[xj] Rear rotor replacement/camber change

Hi everyone,
Like most everyone, I assume, I have a project list of things to do on my
Jag and one of them is replacing the rear rotors (along with axles seals,
repair e/brakes, new rear shocks, etc—all at once) and I need help with a
logic question. The answer may be so simple that I just can’t see for forest
for the trees. Here goes…

As we know, it is admonished that the shims on either side of the rotor
mounting flange must be kept in order and reinstalled in same position to
maintain correct rear wheel camber. Right ? Well, in my simple mind, this
only makes sense if one assumes that the replacement rotor mounting
flange is of the exact same thickness as the original. If it is either
thicker or thinner then the over all length of the drive-axle must change,
yes ? According to ROM, .020" will effect camber by 1/4 degree. Should rear
camber be checked after rotor replacement ? Or, in actual practice, are the
various rotors all made to close enough spec to make this a non-issue ? Or,
I am missing something?

Thanks for setting me straight,
Doug Dwyer

Doug,

Thanks for asking that question, because I would have just put mine back
together. I have marked the shims L & R (two on one side, one on the other).
You seem to indicate that the order of the two shims is important, or were
you referring to the two types of shims, the ones at the diff and the ones
outside the rotor?

“Mark 1” Mark Stephenson
1952 XK120 Roadster #S673129 (w/XK140 engine and C head)
1958 3.4 Litre Saloon / 1984 XJ6 4.2L / 1985 XJ6 VDP
Jaguar Club of Central Arizona (USA) – www.cableone.net/jcca----- Original Message -----
From: “DOUGLAS DWYER” DWYERD@email.msn.com
To: “XJ List” xj@jag-lovers.org
Sent: Tuesday, April 04, 2000 9:52 PM
Subject: Re:[xj] Rear rotor replacement/camber change

Hi everyone,
Like most everyone, I assume, I have a project list of things to do on my
Jag and one of them is replacing the rear rotors (along with axles seals,
repair e/brakes, new rear shocks, etc—all at once) and I need help with
a
logic question. The answer may be so simple that I just can’t see for
forest
for the trees. Here goes…

As we know, it is admonished that the shims on either side of the rotor
mounting flange must be kept in order and reinstalled in same position to
maintain correct rear wheel camber. Right ? Well, in my simple mind, this
only makes sense if one assumes that the replacement rotor mounting
flange is of the exact same thickness as the original. If it is either
thicker or thinner then the over all length of the drive-axle must change,
yes ? According to ROM, .020" will effect camber by 1/4 degree. Should
rear
camber be checked after rotor replacement ? Or, in actual practice, are
the
various rotors all made to close enough spec to make this a non-issue ?
Or,
I am missing something?

Thanks for setting me straight,
Doug Dwyer

MARK,
Neither. I am referring to the overall thickness of the original shims
with the new rotor compared to overall thickness of the original shims
with the old rotor. Picture the area of the rotor where the shims lay
against… What if the new rotor is thicker or thinner in that area ?
Wouldn’t that change the overall length of the assembly and hence the camber
? For example, if new rotor is .020" thicker in that area then the entire
length of the assembly would be .020" longer which must change the camber.
Using this example, if new rotor was .020" thicker at the mounting area then
one would need to reduce the shim packs by .020" to maintain correct camber.

Am I making any sense at all ?

Remember, I am not referring to thickness of the rotor where the brake pads
are but the thickness of the rotor where the shims go.

Thanks,

Doug----- Original Message -----
From: Mark Stephenson marks@trnpa.com
To: XJ Lovers xj@jag-lovers.org
Sent: Wednesday, April 05, 2000 12:21 AM
Subject: Re: Re:[xj] Rear rotor replacement/camber change

Doug,

Thanks for asking that question, because I would have just put mine back
together. I have marked the shims L & R (two on one side, one on the
other).
You seem to indicate that the order of the two shims is important, or were
you referring to the two types of shims, the ones at the diff and the ones
outside the rotor?

