Lurching under braking

[AJP]

Hi

I've noticed a few times that under moderate to hard braking, usually from mid to high revs, that the car isn't smooth in decelerating.

It's not a brake issue, more that the engine braking is a bit 'lumpy'.

I probably haven't described it very well, but I'm guessing it could be something like an engine mount - mass moving more than it should which affects the momentum of the car.

Sound familiar to anyone?

[AJP]

Bump

[AJP]

Got to bump this again, could do with a bit of info guys.

Mount? Flywheel? Something else?

Hope someone can at least offer an idea!

[lukemk5gti]

Record it with a dash cam and put the video up... Very difficult to picture what you mean.

First thing came to mind was maybe your a.b.s.?

[AJP]

Don't have a dash cam unfortunately.

It's quite hard to explain!

I'm 99% percent sure it's engine related rather than brakes though.

If I for example rev up to 4000rpm then lift off, the car slows smoothly under engine braking. But if I apply the brake under the same conditions, it's as if the engine can't adjust its revs in line with the foot brake - and staggers/lurches from say 4000rpm down to 1500rpm. Almost like the revs hang then suddenly drop, making decelleration lumpy. It takes a bit of fun out of the odd blast.

[lukemk5gti]

Get a passenger to record it with their phone, both out the window and whilst looking at the rev counter...

I've never heard of it so I'd say it's an uncommon issue but maybe someone else on here has had a similar experience!

[AJP]

Could this be the subframe bolt issue?

Just bumping this after reading up and putting 2 and 2 together. It does seem like there's some weight 'shifting' when it shouldn't.

I'm going TTRS at the front soon so want to get this sorted first, rather than have the extra braking force accentuate it and make things worse!

[rich83]

DSG?

[AJP]

DSG?

Manual.

[rich83]

hmm... strange one... 

Does the same happen if you brake after youve dipped the clutch?

[Dan_FR]

Sounds quite normal to me under heavy braking. Heavy braking in gear will result in slowing the engine very quickly against a huge rotating mass, with the engine fighting to idle/maintain the revs in a smooth manner. If it didnt do this, every time you lifted off throttle in gear, you would have a huge lurch forward with the sudden and drastic engine braking as opposed to the fairly smooth transition you should have.

If its a much more physical issue, where you can actually feel weight/mass shifting under heavy braking, then i would explore further, checking engine and gearbox mounts, front arm bushes, subframe etc.

[AJP]

hmm... strange one...  opcornsoda:

Does the same happen if you brake after youve dipped the clutch?

Can't say I've tried Rich, but I'll give that a go at some point - I see your thinking.

[AJP]

Sounds quite normal to me under heavy braking. Heavy braking in gear will result in slowing the engine very quickly against a huge rotating mass, with the engine fighting to idle/maintain the revs in a smooth manner. If it didnt do this, every time you lifted off throttle in gear, you would have a huge lurch forward with the sudden and drastic engine braking as opposed to the fairly smooth transition you should have.

If its a much more physical issue, where you can actually feel weight/mass shifting under heavy braking, then i would explore further, checking engine and gearbox mounts, front arm bushes, subframe etc.

Agree in principle Dan, although I've never heard the mk5 GTI being described as lurchy... so I think it may well be an underlying issue rather than a characteristic of the car.

I did wonder whether it was flywheel related, then read more about the subframe bolt issue and it kind of makes sense. That, or as you suggest, a worn mount.

May well have a drive over to Statller at some point, see if they can take it for a little diagnostic spin!

[AJP]

And cheers for the input by the way guys

[grumpy]

Hi,
just wondering, does your car have the whiteline ALK?

I know someone who had the whiteline fitted, he said it became 'grabby' at times and needed lubricating to eliminate what you're describing. I think he used silicone spray on it. A while later he fitted the better designed superpro ALK and no more grabbiness - something to do with a metal collar - and why I went for the superpro kit.

Either way, hope you get it sorted.