Front brake application uneven (MOT fail)

[jason_rmh]

Hi All,

My golf was in for MOT today. Failed due to front brakes not braking evenly. The drivers side caliper is weaker than the passenger side.

Background
Its a 2006 Mk5 2.0 GT TDI (BKD). Ive owned the car for over 5 years now and like most on here, its been looked after like a baby with nearly all of the maintenance / modifications carried out myself.

The car is now getting to high mileage (172,000) but drives great and no major issues, has been well maintained, serviced regularly and generally well looked after but is modified.

In 2014 i fitted fully reburbished R32 front and rear calipers / discs / pads and VAG 10 HEL front and rear braided stainless steel hoses along with a brake fluid change and bleed.
I fitted Mintex 144 Fast Road Front Brake Pads at the same time.
The discs and pads are due for replacement soon but perfectly fine for now.
Once a year I have stripped them down, cleaned and reassembled.

My car has the MK60 abs pump, (1K0 907 379 AA)

I noticed last week when I had to brake sharply on the motor way, the car pulled to the left.

Problem
At MOT today the car failed due to drivers side caliper being considerably weaker on the brake test than the passenger side, which ties in with my experience pulling to the left.

Trouble shooting
So far, the following has been done (by the garage) in attempt to diagnose the issue:

• Drivers side caliper stripped, cleaned re assembled (inc slides, surfaces etc). Re tested, same result.
• Drivers side caliper off again, piston removed and checked. Piston was clean and moving freely. Cleaned re assembled. Re tested, same result.
• No faults showing on ABS system (according to garage)

The garage then ran out of time so will be looked at monday.

Im thinking the caliper itself is ok, so I'm maybe it may not be getting correct pressure through the brake lines?
The following is what I can think is possible causes, but I'm hoping for suggestions on how to pin point the issue / rule out potential causes:

• Faulty / sticking caliper (seems to be ok?)
• Faulty / contaminated pads?
• Discs / pads?
• Blocked / collapsed / faulty brake hoses
• Air in system (re bleed)
• ABS pump faulty?

I am going to the car on monday and will scan with vcds.
Is there any measuring blocks in VCDS that will show if the ABS system is working?

Garage suspects ABS pump may be faulty so I would like to be able to confirm or rule this out.

I've done some searching and aside from the common brake pressure sensor fault, I've not found any cases of faulty ABS pumps displaying my symptoms.
Advice appreciated.

Jas
 

[Andy]

we had this as work today,we swapped the pads around and it worked OK
it also could be the flexi pipe

[jason_rmh]

You used the same pads but swapped sides or fitted new pads?

[Andy]

used same pads just swapped them around

[jason_rmh]

So I popped to the garage this morning. Brake application test shows the % difference between the OS and NS front brakes.
The limit is 30% difference.
The test was varying from 29% up to 42%.

We swapped pads for a new set as it came down to 12% which is a pass.

Don't really know why the old pads were doing that, they had life left in them.
They were slightly un evenly worn eg inner pad vs outer pad on the weak caliper.

Who knows.
Jas

[lukemk5gti]

One caliper could have been sticking intermittently grinding down the pad every now and then.

Eventually when the caliper does decide to then work it would have an uneven wear like mine 

I replaced both calipers instead of just the one for peace of mind and it's fine now!

[Andy]

So I popped to the garage this morning. Brake application test shows the % difference between the OS and NS front brakes.
The limit is 30% difference.
The test was varying from 29% up to 42%.

We swapped pads for a new set as it came down to 12% which is a pass.

Don't really know why the old pads were doing that, they had life left in them.
They were slightly un evenly worn eg inner pad vs outer pad on the weak caliper.

Who knows.
Jas

good to hear it passed