36 replies to this topic

[barlar]

Hi.

 

I live in Sweden and have a Mini 1000 Mk3 1973 that have been in the garage for a couple of years. A few weeks back I started to rebuild everything chassis-wise. Suspension, brakes, half the engine etc. Everything has gone fairly smoothly EXCEPT getting my brakes to work as they should. It has drums all around with a yellow tag master cylinder, 23.8mm cylinders in the front and 15.9mm in the rear. Before putting it in the garage brake feel was never good, but adequate. Never bothered with it since I planned to do everything eventually. All wheel cylinders are brand new. I've routed all new lines and steel braded hoses to the rears, but fronts still have original pipes, but new steel braded hoses. 

 

After working out all small leaks etc. I really struggled with bleeding the brakes. Took me almost a week until I got help from a 2nd person to bleed the brakes the traditional pushpedal/bleed valve technique and it turned out that the rear bleed nipples were actually wrong and did not seal! Made me completely mad, but that seems to be sorted now. Was impossible to notice it while only gravity bleeding.

 

The issue right now is that I do have a great initial pedal feel. All brakes work pedal gets stiff. BUT as soon as you let off a bit of pressure to the pedal and then apply some again you get bite a bit further down. Repeat this a few times and you hit the floor. I've never experienced this exact behaviour before. Master cylinder leakages I've experienced have all included a sinking pedal while putting pressure on it.

 

So my faul searching is still on-going, and since I likely end up manufacturing all new brake lines also for the front while doing it, I have questions about how the system should be set up? I have little knowledge about different model years and how they should be setup. The only components left checking are master cylinder, brake limiter valve and inertia valve. 

 

What are typical symptoms of bad inertia valves or limiter valves? I've never worked on these before. Should my car have both? I have the limiter valve on the bulkhead and the inertia valve on the rear subframe on the right side.

 

If I now end up routing new lines, what would you recommend, eliminating one of the two, or still use both? I'm so sick of all brake issues that I'm open for ANY suggestions that keep the brake system as simple as possible!

 

 

 

Attached Files

•  2.JPG   41.95K   3 downloads

Edited by barlar, 22 June 2021 - 12:09 PM.

[GraemeC]

I don't think you should have both.

It sounds as though the limiter on the subframe is doing its thing when you first push the pedal, then when you release it is resetting and letting you push a little further until it locks off again.

I would suspect you still have air in the rear lines after the limiter.

[cal844]

Eliminate the bulkhead valve and just use the inertia valve. Much more reliable.

[barlar]

Awesome! Thanks for the quick responses. This is the first classic mini that I've ever worked on, and the way that the front brake lines are routed is kind of awkward to me, having them in series. First of all that banjo coupling from the LH brakes forwarding it to RH is kind of tedious to access to. Do you have any good pointers on how to, since I'm going to redo them and eliminating the limiter, best route them? Does everyone still use the banjofitting and having the brakes in series?

 

What are the typical symptoms of failing limiter/inertia valves?

 

I snuck down to the garage and took a couple of pictures on the monstruous setup.

 

So if I reroute it all with new lines, what do you think is the best/simplest way? The front brakes are fed from the bottom of the master cylinder by the way.

Attached Files

•  limiter.JPG   32.94K   4 downloads
•  inertia.JPG   57.74K   4 downloads

Edited by barlar, 22 June 2021 - 01:02 PM.

[sonscar]

Does the bulkhead thingy have wires to it?it may not be a pressure limiter but a circuit failure device.I think you have to remove the switch to bleed the brakes.A long time since I saw one so I could be wrong.
Fluid does not compress so travel is air or leaks or the shoes moving,but I am sure you know this.Good luck,Steve

[barlar]

Again, many thanks. I honestly didn't expect these fast responses. Much appriciated. Yep, it does have two wires going to it. I do think I have general knowledge about the whole fuid dynamics behind it all, but sine I've never worked on classis minis before I'm very humble to the specific setups of this beast.

I'm still crossing my fingers that it is air in the system or a component failure that is NOT the master cylinder. Tried to get the brake pedal split pin out. Its well rusted in there, and getting it out will be tougher than raising my kids right.

[Icey]

I've not worked with those components before but what you describe I would normally put down to a worn/faulty master cylinder (for the pedal to hit the floor you're either losing pressure or not building it). However! It looks like the valve on the rear is P/N 13H7757 - an inertia proportioning valve. Question for anyone that knows how these things operate - could jumping on and off the pedal cause the balance to shift, softening the pedal feel?

 

Edit: Apologies, having re-read the OP, these questions were already asked.

Edited by Icey, 22 June 2021 - 01:44 PM.

[sonscar]

Read up on the pressure failure device.My TR7 has a similar thing on the master cylinder and you have to remove the switch before bleeding and reset it if activated.Again I am not familiar with the MINI one.Steve..

