Dual 7" Servo
 

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I made a leap of faith and ordered the Dual 7" servo from Ducksville yesterday, and it arrived at 9am this morning.
The above shows that the trial fit is very good news. The studs attaching to the pedal box are on 85mm centres compared to the Metro ones at 90mm, so only minor hole fettling is required to make them fit.
The maximum diameter around the seam is identical to the Metro servo, so it fits the space available between engine and side panel.
The length front to back is 2" longer than the Metro, but the secondary chamber is 1" smaller in dia., so remains inside the bonnet line.
I am reasonably confident that after I have made a new adaptor plate and extension pushrod between servo and master cylinder it will still fit under the height of the bonnet.
And if I can get away without new brake pipes it will all have been so easy its untrue.
I am well chuffed - Thanks Jason for a very good spot!

Well - now we know it fits. All we need now is an on the road assessment of performance! :)

I may have to get one myself. I might have to splash a little extra for a chrome one though, to bling up the engine bay. :D

Hey Mike that is good news for all of us with doubts about brake performance. What about the connection between the Servo and pedal - does that look OK as well?

Cheers

Robin

Jason/Robin

You are welcome to borrow mine if you would like to "try before you buy". There will be a bit of work as it will need a new adaptor plate, and push rod conversion, and probably an extension piece between servo and cylinder?
I will make permanent alterations to mine as I do not like Marlin's double pivoted extender, but I can do all that later if you are up for giving it a test?

I shall not have my car on the road for a few months yet, so I'd be interested to see what benefit you guys who have your cars on the road feel it gives. Let me know.....................
I thought about Chrome but ................American chrome? They do a polished Stainless one though.
Mike

Robin

I will post some photos of the new Dual 7", but it will require some adaption to make it fit the pedal. I plan to weld an extension to the push rod as I did with my Metro one, so there are no potential pivot points, and I will now have a back up servo if this one ever goes wrong.

My Metro servo adapted

http://farm7.static.flickr.com/6221/...0cf03fe1_z.jpg
http://farm7.static.flickr.com/6236/...7205931e_z.jpg

I would say the Dual 7" servo seems a lot more sturdy than this Metro - typical American engineering - big and heavy!
Mike

Bah! Duksville are out of stock now. :(

Thanks for the offer of a try before you buy - but as you're going to weld / modify the pushrod - and no two sportsters are the same... I'll get one of my own once they're back in stock and modify it so it fits Vikki.

:)

I suspect the new servo will need a longer extension between servo and cylinder than the Metro, as the output push-rod is inset deeper within the servo. The adaptor plate will be bigger too as the fixing hole centres are wider. The push rod is threaded and more substantial, so it will be easier to make this rigid, yet adjustable, by making a threaded extension with a fixed yoke. This will be better for adjusting/setting the final position of the brake pedal after driving it for a while.

http://farm7.static.flickr.com/6037/...96216e11_z.jpg

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Wow - seeing the metro and the dual side by side really reinforces how much more assistance you'll get. :)

My calculations, based on the surface area of the diaphrams, assuming there is one at say 6", and one at 5", suggest around 55% more boost.
However, I read in one of the adverts the gain is only 25% more?

I'll eagerly await your proper road test!
Mike

Jason

Just a thought..... could the Sportster take an " 8" " booster on the basis the 7" is exactly the same maximum diameter as the Metro?
It would be very tight in the Cabrio, but might have been possible?

You are welcome to try mine before I alter it, as I'll be several months before I am ready to put it in for the dreaded test.

Yes, but 25% more compared to what? I'd assume that's against a stock yank wagon booster - which when you look at their engine bays (Not small), and the size of the cars (enormous), it wouldn't be a tiny metro-ish servo.

:)

I've just found this whilst googling:

How much pressure should I be getting to the wheels with a power booster?
Typically you should expect about 1000 psi. to the wheels for a disc brake system. A disc brake system requires this amount of pressure so be careful when using a smaller 7" booster that puts out only 900 psi pressure. Use our AC2004K Pressure Tester Kit to get a pressure reading at any point in the braking system.

What size booster do I need?
For lighter weight vehicles like street rods a 7" booster will work fine for disc/drum set ups. For a 4 wheel disc system a 7" booster will not give enough assist. An 8" dual diaphragm booster is the ticket for 4 wheel disc.

Hmmm - proof is in the pudding, but I'd put our cars in the lightweight 'street rod' catagory. And does the 7" they talk about there have dual or single diaphragms?

This is interesting - it is obviously a true "dual". Even though the 7" is not a 7" diaphragm.

Therefore, as the diaphram is the same as the original Metro it ought to offer double the boost?

http://image.superchevy.com/f/130013..._diaphragm.jpg

You didn't have to get the angle grinder out Mike... ;)

Just rang Duksville. No more Duals until after Christmas, as if he orders them he has to get 50 at a time. Rats.

