Dual 7" Servo

[oaktree11]

Mike,

I will give one a go. I dont think headroom is going to be an issue. PM me the damage etc!

Thanks

John

[Mike]

Hi John

Good man! I'll put one in the post tomorrow.

Can you let everyone know how it fits, please.

Do you have a Ford BMC to test it with?

Mike

Originally Posted by oaktree11

Mike,

I will give one a go! I dont think headroom is going to be an issue! PM me the damage etc!

Thanks

John

[oaktree11]

Mike,
Therein lies a tale as they say. I have one coming which is either a Sierra one or a Cortina one. I think it will be the former Its a long story.....

[peterux]

Originally Posted by Mike

Peter

Can I ask a couple of questions so that others can consider their options?

Have you fitted standard BMW brake parts in the rest of your system?
Do you know the bore size of your original m/c? - you say it is dual diameter bore size? Are you suggesting the two bores are different sizes?

The reason I ask is you are negating a significant part of the impact of increasing the servo pressure, by opting for the larger bore master cylinder.

Robin has stated his BMW bore size is 20.6mm in his standard set up. I know it does not sound much different, but the pressure in the brake system transmitted by the bore is related to the surface area: the bottom line is the 22.2mm m/c will be 16% harder to press than the 20.6mm. This is significant, given the reason for going to all this trouble is to make the brake pedal easier on the leg muscles.

I chose the 22mm bore m/c as it matches the original Ford Sierra spec to go with my Ford Sierra brake set up. The dual servo gets closer to the original Ford 8" servo, so I should have a system as close to Ford's original spec as possible. By opting for the 22mm bore you are making yours 16% harder to press than in the donor BMW (using Robin's bore figure)


There are, of course, other considerations. The pedal travel on the 22mm bore will be 16% less than the 20.6mm bore and it may be felt that this is worth having - I am in no position to comment as I do not know what it feels like in a BMW based car.

I do not wish to suggest you have got it wrong, but others following this thread need to understand that all our cars are not the same, and that a m/c that works in a Ford set up will not necessarily perform the same in the BMW set up. All other things being the same in the brake set up, my preference would be to opt for a m/c with the same size bore as the donor?

Of course you can suggest Jason has fitted the 22mm bore in his BMW set up and is happy. Given the opportunity to do it again with a 20.6mm bore and 16% less effort, but longer pedal, what would he do next time?

Please take this as a constructive question, for the benefit of others who are still able to choose their set up.
Regards
Mike

Hi Mike,

OK, no problem. Let me answer your questions and take you through my decision logic. (But only time will tell if I got it right )

My brakes currently are all standard BMW, but I am a little different to most BMW builders as my donor car was only a 2 litre so was fitted with drum brakes at the rear.
According to realoem there are lots of options fitted to these cars with some fitted with dual bore MC's 22,20/17,46MM.....others were fitted with 20.6mm,
but that's now irrelevant as I fitted a new MC that I bought as NOS from eBay.
Unusually for BMW parts, I can't read any part numbers on it but I can now see that the back section of my current one has a larger external diameter than the front. The front piston drives the real wheel cylinders which are quite small in volume so presumably Dr. BMW decided they needed less fluid than the front disk callipers.(for the same piston travel)
My longer term strategy is to upgrade the back axle brakes to disks (but don't tell my wife ), so I opted for the 22mm bore Sierra MC.
I was close to ordering a Cortina MC with the 20.6 bore but I was concerned that when all four wheels have disk callipers they might need too much pedal travel.

Can you see my logic?
...peter

[peterux]

OK, I've just done a trail fit using only gravity as my mounting bolts!

No surprises, it all seems to fit just fine.....


Sierra Master Cylinder by marlinpeter, on Flickr


Sierra Master Cylinder by marlinpeter, on Flickr


Sierra Master Cylinder by marlinpeter, on Flickr

The adaptor plate fits perfectly and I'm glad I didn't need to make one. Thanks Mike!

Fitting will follow ....
the completion of the M20B28 engine conversion....
repair my steering rack boots....(damaged by the hose clip end stops recommended by Marlin)...
replace front wishbone ball joints as the rubbers are already perished....
refit all the bodywork.....
engine testing....
...peter

[Mike]

Peter

The only issue I have with the fitting is that my reservoir cap is close to the underside of the bonnet at the top. As you will have to file the firewall holes out - the new servo has 85mm centres compared to the existing 90mm for the metro servo - it would be best to file the top holes down the full 5mm. This will lower the servo and make the clearance less of an issue.

If you have a remote reservoir this is irrelevant, but the point is being made for anyone planning to fit a direct mounted reservoir.


Glad you like the kit!
Mike

[mashtun]

Here's what the chromed unit looks like with a Sierra master cylinder fitted:


Dual Diaphragm Servo with Master Cylinder by Mash_Tun, on Flickr

The adapter plate needs a little cleaning up and then painting so this was just a trial fit to see that everything lined up and went together correctly - and it all does just perfectly, I'm very pleased:


Dual Diaphragm Servo with Master Cylinder by Mash_Tun, on Flickr

[Mike]

Bambi was tentatively lowered on to all four wheels today, and taken for a test drive. My first impression of the brakes is much better than I expected! The pedal actually feels quite soft - certainly softer than I expected: though the pedal travel is more on the road than sat in the garage. I hope as the pads and discs bed in the pedal travel will reduce.