[GraemeC]

Now I've seen the photos, I retract my earlier post!

That is indeed a true inertia valve on the rear and won't shut off like a pressure limiter. The front valve being a Pressure Differential Warning Actuator (PDWA) unit with a warning switch. So neither are brake pressure limiters as such.

This isn't a common set up.

 

 

I wonder if the PDWA needs some special bleeding technique as I suspect that if you open a circuit to bleed it it would then act to isolate that circuit.

[barlar]

Ooh, my lack of knowledge about the mini continues to show I'm afraid. I was wrong in claiming I had a yellow tag master. Could this be GMC159 perhaps? DO you guys know if this changes anything about the previous discussion, could I still just remove the PDWA to eliminate one possible cause of misery?

Attached Files

•  master cylinder.JPG   51.22K   3 downloads

[Spider]

It sounds to me like the issue here is the Master Cylinder.

 

The Master you have isn't a Yellow Tag but a GMC159 (or GMC160). Kits are still available for these.

 

This isn't a common set up.

 

 

I wonder if the PDWA needs some special bleeding technique as I suspect that if you open a circuit to bleed it it would then act to isolate that circuit.

 

Actually, the fundamental components are somewhat common outside of the UK.

 

The PDWA Valve can 'trip' when bleeding and they don't self reset. To reset them, one removes the switch, stands on the Brakes hard, then refits the Switch, though, this doesn't always do it and sometimes they need a little help.
 

[barlar]

As always GREAT info thanks. Seeing that it is apparent about my lack of experience on these cars and that I'm almost at a point where I'm contemplating to remove everything and just replace the still-not-new-parts, is there a big benefit of using the infamous yellow tag master cylinder instead of the GMC 159 which I seem to have? I'm going to test the master cylinder as soon as I get a chance to, but if it is faulty then while I'm at it, I'm thinking of replacing the GMC159 with a "better" one so that I don't have to do it again.

 

Sometime in the future (god knows when) I might end up putting discs in the front. If doing that, is there an obvious downside/upside to using the GMC159 or the yellow tag? What do you think the brake performance would be with my 23.8mm front and 15.9mm rear cylinders as I have them today (with inertia valve) and would it be any different in practice with a yellow tag?

 

......the only thing I'm still dreading is the /&%!&!"¤!&%!!! split pin on the brake pedal. Manufacturing new pipes for the whole car can be counted in minutes. Getting that pin out might be counted in weeks.....

Edited by barlar, 22 June 2021 - 09:24 PM.

[Spider]

The Yellow Tag Cylinder is generally a better Cylinder to use. The GMC159 and GMC160 became NLA eons ago, so finding a complete unit would not be easy these days.

 

If you do got to the Yellow Tag Master, you'll ideally want to do away with the PDWA Valve, it can stay there, but just another potential point of trouble. The wires that are connected to the Switch on it, you'd swap the the Cap Switch in the Yellow Tag. Be aware here too, that the front Brakes must be piped to the Top Port on these Masters.

 

Just before going down the Yellow Tag route, I would suggest you check your local Registration Rules as these are not compliant in all countries. There's nothing wrong with them per se, but for example here in Aust, they don't comply as the Reservoir for the Front Brakes is too small (it needs to have enough capacity for the front brakes to wear from new to (basically) metal to metal). In other markets, the Push Rod must operate the Circuit that the Front Brakes are connected to (that is in our case, the lower port).

 

Somerfords sell R Clips that you can use in place of the Split Pins. If fitting R clips, just be sure they are not too long or they can be displaced from normal use.

[barlar]

Thanks again Spider, really helpful. OK so if I summarize it all, I guess this is what's going to happen.

 

1. Check master cylinder without having it connected to the system

2. Remove the PDWA valve regardless

3. If master cylinder is faulty, replace it with a yellow tag, or if parts are scarce (I live in Sweden where the summer is short and mini part delivery times sometimes are about the same duration as a decent summer) then rebuild the GMC159 and go at it. I guess I can keep the rear inertia valve regardless if I go down the yellow tag road.

 

Took my 3 days to replace cylinder head, exhaust, inlet (with port matching), rebuild carbs, rebuild cooling system etc.........I'm now up to day 8 of the brake conundrum.....seems reasonable....?!

[barlar]

And the next episode in the neverending series "Game of Brakes" is that last night I managed to isolate the master cylinder itself and test it. Simply put, make 2 nipples with dead ends, bleeding it, and the result is that the pedal gets extremely firm. There's no way it'd budge regardless on how much pressure I apply or if I let go a bit and then stomp on it again. It also releases pressure as it should. All in all, it feels absolutely fine! I'm still keeping my fingers crossed that it is OK and that I, at least not immediately, have to replace it. 

 

Next episode involves eliminating the infamous, much hated, PWDA Lannister and see where I end up.