I knew I should have kept this to myself... :eusa_shhh: :icon_wink:

I am totally bemused by this now.
I found an American site showing a 7" servo as 7" across the diaphragm chamber - which is what you would expect.
Yet the Dual 7" that I have measures only 6" across the diaphragm chamber.

So what have I received?

Maybe the 8" is actually the 7", and people are taking the external diameter and selling them as such, rather than the more accurate internal diameter.

I spoke to Paul at Ducksville and he says the 7" is a 6" diaphragm. He reckons these Dual ones are used on big American Chevys etc., so it should stop a little old Marlin.

Interesting stuff, this is what happens when I don't look at the forum for a few days!!! :)

I have begun the process of making adaptors to allow me to fit the Dual 7" servo:

http://farm7.static.flickr.com/6221/...f05afa416f.jpg

The steel backplate is made from 6mm mild steel, and turned out on a very old lathe.
The Metro push-rod, seal and nipple are from a standard servo. I plan to use the yoke to attach the servo to the pedal.

Useful tip: there are plenty of Metros in scrapyards, but removing a servo is incredibly difficult. Buy one cheap from ebay, or.......
Go to scap-yard - find metro - remove clevis pin to pedal: remove master cylinder ( 2 x 13mm easy access nuts): then use brute force and intelligence to drive a sharp chisel into the servo and smash the plunger out the bottom. 15 minutes start to finish - trying to remove the servo could take hours - if you don't give up in total frustration!..... (Like me!) Total cost of parts - £2

Had a similar experience trying to remove a Metro server in a scrapyard - the scrappie became increasingly colourful with his language :)
Still, we got it out in the end...

Mike. I suspect that there may be an avalanche of Marlineers interested in this upgrade. I certainly am for my disc/ disc Hunter. Keep the info coming please. You could even manufacture and sell an adaptor kit of parts for us? :icon_smile:

I assume this is the adaptor plate between the servo and the master cylinder? Looks as if you've cut a rebate for the sealing o-ring into it...

Rally Design supply a threaded yoke - 3/8" UNF: £8 delivered
http://www.rallydesign.co.uk/product...ducts_id=14609

http://www.rallydesign.co.uk/images/G1312.jpg

Or CBS do one for £6.60 inc VAT

http://www.cbsonline.co.uk/product/M..._Clevis_CLEVIS

5/16 UNF thread though.

[Edit] - aha! must read the thread properly. £8 delivered is cheaper! :doh: :D

For anyone interested:

I am not sure whether the Dual servo requires a seal to be maintained between the servo and the master cylinder. The Metro unit definitely does, but the Dual probably does not.
I have made this back plate as a trial for testing, and will deliberately leave a leak to confirm whether the seal is necessary or not.

http://farm7.static.flickr.com/6233/...66f5ecf968.jpg

This photo shows the exposed chamber of the Metro, whereas the Dual clearly has a sealed chamber.


Jason, and anyone interested
I know you are attending metal work classes, so you could make a back plate.
Dimensions are:
Plate - I chose 6mm mild steel: 5mm would be OK
Outer diameter: 108mm nominal
Inner diameter : 40mm for my Sierra master cylinder: generally to suit your own master cylinder
Recess diameter : - if required +5mm on diameter
Recess depth : 1.5mm when using 6mm plate
A cut out will be required for the vacuum elbow : drill 30mm diameter offset centre from perimeter approximately 5mm

Holes for servo fixings :2 x 10mm dia. on 87mm PCD
Studs for master cylinder : M8 x 20mm projection for my Sierra master cylinder, but generally to suit your master cylinder
Offset of servo holes to master cylinder studs : for my Sierra master cylinder approximately 75 degrees, generally to suit your own master cylinder

You may require a spacer between the servo output push-rod and the master cylinder : my Sierra one will require approximately +6mm

And it has to be a 3/8" UNF !

Jason

If I make this back plate to suit your BMW master cylinder and buy the adjustable clevis pin, are you up for testing it? - I can deliver it all to Northampton on my travels.

The only sticking point could be whether your brake pipes can move 2" further? Though I seem to remember you have used flexible pipes, so this should not pose a problem.
There appears to be quite a lot of interest in this, so you'll be doing all of us a favour, as I will not get my car on the road for several months yet.:playball: :nod:

Sure - why not. I don't think there'll be an issue with by brake hoses... Not sure about the fluid feed lines from my remote resevoir. But I can get some more and rig up some longer lines during the test.

Good man:eusa_dance:
What is the hole size for the studs to secure the master cylinder?
What is the centre to centre dimension of the holes
What is the thickness of the master cylinder mounting plate? (to determine stud length)
Relative to the vertical, what is the degree of rotation for the centre line of the studs? - from your website it looks around 30 degrees. As you have a remote reservoir, I guess this is not too critical within +/- 5 degrees?
What is the diameter of the male part of the master cylinder which enters the servo?

I'll do some measuring tonight when I get in from work.

