Re: Rear hub bearings

[Peter Roberts]

Another aspect of the rear bearing pinch up can be found in Mike Sherrill's
marvelous book, "TCs Forever".

On pages 107-8, he illustrates how proper pinch up can be frustrated because
the bearing nut only pinches up the inner race.. He observes that the "hub
extension" (that portion of the hub extending into the bearing carrier)
varies from hub to hub, and the gasket thickness often varies considerably.
Yet this extension must tighten up firmly on the outer bearing race when the
hub is bolted up, or the entire stub axle and bearing will rock under load.
He adds that this is probably the cause of many half shaft failures, as well
as the source of most rear axle oil leaks.

Thanks, Mike!


_Peter
TC0602

----- Original Message -----
From: "Dave & Diana Dwyer"
To: "MG-TABC Group"
Sent: Sunday, December 22, 2002 8:48 PM
Subject: Re: [mg-tabc] REAR HUB BEARINGS


> Joe
>
> When you say "play" in the hub, do you mean in-and-out, or do you mean
that
> the wheel wobbles?
>
> The rear wheel bearing comes in two versions: 6208 (standard) and 208
(heavy
> duty). Vertical load ratings are 6208= 2900Kg, 208= 3800Kg.
>
> A TC weighs approx 800Kg, so each rear wheel bears about 200Kg of vertical
> load. This means the 6208 has a safety factor of about 14 in the vertical
> plane.
>
> The axial load rating of the 6208 is 1800Kg. At the point of sliding you
> should be able to exert a max side load of 200Kg to each wheel (OK, weight
> transfer might mean 300 on the outer wheel). In this case the safety
factor
> in the sideways plane is about 6.
>
> The TC axle construction is described as "semi-floating" and in this setup
> the halfshaft takes the 'wobble' load. The bearing has no leverage to
> withstand that kind of load: if that load were intended, there would be
> #two# bearings spaced about 6" apart as in the Lotus and other IRS cars.
>
> If the halfshaft is loose in the splined hub your wheel will wobble,
> regardless of the bearing. Shimming the fit of bearing/bearing
> carrier/splined hub will reduce the possibility of the bearing carrier
> sliding in/out on the bearing outer shell, but it won't stop any wheel
> wobble.
>
> All of which is a long way of saying that I don't see any point in using
> double row bearings.
>
> Regards
>
> Dave Dwyer
> J2, TA, TC
>
>
>
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>

[Dave & Diana Dwyer]

Peter

I have the greatest respect for Mike Sherrell's achievement in producing
that book, and I've made use of much of the information therein. However, in
some things I disagree with him.

The matter of bearing retention stopping wheel wobble is one of them.
Certainly the bearing outer will benefit from being neatly retained by the
inner protrusion of the splined hub, to prevent the bearing housing (and the
attached wheel/splined hub/halfshaft assembly) attempting to slide in and
out on the bearing outer case.

However, the ballrace is only about 2 1/2" in diameter, and the tyre is
about 28" - a factor of say 11.
Thus a wobble of 10 thou at the bearing will allow the tyre tread to move
about 1/8", which is unacceptable. Similarly, a cornering load of 100Kg
applied at the tyre tread will appear as a bend force of 1100Kg trying to
twist the bearing and its nut off the end of the axle.

On the other hand we could believe the text books of vehicle construction,
which state that this style of axle uses the halfshaft to carry the bend
loads. In this case the bearing doesn't have to withstand twist loads, and
any play it has in the 'wobble' mode is restrained by the considerable
leverage of the halfshaft with its other end engaged in the diff.

Perhaps Roger Furneau and Bob Grunau could advise on the forces required to
bend halfshafts?

Regards

Dave Dwyer
J2, TA, TC

[Peter Roberts]

Dave,

All of your arguments are quite compelling, and no doubt capture the forces
involved. Michael offers his observation about pinching up the outer race
primarily in terms of oil leaks. As a contribution to the over-all
management of shearing forces on the half-shaft, it would be minor but
material. All of my half-shaft breaks have been clearly due to torque.


