I'm not normally a fan of blatant cross-posting, but in this case I think the value is there since we've had so much interest for any information in upgrading the X300 brakes over the years without any success.

Within the following thread in the X308 forum, one can find some information on a member's work in fitting larger rotors and calipers from an XK8 to an X300 XJR as well as his X308 that he is installing a GM LS2 motor into.

He has said he'll post a full write up in the X300 forum once he has it all worked out fully, but in the interim I'm posting this link as a placeholder for anyone searching for this topic for the X300:

https://www.jaguarforums.com/forum/x...2-swap-162313/


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I'm not exactly sure when I will change the X300 over, so in the meantime I will at least post the pictures and information from the X308 swap. In short, there was no certainty this would work, there just seemed to be enough similarities in the parts catalog to give it a shot. That said, I can't gaurantee fitment - I did NOT go by Jaguar part numbers, I just ordered calipers with brackets from eBay listed for 1999-2006 XK8, and pads and rotors from Rock Auto for 2006 XK8. I HAVE NOT tested the brackets on the X300 yet; my concern is the hub arrangement is completely different between the X300 and X308. Anyone interested in doing this may want to wait until I can verify fitment.

Parts list for REFERENCE:
RH caliper MJD7842AA (appears to be XK8 only)
LH caliper MJD7843AA (appears to be XK8 only)
Caliper bracket MJD7861AA (1997 XJR and 1999-2006 XK8)
325MM rotor C2C41250 (2000-03 Vanden Plas, 1998-03 XJR, 1999-06 XK8, 2000-02 XJR)

First pair of XK8 calipers that went onto the 2003 XJ8:


Mocked up as received on the new rotor (the rotor barely clears the dust shield):


17" XJR wheel mocked on completed brake swap:


Plenty of room with the 17":


Second pair of XK8 calipers to go onto the 1997 XJR:


I will be checking a 16" kiwi wheel and 15" lattice wheel, and will also check the bracket on an XJ40 spindle. That's all for now.

 

Thanks, appreciate anything you can find out.

The difference in the X300 and X308 front hubs indeed has been one of the hangups for any "bolt on" X300 brake upgrades, so it will be interesting to see if you can make it work without major modification.

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I am going a different route with brake upgrade
I have ordered a full set of EBC red stuff pads for all 4 wheels and dimpled/slotted EBC front discs/rotors from the NZ EBC agent. I'll also go for 'hotter' brake fluid - 50'C increase in boiling point can make all the difference.

The shipment with the rotors probably won't arrive until February but that's OK, no hurry.

I have been down this road before with my Ford Falcon, with slotted rotors and track-day pads - vast improvement in stopping, and zero fade ever

 

The offset of the rotor is my immediate concern:


This could get interesting...

 

Hey gang, this is just a confirmation that the rotor offset is the limiting factor off the bat. The following is a shot of the stock X300 front brakes to observe the bracket and rotor orientation:


The next image is of the stock X300 rotor with the XK8 bracket and caliper:


It isn't so neatly centered in the bracket, but could likely be compensated for by the fact that it is a floating caliper as opposed to fixed, or shimmed (from behind) in the worst case. It does cement the fact that the offset of the XK8 rotor is a no-go. Simplest route would be to find a rotor with the correct diameter and offset to accommodate the XK8 bracket and caliper. I have notes at work on several GM rotors compared to a few Jags, I will find that later.

Th next route would be to use stock XK8 rotors and just shim the caliper bracket accordingly; just measure the difference in rotor offset and you have the thickness of shim needed - seems simple enough. Otherwise it would be more than a hub change, but a knuckle change also, and upper and lower control arm change to accommodate the newer knuckle (I DO think you could put X308 control arms and knuckles on an X300 - someday I will try it)!

 

Pictures don't show....just the photobucket upgrade box...