# Transmission pilot bearing yes/no?



## dillond666 (Dec 27, 2010)

The pilot bearing is definitely required to support the gearbox input shaft.

I used a fenner HRC type coupling on my vehicle and machined up a brass bush to support the input shaft inside the Warp motor shaft.

The problem with omitting the pilot bearing is that your coupler will probably not have the required fit on the gearbox input shaft (especially if reusing the splined centre of the clutch disk) and therefore will have excessive play in the gearbox input shaft bearing.

The motor coupling should be shrunk on or at least be a taperlock.

Derek


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## dougingraham (Jul 26, 2011)

Clutchless doesn't need it. If you keep the clutch you will need it.

I choose to keep the clutch in my conversion. But I find I dont use it all that much around town. I generally keep it in 3rd gear all the time only using 4th when I go on the highway.

The potential wear between the motor shaft coupler and splined input shaft on the transmission is just that. A potential. If your coupler is designed and manufactured correctly and the runout on the motor shaft is good there should be less wear on the input spline than with an ICE/flywheel/clutch arrangement. The coupler is the support for the end of the transmission input shaft.


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## TheSGC (Nov 15, 2007)

I am about to start a transmission rebuild of my main input shaft on my EV. I don't know if age (183K miles) or that fact that I just found my Pilot bearing in my tool box caused the issue. 

If you are using a clutch, try and keep the the pilot bearing.


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## piotrsko (Dec 9, 2007)

My $.02 I'd keep it. 

I feel that the splines have too great a tolerance for wobble especially if you are using a clutch disc hub for the adapter. Probably not enough for destroying the input bearings but enough to eccentric the shaft. Now on the other hand: if the splines have to be greased and warmed slightly to mate the I'd go bearing-less.


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## poprock (Apr 29, 2010)

Unless it is like this shaft on a 1000cc 3cyl Daihatsu which is supported by internal gearbox bearings.


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## dillond666 (Dec 27, 2010)

@dougingraham
"Clutchless doesn't need it. If you keep the clutch you will need it."

"there should be less wear on the input spline than with an ICE/flywheel/clutch arrangement"

Perhaps you misunderstand where the wear will occur. The reason the pilot bearing is so important is to preserve the bearing alignment of the input shaft bearing on the gearbox.
Poprock makes a valid point about certain FWD gearboxes having a different input shaft bearing arrangement but most RWD gearboxes absolutely require the pilot bearing for adequate support and alignment.

@piotrsko
"I feel that the splines have too great a tolerance for wobble"

Correct

Derek


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## TigerNut (Dec 18, 2009)

Most (if not all) rearwheel drive gearboxes have the input shaft terminating just behind the front bearing - it has the input gear which drives the countershaft, and then the synchro dog and cones to drive the direct drive coupling to the output shaft, and that's it. On these gearboxes, the pilot bearing provides the location and stability to the input shaft. As noted by piotrsko, the clutch disc splines (on a clutchless coupler) might provide enough location for things to work with a tolerable amount of vibration, but it will likely reduce the life of the gearbox internals by a factor of 10.

On the other hand, front-wheel-drive transverse gearboxes don't have a direct-drive coupling between the input and output shafts and the input shaft is supported at each end of the transmission case, so a pilot bearing is not required (and actually is not desirable because it overconstrains the input shaft). In this case driving through the clutch disc splines alone is sufficient.

Basically, you should keep the locating components that the original ICE arrangement used... whether you go clutch or clutchless.


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## dougingraham (Jul 26, 2011)

dillond666 said:


> @dougingraham
> "Clutchless doesn't need it. If you keep the clutch you will need it."
> 
> "there should be less wear on the input spline than with an ICE/flywheel/clutch arrangement"
> ...


You only need the pilot bearing in a clutch system because when the clutch is depressed there is nothing to keep the clutch disc centered and this would produce high radial loads on the transmission input shaft. It needs to be a bearing because when the clutch is depressed the shafts will turn at different speeds. In the case of a clutchless system the shafts will always turn at the same rate so you dont need a bearing. The motor bearing in essence becomes the pilot bearing input shaft support. It would be a good idea to machine into the coupler support for the end of the transmission input shaft but if the splines match up and the shafts are in alignment this probably would not be necessary. If the alignment is poor it doesn't matter what you do as there will be wear on the splines and side loading of the input shaft bearings.


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## EVfun (Mar 14, 2010)

There have been a number of transmission failures related to cutting off the pilot bearing part of the input shaft on a traditional RWD transmission. The 2 bearings that support the input shaft are the pilot bearing and a bearing just behind the seal where the input shaft passes into the transmission. The splines do not provide accurate enough support to replace the pilot bearing. Even worn pilot bearings cause failures in many RWD transmissions. If you adapter is clutchless it doesn't need this support to be a bearing as there will be no relative motion between the motor coupler and the input shaft, but the pilot shaft still needs to be supported. 

Front wheel drive vehicles have very different gear box designs and a pilot bearing may or may not be needed.


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## skooler (Mar 26, 2011)

FWIW I run with a clutch and cut off the pilot bearing / end of the input shaft!

It just wasn't practical to keep it due to the flywheel being supported by a single 2 1/8" nut in the center!

From the research I did at the time, providing the input shaft has adequate support from the gearbox (i.e. 2 bearings) vibration will be minimal.

I have 700 miles on mine now with no issues relating to the coupling.

My advice would be to keep it if you can.

Hope this helps


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