Brake bed-in?

[Simon Baxter]

New problem:

After a week in storage today I went a small trip with the van.
The brake pedal is softer and seems to grab on lower than before. If I pump it up then it is OK for a few hundred meters then it sinks again.

Fluid level is fine, and I cannot see signs of brake fluid around the wheels or the master cyl.

The only thing I did last time was changed the pads and rotors and changed fluid (two person pump and bleed method)

What did I mess up.

Bleeding brakes is a bad idea.
The inside of the master cylinder can become rough and corroded on the parts of the cylinder which are not normally used.
By pumping the brakes you run the master cylinder seals over the rough part of the master cylinder and damage them.
Gravity bleed only for me.
It just sounds like you finished off the last of the life in the master cylinder.
 

[ZsZ]

New problem:

After a week in storage today I went a small trip with the van.
The brake pedal is softer and seems to grab on lower than before. If I pump it up then it is OK for a few hundred meters then it sinks again.

Fluid level is fine, and I cannot see signs of brake fluid around the wheels or the master cyl.

The only thing I did last time was changed the pads and rotors and changed fluid (two person pump and bleed method)

What did I mess up.

Bleeding brakes is a bad idea.
The inside of the master cylinder can become rough and corroded on the parts of the cylinder which are not normally used.
By pumping the brakes you run the master cylinder seals over the rough part of the master cylinder and damage them.
Gravity bleed only for me.
It just sounds like you finished off the last of the life in the master cylinder.

I did change it relatively recently. In 2018 IIRC...
 

[ZsZ]

You must totally dismantle the right side hub to see what is happening. I suspect that the nut was too tight and now one of the bearings has failed.
The flat screwdriver test tells you nothing, the washer could move with only 0.01mm end float and that is far too little!

Yes I have to disassemble and check it.
Unfortunately I have no magnetic stand for the indicator to check the float. The washer method is my only way.
Then tightening it more to have less play with the wheel on was not a good idea.

[ZsZ]

I did disassemble the right side. It seems like there are at least two seaparate problems.
The brake caliper pistons dust seal was damaged and possibly pinched betweslen the pad and the piston.

The spindle is not perfect but I did not measure huge wear. It is the late 22mm one.
I measured 40.90 mm spindle OD for the 41.00 mm bearing ID and 21.90mm OD for 22.02 mm ID with my cheap digital caliper. Tried to put the inner races on without the hub and they slide on easily and they dont seem to waggle on the shaft.

Fully tightened the nut while turning the hub until I could not turn it any more, then loosened and hand tightened it.
Then the washer cannot be moved only by levering the screwdriver on the edge of the hub and the play with the wheel on is about the same as the other side tightened to be able to the push washer with a screwdriver. The hub turns freely.
The washer seems to be straight and flat measured around with the caliper, but the side with the tab seems to grab first on the nut and lock it in place. Is it sided in/out?

I think the brake problem was caused by the rubber as the play is really tiny.

[ZsZ]

Update:
I have replaced the caliper seals on the right side and gravity bled the system.

The pedal is firm now, but still not consistent in height.
Eg.: the pedal is sometimes lower when braking in reverse.

I think I will replace the spindle on the end as I have a spare, but first I need to source good quality lower ball joints.
Is TRW still good, or only the T3 technique ones from BW have the machined cap?

[SurfT25]

Correct me if I am wrong, but iirc there are 2 bleed nipples on each of the front brakes. Did you bleed all 4 ?

[ZsZ]

Correct me if I am wrong, but iirc there are 2 bleed nipples on each of the front brakes. Did you bleed all 4 ?

The late sliding caliper setup only has one bleeder per side.

BTW update:
Pedal feel is still firm, but they get really warm and stinky (still can touch the hub for a sec or two, so I would not say thay are hot). And they squeak a tiny bit.
The braking power is less than before.

In the next few days I will disassemble them again to check.

[ZsZ]

I disassembled and put together everything agin and moved the pistons in and out a few times. Seems better now.

Observed a few things:

The the sound deadening lining on the back of the brake pads is crumpled where the piston contact is.

The grease in the outer bearing of the bad spindle started to go black. The wheel has play in 6-12 direction but not much in 3-9 direction.

On the pics I found of original VW pads it seems that they had either different thinner sound deadening lining or they had none.

[silverbullet]

You need a new or better condition steering knuckle. The grease has gone black because the bearing has overheated, due to insufficient end float which you cannot acheive due to wear on the stub axle.

[ZsZ]

You need a new or better condition steering knuckle. The grease has gone black because the bearing has overheated, due to insufficient end float which you cannot acheive due to wear on the stub axle.

Yes, I know.
I have some spares in storage but have to check them and buy lower ball joints.

Maybe next month, we have a deadline at the end of this one.

[ZsZ]

Did some driving this weekend.
City traffic + some highway.
Hard braking is fine but light is not as sharp as it was before.
Left side was fine temperature wise, right side was a bit warmer.