66 replies to this topic

[miniGTS]

https://www.somerfor...egulating-valve

 

or

 

https://www.classicm...a1774-reg-valve

 

Thanks, somerfordmini says no stock and I've contacted classic mini spares NZ for a costing on shipping. 

[Spider]

 

https://www.somerfor...egulating-valve

 

or

 

https://www.classicm...a1774-reg-valve

 

Thanks, somerfordmini says no stock and I've contacted classic mini spares NZ for a costing on shipping. 

 

 

It's worth calling Somerfords to check, their stock levels on the web aren't always right.

[mbolt998]

With the Yellow band types, the rears are normally connected to the lower port.

 

I have a yellow band, drums, and the lower cylinder is connected to the fronts. It was always like that since that MC was fitted by a garage of dubious competence in the early 90s. The lower half of the master cylinder does look like it has a wider bore (as Ethel mentioned). If I connect them the other way around, will I get a higher mechanical advantage on the front brakes? But this is probably not something I want as pedal travel is the more limited resource.

[mad4classics]

 

With the Yellow band types, the rears are normally connected to the lower port.

 

I have a yellow band, drums, and the lower cylinder is connected to the fronts. It was always like that since that MC was fitted by a garage of dubious competence in the early 90s. The lower half of the master cylinder does look like it has a wider bore (as Ethel mentioned). If I connect them the other way around, will I get a higher mechanical advantage on the front brakes? But this is probably not something I want as pedal travel is the more limited resource.

 

I always understood the yellow tag was lower to rears according to the sheet that comes with the master cylinder (nb. I've highlighted the pipe reversal in yellow)

 

However I note Spider says "normally"; are there cases when this is not true?????

 

 

 yellow tag.jpg   63.94K   4 downloads

[Spider]

 

 

With the Yellow band types, the rears are normally connected to the lower port.

 

 

I have a yellow band, drums, and the lower cylinder is connected to the fronts. It was always like that since that MC was fitted by a garage of dubious competence in the early 90s. The lower half of the master cylinder does look like it has a wider bore (as Ethel mentioned). If I connect them the other way around, will I get a higher mechanical advantage on the front brakes? But this is probably not something I want as pedal travel is the more limited resource.

 

 

However I note Spider says "normally"; are there cases when this is not true?????

 

As a straight forward set up, yes, the lower port on the Yellow Tag Master would connect to the Rear Brakes, as Ethel and Mad4 has mentioned.

 

The part of the Cylinder that the Lower Port uses has a larger diameter (from memory 19.00 mm), so this will displace more fluid but be at a lower pressure that the upper port (the cylinder here from memory is 17.00 mm). By having a Master Cylinder configured (and connected) in this way, it reduces the pedal travel while getting enough pressure for the front brakes to operate satisfactorily.

 

It is theoretically possible to connect this cylinder the other way around and still have satisfactory braking performance, but ideally you'd also want to calculate appropriate wheel cylinder sizes and the rear shut off pressure. In considering this too, you'd need to be mindful that within the Master Cylinder itself, the upper and lower pistons are hydraulically coupled so even here, there's a hydraulic ratio (19/17) that needs to be taken in to account.

In practice, having it plumbed up with the Fronts on the lower port in an otherwise standard arrangement will still work. I'd need to crunch some numbers to be 100% sure, but I'm pretty sure the only down side is a longer pedal travel and a higher pedal pressure than otherwise should be the case here. Normally, a longer travel would reduce pedal effort (when the system is working correctly, ie, all bled, adjusted properly etc).
 

[Spider]

Yes because the dead circuit will lose you about half of the travel. But in my car anyway there's very little travel to play with ever, which is why I often pump a bit in normal driving anyway-- to compensate for drum fade and also just to get the pedal where it like for blipping.

 

Was watching "Furious Driving" on YouTube the other day. He had a fluid leak from a rear wheel cylinder in a Land Rover Freelander, and reported immediate loss of all braking. So dual circuit brakes don't seem to do much for you even on newer cars.

 

Thanks for the clip and well,,,,, it seems the issue isn't isolated to Minis !

