Brakes and frustration Mk10

There is no technical reason to upgrade a MKX/420G brakes

They brake very well with 4 wheel discs, I can understand with a drum braked vehicle

If the original parts are totaled, it may make some sense, but it will be more expensive than OH the original parts

This is especially true for thar 420G which does have a larger brake pad swept area than early MK10


Thank you for your help. I tried the compressed air and that did nothing. Next up I will try the grease gun method.

Is your brake master cylinder on the vehicle?

If so, this is very easy way to push them out, split calipers, plug any holes with bleeders, connect brake hose, block piston from spitting out with G-clamp, knock piston right back in to break any corrosion seal, use foot pedal and hydraulic pressure to push out piston, just as intended, does not need power assist from booster/engine (hard leg pushing)

works every time

Hello Tony,
The cylinders are off the vehicle. They are spares that I want to do up.

my method will work easily,

remove front DS wheel,

disconnect brake hose and use that to do the individual caliper halves

reconnect when done, you will just need a very light bleed of that wheel cyl only

I have several 420G calipers to do. This is the way I will do them.

I pre-soak the whole unit in a bucket of my penetrating oil mix

If you use your G-clamp carefully, you will use very little brake fluid, a small bottle is enough to do a couple of calipers

pull the last bit of piston out with big multigrips (or a very good recent post has a homemade special tool…you really should find that post!

The biggest problem is if the chrome on piston has blistered allowing the steel piston to corrode and jam in the cylinder.

That is why I first knock the piston back into the caliper a bit, breaks the frozen piston, starts it moving

If your vehicle has engine power, all the easier

What year is your MKX ?

MKX-420G had several different calipers. FRONT ones are all exceedingly rare and expensive

Good you have spares, be careful to not damage them

Rear ones are similar to many other Jags, so not as critical

use some heat if the bleeders are at all stubborn

In addition to Tony’s excellent advice:
Question: Specifically which model MC are you referring to and is it Dunlop or Girling MC?
This is IMPORTANT as The Girling has a tipping valve held by a 1/2 Allen head set screw in the cylinder casting.

Method for removal:
Obtain a 1/8NPT to 3/8-24 UNF or 7/16-20 UNF SAE 45 degree male flare adaptor.
Most grease guns and air compressor nozzles are 1/8 NPT although some are 1/8 BSP.
The ports to the MC are 3/8-24 UNF for the Dunlop MCs and the Girling MCs, depending on which version, also have a couple of 7/16-20 UNF ports.
There is a company in Australia that likely has the components you would need. RYCO.

Compressed air and wood block or thick cloth for safety up to about 120psi max and vey explosive if it releases.
Grease gun filled with RED RUBBER grease to avoid contamination and up to about 500psi and gentle built up and release.
Or better yet, fit to the servo on the car and available pressure up to in excess of 1000 psi.

I have resorted to all 3 methods and can say that in many instances the 120PSI air compressor was simply not up to the task!

Good luck

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