Braking issue with my D4

**Barraman** · 18th March 2019, 01:49 PM

I have a 2015 D4 with 125,000 km on the clock - always serviced by the dealer, to the letter.

Under firm braking (also does it under more severe braking), from no more than 40-50 km/hr, my Disco "bumps" about halfway between the application of the brakes and stopping. It feels like the brakes grab and then let go slightly - resulting in a noticeable "bump" sensation. It brakes smoothly up to and after the "bump".

Its been checked by the dealer, who found nothing wrong - pads, rotors, fluid levels all good.

They tell me its "just the ABS unit doing its job" but I don't think the braking is hard enough to get the ABS involved and I am sure that it didn't used to do it.

Any suggestions?

**loanrangie** · 18th March 2019, 03:30 PM

ABS should be virtually unnoticeable unless under very braking, is there any abnormal movement felt thru the steering wheel ?

**RobA** · 18th March 2019, 03:33 PM

Sounds like an ABS activation to me. Can happen on bumpy surfaces along with loose ones

Rob

**BradC** · 18th March 2019, 04:16 PM

Originally Posted by RobA

Sounds like an ABS activation to me. Can happen on bumpy surfaces along with loose ones

I've had the same issue on a vehicle of different make. It turned out to be a dicey ABS sensor. Intermittent fault, happened rarely and was a bear to track down. The faulty sensor just seemed to occasionally stop sending the signal to the ECU, which the ECU identified as "wheel stopped turning, get of the stoppers". It'd just as suddenly start working again and the brakes would go back on.

I eventually nailed it as I started to pay attention to the feel and noticed the slight pull on the wheel each time it happens which allowed me to narrow it down to one corner.

No codes, no diagnostics and the occasional brown trouser moment when pulling up to traffic lights approaching an expensive vehicle.

**loanrangie** · 18th March 2019, 04:30 PM

Dodgy ABS sensor been known to activate the DSC which gives a grabbing almost crunching like sound.

**Barraman** · 19th March 2019, 08:36 AM

Originally Posted by loanrangie

ABS should be virtually unnoticeable unless under very braking, is there any abnormal movement felt thru the steering wheel ?

No

**cruiseh** · 19th March 2019, 09:02 AM

Any chance its just a gearbox downshift thing? ive noticed mine has noticable downshifts if braking lightly, especially if in sport mode.

**Barraman** · 19th March 2019, 09:56 AM

Originally Posted by RobA

Sounds like an ABS activation to me. Can happen on bumpy surfaces along with loose ones

Rob

This happens on smooth road surfaces.

**Barraman** · 19th March 2019, 09:58 AM

Originally Posted by cruiseh

Any chance its just a gearbox downshift thing? ive noticed mine has noticable downshifts if braking lightly, especially if in sport mode.

Hmmmm, now that is a possibility! I have only recently started to use Sport mode. Will drive it in Drive to see if it still does it.

Thanks!

**Ferret** · 19th March 2019, 11:10 AM

Originally Posted by Barraman

... Under firm braking (also does it under more severe braking), from no more than 40-50 km/hr, my Disco "bumps" about halfway between the application of the brakes and stopping. It feels like the brakes grab and then let go slightly - resulting in a noticeable "bump" sensation. It brakes smoothly up to and after the "bump".

Noticed something like that myself about a year ago, a single clunck on mid / heavy braking. Though maybe it was a loose calliper or something since I had recently done some work on the rear parking brake.

Anyway on having a poke around again at the rear I found this - upper rear control arm bush had failed.

DSC00688.jpg

Now I have since changed the upper rear control arms plus all discs and pads at the same time so I can't be certain what was causing it but a failed bush could be a plausible explanation for the 'clunk' noise.

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