is bad but every gear we checked here fits just fine. However, you can't just set the gear on the drive shaft and check it. it must be properly seated on the drive shaft. You do this by tightening the Drive shaft nut. This will properly seat the gear. When the nut is properly tightened it will drive the Drive Shaft sleeve to it's proper position setting everything in their proper setting and fit. WE have checked the pinion gear fit to the ring gear and it is perfect. This means that the taper is fine. Again send us the gear and we will check it. Sxxt happins. Glen

This is the value of the forum. Thank you all.

Tim.

Scot is correct, The thickness of the gear determines the ID of the smaller end of the hole. So this is a variable and cannot be used to determine if the taper is correct. The proof of the pudding is how the gear fits the taper of the Drive shaft and how the gear is aligned with the ring gear. All of this is perfect with our new 12 tooth pinions.

Update- I drove new Pinion on snug. It moved the inner bearing sleeve .037 up from the original gear location. Removed the new gear and the contact seemed consistent on the taper.

At setup I notice the pinion teeth looks to hang off the ring gear on one end and shy on the other. All the inner components are brand new from Chaffins which do an amazing job on reproducing these Ruckstell parts. I know this depth is determined by the inner bearing sleeve, pinion thrust bearing, and the other way by the ujoint thrust bearing. The setup retains a new pinion thrust bearing and there is .002 driveshaft end play at the ujoint thrust bearing.

Agreeing that the pinion gear is correct, what else could cause the two gears teeth to not have full linear contact ?

Nothing has been modified, using stock style pinion spool inners, and I have exactly .010 lash with the assembly standing on end.
Will

https://photos.app.goo.gl/oLWLYAToZ59q89cR7

https://photos.app.goo.gl/twfTag6heKHxRzhV6

My bad.. after closer examination, the pinion is not hanging off the outer edge of the ring gear. It is flush.
I have done lots of Ts but never invested so much time and $$ to have a perfect Ruckstell.

All is good and a huge thanks to Chaffins Garage for manufacturing such great accurate parts !!

Thank you for the apology Willie. It take a real man to admit he was wrong. Enjoy your Ruckstell Glen

I have no problem admiting when I am wrong or even voicing my experiences. Thanks again and have a great day.