On my Cobra - Jag XJ6 suspension,single Master cylinder with booster and auto box, if you park on loose gravel when you brake the front locks up and the idling motor overcomes the rear brakes and walks the car forward until you knock it into drive or neutral or grab on the handbrake This can get exciting if there's something hard close to the nose and you have forgotten about the problem .

How can I check how well the rear brakes are working?

They are Jag inboard rear brakes (IIRC)....they just dont work. Simple

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Originally posted by flak monkey
They are Jag inboard rear brakes (IIRC)....they just dont work. Simple

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We get the same result here in the snow with cars with automatic transmissions and engines running on choke.
Fronts lock up rear drums don't, car slides into the intersection, oops.
Try standing on the brakes to get the rear discs to bite.

60s/70s/early 80s Jag handbrakes weren't great but ok if adjusted properly and no oil on the rear disks.
If it is creeping with handbrake on something is wrong --- slacken everything back and re-adjust by the Jag WSM starting from the H.B calipers. Also check the idle speed isn't too high ---- car should only creep forward slowly with handbrake off..

Foot brakes were always fine..

Local mot station i would think would check them in the rollers for a drink.

I used to cring when taking my XJS's in for an MOT, nightmare to strip and adjust..... On an XJ6 I cut a hole from above so I could better access the buggers, commonly done BTW.

They can easily get covered in grease from the UJ's, suggest you give a good clean with brake cleaner, if you have driven with the brakes on they will glaze instantly as very small so probally need a new set of pads.


Regards Mark

Last time it snowed I was sat of the motorway next to a mercedes auto. Car in drive, brakes on, rear wheels turning on the ice. So your not alone. My vito van will overcome the handbrake if it's not on fully (very last click) (rear wheel drive)

Iv never done it but apparently its quite easy to change inboard to the later outboard and full XJ40 axles come up on eBay fairly regularly.

Thanks for that Speedy - the problem is that I have a narrowed rear on the Cobra fitted to the XJ6 diff & brakes - can't remember from which jag as it was 24 years ago but think it was a 380 if there is such a thing - so a change to XJS would mean cutting and welding the lower arms and possibly driveshafts, something I would prefer not to do.

Access to my rear calipers and pads is not a problem as I have an access hatch in the rear panel of the cockpit that gives easy access to everything - I've had the calipers off and on before and it's an hours job at most.

I think the final answer to my problem is to change to a dual MC with balance bar and change balance so that rear brakes "just" don't lock + a bit. Then I would know they are doing their fair share of the work - I never worried before as I the car stopped reasonably but now that I am setting it up for track days with almost 50% more power I want better braking.

Of course a change to twin MC's and no booster opens up a whole new ball game of MC size selection and cockpit and or engine bay modification to fit it all in to give reasonable access for adjustment and reasonable pedal pressures plus cost factors.