Dual 7" Servo - Page 18

peterux · #1 11th February 2012, 09:34

Quote:

Originally Posted by denniswpearce

I took it down our private road and it worked but I would not want to stop in an emergency on the main road. Something still amiss.

Any suggestions as to what my problem is ?

DSC00350 by denniswpearce, on Flickr

Hi Dennis,
I think you must still have air in your brake lines, and I think you may need to rotate your master cylinder by 180 degrees. At the moment, air trapped in the top half of the cylinder has no way of escaping as your exit pipes are at the bottom.

...peter

P.S. The new wing stays look good!

AlanHogg · #2 12th February 2012, 18:13

Hi Dennis
i believe your problem is likely to be the orientation of the master cylinder and the route your supply pipes are taking.I would suggest that you rotate the M/c so that the supply inlet is vertical and that the supply pipes take a more direct route rather than dropping under the servo and then rising again.Its a bit like trying to bleed a caliper with the nipple at the bottom, almost impossible to achieve.

denniswpearce · #3 12th February 2012, 20:39

Guys thank you so much for all these helpful words.

Robin that is an option I am thinking about.

Nigel bleed nipples are at the top so possibly not the solution.

Alan I have added a pic showing modified supply pipes which are now a much shorter route and not under the new servo. But as explained in a previous post, the reservoir was held vertically well above the m/c after shortening and the pipes were tapped until all no air bubbles came out of the supply pipes. Then a big bleed, 20/25 pumps per wheel, till only fluid came out for another 5/6 pumps.
Unfortunately air is still in the system.

Thanks guys

DSC00363 by denniswpearce, on Flickr

Grey V8 Pete · #4 10th February 2012, 21:27

Hi Dennis.
You need to hold your hydraulic fluid reservoir up above the highest master cylinder inlet boss, so gravity gets all the air bubbles out, before you start bleeding the brakes. This will need a re-route of your pipes to above the M/cyl to allow this.
I made a fancy new bracket to lift my remote reservoir higher only to find it fouled the bonnet, so I had to replace the old lower one. I am hoping that the above technique will work on mine and that no air will "escape" from the brake fluid over time. Peter.

denniswpearce · #5 10th February 2012, 21:47

Thanks Peter, it makes sense. I have made a natural trap for the air with no escape for it. I will do as you suggest.
Thanks again.
Dennis

denniswpearce · #6 11th February 2012, 14:16

Interesting reply Peter. My understanding of m/c, s is, after the post from Grey V8 Pete, that the rubber pipes from the remote servo to the m/c are not under pressure, they are supply pipes, whereas the copper pipes are the pipes that go to the wheels and are under pressure when you apply the brakes, but not the rubber supply pipes. So surely when I bleed the brakes air will be expelled from the copper pipes. Cannot see why it matters if they are on the top or the bottom.
I shortened the rubber supply tubes this morning to a more direct route and before I bled them I held the remote reservoir up in the air well above the m/c. Air did not come out until I tapped the tubes then small air bubbles came out for about five minutes of continuosly tapping the pipes. Eventually the bubbles stopped so I bled the system. Brakes do have a feel to them and the car will stop but I again would not want to take it out on the main road. Pumping the pedal makes the brake marginally better.
Something is still not right.

peterux · #7 11th February 2012, 16:24

Quote:

Originally Posted by denniswpearce

Pumping the pedal makes the brake marginally better.
Something is still not right.

That is the classic symptom of air in the copper brake lines.
Have you bled all four brakes?

What do others think?

Grey V8 Pete · #8 11th February 2012, 16:44

Hi again Dennis. You have most certainly still got air in your system, in particular I suspect you have still air bubbles trapped in your master cylinder itself. I had a similar problem some years ago after I replaced the M/C seals in my 2.0 GL Sierra, which had a similar setup as "our" cars. I eventually cleared the air by using a Gunsons Ezibleed to pressurise the system and then got someone to help me pump the brake pedal for a conventional bleed while the system was pressurised in this way. It also cleared a lot of gunge from the lines so must have been shifting quite a lot of fluid through them. I wouldn't worry about the outlets from the M/C being underneath. The standard Sierra set up had one underneath anyway as the fixed reservoir on the top dictated this. You can also wrap a rag around the M/C outlets and just crack the pipe nuts open to assist priming the M/C. Also only use fresh fluid! Don't be tempted to re-use the old as it will still have microscopic air bubbles in it and being hygroscopic will have picked up lots of water anyway over time. For bleeding a previously empty system I always leave it overnight after the first bleed session and then re-bleed again. This allows any small bubbles to form one big one which is easier to expel. Peter.

denniswpearce · #9 11th February 2012, 21:58

Answers to both Peters now, I have bled all four wheels several times now at different stages ie when I had new longer rubber supply lines several times plus the new shortened route several times but all with the same result, insufficient pressure. I always do a full bleed, furthest wheel first.

I do know of the pressurised system which uses the pressure from your spare wheel to a bottle full of fluid, then a line from there to your reservoir with a replacement screw cap supplied with the kit. With it all connected you go round each wheel in turn, furthest first and open the bleed nipple with a tube into a jar of fluid and hopefully with the whole system under pressure it should expel the trapped air from each wheel in turn. I believe you don,t need to pump it with this system.
Obviously going to buy one tomorrow morning to try that out.
Never use old fluid only new each time.

Oh, the joys of motoring.

Thanks boys

Grey V8 Pete · #10 11th February 2012, 22:05

No in theory you are right and the Ezibleed is designed to be a one man operation but the fluid only trickles out.
However if you do also pump the pedal it really wooshes out so all air is really purged through the lines. Worth topping up the reservoir more frequently as it really shifts some fluid this way.

Just a thought. Is your master cylinder and seals new? If a primary piston seal has gone it is possible that you are pulling air in that way? Peter.

Grey V8 Pete · #11 11th February 2012, 22:11

Another trick is to prise the front brake pads back enough to get a piece of shim in between the pads and the pistons, then bleed as usual. This worked a treat on an old Cortina that I had as it got rid of any air bubbles trapped in the calipers themselves. Worth a try anyway. PS don't forget to remove the shims afterwards! Peter.

denniswpearce · #12 12th February 2012, 11:11

Thanks for all the advice Peter. which I would use, however, I bought a Gunsons eezibleed this morning and the selection of caps they provide are all the wrong size. So I have a kit I cannot use.

For those of you who have remote servo,s, like the three feed type then the Grunson eezibleed will not fit because your reservoir is a quarter turn twist to lock cap and not a screw cap, so said kit is u/s

Hey ho,
May have to take it to my local garage for assistance.

MartinClan · #13 12th February 2012, 16:13

I also suspect that the problem is due to the peculiar orientation of the master cylinder causing air traps. Why not swap it for the 22mm Sierra one as Peter (and now me) have purchased. The fluid feed is then on the top and the brake lines on the engine side. Much easier to plumb in without creating air traps. I know it's more money but probably cheaper than a visit to the garage and it looks much more of a "proper job" when the fluid enter and exit ports have the correct orientation.

BTW I used an Easibleed with my remote reservoir when I first bled the brakes (I guess I have a different one) and it worked a treat. One man bleeding and not a lot of fluid wasted.

Cheers, Robin

NigelB · #14 12th February 2012, 17:10

Dennis,

At the risk of emberrassing myself (but it was a long time ago now), step back from it for a while and check the obvious..............

Back in the late 8o's, when I built my Marlin Roadster, I refurbed the brake calipers with new seals etc and fitted them to the hubs with the pistons pushed right back in the pots. I bled the brakes, passed MOT and everything was 'hunky dory'.

A couple of years later I needed to change the m/c (can't remember why) and having done so I tried to bleed the brakes once more. 3 months later, with three months of spongy brakes, 3 months of head scratching and a wife with a right leg muscle that Usain Bolt would be proud of I was under the car again and when suddenly I had my Eureka moment.

The beed nipple was on the bottom of the caliper and the fluid supply at the top. So all the air at the top was just stayng and there was nothing but fluid coming out the bottom.

