If the wheel is given a "big wheel of fortune" spin with both hands,
how many revolutions should it spin after release?

This is presuming that the car is just lifted off the ground with the
caliper sitting at rest.

 

Can I win a stuffed animal?
It is really hard to answer how many revs. I try to see if they both turn about the same relative to each other and call that harmony. I also point a laser infrared thermometer at the discs right after driving. If the are close in temp - more harmony.


I have found dragging calipers on my other cars by measuring disc temp and seeing a big difference in temps side to side. They infrareds are pretty inexpensive now

 

Don't you already own a stuffed animal by virtue of the VDP?

The wheels are turning, and with about the same amount of effort.

It's just that I think it's too much effort. I don't think they would
spin more than one full turn after letting go.

Maybe the anti-rattle clip on our calipers cause more drag at testing
efforts than in other types. I'll try it after removing them just for
observation purposes.

I'm chasing a wicked steering shake on braking from 80 mph.

Anyone know the first year XJR's started using 325mm rotors?

Might scrounge some rebuildable calipers from a local parts
car.

 

Had the same problem: new rotors took care of abut ~80%; rebalancing bought me closer; cleaned and lubed the caliper pistons (one forum member - remember - was religious about it), got me close enough -- last bit was roads, particularly one off ramp on I 264 when braking from 70.

 

Do you mean lifting the dust boot, then clean/lube and
reseating the dust boot?

 

I pulled the pistons out and cleaned the cavity, then reassembled. DID NOT HONE; a scary process for an amateur. But if the pistons move freely, not sure it is worth the effort; but I had the calipers off to change the rotors . . . .

 

I have read that honing is actually not needed as long as there is no
rust interfering with the piston.

A professional rebuilder pointed out that the piston bore has exactly
nothing to do with sealing the piston. It is all done by the seal itself.
On the other hand, the piston must have a smooth finish or it rips up
the seal.

The lift dustboot, clean, reseat came from some site where the writer
said you "can play this game for years". Can't find the site now

 

I just did an oil change on my older "R" yesterday and was looking the car over (I did the brakes about 6k ago)-- the wheel should spin more then one revolution. You have to get the wheel moving so the pads are floating to check them. Watch how it stops -- you can tell if they are grabbing. Also -- they car needs to have been driven -- and rust from sitting overnight will grab.


The X308 are sensitive to any rotor imbalance -- Thats why they sell the rotors in balanced sets. I have never had the sticking issues that is common place with my MB's -- but thats not to say it's not possible at this age.

I have had bad luck trying to rebuild calipers. It was common place years ago -- but for whatever reason it's less successful with later cars. I bought a set of rebuilt rotors for my MB wagon last year and was surprised how cheap I could get them (especially the odd rears) -- about $50.00 each and $60.00 to ship all the cores back.

 

Balanced sets? Could you explain please.

 

Jaguar only sells the front rotors in sets (2) -- the rotors are balanced.

The front suspension is of an old design -- it does not like any imbalance.

 

Rotors of even modest quality are individually balanced to meet a certain spec. They either make the spec or they don't. There is no need or benefit in making 'matched sets' for balancing or any other purpose.

JEPC makes no mention of selling rotors in sets of two, matched or otherwise.

Balancing a rotor would have no effect on the condition the OP describes.

 

Absolutely. Most rotors, including those for Jaguar, are able to be turned at least once. Once they're cut into any matching balance is lost.

 

[QUOTE=Mikey;1346606]Rotors of even modest quality are individually balanced to meet a certain spec. They either make the spec or they don't. There is no need or benefit in making 'matched sets' for balancing or any other purpose.

JEPC makes no mention of selling rotors in sets of two, matched or otherwise.

Balancing a rotor would have no effect on the condition the OP describes.[/QUOTE


Think what you wish -- Jaguar only sells rotors in the USA for the x308 in sets.

My fist car was my dads XJC back in the 70's -- I know what I speak.

I did not imply anything regarding the op and matched sets .. I am saying that x308's are very sensitive to any imbalance. It also a design that does not do well with large tires/ low profile -- that's why the XJR can be such a pain with tramlining

 

Most manufactures don't recommend it -- most rotors have very little wear surface -- I think my Porsches have something like 2mm. The Jaguars do have a bit more then most -- I never cut them but can always get two pad sets out of the fronts.

 

Possibly they do. The theory of it being something to do with balancing holds no water.

The OP's problem has nothing to do with balancing, large/low profile tires or tramlining. He is concerned with excessive friction when rotating the wheel while it is off the ground. The first response posted by rocklandjag was spot on.

 

I did not imply anything regarding the op and matched sets .. I am saying that x308's are very sensitive to any imbalance. It also a design that does not do well with large tires/ low profile -- that's why the XJR can be such a pain with tramlining[/QUOTE]

The OP's problem has nothing to do with balancing, large/low profile tires or tramlining. He is concerned with excessive friction when rotating the wheel while it is off the ground. The first response posted by rocklandjag was spot on.[/QUOTE]


I answered .. a bit quickly .. I my have come off sounding a bit rude .. sorry. I understand it's odd .. I can only tell you that it occurs. The suspension on these cars has origins going back to the 60's -- they were all about deep pivot points -- long travel and unsprung weight.

 

I'm pretty sure it's pad drag because the problem is temperature sensitive.

Rolling out of the garage cold, the problem is not evident.

Go fast down the street, and it shows up quickly.

Go slowly across town, and it takes a while to show up.

The problem is locating the exact cause.

Your MB and our Jaguars both use the same style of caliper which features
the outboard spring which *may* be a complicating factor in spinning the
wheel as a test. It pulls the outside face towards the center of the rotor.
That might contribute to a preload.

My current WAG is that the seal itself is getting lazy and failing to pull
back the piston enough.

It might be all moot because I picked up a complete set of rotors/calipers/brackets
for the princely sum of $40 this afternoon. That included freshly cut rotors.

I have never had a problem with properly turned rotors and actually prefer
them since any set that they are going to take has already taken place.
The faces will remain parallel for a long time.

The spare parts box already contains rebuild kits, hardware kits, pads,
and ATE SL-6 brake fluid.

It might take a while because I'm leaning towards derusting and painting
the whole works.

In the meantime, I can always use the old trick of exercising the piston/seal
interface by pushing the piston in and out several times. I had a badly stuck
caliper on a Supra. One in and out lasted six months before the problem
resurfaced. Several in and out cycles then completely cured the problem
for ten more years until the car was sold.

 

I was answering another post within the thread

 

The problem is much more prevalent on the MB's ... it could be the dirt from soft pads ... they just seem to rust more ...especially on the less maintained rears. With the cost of the rebuilds being so cheap ...its my normal fix to go that route. I just replaced the rear pads on my original 02"R" 65k (I bought new) The original pads started to show cracking -- so I switched them out. The pad backing was showing some rust but the rest was free,

Mintex pads created a hang up with at least two friends -- looking over the pads we could not see the problem .. but switching them out solved it.

Best luck.

 

I'm green with envy

A common problem with pads is the ears being slightly too big.
That causes them to be more prone to hanging in the slide.

The ATE caliper is even more sensitive to this due to the way
the pad to bracket load is taken. The actual caliper has nothng
to do with the load other than applying pressure.

Been doing lots of thinking on this