Soft Brake Pedal When Stationary

[th3_f15t]

Evening all. I have an issue with my Golf R's brakes. I recently fitted Porsche Cayenne 6 piston Brembo calipers and rear stainless steel lines which have massively improved the braking. However, when stationary, the pedal goes soft and I can depress is almost to the floor (same in neutral). Car is DSG for info.

I suspect it's the master cylinder not being able to maintain enough pressure in the system when still but I could be wrong. When I bled the system, I did the rears first, then the fronts, then cycled the ABS pump a few times but hasn't seemed to cure the issue. Made sure that clean, air free fluid was coming out the calipers when bleeding. Any other suggestions to try?

[r5gtt]

I'd say you've got a weak master and it needs upgrading from the forum reads re brake upgrades and you're running 6 pots so that maybe the reason.

Rear left rear right front left then front right high performance fluid should be used to maintain pressure at a high boiling point.  hope I'm not talking jibberish 

[doylebros]

My first thought is

What equipment was used for the bleed operation, pressurised or manual equipment.

What start and finish point.

[vRSAlex]

Is it fine when driving?

Jump into another R with stock brakes and you will find that they all do it.

[omeydz]

Did the reservoir go empty at all?

When I was replacing faulty ABS MK60 to the EC1 version that happened to me and kept sinking to the floor with my pressure bleeder.

Apparently repeated pressing of the pedal this low can affect the master cylinder seals somewhere I read.

Got a garage to finish the bleed with their kit and the pedal takes a little more travel to bite the brakes compared to standard (OEM brakes). Almost more progressive than biting high up on the brake pedal travel cycle. Passed MOT etc fine and no leaks.

So think the master cylinder would probably need changing to make it perfect if what I described above has happened.

Hope that helps 

[Shoduchi]

I'd say you've got a weak master and it needs upgrading from the forum reads re brake upgrades and you're running 6 pots so that maybe the reason.

Rear left rear right front left then front right high performance fluid should be used to maintain pressure at a high boiling point.  hope I'm not talking jibberish 

My Ed. 30 has the same 23 mm3 MC and the same brake setup as @th3_f15t. The pedal is firm in any situation. I can put all my weight on it and it won't sink to the floor.

[Shoduchi]

Maybe omeydz has a good point.

My GT Sport with R32 front brake setup and 22 mm3 MC does have a sinking brake pedal when stationary. While driving I just have to make a small pressure for the car to stop fast and it never sunk to the floor when I braked hard.

[r5gtt]

I'd say you've got a weak master and it needs upgrading from the forum reads re brake upgrades and you're running 6 pots so that maybe the reason.

Rear left rear right front left then front right high performance fluid should be used to maintain pressure at a high boiling point.  hope I'm not talking jibberish 

My Ed. 30 has the same 23 mm3 MC and the same brake setup as @th3_f15t. The pedal is firm in any situation. I can put all my weight on it and it won't sink to the floor.

Oh well in that case it's probably not been bled properly.

[omeydz]

On my MK6 Iv got R20 345/310 brakes and standard master cylinder ,,, totally oem feel no matter what and good braking power!

[th3_f15t]

The brakes are spot on when driving, just when stationary. I bled the system using a pressurised bleeder, going to use slightly better fluid and re-bleed tomorrow anyway just for the sake of it then see how things are. The pedal is getting better as the brake bed in so may just be a teething problem.

Still, an upgraded 25mm master cylinder will still be done at some point, Wilwood Brakes do a range of upgraded MC's so going to save and enquire.

[Shoduchi]

You can also consider contacting @DaveB@Vagbremtechnic or @vRSAlex to see if they can source you a RS3 MC. I really don't think you'll need it but it's your call... I've put my foot to the brakes enough to make my road tyres Contis Sport Contact 5 melt a bit on track but never felt brake fade with EBC Redstuff at the front.

[AJP]

Not sure if it applies to the mk6 R, but I'm sure I've read that there's something a bit iffy about fitting the ttrs/rs3 mc to a mk5 gti at least. I think it might be a problem with the servo. So that might need swapping too.

I also read an old thread where Dave was quite hesitant to recommend a certain mc upgrade - I can't remember the exact application but it was quite possibly a ttrs mc in a mk5 - it sounded to me like mix and matching parts might create a setup that in some cases was dangerous.

It'd be great if someone could dig out the thread. I think Dave can be quite hard to get hold of but I'm sure he can advise on the best plan.

I'm sure you know but the 18z is a good 200mm sq bigger in piston area than the standard R caliper. It should still work, but won't be ideal for the stock mc.

Best of luck sorting it pal.

[Shoduchi]

Yeah @AJP! You're correct. Not all MC and booster from the RS3 work in the Golf, that's why I recommended contacting who knows what is good and what isn't. For what I recall @DaveB@Vagbremtechnic was trying to order a batch of good RS3 MC for Golfs mk5.

I also know about the lack of MC size for Brembos 18Z but in daily and track use I can't complain about anything. The brakes are powerful and much more progressive than stock or R32 front brakes. I like it a lot and it makes it easier to brake smoothly with a DSG gearbox. With a manual it's much easier to make the last bit of the braking being smooth. With on/off brakes and a DSG it isn't.

[th3_f15t]

So I very carefully and thoroughly re-bled my brakes today, the pedal feel is slightly improved but the spongy feeling is still present when stationary although not as bad. I never noticed it when my brakes were stock as I only discovered it during testing my new brakes.

Likely I'll remain on the OE master cylinder for a little while, as it does have a very nice and natural feel when driving, but I will end up upgrading to a larger master cylinder soon because I would rather a more aggressive feel to my brakes. Either RS3 or a Wilwood upgrade, likely the latter as I know a couple of VW Cup cars run them which appeals to me.

[jason_rmh]

After fitting r32 front and rear calipers I had the same issue.

After a few attempts at bleeding, the brakes are good, and not so spongy but the pedal does slowly travel when car is stationary and foot pressed on brake pedal.
I've read all sorts of conflicting posts as wether there is a fault in the MC or not.

However, the brakes work fine and passed mot since, so I've not really followed it up.

Jas