What had happened was that I had fitted the calipers on the wrong sides when I built the car, and I guess that because the pistons were right back in their pots when I first charged the system any air that was in there was forced out before the fluid reached the calipers. Not sure.

But I swapped the calipers over, replaced the pads and all was fine.

Now you cant fit the BMW calipers the wrong way round, but that experience was certainly a good lesson in 'check the bl**ding obvious' first.

GreatOldOne · #15 13th February 2012, 11:20

Quote:

Originally Posted by denniswpearce

Thanks for all the advice Peter. which I would use, however, I bought a Gunsons eezibleed this morning and the selection of caps they provide are all the wrong size. So I have a kit I cannot use.

For those of you who have remote servo,s, like the three feed type then the Grunson eezibleed will not fit because your reservoir is a quarter turn twist to lock cap and not a screw cap, so said kit is u/s

Hey ho,
May have to take it to my local garage for assistance.

Dennis - do you have an air compressor? If so, I could lend you my pneumatic brake bleeder - it connects to an air line and when you pull the trigger the escaping air creates a vaccuum in the collection pot. You just have to attach the tube to the bleed nipple, crack it open and pull the trigger until all you get out is fluid.

cabrioman · #16 13th February 2012, 16:55

Not wanting to state the obvious but if Ford designed the brake system to feed the front brakes from two outlets from the Mcyl, you would tend to think they had a good reason, as the cost savings in production terms to run both front wheels from one outlet would be huge.

Both front outlets are linked, so failure in NS or OS calipers or pipework would result in total failure of both front brakes, so no advantage to two outlets from that perspective.

Could it be a pressure thing, ie running each front wheel from a separate outlet provides greater brake pressue than running both wheels off one, or that the amount of fluid required by the calipers needed separate feeds.

I can't see why Ford would have chosen to incure the additional costs of a second outlet pipework configuration if it wasn't needed, when you think of the additional costs of just adding the additional brake pipe multiplied by the number of cars rolling off the line you would be into millions worldwide.

There must be a reason for running with two outlets to the front brakes.

John

Grey V8 Pete · #17 13th February 2012, 18:21

The primary cylinder goes to the rear brakes. The Secondary (front) cylinder goes to the front brakes. Both front outlets feed from this cylinder so the pressure is equal to both front brakes. If say either of the front hoses fail there will be a loss of pressure to both front brakes, the floating front piston in the MC will move forward until it physically contacts the end of the bore and pressure will then be exerted in the primary (rear) cylinder to still actuate the rear brakes. I suspect the reason that Ford used two pipes for the front is due to the geography of the front of a Sierra which will affect the fitting of brake pipes to the bare body shell. For the N/S brake to be fed from a Tee the pipe would have to go to the front of the vehicle and then across and back to the N/S front wheel. There is not much transverse fixed body at the front of a bare Sierra and the pipe run would be quite long, whereas the bulkhead area is easily accessible for pipe fixing. The cost of the extra pipe length, plus the brass Tee, times say 100,000 cars would almost certainly have figured in Ford's production costing. Peter.

peterux · #18 13th February 2012, 19:53

I have a concern about using BMC4052 master cylinders with cars fitted with REAR disk brake callipers that I ought to raise.

The discussion above about brake pipes got me reading some more theory on Brake master cylinders and how they work. During this bit of self tution I found a reference to Brake Master cylinders designed for drum brakes have residual pressure valves built in.
According to this article....
http://www.hotrodheaven.com/tech/brakes/
the guy reckons that if you use a M/C designed for drum brakes with disk callipers it can cause them to lock up!

Now the BMC4052 was used on pre 1988 Sierra's that were fitted with drum brakes at the rear (as far as I can tell from Brakes International website).
So I'm guessing it may have a residual pressure valve built in and the Master Cylinder is not suitable for rear disk brake callipers.

