Inboard brake question

Not that it really matters, but I do have a XKE, but I am posting a question here as I need your help on an XJS question.

I am mulling over getting a project car (TVR) that has a diff from a 1986 XJS S/N SAJNV5845FC120610 installed and I would like to have inboard brakes, and have a few questions:

  • Did XJS’s come with inboard brakes?
  • Are they much the same as the E type? I’m familiar with?
  • I’m not sure how many holes are on the flanges of this XJS diff, are they all four bolt?
  • Any idea from the S/N of the car it came out of if it is a posi or not, and the gear ratio?
  • Any idea what I would expect to pay for a set of used ones?
  • Any other thoughts would be appreciated!
    Thanks all, Pat

The pre-94 XJSes came; with inboard PITA rear brakes … :angry:

  • Did XJS’s come with inboard brakes?

  • Are they much the same as the E type? I’m familiar with?
    Almost identical, I think they have different track and different handbrake cable/lever mechanism.

  • I’m not sure how many holes are on the flanges of this XJS diff, are they all four bolt?
    You mean the output shaft assemblies ? They have five bolts, tapered bearings and a crash sleeve for setting preload. Normally it would be a Salisbury diff.

  • Any idea from the S/N of the car it came out of if it is a posi or not, and the gear ratio?
    Most definitely posi, don’t know the ratio.

Hope that helps.

You might want to check for a drain plug on that diff. For a couple of years around that time, Jaguar switched from a Salisbury diff with a drain plug to a Dana diff with no drain plug. Then they switched back. Either diff works OK, but many don’t care for the Dana because it’s harder to get parts for. And the later “Salisbury” diffs are actually made by Dana, thanks to some buyouts and mergers in the diff biz. The Dana requires holes in the discs to access the caliper mounting bolts.

If the 86 is a US-spec car, the ratio will be 2.88:1. I dunno about cars for other markets. All XJ-S’s came with posi.

The output flanges on the diff are four bolt, possibly the same as the E type. The stub shaft assemblies bolt into the diff with 5 bolts on the Salisbury and 3 bolts on the Dana.

I’m pretty sure the inboard brakes are different. The calipers moved to a later design somewhere in there. The general design is similar, though.

No. You wouldn’t. Avoid.

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Make sure you have vented discs as you most probably aware it get very hot around the onboard breaks
I have heat rapped the exhaust through the suspension cage which really help in reducing
Heat .

Wow, thanks guys/gals this is really good information! A few follow up questions if I may:

  • Why are don’t I want them, what makes them a PITA? As they would be going in to a tubular chassis, I have full access for installing/adjusting.

  • Is there a particular year car I should (or should not) search for to get the best system from?

Thanks, Pat

Opinions vary a lot on this.

The inboards are more difficult to service when calipers and/or rotors need to be replaced. Big job. Changing brake pads, though, is no big deal.

Personally, I have no complaints. I’ve been using inboard brake Jags as daily drivers for over 20 years and have had no problems. In all cases I went thru the process of replacing calipers, rotors, hoses, pads…and then drove trouble free for years and years in each case.

Heat build up can be an issue. The area isn’t well ventilated. But, again, whether or not this would be a problem may depend on driving habits and conditions. I like fast-ish driving and give the brakes a workout from time to time…but I’m not a wildman-with-his-hair-on-fire type so the brakes are not subjected to severe use in my case.

Others will chime in


Yes, bleeding and pad changing are more work, but how often is it needed? Not much.

My 88 XJS i bought with 48K. Replaced rear pads and bled, but that was all that was needed.

One day when i need to drop rear suspension, ill go ahead and rebuild calipers, replace pads/discs, and service hand brake. At that point, i should only have to bleed every two years for the next 10 years.

I also got ceramic pads. Much better with heat. They’ll wear the discs down faster, but not that bad.

I like the idea of wrapping over axle pipes. I’m replacing mine next summer, so will do that.

I also like to imagine the less unsprung weight as i come out of corners :wink:

Those pipes radiate a lot of heat. The items most susceptible to that heat, though, are the output shaft seals on the diff, and the brake rotors themselves serve as a heat shield to protect those. That’s yet another reason why vented rotors are recommended there.

The heat from those pipes could also toast the U-joints in the axles, but they also come with their own heat shields – unless you remove them and toss them, as I did.

But over axle pipes are probably the coolest part of the exhaust system, right? Compared to downpipes?

I’m pretty sure bends get hotter than straight sections. But yeah, closer to the engine is hotter.

A 1986 XJS would have had inboard discs as standard and they have four bolt flanges.
All XJS’s came with LSD as standard.
I always re route the exhaust pipe between the lower wishbone and the half shaft to reduce the heat radiated to the caliper (as per photo, 2.25in pipe.
I also fit modified calipers, fitted with pistons from a front caliper to improve brake balance together with the ventilated disc for better cooling.

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How do you reroute? Do you have to bend your own exhaust pipe?

Yes Greg, any exhaust shop can do that

LSD??? :crazy_face:

Hello AttyDall - LSD = Limited Slip Differential - Tex Terry, II - 1991 XJS V12 Classic Coupe, 1986 XJS V12 Coupe - sent 11/19/2020 0009hrs. EST USA.

Ah k. thanks … !!! (rats, here I was wondering where Superblack and Superblue were hiding their stashes … :laughing: )

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The handbrake calipers and pads are also painful. I know everyone in the US don’t much care but it’s a safety check item in the UK and I have had 1 caliper failure and two pads delaminate. That’s three times lying on my back swearing for 4 hours.

If you have a choice, go with outboard brakes. The only reason that has been proposed for inboard brakes is the performance benefit from the reduction in sprung weight at the wheel hub. Now go out and look at any modern Jaguar, Porsche, Ferrari, Aston Martin, etc and see how many have inboard brakes.

The handbrake set-up isn’t very good, I agree.

Jaguar itself began abandoning the inboard brakes in 80s, when the XJ40 was on the drawing board with a redesigned suspension. I presume it was manufacturing cost-versus-real world benefit decision…with the latter not being enough to outweigh the former.

I wonder if the unsprung weight issue is of more importance on a tiny car like the TVR? I’m not sure how that would play in; I’m only on my fist two sips of coffee :slight_smile: