uneven braking

[wnderer]

under light braking the car pulls straight & true however under heavy braking my car pulls sharply to the left then right then left then right again until the car stops or I let up on the brake,
Im suspecting its an ABS issue, has anyone experienced similar?

car is a 1992 4.0

[XjRestorations]

Hi,

My first thoughts here would be wishbone bushes.
A partially siezed calliper would pull one way - but worn bushes would allow the front geometry to wonder - and this is exaggerated under heavy braking.
Lift the car and check firstly the upper wishbone bushes for excessive movement or rust trails coming out from the bushes.
Also check for unusual tyre wear.
The lower bushes really require the springs to be compressed to test fully - although in extreme cases - they will be visably split and worn out.

Kind regards,
Keith

[wnderer]

checked the wishbone as suggested can see nothing wrong with them so I'm thinking abs rings on the hubs as it only happens when the abs is working

[PaulGover]

checked the wishbone as suggested can see nothing wrong with them so I'm thinking abs rings on the hubs as it only happens when the abs is working

If an ABS valve were playing up, you should get (a) the ABS warning light coming on on the dashboard, and (b) a stored fault code. I know this 'cos I took my 91 facelift V12 for a spin a couple of months ago, and up came the ABS light.

I'm assuming the 4.0 cars share the same ABS system.

To get the fault code, you need to bridge the brown&pink wire to the black in the 3-way diagnostic plug in the boot over the left wheel arch (behind the panelling and lurking around the fuel filler piper). Then you turn on the ignition and watch the count the lamp flashes, two groups of flashes, each group representing one decimal digit of a 2-digit number. The details and code explanations are in the workshop manual volume 4 and on the various CDs and DVDs from Jaguar Heritage.

As I say, I know there's one there for a dickey valve. The repair hint is to hope it goes away. Otherwise you're probably looking for a replacement pedal/master cylinder/control-valve assembly. I got one from a breakers a few years ago, not too hard to install, and less expensive than the new plastic brake fluid reservoir (needed cos the old one was full of crud and there's no earthly way of cleaning it given the labyrinthine internal baffles).

[wnderer]

checked the wishbone as suggested can see nothing wrong with them so I'm thinking abs rings on the hubs as it only happens when the abs is working

If an ABS valve were playing up, you should get (a) the ABS warning light coming on on the dashboard, and (b) a stored fault code. I know this 'cos I took my 91 facelift V12 for a spin a couple of months ago, and up came the ABS light.

I'm assuming the 4.0 cars share the same ABS system.

To get the fault code, you need to bridge the brown&pink wire to the black in the 3-way diagnostic plug in the boot over the left wheel arch (behind the panelling and lurking around the fuel filler piper). Then you turn on the ignition and watch the count the lamp flashes, two groups of flashes, each group representing one decimal digit of a 2-digit number. The details and code explanations are in the workshop manual volume 4 and on the various CDs and DVDs from Jaguar Heritage.

As I say, I know there's one there for a dickey valve. The repair hint is to hope it goes away. Otherwise you're probably looking for a replacement pedal/master cylinder/control-valve assembly. I got one from a breakers a few years ago, not too hard to install, and less expensive than the new plastic brake fluid reservoir (needed cos the old one was full of crud and there's no earthly way of cleaning it given the labyrinthine internal baffles).

abs light not on but will check for fault code just in case a PO has removed the bulb if it does need a pedal/master cylinder/control-valve assembly I've got a complete V12 pre facelift that I can rob for spares