This may not be the case but I have no way of telling so I thought I should bring this to peoples attention.
My apologies to anyone who has bought one of these M/C but I'd rather you didn't fit it and have your rear brakes lock up

Mike · #19 14th February 2012, 11:07

Hi Peter

Whilst I fully understand the reason for your concern - no one wants to be responsible for causing others problems of a potentially serious nature, however small the risk (I declined to supply adaptor plates made in stainless for exactly the same reason), may I offer a reasoned response for others to consider?

Like GOO, I'm not too sure that there is a real problem here, let alone one that merits action. GOO, Andrew Curtis, myself (and possibly David Siddall and Alan Hogg) all have this MC, and we all have tested our cars without any initial problems, so I do not believe there is a fundamental problem. Of course there could be an issue in the event of a valve failure, but I do not see that as a justifiable reason to ditch these MCs.

I am, therefore, quite happy to continue with my set up.

Like you, I came across this guy's web page when researching servos. On balance, I am not convinced by his comments. If you give his proposition some thought it is just not rational to assume a low pressure residual valve can cause brakes to lock up to such an extent that they will skid.

Bear in mind the original reason for all of us getting involved with this project. It was because of the inabilility to generate sufficient braking pressure at the wheels to slow our cars down in an emergency. Few, if any of us, using a Metro servo could lock the brakes up whatever the pedal pressure applied. Fitting a residual pressure return valve does not change that. The brakes can only lock up when an excess of pressure is applied. This is a function of pedal pressure, the servo boost, and the MC bore size. Pressure does not build cumulatively through repeated use of the brake pedal. Even with a failed residual pressure valve which prevents all return pressure being released, the pressure can only reach the maximum applied by the MC at any one time.

Front and rear brakes were designed by manufaturers (pre ABS) to ensure the fronts would skid before the rears. Therefore the rears should never reach a point where a skid is induced, and the residual pressure valve can do nothing to increase that pressure.

My view is that the worst that can happen is the rear brakes bind if the return valve completely fails. An equally likely failure would be for the main bore seals to fail, in which case we would not drive our cars at all.

More research is required to establish :

That there is a residual pressure valve in this MC.
That it was not fitted to MCs for Sierras/BMWs with rear brake discs
If it was not originally fitted, do others support the view that it could cause a problem.
What are the potential problems
What is the likelyhood of any of those problems occuring
What are the consequences of those problems if they occur.
Until we have answers to all these we are not in a position to make an informed decision.

In the meantime, and I can only speak for myself, I am prepared to accept what I consider to be a very low level risk.

To use the H&S jargon from work, I have assessed the risks as very limited: I have assessed the consequence as very limited: therefore the decision is to take no further mitigating action, other than to seek more information, and reassess that decision in the future.

But, I do understand your concern, and I did the same as you by dipping out of supplying stainless steel adaptors when the risk was probably just as small.
The consequences, however remote, are not worth the worry when it involves someone else. If you have highlighted the issue, and others continue with this MC you have done all that could be expected of you, and they must be accountable for their own informed decision making.

Mike

Quote:

Originally Posted by peterux

I have a concern about using BMC4052 master cylinders with cars fitted with REAR disk brake callipers that I ought to raise.

The discussion above about brake pipes got me reading some more theory on Brake master cylinders and how they work. During this bit of self tution I found a reference to Brake Master cylinders designed for drum brakes have residual pressure valves built in.
According to this article....
http://www.hotrodheaven.com/tech/brakes/
the guy reckons that if you use a M/C designed for drum brakes with disk callipers it can cause them to lock up!

Now the BMC4052 was used on pre 1988 Sierra's that were fitted with drum brakes at the rear (as far as I can tell from Brakes International website).
So I'm guessing it may have a residual pressure valve built in and the Master Cylinder is not suitable for rear disk brake callipers.

This may not be the case but I have no way of telling so I thought I should bring this to peoples attention.
My apologies to anyone who has bought one of these M/C but I'd rather you didn't fit it and have your rear brakes lock up

MartinClan · #20 14th February 2012, 12:42

Thanks to Peter for raising his concerns - its just as well to know that there is a potential problem however uncertain it is.

Personally - I will be taking my car in for an MOT soon - certainly before I tax it this year. I guess if there are any problems that should show them up.

Chhers

Robin