Length of front driveshaft bearing?
 

I discovered that the speedo drive gear on the drivshaft has about 1/4" fore-aft movement. It seems to be aligned with the speedo gear when in the forward position against the snap retainer ring, but can slide easily rearward and "disengage" with the speedo gear. The thrust washer is in place, and the drive gear is inserted properly (gear end toward front). The only thing I can think would allow this movement is if the roller bearing is too short. It measures about 1 3/4" and appears to be an original Hyatt type bearing, but has no part number markings. It is about even with the front end of the race in the torque tube. Does anyone know the proper length of the original bearing? It is listed in the Ford parts book as A4645B, but does not list any dimensions.
Thanks,
Jack

Re: Length of front driveshaft bearing?
 

the rear axle assembly I am working on right now has an original torque tube roller bearing with the spirals and it measures 1 & 3\4". There is usually a gap between the speedo drive gear and the snap ring, 1\4" seems like a lot. I didn't think the speedo drive gear could move once the driven gear housing was bolted down.

it is possible the seal is missing and is allowing the bearing to drop down further than it should.

Tom Endy

Re: Length of front driveshaft bearing?
 

I agree with Tom. The race has to be removed to install the driveshaft seal. If the seal is missing it allows the the roller bearing, thrust washer, and sprial gear to move back and forth which will disengage the speedometer drive gear which is in a fixed position.

Ron

Re: Length of front driveshaft bearing?
 

Thanks for your replies, but the driveshaft seal is new and intact beneath the bearing (I installed it), so I don't think that is the cause of the gap. I measured the bearing again, and it is 1 11/16" long.

Re: Length of front driveshaft bearing?
 

All of the bearings I have removed have been 1 3/4" long. If there is still to much play and extrs thrust washere does not hurt any thing. ken

Re: Length of front driveshaft bearing?
 

I have measured 2 new replacement bearings ( bought years apart) and both of them are the same length as Jack's bearing 1 11/16.

Now, as to adding more thrust washers, I am worried that the lube of the driveshaft bearing, may suffer. The thrust washers have holes drilled that will allow the grease from the Ujoint to easily reach the bearing. With several washers, the holes in the washers will hardly ever align, and the grease flow to the bearing will be hampered.

What do you think ? Anything to worry about ?

Re: Length of front driveshaft bearing?
 

Thanks for all of your responses, after putting the rear axle back in , the speedo gear was in the right place without too much play fore and aft,
Jack

Re: Length of front driveshaft bearing?
 

So what did you do then Jack ? Did you add more washers ? If so, do you think that the bearing is still sufficiently lubed ?

Re: Length of front driveshaft bearing?
 

I did not add any spacers, it must be that the rear surface of the u-joint keeps the gear from moving too far forward, rather than the snap ring limiting its movement.

Re: Length of front driveshaft bearing?
 

The rear surface of the U-joint is not relevant to this. First, the problem is that the speedometer gear slides to far to the rear. The u-joint is at the front of the gear, and also to the front of the snap ring, so it will not limit the speedometer gear movement, unless the snap ring has been lost

The problem is speedometer gear moving to far to the rear. The shorter replacement driveshaft bearing would explain only 1/16" of that movement, and the free movement of the speedometer gear between the thrust washer and the snap ring is in excess of 1/4"

Any suggestion of how to solve this problem ?

How much axial play is allowed for the speedometer gear ?

How much misalignment between the centre of the speedometer gear and the centre of the hole in the torque tube for the speedometer gearbox should be allowed ?

Re: Length of front driveshaft bearing?
 

I have a NOS Drive Shaft Bearing, still in the original "Ford" box marked B 4645-A, the bearing measures 1-11/16" long.

Ron

Re: Length of front driveshaft bearing?
 

Thank you Ron,

Any suggestions on how to actually solve my problem ?

C'mon Guys ! Please help, if you have answers to my questions above. It's actually my birthday today !!

Re: Length of front driveshaft bearing?
 

i have the same thing goin on. seems like the bearing could slide forward and not be all the way in the race.

Re: Length of front driveshaft bearing?
 

I made a custom thrust washer 3/16 thick. Took up most of the slack and made the gear on the driveshaft ride in the middle of the speedometer cable gear.

Re: Length of front driveshaft bearing?
 

but why is there a gap in the first place?