24 replies to this topic

[John K Series]

Have yellow tag dual system cylinder. Doing rebuild. The primary piston came out with a spring compressing screw in the end (i'm new and cant see how to put pics in) making the spring nearly fully compressed. Videos of rebuilds i have seen do not have this screw and the spring does what a spring normally does. Putting back together now, do I leave the screw in? If not how will the cylinder work? The car is a project and it seemed to work previously but the spring does not make sense. Also have a query re the 2 slotted shims between cylinder and reservoir. Do the slots go in line with the length of the cylinder or 90 degrees to? The xar is 4 wheel disc by the way if it makes a difference No pics, see above. Be gentle and basic technically please. Thanks

[bpirie1000]

4 wheel disc? Fronts disc, rear drums..

Try diagrams such as this.

https://www.somerfor...ster-and-servos

Or this more suited to your issue..

https://www.somerfor...rols-up-to-1988

[Spider]

I am guessing here you have the late Horizontal Tandem Yellow Tag Master Cylinder ?

 

Or or I suspecting thing might not be a Master Cylinder for a Mini ?

I've not found any original Master Mini Master Cylinders that have a Screw for compressing the springs within them.

 

You can upload photos directly to the forum as a .jpg up to 2mB in size and seeing what it is you have might be helpful here.

[John K Series]

Thanks for replies. It a vertical dual system GMC227. The mini is a conversion with a K Series Rover 1.8 but the brake cylinder looks standard mini.Im new here (and 58!) and cant see how to upload a pic. Mine def has the restricting screw and I just don't know why. Your pic has "normal" washers with round holes. The shims on here are slots. Will try to see how to upload. Thanks again

[John K Series]

by the way, it is 4 wheel disc. Has converted rears. Still cant see how to upload

[Spider]

This is the Yellow Tag Vertical type

 

 

If you click on 'More Reply Options next to the Post button, there's an option there to upload photos
 

 Untitled-2 copy.jpg   60.59K   0 downloads

[stuart bowes]

an alternative method if that isn't working, upload pics here and copy/paste the code it gives you as a new reply

 

https://imgbb.com/

 

don't pay anything or create an account, just 'start uploading'

Edited by stuart bowes, 13 March 2026 - 10:40 AM.

[John K Series]

Nice one. That was easy. https://ibb.co/TM1vKZ02
https://ibb.co/849mGJ4M
https://ibb.co/G3p1Fbhb
https://ibb.co/Y9LQFLR

[John K Series]

From your pic Spider (which is my cylinder GMC227) you can see no spring compressing screw in the end of the piston. See my 2 pics- one with screw in, one out. And no shims at all on Spider pic between the 2 reservoir rubbers and the cylinder. Any help appreciated. Mates have said leave screw in if it was working previously, which it was. Any thoughts? And still have shim query.
Thanks

[Ethel]

The lower piston has a rod extending out the front so that, if the lower circuit fails, the rod will push the upper piston. If you're referring to the sleeve inside the upper end of the  spring it will be equal to, or shorter than, that rod, so it doesn't shorten the effective spring, it just prevents the coils distorting sideways & contacting the cylinder bore.

 

 

... I only noticed the lower piston in your piccies: you are aware there's a pin (number 3 in Spider's diagram), where the reservoir fits that keeps the top piston in the  top of the cylinder? If you weren't, use a long screwdriver or similar inserted up the cylinder to compress the upper spring & you should be able to remove the retaining pin with some pointy pliers

[Spider]

It was because you mentioned the shims between the Reservoir seals that I guessed this may have been a horizontal Master.

 

It's been modified, which I'm never crazy about. In this case, the screw will limit the lower piston travel, and if plumbed up conventionally, will limit, in a very crude and unmeasured way, the pressure to the rear brakes. My advice is to leave the screw out.

 

As Ethel suggests, I'd be removing the upper piston to see what's been done there. There is a trap with these masters, in that the lower seal on the upper piston must be fitted reverse to all the others, so I'd be checking for that, as all too often, they end up being fitted the same way around. I'd also want to check for what other modifications have been made.

[John K Series]

Thanks for replies. The piston further in is not restricted, I gave had the pin out, piston out and done the rubbers. Ok I'll take the advice on letting the screw out to allow the spring to do its thing. What about the shims? Leave them out? Leave in put the slot in line with the length of the cylinder or 90 degrees to?

[Spider]

I've not come across the vertical Yellow Tags that had the shims fitted, though it is possible it's something they may have done at some point in time. As they are not indexed in any way, if they do belong in there, their orientation wouldn't be critical.

[John K Series]

Thank you very much for your help. The brake fluid has to get through from reservoir to cylinder so I will fit them best I can so that happens. The pipe connector on the cylinder nearest the pedal has 2 holes in line so that one is ok to line up the shim slot. The other one has 2 holes and the pin (previously referred to) which is also hollow, so that's a little trickier (as the slot can't accommodate all 3 holes). I would guess put the shim slot in line with the 2 standard holes? Am I looking too far in to this? Suppose brake masters matter so care is needed. Thanks again

[Ethel]

Sounds good. The hollow pin is a new one on me & I've seen cylinders without the shim, though they must have added them for a reason. Without digging out an old master, I think they were slightly counterbored to  stop the rubber bungs  going all the way in & blocking off the fluid ports.  As far as aligning the slot it needs a port above the piston seal, but also a port below the piston. Otherwise you could get hydraulic lock behind the piston preventing it from pushing fluid anywhere - align the shims accordingly.