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Jaguar E-Type and XJ Inboard Brake Upgrade

Jaguar E-Type and XJ

Inboard Brake Upgrade

(Replacing Solid Rotors w/ Vented Rotors)

Here's the idea:  take out the rotors that look like this:

and install rotors that looks like this:

This is a popular modification, and three reasons are generally given for making the mod:

    1.    Improved brake cooling.  This generally isn't of much importance unless the car will be raced or driven down mountain roads, since the solid rotors seem to perform well enough for most street applications.

    2.    Improved cooling of the output shaft seals on the differential.  The inboard brakes surround the output shafts, and the brake rotors are bolted to them.  Hence, the seals may get heated by radiant heat coming off the brake rotor, or they may get cooked by heat from the rotor soaking through the output shaft itself.  Either way, vented brake rotors address the problem; they cool off faster after hard braking, so less heat gets to the seals either by radiation or soaking through metal.  Also, they should increase the airflow in the area by sucking air from around the differential housing and blowing it out the bottom of the car, so the oil and metal inside the differential should run a little cooler.  Whatever, there is some evidence that the differential output shaft seals -- notorious leakers -- do last longer on cars fitted with vented brakes.

    3.    Avoiding oily brakes.  When the output shaft seal leaks, the oil runs down the inboard side of the solid rotor.  Since the inboard side friction surface is thus well lubricated, it provides almost no braking action, and all braking from the rear has to come from the outboard side of each rotor.  Typically, it is evident that this is going on because the inboard pads are not wearing at the rate the outboard pads are wearing.  Once vented rotors are installed, oil leaking from the output shaft seals goes through the cooling passages instead of running down the inboard side, and therefore gets out the bottom of the car without lubricating the brake rotor friction surfaces on its way.  It also might help due to the airflow caused by the vented rotors; in pulling air from around the differential housing and blowing it out the bottom of the car, it may tend to draw airborne oil droplets into taking the same route.  Owners having performed this upgrade have reported the brakes seem to work better when cold (there would be no change if oil on the friction surfaces wasn't an issue), and there is evidence that cars with vented rotors do not demonstrate the unequal brake pad wear that is so common on cars with solid rotors.

Whether or not you buy any of those reasons for making such an upgrade, there are only two reasons not to make the upgrade: time and expense.  The upgrade will most certainly result in a better braking system, and can't possibly hurt a thing.  If you are having to perform some sort of maintenance on the rear brakes anyway -- especially if it involves installing new rotors -- then time for installation isn't much of an issue, because it takes barely any longer to install upgraded brakes than to install the OEM brakes.

In general, there are two ways to upgrade your XJ to vented rotors:  Buy a kit, or fabricate all the stuff you'll need yourself.  Since this is a common upgrade and there quite a few Jaguars out there that have the same basic rear brake arrangement, there are several outfits that offer such kits.

XK's Unlimited offers a kit, but little is known about it at this juncture.  Judging from the sketch in their catalog, it appears to use a two-piece rotor: the vented outer disc portion is attached to a hub with a circle of bolts (as in the photos above).  This is a common method of constructing brake rotors, especially for unusual or custom applications.  When the disc is worn, only the outer half of the rotor needs to be replaced.  When buying such replacement outer discs, you can return to XK's Unlimited, but you don't have to; several places such as Essex will make them to order to your specifications.

The kit offered by Terry's Jaguar Parts , judging from the photograph in their catalog, uses one-piece rotors.  This means that when the rotor is worn an entire new one must be purchased -- and such rotors are not going to be easy to find, so you will probably need to go back to Terry's for replacements.  Of course, you could opt for installing two-piece rotors then.

Bob Greene Developments in the UK offers a kit.

Theoretically, you could actually get the parts necessary for this upgrade from Jaguar; the TWR XJ-S came off the showroom floor with two-piece vented rotors.  Be forewarned, however, that TWR owners have some trouble getting parts to maintain their brakes from Jaguar, and sometimes opt for some of the ideas presented below for finding parts instead!

There is now one more source for a kit: Essex.  Read about it on the page describing how to obtain a two-piece rotor .

The other way to upgrade your rear brakes is to fabricate the necessary hardware yourself, or have it fabricated locally.  This has the potential of saving a bit of money compared to the kits, but will require some time and skill to assemble the various parts.  If you happen to have the ability and equipment necessary for machining the hubs required, it could save you a lot of money; the actual dollar outlay will be comparable to a simple brake overhaul.  At the other extreme, you could just hire a machine shop to make all the parts, but that might not save you any money over buying a kit!  It is suggested that you read through the two pages linked below and decide for yourself if you're up to the work.

Kirby Palm did this upgrade by fabricating some of the hardware and having the rest made special order for him.  The details of the work are presented in the Book for the benefit of others who would like to make the same upgrade.  Some pictures are presented here in two pages; one page describes the two-piece rotor itself, including the outer disc, the inner hub, and the bolts to hold it together.  The other page describes the small parts needed for the job, most of which are involved in spacing the caliper wider.

Here's what Palm's brakes looked like when done:

All of the upgrades described above actually use the original calipers; to make room for the wider vented rotors, the calipers are separated and reassembled with spacers between the halves.  This works fine -- but most people don't even get involved in their rear brakes until there is a problem, and that problem as often as not is that the calipers need rebuilding or replacement.  Hence, you might consider installing an all-new high-performance brake system such as those made by AP and others rather than simply upgrading the existing brakes to vented rotors.  The cost of renovating the original calipers plus the parts needed to widen them would go a long way toward paying for a really nice set of aftermarket high-performance calipers. 


One final comment:  If you talk with Jaguar "experts", you may hear that installing two-piece vented inboard brake rotors is difficult and problematic.  There's a good reason for those reports.  An outfit called Gran Turismo Jaguar once offered a vented rotor kit that was horribly designed -- requiring grinding on the differential output shafts to install, believe it or not -- and shoddily machined, usually resulting in runout problems.  Unfortunately, this was probably the most popular kit of its time, since GT Jaguar was more adept at promotion than most such outfits.

Gran Turismo Jaguar is now history, which is probably fortunate -- reports were that many of their other products were little better than their vented brake kit.  But the stories about problems with brake upgrade kits remain as their legacy.  Please don't take any heed; a properly-designed kit from one of the suppliers listed above or a set of parts fabricated according to the instructions provided will bolt right in and work splendidly.  It's really an easy, no-hassle upgrade.

 


 

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