57 replies to this topic

[Spider]

My master cylinder does indeed have a yellow tag. I assume that's a global standard then and no difference between your yellows and ours

 

To be clear, I'm referring to the GMC227

http://www.minispare...|Back to search

 

To be additionally clear, I'm not at all saying it's a rubbish cylinder, it's not. It's just doesn't meet the various standards in all markets.

 

 

Probably straying from the topic here, but the concept as I understand it of Tandem Brakes in general, is so that should a hydraulic failure occur in one circuit, the other will still work, just with a lower pedal and reduced braking performance. I've found with both the GMC227 and the GMC167 that this is not the case, a failure in either circuit will result in the pedal hitting the floor long before any pressure is made in the healthy circuit.

[mbolt998]

 

My master cylinder does indeed have a yellow tag. I assume that's a global standard then and no difference between your yellows and ours

 

To be clear, I'm referring to the GMC227

http://www.minispare...|Back to search

 

To be additionally clear, I'm not at all saying it's a rubbish cylinder, it's not. It's just doesn't meet the various standards in all markets.

 

 

Probably straying from the topic here, but the concept as I understand it of Tandem Brakes in general, is so that should a hydraulic failure occur in one circuit, the other will still work, just with a lower pedal and reduced braking performance. I've found with both the GMC227 and the GMC167 that this is not the case, a failure in either circuit will result in the pedal hitting the floor long before any pressure is made in the healthy circuit.

 

My car has drums all round. It's not necessary to top up the master cylinder as they wear-- just when you're bleeding it or if you have a leak. You often have to pump the pedal anyway unless you adjust the drums very often and don't drive fast. But you make an interesting point. I have never trusted the dual circuit. If there is a major leak anywhere I suspect the level in the MC will drop enough that it just sucks air into both circuits. I have seen pictures of MCs on other cars where the reservoir is split vertically into two compartments. But I don't know if the Mini's is actually like that. It looks like it's basically just a single reservoir for both circuits.

 

In a (1980) Renault 5 if the rear pads wear down completely the slave cylinders can actually pop out causing total fluid loss. This is an awful design fault.

[gazza82]

Bit off-topic but a lot of moderns use the same reservior to feed brakes and clutch now (cost-cutting I assume!). If you do lose fluid, and the clutch slave it the likely culprit (or in my case the hose feeding the slave that was rubbing on a chassis edge!), you will lose the clutch first as it is fed from the higher outlet. The brakes would continue to function.

Unless of course the leak is in a brake pipe/hose/caliper/piston but you've probably notice that sooner!

And most have a low-fluid sensor in the cap.


I'm fitting a split-circuit Rover 100 master to my "Bitza" and have included a low-fluid warning lamp in the dash layout.

[Spider]

All these types of master cylinders, for Tandem Brakes and also those Gazza mentioned are internally partitioned, They have a single fill point, but have 2 or 3 chambers within so a failure in one circuit doesn't drain the fluid from the others.

I have one I've cut apart, if I remember tomorrow, I'll post up some pics.

[Ethel]

Bit off-topic but a lot of moderns use the same reservior to feed brakes and clutch now (cost-cutting I assume!). If you do lose fluid, and the clutch slave it the likely culprit (or in my case the hose feeding the slave that was rubbing on a chassis edge!), you will lose the clutch first as it is fed from the higher outlet. The brakes would continue to function.

Unless of course the leak is in a brake pipe/hose/caliper/piston but you've probably notice that sooner!

And most have a low-fluid sensor in the cap.


I'm fitting a split-circuit Rover 100 master to my "Bitza" and have included a low-fluid warning lamp in the dash layout.

 

That could be a potentially good design if the outlets are arranged to run the clutch dry before the brakes. I imagine it has more to do with dumbing down owner maintenance, like colour coding dipsticks & oil fillers...

 

I reckon the yellow band master was just an attempt to improve the brakes without adding the cost & complexity of a servo. They managed to delete a servo by going to 8.4 discs and the next mod after the yellow band was to reintroduce one.

 

Likewise, the brake warning was a pressure differential sensor between the dual circuits, so I'm guessing somebody realised the regulation could be met with a cheaper float switch. You could argue it's better as the fluid can get dangerously low without losing pressure in just one circuit and a stepped bore master is intended to create a pressure differential.  

 

The puzzler is why they achieved a very similar set up on the Metro by just using smaller wheel cylinders on the rear. The entire rear brakes are interchangeable with a Mini too. 

[Spider]

I have one I've cut apart, if I remember tomorrow, I'll post up some pics.