 

In our local rules, this is what that says for Tandem Brakes (or as it's worded "Split Service Brake System") ;-

 

There are later versions of this set of rules, but they are all worded the same way.

 

While I've not read what the UK, European and US Rules are, I'd be sure they'd be quite similar to this.

 

I'd also say, in regards to compliance with these rules from an original design and manufacture perspective, they were not likely independently checked and tested to see that they met these rules, or, as we saw in recent times with VW, they pulled a swifty of some sort at least on the vehicle(s) submitted for test.

 

 

In regards to your own brakes, clearly, there's something not right there. It sounds like the system has some air in it and / or some further adjustment is needed. There could be other reasons for this too, but that's where I'd start with it.

[miniGTS]

I have a remote Lockheed servo that needs to be rebuilt, is it worth the cost and effort for a bit of improved pedal feel?

[Ethel]

Depends, is my answer to pedal pumping.

 

If the pedal's not on the floor then you likely have access to as much braking effort as you'll get - push harder!

 

If it is, and the cause was a leaking seal, stamping hard on the pedal might force the cup out to seal without as much fluid getting by, or close a regulator valve similarly. More than one or two goes and you're likely to only be lubricating your brake shoes to make wrenching on the handbrake less effective too.

[sonscar]

I understood that the halves of the master cylinder are independent once operated and the filling hole has been passed.Thus each part will have operating pressure on it operating the front and rear circuits independently.When one circuit fails the other will be pressed harder as you are applying foot pressure to less cylinder area.The remaining circuit should work at least as good as it ever did.This only applies for this one application.If you pump the pedal it empire the fluid and could introduce air into the working cylinder.You only get one press.Steve..

[Ethel]

The lower piston has to make contact with the upper piston, or the upper piston has to hit the end of the cylinder 'n stop moving, so you can increase the pressure in the remaining  good cylinder. That should happen before the pedal hits the floor, but you'll be nearer to hitting the floor if there are other issues. You won't get more pressure, it was equal & opposite on both sides of intermediate (upper) piston when the cylinders were shoving each other with brake fluid.

[mbolt998]

 

 

In regards to your own brakes, clearly, there's something not right there. It sounds like the system has some air in it and / or some further adjustment is needed. There could be other reasons for this too, but that's where I'd start with it.

 

My brakes have always been like that for as long as I can remember. Soon after I bought the car (in 1992) a garage changed the MC as part of fixing a leaking pipe (I don't think it even needed changing). They fitted a yellow tag one (previously I had a different one, with a pressure switch rather than a low-fluid-level light), and they connected the bottom piston to the fronts, probably copying the old MC and not reading the instructions.

 

About a year ago. I changed all the brake pipes and hoses and bled it all and there's definitely no air in it-- it works how it always did. But I'm now wondering if I should try swapping it bottom circuit -> rears as it is supposed to be set up. Can't hurt to give it a go. If I do I will report back.

[mbolt998]

 

 

With the Yellow band types, the rears are normally connected to the lower port.

 

I have a yellow band, drums, and the lower cylinder is connected to the fronts. It was always like that since that MC was fitted by a garage of dubious competence in the early 90s. The lower half of the master cylinder does look like it has a wider bore (as Ethel mentioned). If I connect them the other way around, will I get a higher mechanical advantage on the front brakes? But this is probably not something I want as pedal travel is the more limited resource.

 

I always understood the yellow tag was lower to rears according to the sheet that comes with the master cylinder (nb. I've highlighted the pipe reversal in yellow)

 

However I note Spider says "normally"; are there cases when this is not true?????

 

 

yellow tag.jpg

 

Thank you for that! I think I may experiment with hooking them up the other way around, as the instructions say they should be.

[Jimnz]

Hi all, sorry to hijack your thread MiniGTS, but I'm kind of in the same situation as you. A NZ new 78 LE, with diagonal split drum brakes all round and every component is shot, nothing is salvageable except the two 3-way splitters. I'm going to upgrade to disk, just not sure on 7.5" or 8.4", more than likely I will go with an 8.4" set up as I will be having 12" wheels. I have the front hubs, uprights and CV stuff for the change, previous owner had already bought these items, and the car came with a 1275+ already in it. (yeah they done an engine change, then left it sitting to rot). 

