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[PhatDave]

I have a 1954 Riley RME for my sins, and am currently working on making it roadworthy.

Today's problem is to do with the master cylinder, which I have removed, disassembled, soaked in white spirit and rebuilt with new seals.

Despite the new seals and a new spring the piston is sticking in the cylinder and not returning to the correct position.

Is this just because the seals I have bought are not very good? Or has anyone got a suggestion on how I can get it working?

It's a girling(?) hydraulic system, unassisted and pretty much as simple as these things get surely!

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[Dave69]

did you lubricate the piston with brake fluid before putting it back through the seals?

[PhatDave]

I put brake fluid on everything before putting together.

I have taken it apart again and rebuilt it with the original end seal and it now returns unassisted and doesn't appear to leak but still doesn't operate the brakes, pedal just pumps and never has resistance, fluid in the reservoir, can't find any leaks...

What have I done wrong?

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[Dave69]

Sounds like you have trapped air in the system where the pedal hasn't sufficient pressure to bleed it out. If the cylinder now moves and returns freely I would use a pressure bleed process or a vacuum pump to pull the fluid through to the wheel caliper/cylinder.the other option is to prebleed the master cylinder assembly prior to connecting the main brake lines which used to be the normal process in older cars
 

[Bubba]

 

[wildwood]

Maybe.....if you haven't done so already....

Bench bleed the master cylinder first?

[PhatDave]

Ah, I didn't know pre-bleeding was a thing! I have recently purchased one of these pressure bleeding jobbies because I'm finding it difficult to get an unwilling volunteer now we have a small hoomin running around, wife says she is busy with him and he loves to help but is not very useful with listening or doing (15 months).
I have now started on the front cylinders as they look scabby, new seals and things to go in, once all the seals and rubber flexi hoses are replaced I will have a go with this bleeding thing and hopefully that will be another job off the list!

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[bgbazz]

You need to be very wary of these 'small hoomins' ...there's a good chance they will take over the world as we know it!!

[PhatDave]

Tomorrow's leaders and all that chuff... Not mine though, I think its a bit special.

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[bgbazz]

 

[Dave69]

http://www.mityvac.com/pages/products_bcbe.asp

personally the above is better than pressure bleeding as you only work from the brake at the wheel