I've noticed that when braking, the brakes will operate normally (although most of the caliper carrier pins I think have seized). The rear inner brake pad seems to be worn right down, yet the outer pad is fine. I've checked the piston and the seal that usually covers it has perished / non existant (perhaps this is where the issue lies?). When the brake pedal has full travel, it will harden as expected, however you can feel the pedal slowly sink to the floor. Any ideas where I should start for diagnosis? I thought about replacing the carrier pins and then bleeding each caliper and then try again. Any ideas would be helpful, many thanks.

15 minutes ago, Frosty99 said:

the caliper carrier pins I think have seized)

Either this or the pistons are seized in the calipers based on what you've said. Either way, bleeding the calipers before sorting that and replacing the rear pads is a waste of time and money since you'll be treating the symptom of pedal sink without first curing the problem.

Edited 12 April, 20215 yr by KenONeill

If the brake pedal goes hard but then continues to sink to the floor, & there are no leaks in the system, the master cylinder seals must be leaking.

 

That is on top of the other problems you have highlighted.

 

Sounds like the whole braking system need an inspection & overhaul.

When sat on the drive no engine on, I'll pump the brakes and the'll harden but they'll still sink when holding pressure on the pedal. From what I can see there isn't any leaks coming from the calipers, so perhaps this is an internal leak? If it is the master cylinder as you say, is that relatively difficult to repair as a 1 man team? Cheers

17 minutes ago, Frosty99 said:

sat on the drive no engine on, I'll pump the brakes and the'll harden but they'll still sink when holding pressure on the pedal.

That's perfectly normal behaviour when the engine is off; you need the engine running to maintain servo vacuum and hence pedal consistency.

 

I still say you have a separate problem with piston or caliper pin(s) seizing, causing excess wear on rear outer pads though.

Cool, I'll give it a go tonight and report back if it's the same or not. Yeah I had a feeling I might have a piston issue. Do you know if the self bleed kits are any good? I was looking at getting one that uses tyre pressure to provide the "pumping of the brakes". Thanks for the help

2 hours ago, Frosty99 said:

When sat on the drive no engine on, I'll pump the brakes and the'll harden but they'll still sink when holding pressure on the pedal. From what I can see there isn't any leaks coming from the calipers, so perhaps this is an internal leak? If it is the master cylinder as you say, is that relatively difficult to repair as a 1 man team? Cheers

This is normal behaviour for a vacuum servo.

25 minutes ago, Frosty99 said:

Cool, I'll give it a go tonight and report back if it's the same or not. Yeah I had a feeling I might have a piston issue. Do you know if the self bleed kits are any good? I was looking at getting one that uses tyre pressure to provide the "pumping of the brakes". Thanks for the help

Brake bleeding is a waste of time and money unless you correct the siezure first, but I'd be entirely happy to use a one man bleeding kit.

2 hours ago, KenONeill said:

3 hours ago, Frosty99 said:

sat on the drive no engine on, I'll pump the brakes and the'll harden but they'll still sink when holding pressure on the pedal.

That's perfectly normal behaviour when the engine is off; you need the engine running to maintain servo vacuum and hence pedal consistency.

Did you read the whole sentence Ken?  This bit? - "they'll still sink when holding pressure on the pedal"