Master cylinder question.

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GDCobra
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Re: Master cylinder question.

Post by GDCobra »

DaveEFI wrote:
Wed Aug 04, 2021 11:05 pm
stevieturbo wrote:
Wed Aug 04, 2021 9:14 pm
The pipes are too small for air locks to be an issue.

However....control valves etc can cause issues. What is the nature of the balance valve ?
My mechanic neighbour was available today. And after trying conventional bleeding, he came to the conclusion the balance valve is faulty. After we swapped master cylinders once more. The flow from the rear bleed nipple is tiny compared to the fronts. And we agreed the only thing that could cause this is a faulty balance valve.

There is a problem there. Rimmer list two - one for all SD1 except the Vitesse. Vitesse one NLA. No mention of my EFI which has the same brakes as the Vitesse.
Is it possible to swap out the balance valve with a union or section of pipe as a test to see if that is the problem, I know it sounds like a bit of a faff but you've swapped master cylinders a time or two so should be no worse and at least it would save you trying to track down a difficult to find part only to find it's not the problem.
Alternatively you could even terminate the line where it enters the valve and bleed air out at that point this would at least eliminate anything downstream as the issue.
Bear in mind that for a given pedal pressure the valve will restrict fluid to the rear line, that's its job, although it's possible that the restriction is dependent on input pressure they are not a device I'm too familiar with.

I think the non-level nature of the car could cause an issue if it is severe enough. If the outlet from the brake calipers is not at the highest point and there is air trapped in there then it will not come out, presumably the calipers are designed for this to be the case when the car is level. Could you stand the low end of the car on axle stands to level it out?
It's also possible to get a similar thing if the car is not level side to side (in roll), this is worse if the caliper pistons are extenced I generally retract the pistons which is the case if fitting new pads but if I'm not then I wedge the pistons back.



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Re: Master cylinder question.

Post by DaveEFI »

Not really possible to replace the balance valve with T's - it has 5 ports. Being for dual circuit brakes.

Over the many years I've had this car, I've replaced most of the braking system, bit by bit. So have bled the brakes many times. Where it's parked is a slight slope, but which way it is parked on it would depend on which end I'm working on. So almost certainly will have bled the brakes with it in this position before.

I've ordered up a new valve from Rimmer. It will fit OK - but not sure the front back balance is right for the brake version on my car. But will prove if the old is faulty either way.

It's urgent as the VED has run out, as well as the MOT. So the main thing is to get it legal again, and worry about niceties afterwards.
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Re: Master cylinder question.

Post by GDCobra »

DaveEFI wrote:
Thu Aug 05, 2021 10:03 am
Not really possible to replace the balance valve with T's - it has 5 ports. Being for dual circuit brakes.
Ah, presumably that is 2 inlets (front and rear circuit) and 3 outlets (assuming one outlet to rear circuit and two fronts, one to each side?).
Still it should be possible to bridge that out with a 2 and 3 outlet union. Must admit I'm struggling to understand how this valve would cause a flacid pedal (although I can see other problems), that would really indicate air in the system (system compressible), master cylinder seals not doing their job hence no pressure generated or a leak, the last 2 you seem to have eliminated unless you have two faulty master cylinders in which case I'd not bother buying a lottery ticket this week!
I guess it's possible that a faulty valve could be interfering with your bleeding process but can't quite understand how.

Do you know if the purpose of this valve is to limit the pressure in one circuit (presumably rear) or if it is to shut off one circuit in the event of a leak (pressure out of balace so a shuttle valve moves over to close that circuit). If it's the latter I guess this could be operating during bleeding as it's seeing the opened circuit as being a leak and messign up that process, this may be made worse by using an easy bleed which is a shame as I think that is a good way of bleeding. Mind you it sounds like you are getting plenty of fluid through so probably not an issue.

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Re: Master cylinder question.

Post by GDCobra »

DaveEFI wrote:
Thu Aug 05, 2021 10:03 am
Over the many years I've had this car, I've replaced most of the braking system, bit by bit. So have bled the brakes many times. Where it's parked is a slight slope, but which way it is parked on it would depend on which end I'm working on. So almost certainly will have bled the brakes with it in this position before.
I understand that, but as financial folks are always keen to point out "Past performance is no guarantee of future success", when I have a problem and don't know the cause I treat everything as being possible and rule out as many possible contributing factors as possible.

DaveEFI wrote:
Thu Aug 05, 2021 10:03 am
I've ordered up a new valve from Rimmer. It will fit OK - but not sure the front back balance is right for the brake version on my car. But will prove if the old is faulty either way.
I guess that's fair enough similar to what I was suggesting, my suggestion was simply an attempt to try and save time and money of course I guess that would depend on having the fittings to do it, just thought that as you'd just replaced a load of pipes you may have some spare.


