Technical Master Cylinder Seal Repair too tight

[Avspotter]

Hi all,

I bought some new seals for my mk1 master cylinder (not the mk2 readily available online) from Brake Parts UK (linked below) - an Autofren Seinsa kit:
https://brakeparts.co.uk/.../Hydraulic.../BMS1237

The seal pictured from the primary cylinder is FAR too tight, such that the piston fails to retract once pressed in by the brake pedal (takes about 10 minutes to reset itself it the brakes released position). You can see the small nick taken out of it from when I removed the piston - it's so tight it tears itself apart each time I remove the piston, so I'm reluctant to fiddle with this all much further. It needs an extreme amount of force from me to manually remove it due to the tight seal. Even after lubricating the seals and bore with brake fluid, there was no improvement once the piston was in (presumable because the seal was so tight it dried itself out by wiping fluid off).

I was wondering if anyone else had experienced this problem with overtight seals once they'd replaced them, and if you had been able to do anything about. Or any other ideas I could try to relieve the "tightness" of the seal, without compromising the cylinder.

These are the right seals as they are specified for the mk1 cylinder with 19mm bore, but I'm a little stuck here with it!
Cheers all
H

 

[porta]

Hi all,

I bought some new seals for my mk1 master cylinder (not the mk2 readily available online) from Brake Parts UK (linked below) - an Autofren Seinsa kit:
https://brakeparts.co.uk/.../Hydraulic.../BMS1237

The seal pictured from the primary cylinder is FAR too tight, such that the piston fails to retract once pressed in by the brake pedal (takes about 10 minutes to reset itself it the brakes released position). You can see the small nick taken out of it from when I removed the piston - it's so tight it tears itself apart each time I remove the piston, so I'm reluctant to fiddle with this all much further. It needs an extreme amount of force from me to manually remove it due to the tight seal. Even after lubricating the seals and bore with brake fluid, there was no improvement once the piston was in (presumable because the seal was so tight it dried itself out by wiping fluid off).

I was wondering if anyone else had experienced this problem with overtight seals once they'd replaced them, and if you had been able to do anything about. Or any other ideas I could try to relieve the "tightness" of the seal, without compromising the cylinder.

These are the right seals as they are specified for the mk1 cylinder with 19mm bore, but I'm a little stuck here with it!
Cheers all
H

Did you soak the seal in brake fluid beforehand, works especially for tight fittings…I was taught to rebuild the whole thing immersed in brake fluid

 

[Avspotter]

Did you soak the seal in brake fluid beforehand, works especially for tight fittings…I was taught to rebuild the whole thing immersed in brake fluid

Interesting, thank you! I’d covered the seals in fluid but it wasn’t “immersed” in fluid per se - I’ll give that a crack tomorrow.

 

[porta]

It’s only a suggestion, as it wouldn’t be the first time an OEM part isn’t the right part

 

[Avspotter]

Ok so this made it a little better, but still takes a while for the piston to retract... Anywhere I could just find a new mk1 master cylinder (I understand they're hard to come by) unless there are any other ideas?

 

[porta]

What I do for seals, if they’re no longer available, is take the complete part, with seals, to a local hydraulics place, in my case Active Hydraulics in Keighley…they have never let me down

 

[Avspotter]

Now that's an idea.... I'll have a look around near where I am (SW London) - I've just ordered a different seal kit from Autodoc so fingers crossed for that, but if that also fails to deliver, looking local is a great idea.

 

[Avspotter]

For anyone reading this later on, Rapid Hydraulics Ltd, Mitcham, CR4 4NA have said they'll be able to sort this out for me.

 

[Avspotter]

For anyone reading this later on, Rapid Hydraulics Ltd, Mitcham, CR4 4NA have said they'll be able to sort this out for me.

Edit - I was then sent to A2 Engineering in Crawley who fixed it as Rapid Hydraulics weren't able to sort it in the end