_Peter
TC 0602

----- Original Message -----
From: "Dave & Diana Dwyer"
To: "MG-TABC Group"
Sent: Monday, December 23, 2002 11:01 PM
Subject: Re: [mg-tabc] REAR HUB BEARINGS


> Peter
>
> I have the greatest respect for Mike Sherrell's achievement in producing
> that book, and I've made use of much of the information therein. However,
in
> some things I disagree with him.
>
> The matter of bearing retention stopping wheel wobble is one of them.
> Certainly the bearing outer will benefit from being neatly retained by the
> inner protrusion of the splined hub, to prevent the bearing housing (and
the
> attached wheel/splined hub/halfshaft assembly) attempting to slide in and
> out on the bearing outer case.
>
> However, the ballrace is only about 2 1/2" in diameter, and the tyre is
> about 28" - a factor of say 11.
> Thus a wobble of 10 thou at the bearing will allow the tyre tread to move
> about 1/8", which is unacceptable. Similarly, a cornering load of 100Kg
> applied at the tyre tread will appear as a bend force of 1100Kg trying to
> twist the bearing and its nut off the end of the axle.
>
> On the other hand we could believe the text books of vehicle construction,
> which state that this style of axle uses the halfshaft to carry the bend
> loads. In this case the bearing doesn't have to withstand twist loads, and
> any play it has in the 'wobble' mode is restrained by the considerable
> leverage of the halfshaft with its other end engaged in the diff.
>
> Perhaps Roger Furneau and Bob Grunau could advise on the forces required
to
> bend halfshafts?
>
> Regards
>
> Dave Dwyer
> J2, TA, TC
>
>
>
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>

[CFritz7001@aol.com]

In a message dated 12/24/2002 2:07:25 PM Eastern Standard Time,
mgtc@attbi.com writes:

> All of my half-shaft breaks have been clearly due to torque.
>

Once again, I offer the thought that the half-shafts may be TOO STRONG in
their resistance to torsional stress, thus causing breaks where the stress is
concentrated by machining (as at the ends of splines) and/or surface defects.
I can't help but think that if some degree of torsional compliance (ie
"give") were designed into the physical shape of the shaft and / or the
choice of its alloy, those shafts would be able to better absorb the torsion
stress & shock without failure.
When was the last time you heard of a suspension torsion bar failing in
ordinary service??
Happy Holidays, all,
Regards,
Carl Fritz
TC # 6756 (Betsy)
VA # 2009 S (Abigail)
Gainesville, Florida

[Mark McCombs]

I would think we could make a determination on this if anyone has a broken
half shaft..
Is the fractured end running in a 45 degree angular break- or is it slightly
elongated at the fracture?
Merry Christmas from Ohio-
Mark TC8126

----- Original Message -----
From:
To: ; ;
Sent: Tuesday, December 24, 2002 5:38 PM
Subject: Re: [mg-tabc] REAR HUB BEARINGS


> In a message dated 12/24/2002 2:07:25 PM Eastern Standard Time,
> mgtc@attbi.com writes:
>
> > All of my half-shaft breaks have been clearly due to torque.
> >
> Once again, I offer the thought that the half-shafts may be TOO STRONG
in
> their resistance to torsional stress, thus causing breaks where the stress
is
> concentrated by machining (as at the ends of splines) and/or surface
defects.
> I can't help but think that if some degree of torsional compliance (ie
> "give") were designed into the physical shape of the shaft and / or the
> choice of its alloy, those shafts would be able to better absorb the
torsion
> stress & shock without failure.
> When was the last time you heard of a suspension torsion bar failing
in
> ordinary service??
> Happy Holidays, all,
> Regards,
> Carl Fritz
> TC # 6756 (Betsy)
> VA # 2009 S (Abigail)
> Gainesville, Florida
>
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>

[Ray]

Guys,
Axles aren't torsion bars.
Axles are designed to NOT twist. If twisting axles were a good thing, race cars would run rubber bands.....
I am BillGatus of Borg. Resistance is futile. You will be assim
[General Protection Fault]

----- Original Message -----
From: CFritz7001@aol.com
To: mgtc@attbi.com ; mg-tabc@yahoogroups.com ; dmdwyer@optusnet.com.au
Sent: Tuesday, December 24, 2002 4:38 PM
Subject: Re: [mg-tabc] REAR HUB BEARINGS


In a message dated 12/24/2002 2:07:25 PM Eastern Standard Time,
mgtc@attbi.com writes:

> All of my half-shaft breaks have been clearly due to torque.
>
Once again, I offer the thought that the half-shafts may be TOO STRONG in
their resistance to torsional stress, thus causing breaks where the stress is
concentrated by machining (as at the ends of splines) and/or surface defects.
I can't help but think that if some degree of torsional compliance (ie
"give") were designed into the physical shape of the shaft and / or the
choice of its alloy, those shafts would be able to better absorb the torsion
stress & shock without failure.
When was the last time you heard of a suspension torsion bar failing in
ordinary service??
Happy Holidays, all,
Regards,
Carl Fritz
TC # 6756 (Betsy)
VA # 2009 S (Abigail)
Gainesville, Florida



Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/



[Non-text portions of this message have been removed]

[Peter Roberts]

Well, Carl,

Why not try Geoff Healy's solution? Simply use mild steel on the hub bolts
so they will shear under heavy torque? Admittedly, this may provide a good
deal of excitement when it happens, but it will certainly save replacing the
half-shaft.

....and a Happy New Year to you!


_Peter
TC0602

----- Original Message -----
From:
To: ; ;
Sent: Tuesday, December 24, 2002 5:38 PM
Subject: Re: [mg-tabc] REAR HUB BEARINGS


> In a message dated 12/24/2002 2:07:25 PM Eastern Standard Time,
> mgtc@attbi.com writes:
>
> > All of my half-shaft breaks have been clearly due to torque.
> >
> Once again, I offer the thought that the half-shafts may be TOO STRONG
in
> their resistance to torsional stress, thus causing breaks where the stress
is
> concentrated by machining (as at the ends of splines) and/or surface
defects.
> I can't help but think that if some degree of torsional compliance (ie
> "give") were designed into the physical shape of the shaft and / or the
> choice of its alloy, those shafts would be able to better absorb the
torsion
> stress & shock without failure.
> When was the last time you heard of a suspension torsion bar failing
in
> ordinary service??
> Happy Holidays, all,
> Regards,
> Carl Fritz
> TC # 6756 (Betsy)
> VA # 2009 S (Abigail)
> Gainesville, Florida
>
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>

[Roger Furneaux]

hello Madhu - I would have to hunt out my old bearing catalogues to prove
it, but I'm pretty sure that the M208 (which is equivalent to the R. & M.
LJBL40 originally fitted by Abingdon) has a greater load bearing capacity
than the 6208 - being a case of 12 (or 13) balls versus 9.

ocTagonally

TCRoger

Madhu Paroor wrote:

> I replaced all the six bearings of four wheels with ZZ type. I paid for SKF
>made in Italy 6208-ZZ 36 for two in the month of April this year. SKF is
>not having the heavy duty M208 in the 2003 catalogue. If you look at the
>load capacity of 6208, I think it is matching to the original bearings.
> Most of the bearings are not installed proper. The best way is to heat the
>bearing ( not very much ) and insert it on the cold shaft. In no case use
>the hammer. If you are pressing the bearing, make sure that you got the
>proper bushes to force them to the seat. If the seating are loose, it is
>going to generate heat. This will destroy the quality of lubricants inside.
>So with the dry lubricant it can not run for a long time. Eventually it will
>break. In my opinion for the normal soft drive of MG Tabc these bearings are
>good enough.

[paroor@t-online.de]

This is also very informative.

http://www.skf.com/portal/skf/home/products?paf_dm=shared&paf_gm=content&paf
_gear_id=4400006&newlink=1_0_1&lang=en


Have a nice week end.
Madhu


-----Urspr ngliche Nachricht-----
Von: Roger Furneaux [mailto:Roger.46TC@virgin.net]
Gesendet: Samstag, 18. Oktober 2003 02:03
An: paroor@t-online.de
Cc: .T-ABCs
Betreff: Re: AW: [mg-tabc] Rear Hub Bearings


hello Madhu - I would have to hunt out my old bearing catalogues to prove
it, but I'm pretty sure that the M208 (which is equivalent to the R. & M.
LJBL40 originally fitted by Abingdon) has a greater load bearing capacity
than the 6208 - being a case of 12 (or 13) balls versus 9.

ocTagonally

TCRoger

[Neil]

As a newbie to the group could I ask for advice on which bearings to use in the rear hubs of my TC. I have found that it has previously been fitted with double row bearings and the rear lip on the hub has been removed. I have new half shafts and hubs, and intend fitting lip seal nuts to keep the oil out. I have decided to revert to the orginal bearings which I believe were SKF 6208, but have seen others listed as -8208, 1208, 6208 and M208. Any thoughts or advice will be very welcome.

Thanks in advance. Neil.