I will tell you that it's not a BMW master cylinder as far as I can tell, as I purchased it from Marlin. It's also mounted to the Metro servo without a mounting plate / adaptor, so the stud dimensions / pcd is as per the metro part.

I don't think it matter too much about the degree of rotation. What it is at the moment is as it fell from mounting the servo in the best degree of rotation to allow easy rounting of the vac hose and to keep the low pressure fluid entry ports relatively topside.

Jason
I've had a look on your website, and I'm sure it is a Ford master cylinder.
I can get the studs sorted out from the metro servo. I just need to be sure the male part of your master cylinder will go through the hole I have already made.

Did you have to make a spacer between the servo output rod and the master cylinder?

Yes - can't remember how big though... I believe I followed Robin's schematic. Hang on...

http://myweb.tiscali.co.uk/martinclan/images/spacer.gif

One of them! :)

Great.
The Dual has an adjustable output rod, so can compensate for the 6mm spacer, making it a direct swap.

http://farm7.static.flickr.com/6217/...b2aa0e4cf3.jpg

I have ordered the adjustable 5/8" UNF clasp, so this should adjust the pedal height.

The prototype adaptor plate is now made:

http://farm7.static.flickr.com/6118/...e646aa73a1.jpg

And fits:
http://farm7.static.flickr.com/6219/...26f7d0dc0c.jpg

http://farm7.static.flickr.com/6229/...09f7c30b4e.jpg

http://farm7.static.flickr.com/6234/...f75915d925.jpg

The adaptor angle has been set to allow my own master cylinder to attach vertically, as I am fitting the standard Ford Sierra reservoir directly to the master cylinder.

Cor, you're keen. :)

Here's some more info:

http://www.greatoldone.co.uk/Servo/adaptorpin.jpg

Adaptor pin / sleeve, as per Martin's diagram (10mm OD, 8mm ID, 2mm 45deg chamfer, 20mm overall length)

http://www.greatoldone.co.uk/Servo/mastercylcasting.jpg

Casting number on the cylinder. No idea if it's of any use

http://www.greatoldone.co.uk/Servo/m...linderstep.jpg

Pic of the stepped nature of the servo end of the master cylinder. The larger portion is 40.5mm in diameter, the smaller 36.3mm in diameter. It's the larger of the two steps that creates the seal between the servo and the cylinder. The mounting holes are 8.5mm diameter, and have PCD of 70mm

http://www.greatoldone.co.uk/Servo/m...ylrotation.jpg

The cylinder from the end looking back, showing the layout of the high pressure brake hoses (stainless) and the low pressure feeds. The studs are at 25 degrees from the vertical

Do you need anything else?

Hi Jason

I had the day off today and am quite pleased with the prototype adaptor, though I'll have to make a minor modification to the angle of rotation for the master cylinder, and then it should be OK.

I just hope when you test it you feel some real benefit!!

Just looking at your photos I may have a problem with the rotation of the master cylinder as it may cause your pipework to foul the side panels - you may need to test the brakes with the side panels off!

All the rest I think will be ok.

I have trial fitted the whole arrangement in my Cabrio, and apart from not getting the angle of rotation exact - it is more critical in my Cabrio as I have the standard reservoir mounted directly to the master cylinder, it fits much the same as the Metro version.

http://http://farm7.static.flickr.co...064b6bde83.jpg

http://farm7.static.flickr.com/6096/...4d76efdc16.jpg

I have not achieved the exact angle of rotation to ensure the reservoir is vertical. This will prevent the bonnet closing, so the final design will need to err towards the engine.
Otherwise looking good!!!!

http://farm7.static.flickr.com/6097/...cc3fd8a99c.jpg

Jason

I think we are now good to go. You will need to fettle the servo hole mounts in the pedal box, as the stud centres are 85mm compared to the Metro at 90mm. My holes were fairly large anyway, so it required very little alteration.
Then as you say the only other issue could be the reservoir feed pipe length?

Can you PM me your Mobile & address please?
Mike

PM sent.

I think I can get away with the lines I have, If I make a gash bracket to move the res foward into the engine bay... I'll have to see.

The only issue with that is how much slack I have on the line feeding the clutch master cylinder as my res feeds both clutch and brakes.

Ok, good.

The bad news: I have received the clevis pin in the post this morning but it is too short for my set up.

http://farm7.static.flickr.com/6049/...b1d91f96e9.jpg

One other small issue may be the size of the pin through the clevis - it is 3/8" too. Not sure what Marlin supplied on their extender arrangement, as I threw it away. My pedal has a 3/8" hole so not a problem for my Cabrio, but others may need to consider this.

The good news: I've found a supplier close to our Birmingham offices so hope to collect a longer version tomorrow.

It was a long time ago but I think the Sportster brake pedal has an 8mm bolt.

I found this very old picture which may help you understand the dimensions?

http://farm1.static.flickr.com/47/15...6abea893_o.jpg
Trial fitting brake servo on pedal box by marlinpeter, on Flickr