Dual 7" Servo - Page 27

cabrioman · #**521** 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 · #**522** 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.

cabrioman · #**523** 13th February 2012, 19:34

Yeah Peter you may be right, it may have just been a costing that influenced the use of 2 or 3 outlet. To be honest its so long since I worked on a Sierra I can't recall the routing of the pipework.

I just wondered if there was an operational benifit to a two feed setup which I hadn't figured out.

denniswpearce · #**524** 13th February 2012, 19:48

Thanks for the offer Jason but my Sportster is due its MOT at the end of the week and its the garage I use for my daily runabout, so I spoke to them today and they are going to purge the system of its trapped air using their compressor as well as carry out the MOT.

So your offer is very much appreciated but not needed.

peterux · #**525** 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

Patrick · #**526** 13th February 2012, 21:59

hmm lock up would be bad

I've not installed yet so no big worry there.

On Richard E36 compact we switched the drums for discs without issue on the back and that been running that way for a number or years now. Could be the BMW master cylinder on there is of a different design though.

morris · #**527** 13th February 2012, 22:18

Hi Peter, just checked eurocar parts for a 1987 1.8 sierra and it offers both drums and disks for the rear. I know they're not much of an authority but it does offer some hope.

Patrick hasn't tried his yet, Robin, have you?

Suck it and see may be the only way to know for sure. I've got mine all installed and have binned the packaging etc so I don't mind charging the system up with fluid to see what happens. I was going to anyway so as to check for leaks. It won't be as good as a rolling test but if the calipers lock on it will still be pretty obvious just by my inability to turn the wheel by hand.

Chris Cussen · #**528** 14th February 2012, 06:42

The standard Sierra (drums rear) set up had a brake limiting valve fitted at the rear of the car and not as part of the master cylinder.

mashtun · #**529** 14th February 2012, 07:02

The Haynes Sierra manual that I have describes it as a "deceleration valve" (and says it was fitted in the engine compartment?), and from what I can tell it seems its purpose was the reverse of a residual pressure valve i.e. it's designed to reduce the pressure to the rear under heavy braking. I didn't fit it to my Cabrio.

If you view the "Hydraulic Actuation" components for 82-86 1.3 & 1.6 Sierras on the Brakes International website and click on the "More Products on Next Page" button at the bottom of the window you'll see a couple of regulator valves (HRV1125 and HRV1069) listed - the HRV1125 looks like the pics in the Haynes manual. The 2.3 V6 had drums at the rear and also has these valves listed.

Peter, have you found anything that describes what form a residual pressure valve inside a master cylinder would take?

Mark.

GreatOldOne · #**530** 14th February 2012, 07:45

Chaps - I think this needless worrying.

I have a Ford 22mm Bore MC, with BMW discs & calipers all round. It works fine!

Mike · #**531** 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 · #**532** 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

cabrioman · #**533** 14th February 2012, 14:49

I think Mike is correct, it may be worry about nothing.

It looks to me like the risidual valves are really aimed at preventing excess travel in the brake pedal.

Wilwood provide write ups about their 2lb and 10lb valves for use in drum and disc applications which seem to provide a pretty clear explanation of the use.

Have a look here http://www.wilwood.com/MasterCylinde...derValves.aspx just scroll down the page a bit.

I guess if doubt remains an email to Wilwood disguised as a pre purchase enquiry might shed some light.

I am using the Sierra MCyl designed for drum rears (which is what i have) I know a couple of the guys in the MOC were using the same cyl/brake configuration and then replaced the drums with Sierra rear disc setups. I haven't heard of any issues after they upgraded. The only comment from the MOC BMW Cabrio tech rep was that his car was borderline overbraked at the rear when tested during SVA but I don't think he has had any issues as such.

John

andrew curtis · #**534** 15th February 2012, 08:25

Go onto the italan manufactures web site [ www.cifam.it] they have a lot of information including brake circuits it may be of help.
With regard to my blacksmiths brake tests ref Mikes report i could not get any lock up on the rear brakes, the car does not have any pressure regulating valve in the rear bake line as is standard on the E30 doner
Andrew

andrew curtis · #**535** 15th February 2012, 08:45

Quote:

Originally Posted by MartinClan

Can I assume then that Andrew blanked off one of the two outlets from the front of the Ford M/C? As I understand it they are siamesed both coming from the front section of the M/C. I was thinking about doing the same as it means I wont have to re-run the brake lines to the front callipers as I have only a single connection with a T-piece at the front.