 

To avoid staying off topic, I've posted this up here with some additional info;-

 

https://www.theminif...stralian-rules/

 

[StefanMini]

In my case the brake warning switch light saved me. Back in 2011 during the IMM in Switzerland the light came on in the mountains, loosing brake fluid on an corroded brake line. So yes..it's necessary!

[Lplus]

In my case the brake warning switch light saved me. Back in 2011 during the IMM in Switzerland the light came on in the mountains, loosing brake fluid on an corroded brake line. So yes..it's necessary!

The later type which indicates low fluid is worthwhile,  The earlier type which operates only when the pedal travel is already obvioulsy excessive is less so.

[Richard e]

With lowish level brake fluid the light on my switch would ever so fleetingly come on when going round a bend mini fashion… that caused me to check the level and top it up - no more flickering light. And yes I should have checked under the bonnet occasionally…

[stuart bowes]

In my case the brake warning switch light saved me. Back in 2011 during the IMM in Switzerland the light came on in the mountains, loosing brake fluid on an corroded brake line. So yes..it's necessary!

 

fair point but just to confirm again I haven't deleted the function of having a warning light, I've actually merged it into the existing orange warning light so it will come on by itself without a need for button pressing, and in a position which is easily noticeable below the speedo 

 

some form of warning light I totally agree is required, it was the button I was questioning

Edited by stuart bowes, 10 June 2023 - 07:20 PM.

[mbolt998]

Replaced my warning light today and realized that previously what I had had was not a low-level light but a pressure differential light, that was supposed to come on when you pressed the pedal if either the front or the rear circuit had lower pressure than the other-- i.e. a leak somewhere. This is described in the owner's handbook. I wonder how well that worked.

 

Soon after I bought the car (in 1992) a garage replaced the master cylinder (unnecessarily and incompetently but I was even more clueless then). The new MC had a cap with a float in it and two spade lugs, intended for a low fluid-level light. The old one had some kind of connector on the side I think where this pressure differential switch thing must have been supposed to go.

 

The garage just left the wire dangling, the switch never worked, and for some reason I had put a fog light switch in there instead.

 

Today I took the fog light switch out, put in a new brake warning light switch from Minispares, and sorted it all out. It turns out the wiring is a bit different for the pressure differential switch so I had to move a few wires around to get the desired behaviour: light comes when you press the switch (to test the bulb) OR when the MC lugs become connected which happens if the fluid drops.

[mad4classics]

Soon after I bought the car (in 1992) a garage replaced the master cylinder (unnecessarily and incompetently but I was even more clueless then). The new MC had a cap with a float in it and two spade lugs, intended for a low fluid-level light. The old one had some kind of connector on the side I think where this pressure differential switch thing must have been supposed to go.

The garage just left the wire dangling, the switch never worked, and for some reason I had put a fog light switch in there instead.

The AP yellow tag master came with an instruction leaflet about the need for conversion kit BAU5654 in those instances where the original type had been fitted. This contained the changed pipework and a conversion loom. Available from your Rover dealer 😁.

That kit is still available from the likes of Minispares.

Edited by mad4classics, 11 June 2023 - 05:23 PM.

[mbolt998]

 

Soon after I bought the car (in 1992) a garage replaced the master cylinder (unnecessarily and incompetently but I was even more clueless then). The new MC had a cap with a float in it and two spade lugs, intended for a low fluid-level light. The old one had some kind of connector on the side I think where this pressure differential switch thing must have been supposed to go.

The garage just left the wire dangling, the switch never worked, and for some reason I had put a fog light switch in there instead.

The AP yellow tag master came with an instruction leaflet about the need for conversion kit BAU5654 in those instances where the original type had been fitted. This contained the changed pipework and a conversion loom. Available from your Rover dealer 😁.

That kit is still available from the likes of Minispares.

 

 

Makes sense! I think based on the wires I had that the pressure differential switch works by connecting the two wires running to it together and then earthing both of them if there is a fault (pressure difference). The second of those two wires runs back to the pins on the back of the switch and so is also earthed if you press the switch. The value of the wire coming back is that when you test the bulb you're also testing that the plug to the MC hasn't fallen out-- if it has the light won't come on even if the bulb works.

 

Purple is 12V, black and white are the wires to the MC, and black is earth. This is how it was wired:

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My modification was to leave the purple wire alone but to make two three-way connections on the other wires. So now the black-and-white goes from the side of the switch to the MC cap, the other black-and-white comes back, but instead of going into the switch it does a T-junction with the earth wire. So if the MC cap connects (fluid low) the switch is earthed and the light comes on. The other T-junction I added joins the black-and-white coming out of the switch into the other switch terminal on the back. This provides its alternative path to earth-- through the switch when you press the button. Not very obvious under the electrical tape (it is soldered under there):

 

 02.jpg   58.43K   0 downloads