 

So, my question is, what system to reinstall? preferably a factory original setup, this makes it easier for the re-certification process for the disk brake upgrade, I'm thinking of either, the front to rear tandem, with the GMC227 MC, minispares 8.4" disc calipers, 3/4" rear cylinders and the PDWA FAM7821 valve, inline with what one version of the 1275GT had in 78,

 

or

 

the single line front to rear using GMC172 MC, 11/16" rear cylinders and the 21A1774 pressure regulator valve, what the 74 to 76 1275GT's had.

 

Then again, I could use the diagonal split 1275GT system with the GMC167 MC and 1/2" rear cylinders and no rear valve, makes the new lines easy as I have the old ones to template from.

 

When done the car will not be going far, I travel for work so will never be home to drive it, it will spend most of its life sat in the garage out of the weather.

 

Any help will be gratefully appreciated.

 

ahhhhhhh too many options.

[Spider]

So, my question is, what system to reinstall?

 

I'd suggest your first port of call would be your local rules in NZ as to what the car should have been fitted with when new to comply and then check further to see what modifications you are allowed to do, to what level and if any engineering certification(s) might be needed.

[mbolt998]

 

 

 

With the Yellow band types, the rears are normally connected to the lower port.

 

 

I have a yellow band, drums, and the lower cylinder is connected to the fronts. It was always like that since that MC was fitted by a garage of dubious competence in the early 90s. The lower half of the master cylinder does look like it has a wider bore (as Ethel mentioned). If I connect them the other way around, will I get a higher mechanical advantage on the front brakes? But this is probably not something I want as pedal travel is the more limited resource.

 

 

However I note Spider says "normally"; are there cases when this is not true?????

 

As a straight forward set up, yes, the lower port on the Yellow Tag Master would connect to the Rear Brakes, as Ethel and Mad4 has mentioned.

 

The part of the Cylinder that the Lower Port uses has a larger diameter (from memory 19.00 mm), so this will displace more fluid but be at a lower pressure that the upper port (the cylinder here from memory is 17.00 mm). By having a Master Cylinder configured (and connected) in this way, it reduces the pedal travel while getting enough pressure for the front brakes to operate satisfactorily.

 

OK I have tried this, and the results are as predicted, but quite dramatic. Connected up the wrong way around, as they were on my car since 1992, the pedal tends to move alarmingly far without doing anything (as all the travel from the narrower bore part of the cylinder just goes to the rears). Then it feels like it's practically hit the floor, but you are now operating the front brakes, which are lower travel and higher effort than they should be. I always pumped the pedal a bit, both to get some confidence that it wasn't going to hit the floor, and to get my foot where I wanted it for "heel and toe" (I like the brake above the throttle). Once you have got it pumped up you have a very firm pedal and you have to push it quite hard. Ultimately of course the brakes work fine and as well as they were ever going to.

 

With them connected up the correct way round, the pedal has a much more natural and progressive feel. You just press it and the car slows down, and will lock the wheels if you want, just like any other car. It's quite light by comparison but with more travel. It also seems to be harder to get a higher pedal with pumping. Not sure why this is, perhaps because pumping (which has to be done quite quickly) tends to work more on the first part of the MC because it's nearer. I appreciate that this pumping business is a bit weird and a quirk of my driving style (in this car). But it worked for me.

 

Anyway it is now harder to heel and toe, so I may actually change them back, but will see how I get on, and am experimenting with other solutions. Just putting a bit of plywood under the carpet seems to work quite well-- my requirement is just to keep my actual heel on the floor at all times. I know some people can heel-and-toe with actually lifting their heel off the floor, which helps with a lower brake pedal, but I think you get much better control if you keep it on the floor. Or maybe I'm just lame.

 

Thank you to Spider, Minimad, Ethel and everyone else. This has solved the mystery of why the brakes always seemed so strange!