BTW I have replaced the small threaded adjusteare at r on the M/C side of the servo with a 35mm long cap headed set screw. Fits in the operating rod of the M/C fine and the cap head means you can use an allen key to adjust and tighten it. I re-used the little locking ring from the original adjuster.

I have "reserved" this coming weekend to do the changeover....

Robin

Yes l did blank of second port but not befor forgeting it and draining half the reservoir thro it onto the floor, The inlet pipes from the reservoir are at TDC and the reservior is in the battery box and is the highest point
Andrew

morris · #**536** 15th February 2012, 17:24

Can anyone tell me if I need to still use number 12 in this diagram with the new servo?

http://www.realoem.com/bmw/showparts...88&hg=34&fg=27

Real OEM calls it "CHECK VALVE SUPPORT" though I think the new servo has a check valve built into the removable vacuum fitting on the front.

is this part just a right angle to keep the hose tidy. I can't find mine and may have left it in the donor

Mike · #**537** 15th February 2012, 17:58

Quote:

Originally Posted by morris

Can anyone tell me if I need to still use number 12 in this diagram with the new servo?

http://www.realoem.com/bmw/showparts...88&hg=34&fg=27

Real OEM calls it "CHECK VALVE SUPPORT" though I think the new servo has a check valve built into the removable vacuum fitting on the front.

is this part just a right angle to keep the hose tidy. I can't find mine and may have left it in the donor

Ian

I think the elbow supplied with the servo is a non return valve, so strictly speaking you do not need item 12. However, you will need at least one right angle elbow.
I have a spare BMW no 12 if you want it FOC before I throw it in the bin?
Mike
PS I'm away till Monday night now.

morris · #**538** 15th February 2012, 21:16

Hi Mike, if you don't mind, it could come in very handy. Like you say, I think more like 4 right angles will be needed if I don't want a vacuum hose draped right across the middle of the engine.

thanks
Ian

peterux · #**539** 17th February 2012, 10:03

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........

..........this may not be the case but I have no way of telling so I thought I should bring this to peoples attention.

Thanks to everyone who considered this potential risk and replied with their views and suggestions above.
I'm still doing some background investigation and I will post an update if I can get anything more definitive.

...peter

denniswpearce · #**540** 18th February 2012, 10:11

Ok I can report on my servo installation now that my local garage managed to purge the system of its trapped air.
I obviously informed the garage owner of what I had done in replacing the metro servo with the dual servo so that he was in the picture.
Firstly their reservoir caps did not fit my reservoir ( same problem I had ), but then they overcame that issue and bled the system of a lot of trapped air.
He said the brakes performed well and he was able to lock the wheels very easily. I drove it home this morning and was anxious to try it for myself.
However, he did give me one bit of advice before I left.
It is a condition of a dual servo that if you pull up at traffic lights and leave your foot on the brake pedal that the travel will be longer than when you are moving, so his advice is not to leave your foot on the pedal when stationary. Fortunately I am one of those who uses my handbrake and not leave my foot on the brake pedal so that I do not blind the driver behind with my brake lights ( not an issue with the Sportster though ).

Anyway, driving down the road from the garage I was very tentative with the pressure but it has a completely different feel to the pedal, the travel is longer and takes a bit of getting used to, but you do not have to apply much pressure before the brakes bite, its very light, more akin to my daily runabout.
Obviously I wanted to stamp on it real hard to see the reaction and I did. The response was an immediate lock up, but it felt like the rear wheels rather than the fronts.
Then I had other cars in the vicinity and could not try that test again. But at junctions and roundabouts the feel and responce is much better than the metro servo. Today is a crap day weather wise so will have to wait for some dry weather to try again.

I am one happy bunny.

Thanks Mike I owe you one and Jason for trying it out and giving the green light. Also thanks everyone on here for all the valuable advice that has helped me with my installation.