Braking issue with my D4

[Barraman]

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]

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

[RobA]

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

Rob

[BradC]

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]

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

[Barraman]

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

No

[cruiseh]

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

[Barraman]

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

Rob

This happens on smooth road surfaces.

[Barraman]

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]

... 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.

149454

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.

[Barraman]

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!

And therein lies the beauty of a forum like this!

Problem solved - it doesnt happen in “Drive”, only in “Sport” mode . Its the gearbox downshifting under firm breaking !!!

[Eric SDV6SE]

Cool, the transmission ECU is an adaptive control module in that it learns how you drive. I had a similar clunk befote i serviced the transmission valve body (a whole other saga) but on almost all gears, except 6th to 5th (downshifting), yet it would hold 5th far too long when upshifting.

Put a Sonnax kit though the valve body, new fluid and filter, no more clunks and super smooth shifting.

I still get a noticeable bump from 2 to 1st, but that's inherent to the transmission because 1st is such a high ratio. Also, in sports mode, the transmission will go into 1st, under normal or D mode, it always starts in 2nd