Based on my first two miles, and all at relatively slow speeds, the brakes are good. I had one one genuine emergency stand on the brakes moment - as my next door neighbour came round an unsighted bend too fast on a single track road - there is so little traffic round here we are all guilty of doing the same. He had his wheels locked up, and I needed to slow right down to pull on to the verge, and felt quite calm about it all.

I would suggest the 22mm bore master cylinder is right for the Sierra set up. I had considered the possibility of swapping my 22mm for a 20.6mm Cortina, to reduce the leg pressure, but this is definitely not necessary, and I would not want the additional pedal travel.

It will be interesting to see what other Sportster owners feel as you start to complete your kits. GOO's initial impressions were that he was happy with his set up with a 22mm bore. Certainly based on my own experience, which is with all Ford mechanicals, I'd recommend the 22mm bore.

[peterux]

Well done, Mike!


I bet your neighbour had a surprise when he saw you coming round the bend on that private road

[Patrick]

Looking good Mike

Originally Posted by peterux

Hi Mike,

OK, no problem. Let me answer your questions and take you through my decision logic. (But only time will tell if I got it right )

My brakes currently are all standard BMW, but I am a little different to most BMW builders as my donor car was only a 2 litre so was fitted with drum brakes at the rear.
According to realoem there are lots of options fitted to these cars with some fitted with dual bore MC's 22,20/17,46MM.....others were fitted with 20.6mm,
but that's now irrelevant as I fitted a new MC that I bought as NOS from eBay.
Unusually for BMW parts, I can't read any part numbers on it but I can now see that the back section of my current one has a larger external diameter than the front. The front piston drives the real wheel cylinders which are quite small in volume so presumably Dr. BMW decided they needed less fluid than the front disk callipers.(for the same piston travel)
My longer term strategy is to upgrade the back axle brakes to disks (but don't tell my wife ), so I opted for the 22mm bore Sierra MC.
I was close to ordering a Cortina MC with the 20.6 bore but I was concerned that when all four wheels have disk callipers they might need too much pedal travel.

Can you see my logic?
...peter

Mine is fitted with a dual bore 22,20/17,46MM and the rear brake (disk) have an extra pressure reduction fitted inline. I just wonder if it will upset the brake balance.

Looks like the 22 might be the better option especially if I swap out the front callipers for something more meaty in future.

[peterux]

Originally Posted by Patrick

Mine is fitted with a dual bore 22,20/17,46MM and the rear brake (disk) have an extra pressure reduction fitted inline. I just wonder if it will upset the brake balance.

Looks like the 22 might be the better option especially if I swap out the front callipers for something more meaty in future.

Yup, mine has the same BMW in-line pressure reducer.
We should be OK as we will have the same config as Jason's car which passed the IVA brake tests with the 22mm master cylinder fitted.

[Patrick]

That sounds fine, need to decide if I stick with the remote fluid reservoir or change to one mounted on the master cylinder.

[Mike]

Originally Posted by Patrick

That sounds fine, need to decide if I stick with the remote fluid reservoir or change to one mounted on the master cylinder.

Ian Morris says his BMW reservoir has the two ports at 85mm centres - the same as the 22mm Ford master cylinder I have.
Is it too much to hope that it might fit without messing around?
Mike

[mashtun]

Originally Posted by Mike

Bambi was tentatively lowered on to all four wheels today, and taken for a test drive.

That must have been quite an occasion - well done!

[Mike]

Hey GOO,
Have have you got your car put back together get?

[GreatOldOne]

Almost. I'm hoping to get the brakes bled today so I can take her for a spin.

[MartinClan]

Originally Posted by GreatOldOne

Almost. I'm hoping to get the brakes bled today so I can take her for a spin.

Not literally I hope....

[peterux]

Originally Posted by GreatOldOne

Almost. I'm hoping to get the brakes bled today so I can take her for a spin.

Originally Posted by MartinClan

Not literally I hope....

You mean when he forgets his got a Capitan America brake booster and all wheels lock up!!

[GreatOldOne]

Brakes bled... (I had to really - I let air get in the lines when I re-did the feed pipes to the MC)

...And back from a shake down blast.

IMHO, It's better than the initial dual servo we tried. I took her up to some miles an hour, stood on the brakes (no one else was around) and she locked up, fronts first. I know this from the tyre smoke that came from the front.

Did it again with less hooliganism, and the pedal feel is spot on. You can easily gauge how much force to put in, and emergency stops are quick and can be down with out locking up. Who needs ABS?

Pootling round town and at speed on the dual carriageway it feels great. A top upgrade!!

[denniswpearce]

May be I have missed a point or I am incredibly thick but the servo looks to have been designed for the m/c to bolt directly onto it hence the two fixing studs. Now for those of you with the reservoir mounted on top of the m/c this creates a problem because the holes need to be further round so that the reservoir sits with its filler cap on top, therefore Mike has been innovative in designing and having made the new 6mm plate which now has offset studs to mount the m/c and at the time nobody new it was a sealed unit. This creates a small problem in that Jasons small extension has to be made to marry up the two operating faces between the servo and the m/c.
But...............for those of us who have remote reservoirs, if this new plate was not fitted and the m/c was fitted direct to the servo the new plate would not be needed and the servo and m/c faces should marry up ( more or less )
Are you still with me or is this gobbledygook ?