DaveEFI wrote:
Thu Aug 05, 2021 10:03 am
It's urgent as the VED has run out, as well as the MOT. So the main thing is to get it legal again, and worry about niceties afterwards.
Totally understand hence my question about the valve function. My experience with 'balance' valves has been with a single inlet/outlet device fitted to a single line to reduce the pressure. I did have a BL car many years ago of a simlar era to your SD1 (still painful to admit) and this had a valve which was fed from both sides of the dual circuit if I remember correctly it's purpose was as described in my previous post where if one circuit generated lower pressure the valve would move that way and shut it off. IIRC it also had an electrical connection which was linked to a dashboard light to warn the user, very hight tech!
Main point is it did not add anything to the braking system in terms of balancing or at all unless there were a problem. If I had this on a car these days I'd simply remove it.

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Re: Master cylinder question.

Post by DaveEFI »

I'll say how I think the balance valve works. The BL manual ain't much help as it really only deals with the early system. On that, it handles front and back as separate systems from the tandem master cylinder. And reduces the pressure to the rear drums to help prevent premature locking.

My late car (Vitesse brakes) has split feed calipers. One side of those is fed, via a T, from the back output of the master cylinder. So doesn't go through the balance valve.

The other master cylinder output is T'd and feeds both the balance valve inputs.

This drawing may help:-

Image
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Re: Master cylinder question.

Post by GDCobra »

DaveEFI wrote:
Thu Aug 05, 2021 1:24 pm
I'll say how I think the balance valve works. The BL manual ain't much help as it really only deals with the early system. On that, it handles front and back as separate systems from the tandem master cylinder. And reduces the pressure to the rear drums to help prevent premature locking.

My late car (Vitesse brakes) has split feed calipers. One side of those is fed, via a T, from the back output of the master cylinder. So doesn't go through the balance valve.

The other master cylinder output is T'd and feeds both the balance valve inputs.

This drawing may help:-

Image
Wow, that's either crazy complicated or I've lead a sheltered life as I've never come across anything like it before. Makes you wonder what problem they were trying to overcome.

So in your split circuit one M/C piston feeds both front calipers and the other feeds a separate set of pistons in the front calipers and also the rear line.
Actually thinking about it it's possible not a bad idea as one circuit failure would always leave you with one 'some' front brakes and as these are the most important that's probably a good thing.

While you are waiting for the new balance valve I think I'd be tempted to disconnect the front port of the master and bung it up then see if you get a decent pedal at least proves the green circuit is good. Then I think I may look at disconnecting and plugging some of the exits from the balance valve (probably stating with the rear line and see if you can get any joy there. What about connecting the blue input line to the valve directly to one of the red outputs, either each in turn or both together if you have a tee piece?

What about removing that valve and giving it a clean?

All depends on how much time you have available and whether you prefer to wait for the replacement which may or may not sort the problem.

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Re: Master cylinder question.

Post by DaveEFI »

The way BL did things fills me with wonder too. Most would call it a bodge.

Access to the balance valve is very limited and I don't fancy bending the new pipes now I've got a decent fit.

I'm wary about taking the valve apart as I'm told it contains ping f**kits. If the new one works, I will. As I think my one is set up differently from the only new I can buy. And may be possible to fit the springs to the new valve - if they are OK.
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Re: Master cylinder question.

Post by GDCobra »

DaveEFI wrote:
Thu Aug 05, 2021 3:30 pm

Access to the balance valve is very limited and I don't fancy bending the new pipes now I've got a decent fit.
Fair enough, I was concerned access may be an issue.

Actually I'm quite impressed with the fact they've effectively created 2 braking systems for the front. I'm assuming when you say the calipers are split that they are 4 pots with the upper pots on one circuit and lower on the other?
I actually dreamed up a system like that for my car once but decided it was not worth the bother.
Only thing I've seen similar, but even more complex, is the combined braking system which Honda used a few years back on some bikes where both the front brake lever (on the handlebar) and the rear brake foot pedal operated both sets of brakes, they didn't do anything as simple as supplying 2 set of pipes to 2 sets of pistons (not initially at least) instead they mounted the calipers on a rotating bracket which was prevented from rotating by a "master-cylinder" hence the force from resiting rotation was passed to a set of pistons at the opposite end. Trick system but very complex and addressed a problem no-one ever asked them to.

Hope the new valve works OK for you. I've got a bit of bleeding to do on my car now, hopefully I have more luck than you!

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Re: Master cylinder question.