“Mark 1” Mark Stephenson
1952 XK120 Roadster #S673129 (w/XK140 engine and C head)
1958 3.4 Litre Saloon / 1984 XJ6 4.2L / 1985 XJ6 VDP
Jaguar Club of Central Arizona (USA) – www.cableone.net/jcca

----- Original Message -----
From: “DOUGLAS DWYER” <@Doug_Dwyer>
To: “XJ List” xj@jag-lovers.org
Sent: Tuesday, April 04, 2000 9:52 PM
Subject: Re:[xj] Rear rotor replacement/camber change

Hi everyone,
Like most everyone, I assume, I have a project list of things to do on
my

Jag and one of them is replacing the rear rotors (along with axles
seals,

repair e/brakes, new rear shocks, etc—all at once) and I need help
with
a

logic question. The answer may be so simple that I just can’t see for
forest
for the trees. Here goes…

As we know, it is admonished that the shims on either side of the rotor
mounting flange must be kept in order and reinstalled in same position
to

maintain correct rear wheel camber. Right ? Well, in my simple mind,
this

only makes sense if one assumes that the replacement rotor mounting
flange is of the exact same thickness as the original. If it is either
thicker or thinner then the over all length of the drive-axle must
change,

yes ? According to ROM, .020" will effect camber by 1/4 degree. Should
rear
camber be checked after rotor replacement ? Or, in actual practice, are
the
various rotors all made to close enough spec to make this a non-issue ?
Or,
I am missing something?

Thanks for setting me straight,
Doug Dwyer

Craig,
Thanks for the reassurance. I thought that this must be the case but didn’t
have the guts to assume it was correct all on my own !

Regards,
Doug Dwyer> Craig wrote:

According to the ROM, you just put the shims back where they came from.
The specification for the disc must be such that the centre boss
thickness is tightly controlled.

Doug,

You made perfect sense, and since I have my rear end apart in a neatly laid
out pile of pieces, the answer was muy importante to me.

It’s a good thing you copied Craig’s reply in this e-mail, because Craig
must have sent it to you rather than the list (at least it didn’t show up in
my inbox). Another reason why I argue in favor of “reply to sender” sending
the reply to the list rather than the individual who originally sent it.
(And my continued harping for the change is probably why Craig politely
ignores me – that and the likelihood that the majority of the list
disagrees with me. But that’s OK, I can handle rejection… )

“Mark 1” Mark Stephenson
1952 XK120 Roadster #S673129 (w/XK140 engine and C head)
1958 3.4 Litre Saloon / 1984 XJ6 4.2L / 1985 XJ6 VDP
Jaguar Club of Central Arizona (USA) – www.cableone.net/jcca----- Original Message -----
From: “DOUGLAS DWYER” DWYERD@email.msn.com
To: “XJ List” xj@jag-lovers.org
Sent: Wednesday, April 05, 2000 6:39 AM
Subject: Re: Re:[xj] Rear rotor replacement/camber change

Craig,
Thanks for the reassurance. I thought that this must be the case but
didn’t
have the guts to assume it was correct all on my own !

Regards,
Doug Dwyer

Craig wrote:

According to the ROM, you just put the shims back where they came from.
The specification for the disc must be such that the centre boss
thickness is tightly controlled.

It’s a good thing you copied Craig’s reply in this e-mail,
because Craig
must have sent it to you rather than the list

Nah. I sent it from the wrong mail profile (c.sawyers@maran.co.uk
rather than c.sawyers@tech-enterprose.co.uk) and it bounced. To me, of
course as list admin. Dur.

And my continued harping for the change is probably why
Craig politely
ignores me

No - I think it is good idea. However, it needs a rewrite of Majodomo’s
code to change the order of the addresses. After all, you (the sender)
sent the message to xj (the recipient). For your e-mail program to
reply to xj as the sender, majordomo would have to swap the sender and
recipient fields in every e-mail message prior to posting to the list.
And it can’t do that, sorry.

Craig

Doug,

The rear rotors I bought from the local auto parts store (stupidly,
BTW–they’re much less expensive through our mail-order supplers) were
significantly different in flange thickness and different from the
originals. I was able to swap around shims to theoretically keep the camber
within specs, though I theoretically ended up shifting both sides a wee bit
more positive. Local alignment shops will not touch the car, and I am too
cheap and lazy to take the car to a Jaguar dealer for alignment until I
invest in new tires, but the car drives fine and tracks straight.

IMHO, get out that caliper and pay attention to this when replacing rotors.

Paul Studebaker
Valparaiso, IN
'85 XJ6 Tungsten/gray>As we know, it is admonished that the shims on either side of the rotor

mounting flange must be kept in order and reinstalled in same position to
maintain correct rear wheel camber. Right ? Well, in my simple mind, this
only makes sense if one assumes that the replacement rotor mounting
flange is of the exact same thickness as the original. If it is either
thicker or thinner then the over all length of the drive-axle must change,
yes ? According to ROM, .020" will effect camber by 1/4 degree. Should rear
camber be checked after rotor replacement ? Or, in actual practice, are the
various rotors all made to close enough spec to make this a non-issue ? Or,
I am missing something?

Thanks for setting me straight,
Doug Dwyer