Rear hub bearings - fresh thinking or already been done?

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Re: Rear hub bearings - fresh thinking or already been done?

Postby silverbullet » 22 May 2015, 14:18

FAG bearings just arrived :D
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Re: Rear hub bearings - fresh thinking or already been done?

Postby garyd » 22 May 2015, 16:25

I am fed up with changing wheel bearings that rapidly become sloppy again so I hope that you are successful with this Ian. It seems like a fairly simple change process. I wonder why no-one has done it before?
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Re: Rear hub bearings - fresh thinking or already been done?

Postby silverbullet » 22 May 2015, 17:22

I have done a quick trial fit and the length of the bearings is similar to the originals (nothing is miles out). The only detail that needs to be addressed is how to locate the outermost bearings outer race. It can't just rely on the press fit, otherwise if it came loose the entire stub axle assembly could migrate inward until the hub flange meets the front of the bearing housing...this is a possible failure mode and it has to be intrinsically safe.

The outer bearing bore is only just long enough for the bearing anyway (either type) but it might be possible to put a circlip groove in there to give it something to seat against, if there isn't too much variation in the forgings. If not, then the housings will need a steel sleeve inserting and securing. I can see a hole being drilled in each side and a decent sized plug weld being the solution.

The original bearing spacer is a bit short, a couple of mm or so, but that gives some room for a nice thick shim spacer.

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Re: Rear hub bearings - fresh thinking or already been done?

Postby silverbullet » 22 May 2015, 19:07

The big issue, nothing behind this one:
Image
Bearings with standard VW spacer:
Image
As assembled:
Image
Split pin hole not far off at all:
Image
The more I think about it, the best solution would be to bore the housing out to behind the outer bearing (removing the inner bearing location shoulder) then press a new stepped sleeve in and secure it with a few welds.
That way both bearings have a secure and controlled location, nothing can creep or escape if ine fails and its best practice all the way.
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Re: Rear hub bearings - fresh thinking or already been done?

Postby windy » 22 May 2015, 19:19

Is it possible to bore the housing out but leave the end un-machined to act as the locating stop? I don't know if the bearing recess is long enough to do this & obviously you would have to use a slightly larger O/D bearing than standard
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Re: Rear hub bearings - fresh thinking or already been done?

Postby max and caddy » 22 May 2015, 20:06

I'm interested...but..are the bearings going to be adjustable via the big nut? I guess not so the sleeve and bearings will have to be a standard size and bang on spec as no correction factor is possible...but mini coopers etc amongst others had that set up and it worked ok in general..also the taper bearings will produce a fair bit more friction than a roller I reckon...at speed will they get hot to a significant degree I wonder?

Also...why is the centre sleeve needed? if a larger sleeve was put between the two outer races could it be omitted and the 46mm nut used as an adjuster? why does it need to be 500 Nm anyway?
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Re: Rear hub bearings - fresh thinking or already been done?

Postby windy » 22 May 2015, 20:34

He said he was going to use shims in conjunction with the centre spacer to adjust them.

I think you may be getting confused with front wheel bearings. These are on driven wheels so the hub needs to be firmly attached to the driveshaft
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Re: Rear hub bearings - fresh thinking or already been done?

Postby max and caddy » 22 May 2015, 20:46

It will be...the massive splines will see to that...so how does one go about setting the preload with a shim in the centre and then in the future to compensate for wear....and the fronts are driven..
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Re: Rear hub bearings - fresh thinking or already been done?

Postby toomanytoys » 22 May 2015, 21:10

Not had a stub axle with a not very tight hub nut then?? The splines wesr at an extordinay rate if the nut isnt done up propper tight.. if the nut is used as an adjuster t hen expect loads of ppay to develop in the stub axle and drive flange...
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Re: Rear hub bearings - fresh thinking or already been done?

Postby silverbullet » 22 May 2015, 21:17

Confusion. Opposed double taper bearings require both outer races to have a shoulder for thrust reaction.
The inner races require a spacer and shims to set bearing preload.
The T3 housing only has one shoulder, for the larger ballrace that controls endfloat, so it is necessary to somehow provide a second in order to contain the end thrust or it will all go pearshaped as previously explained.
There is precious little spare metal in the housing for any kind of changes, that is why I am sticking with the standard bearing sizes and proposing a fixed internal sleeve to solve the second bearing shoulder problem.
For comparison and an example of best engineering practice, google up a cross-section of a Jaguar IRS hub assembly.
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Re: Rear hub bearings - fresh thinking or already been done?

Postby silverbullet » 22 May 2015, 21:20

PS adjustmemt will require the substitution of shims. I will endeavour to find a source of standard parts, being as the bearings are to a DIN standard then shims should also be readily available.
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Re: Rear hub bearings - fresh thinking or already been done?

Postby max and caddy » 22 May 2015, 21:22

Surely not...spline wear on non oil filled splines..sounds like a T5! I know this..just playing along...but I don't like the idea of having to shim the tapers up...to much scope for error and the range of shims would need to be hand..also how is the preload to be determined on a fitted hub with drivetrain attached...? a DTI gauge..or is the Bering to be assumed as a given size and used with a set shim?

technically better but to much faffing and tooling is my opinion at the moment...how about billet rear hubs with oversized one piece bearing as fitted up front? the fronts take a beating and hold out just fine...

:?:
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Re: Rear hub bearings - fresh thinking or already been done?

Postby silverbullet » 22 May 2015, 21:32

Proper engineering, grease filled bearings. Last forever:
[img]http://www.jagweb.com/aj6eng/wishbone_diagrams.jpg[/img]
Yes a complete replacement bearing unit would be great, but no bugger would pay for it.
You know the drill: Durability, convenience, cost. Pick two only.
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Re: Rear hub bearings - fresh thinking or already been done?

Postby silverbullet » 22 May 2015, 21:35

Ok using the old E30 duplex rear bearing as per syncro front might be an option but its meant for lighter duties at the front end. That would definitely require a new bearing unit.
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Re: Rear hub bearings - fresh thinking or already been done?

Postby max and caddy » 22 May 2015, 22:13

silverbullet wrote:Ok using the old E30 duplex rear bearing as per syncro front might be an option but its meant for lighter duties at the front end. That would definitely require a new bearing unit.


New or from something else larger..T5 front for example? a full taper set up is a nice idea but is it needed?

Also..does the syncro not feature near 50/50 weight distribution with transfer to the front under braking? if so a standard front bearing must see some hard hits during its lifetime..
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