# Brake pedal stiffness



## silkman (Jul 29, 2004)

I have a strange problem that needs the help of the forum.

While driving, suddenly the brake pedal will be rock hard to the feel and will need extra force to be able to brake. Brake performance is not affected or compromised but it is scary when you have to brake and be faced with a rock hard pedal.

This *only* happens in a motorway, after I've had a couple of brake-free miles, maybe after driving 10 miles without touching the brake pedal, it will be very stiff at the first press, then it will work normally for maybe the next 10 miles. Engine will be at full working temperature, so the problem needs at least 30 min of motorway driving to occur.

It never happens in city driving.

The U shaped brake vacuum pipe has been replaced (top was broken) with original Audi 









I also checked and have recently replaced all green items on the piping under inlet manifold.









Ideas?

EDIT: After reading this thread, I think hissing is heard on pedal movement but not otherwise.


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## imartyn (Aug 31, 2015)

Sounds like you may be losing your vacuum on longer steady throttle runs, try coming off the throttle well before you need to, to build up some vacuum before you brake.

In town driving you're constantly on and off the throttle and building up the vacuum, just a thought.


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## Hoggy (May 8, 2002)

Hi, As above, brake servo vacuum leak. 
Hoggy.


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## silkman (Jul 29, 2004)

Thanks both for the replies. So I am after a new brake servo or it can be repaired?

Apparently this part is different for LHD and RHD. Parts for vehicles with ESP are
LHD 1J1614019A
RHD 1J2614019A









Audi part is about 340eur, decent aftermarket is about 75eur and I also found a seal repair kit for 3eur! AFAIK Audi doesn't offer a repair kit but the seals are available individually.









Do I need to replace anything else?









EDIT: Or is it the brake booster (the round part in the right of the picture) - EXPENSIVE !! [smiley=bigcry.gif]


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## Hoggy (May 8, 2002)

Hi, That is the Master Cylinder. Check the vacuum hoses & NRV to the *brake servo* for splits/leaks.
Hoggy.


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## silkman (Jul 29, 2004)

Ok got it. The brake servo is the brake booster...


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## iain26 (Feb 18, 2018)

check the hose going to the servo, seems quite common for them to split and cause a vacuum leak


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## desertstorm (Apr 25, 2017)

As above check the routing of the vacuum pipe all the way from the engine to the brake servo. It goes behind the heat shield at the back of the engine and this is where the pipe quite often splits by the non return valve.


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## silkman (Jul 29, 2004)

Thanks for the replies. Sure enough it was the second brake booster pipe (as I had already replaced the other one). Sneaky crack in two places behind the heatshield. Part was 65eur and only original Audi exists. Also Audi recommends changing BOTH at the same time (which I didn't).

A number of part numbers exist for this: Make sure you get the correct one. I had replaced #6 about a year ago and now I replaced #3









New part









Cracked pipe inside the heatshield









TBH this can definitely be repaired with a decent part of automotive pipe (silicone?). The trick is that since this part holds vacuum, the pipe shouldn't bend inwards from the vacuum but hold its place... £10 cost max compared to 120 for both pipes from Audi...

*Thanks to both desertstorm and iain26 for pointing to the right direction * [smiley=cheers.gif] [smiley=thumbsup.gif]


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## desertstorm (Apr 25, 2017)

Glad you found this, poor design really as it seems like a fairly common fault.


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## silkman (Jul 29, 2004)

Poor design or planned obsolescence? :roll:


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## JPatterson (Feb 18, 2009)

silkman said:


> Thanks for the replies. Sure enough it was the second brake booster pipe (as I had already replaced the other one). Sneaky crack in two places behind the heatshield. Part was 65eur and only original Audi exists. Also Audi recommends changing BOTH at the same time (which I didn't).
> 
> A number of part numbers exist for this: Make sure you get the correct one. I had replaced #6 about a year ago and now I replaced #3
> 
> ...


Good work. Was about to comment that based on your symptoms, the leak was probably past the check valve. ( on the servo side of). Glad you found it. Noted: mine is 17 years old too.


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## JPatterson (Feb 18, 2009)

Well! 2 1/2 years later and this exact failure happened on my roadster. Didn't remember this thread at all. Had to diagnose and figure it out from scratch. Memory is a terrible thing to loose. :?


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## silkman (Jul 29, 2004)

A decent fix (apart from replacing the pipes with Audi parts) would be to sleeve over the broken part, provided there is space. By sleeving over I mean put a bigger OD rubber or silicone piece over the broken part and tighten with two hose clamps. And save the 200 or so the two pipes cost from Audi.


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## JPatterson (Feb 18, 2009)

silkman said:


> A decent fix (apart from replacing the pipes with Audi parts) would be to sleeve over the broken part, provided there is space. By sleeving over I mean put a bigger OD rubber or silicone piece over the broken part and tighten with two hose clamps. And save the 200 or so the two pipes cost from Audi.


I used a piece of reinforced rubber fuel line 7/16" id. ( 11 mm) Removed the hard plastic section below the check valve and replaced. Clamps not needed here as it is vacuum only below check valve. Cost? $2.50.


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## sideburnz (May 28, 2020)

Thanks for all the tips guys - this was my discovery today, after a year of putting up with scary brakes and garages telling me they're fine. Short pipe split in exactly the same location. Will get some reinforced hosing and fix as suggested


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## silkman (Jul 29, 2004)

@sideburnz
Glad you sorted it out and cheap! My garage guy was still scratching his head as to what the problem was.

BWS TT also has a video on how to:


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