Post by stevieturbo »

if I'm reading that right.....it has 2 separate lines to each front caliper ? One shared with the rear circuit, one independent ??

Looks bonkers complicated.
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Re: Master cylinder question.

Post by Ian Anderson »

Was it a self bleeding system on the front brakes?
Way back heat generated in the calipers was a problem and in some cars they developed a master cylinder that opened one port slightly earlier than the other so
Press brake pedal and both ports are closed and the pressure clamps the calipers.
Release the pedal and the one port opens earlier than the other so the heated brake fluid returns to the master.
In effect the movement of fluid means they are also self bleeding!

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Re: Master cylinder question.

Post by DaveEFI »

The new (possibly not to the right spec) balance valve arrived. Need a few hours with no rain as working outside, so not fitted yet.
Chatted to an engineer pal on the phone, and here's what we came up between us.

Car hasn't been used since Covid. Even before, can't remember when I'd braked hard. (on the open road I leave plenty room from the car in front, as SD1 brakes were never the best, and not going to stop as quickly as a modern car with ABS, and I'm old, so don't have the reactions of a young man)

At the MOT, the tester did press very hard - hence the pipe giving way then, and not on the drive there. The balance valve also moved to the extreme end of its travel and stuck there. Reducing the flow to the rear brakes to the point where it wasn't fast enough to shift trapped air when bleeding.
Suggested whacking it with a hammer. He was, after all, an engineer. :? And nothing to lose, as I intended fitting the new one.

So between showers, I did just that. Not hard as no room to get a decent swing at it.

Wheels still off the car, so a quick job to bleed them again. Using my trusty EeziBleed.

There was now what I'd say a decent flow out of the rear bleed nipple. Didn't touch the pedal, but moved on to the fronts.

And I now have a nice firm pedal. :D

Not driven it yet as there are other bits to go back on. Did notice one front wheel was dragging a bit, so a caliper rebuild may be needed.

Thanks for all the help.
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Re: Master cylinder question.

Post by GDCobra »

Hey Dave, great to hear you look like you’re on the way to sorting your issue, this is kind of the path I was on when I suggested getting the valve off and inspecting. Didn’t think of the hammer trick as I’ve moved on from when I only had a fitters toolbox containing only a hammer and two spanner’s (one that fits everything and one that fits nothing) but there’s no arguing that this method does work.

Must ad,it I’m surprised the SD1 brakes are pretty poor, presume they could be improved. My car has decent brakes but requires a lot of pedal pressure which was OK but with modern traffic and moronic drivers (who always think they have right of way no matter what I now want brakes which can “turn on” quickly without having to build up too much leg power. In my case I had some easy room for improvement (at least I hope so, not tested yet) as it didn’t have a servo. I’ve just nailed one on and I’m hoping this will give the improvement I want. Just need some water in the cooling system (did some other jobs at same time) and a bit less coming out of the skies (no roof) and finders crossed that will be job done.

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Re: Master cylinder question.

Post by harvey »

I don't know if this has been mentioned previously, but back in the day working at the main stealer whenever bleeding them we had to reset the balance compensator afterwards by (IIRC) removing the switch on the valve, then pumping the pedal to reset the valve in the middle, then refitting the switch. Might be worth trying as if it works it's an easy fix.

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Re: Master cylinder question.

Post by DaveEFI »

harvey wrote:
Sun Aug 08, 2021 11:21 am
I don't know if this has been mentioned previously, but back in the day working at the main stealer whenever bleeding them we had to reset the balance compensator afterwards by (IIRC) removing the switch on the valve, then pumping the pedal to reset the valve in the middle, then refitting the switch. Might be worth trying as if it works it's an easy fix.
No electrical connection to the balance valve on the SD1.
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Re: Master cylinder question.

Post by GDCobra »

DaveEFI wrote:
Sun Aug 08, 2021 11:29 am
harvey wrote:
Sun Aug 08, 2021 11:21 am
I don't know if this has been mentioned previously, but back in the day working at the main stealer whenever bleeding them we had to reset the balance compensator afterwards by (IIRC) removing the switch on the valve, then pumping the pedal to reset the valve in the middle, then refitting the switch. Might be worth trying as if it works it's an easy fix.
No electrical connection to the balance valve on the SD1.
That sounds a like the valve I had on my 1970's BL car which monitored the position of the valve with a switch (how very modern), my understanding was that it also shut off the offending line but did not offer any pressure reduction/balancing which it sounds like yours does Dave. I don't think any pressure reduction was necessary as this car also has anti-lock brakes. There was no electronics or complex systems involved it's just that the brakes were so porr there was no way of locking them up. Even on ice. Probably.

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