BRAKES

[paul]

Re: BRAKES

Hello,
I have a Cabrio V8 3.9 built in 92 - seirra based, when I was doing track days in 94/95 and road use as well.
I had Wilwood 4 pot with 300mm x 30 mm discs on the front with 256mm ford sierra on the rear on fifteen 15"x 205 x 65 VR NTC, to much for the road and very easy to lock the wheels up, I had the standard period servo.

[HunterV8Spain]

Re: BRAKES

Hi, thanks for trying to help me but cannot find the strip nor your email address - I am not the brightest with computers though........

[CosworthCabrioLee]

Re: BRAKES

The cabrio has a std Granada servo with 280 front discs and 260 rears

[Mike]

Re: BRAKES

Hi, thanks for trying to help me but cannot find the strip nor your email address - I am not the brightest with computers though........

Martin

If you select Reply with quote, you should see a drop down box with icons across the top? If you select the third from the right, it will ask you if you want to add an image.
Mike

[HunterV8Spain]

Re: BRAKES

Martin

If you select Reply with quote, you should see a drop down box with icons across the top? If you select the third from the right, it will ask you if you want to add an image.
Mike

Hi Mike, sorry but no drop down box with icons across the top. Also sorry to mess up this thread with my computer problems!!

[Mike]

Re: BRAKES

Hi Mike, sorry but no drop down box with icons across the top. Also sorry to mess up this thread with my computer problems!!

Martin

When you press Reply or Reply with Quote, what are you getting - you obviously have an option to write a response.?

What background colour scheme are you running? I wonder if the icins are there but not visible? If you run your mouse slowly around 1/2" - 3/4" above the box you are typing your response in, do you get any change of picture intensity? - if you then wait a second you will receive a small box flashing ?
Have a go?
Mike

[stevejgreen]

Re: BRAKES

Hello,
I have a Cabrio V8 3.9 built in 92 - seirra based, when I was doing track days in 94/95 and road use as well.
I had Wilwood 4 pot with 300mm x 30 mm discs on the front with 256mm ford sierra on the rear on fifteen 15"x 205 x 65 VR NTC, to much for the road and very easy to lock the wheels up, I had the standard period servo.

Paul has a very good point.
Its worth reinforcing that braking efficiency starts at the contact point between the tyre and the road. Fitting larger brakes etc cannot compensate for having a tyre choice and pressure that is not suitable for its application.
The size of discs and pads on the donor cars are calculated to dissapate the necessary energy of a standard road car. Kit cars are generally much lighter and unless they are used 'on track' the brakes will normally have to dissapte a lot less energy.
There is a danger as Paul highlights that you can over brake a vehicle, increacing the likelhood that you cause the wheels to lock up, breaking their traction with the road surface.
Having said that there is the 'bling' factor and wheels filled with big shiny discs look so much better than many standard setups, but when fitted on a modern road car any overbraking is compensated for by the ABS, releasing the brakes till traction is regained.

[dogoncrazy]

Re: BRAKES

A quick update - I have now completed the fitment of the dual diaphragm servo and can confirm Jason's /Daves findings in that it is a real success, much improved feel and a whole lot less effort at the pedal. A very big thank to Mike for all his efforts in making this happen and for taking the time to ensure that the 'swopover' was straightforward and to Jason for his oh so quick assessment .As my Cabrio is I think in the minority in that it get used all year round, the peace of mind that I now have in that I can actually stop is worth a Kings ransom. Thanks again Guys!

[copperleaves11]

Re: BRAKES

Hi Alan. Glad to hear you'r impressed with the upgrade. Even with my limited testing the improvement was immediately apparant. I can't wait to get the old girl taxed and on the road again to feel the benefits. Regards David.

[Mike]

Re: BRAKES

Hi Alan
Please ignore this post.
I did not realise you signed in as "Dogoncrazy" - Mash-tun pointed out my error!
I hope I quoted you back to yourself correctly!
Sorry.
Mike

However, I hope the message may be relevant to others, so will leave it here for any benefit it may provide.


Hi Dogoncrazy
The weak point in this brake set up, is the Metro servo: it does not have sufficient surface area to give enough boost to the pedal pressure.
There has been a big article on this on the madabout kit cars site:

http://www.madabout-kitcars.com/forum/showthread.php?t=3149

We have sourced a dual 7" servo, which has around 40% more surface area than the Metro, yet is the same diameter. Those who have fitted, and tested the new servo have been very impressed with the improvement. The calculations show this servo has the same capabilities as the original Sierra 8" servo, where the brakes are not thought to be poor.




This is the dual 7" servo temporarily located in my Cabrio. The top fixing stud has to be shortened to allow the m/c to be mated to the adaptor plate. Unlike the metro servo, there is no requirement to achieve an airtight seal between the m/c and the servo, as the servo is self sealed.

The section cut out the side of the panel to clear the servo was not actually necessary, and I plan to weld this back in to restore its rigidity.

Alan Hogg has your brake set up (I beleieve) and was looking for ways to improve their performance. He has just fitted the dual servo, and says it has transformed the brakes: to quote Alan "A revelation". He is delighted and the total cost was just over £100. A very low cost, big gain modification.

Regards
Mike

Ihave at present disc front and rear with metro servo. Front are 240mm vented single piston sliding caliper.What others will fit the sierra set up/would wilwood 4 piston make huge difference.Your thoughts please/what are you using?

[Mike]

Re: BRAKES

Hi Steve/Dave

I take your point about the dangers of over braking our cars, but I think the reason why some Sportster and Cabrio owners are desperately looking for better brakes needs explaining.
Marlin have taken to fitting their own pedal box in Sportsters and Cabrios in recent years, which then only permits the fitting of a small 6" diameter Metro servo. Also with some engine options (the BMW M50 is one) there is only sufficient width available for a 6" diameter servo. However, there is an inherent design fault when the Metro servo is used, as it is inadequate to stop these cars. The additional assistance from these small servos is not sufficient to make the disc brakes work effectively. The pedal has that old fashioned solid feel to it, and no matter how hard one presses the pedal the brakes do not feel good enough. This particularly true when, and I quote Patrick Short, as I love this expression, "Guys in modern tin tops with servos bigger than their engines" brake hard. It becomes a case of "press harder and pray!"
The original Sierra servo has an 8" diaphragm: by comparison the Metro has only a 6" diaphragm. In cross sectional area the difference is even greater - 50sq." compared to 28sq.". Without showing the maths, the standard 8" Sierra servo combined to a 22mm bore master cylinder (sorry to mix units) is designed to produce around 1100-1200 psi under hard braking to operate discs both front and rear. The Metro only achieves 800 - 900psi, which is insufficient to make disc brakes work efficiently.
Many of us, myself included, have tried fitting bigger diameter brakes to help offset this design problem with the limited Metro servo.
The beauty of the new dual servo shown in this thread is that it has a the same overall diameter as the Metro servo, (and therefore fits in the narrow space available), whilst having a similar cross sectional area to the standard Ford 8" servo. As a result, the braking capability is taken back up to, but not beyond, what Ford designed it to be.

This is a major step forward in the safety of any Marlin car fitted with a Metro servo, and should not be confused with any "Boy racer" mods to over brake it, or to add bling.

Mike

Paul has a very good point.
Its worth reinforcing that braking efficiency starts at the contact point between the tyre and the road. Fitting larger brakes etc cannot compensate for having a tyre choice and pressure that is not suitable for its application.
The size of discs and pads on the donor cars are calculated to dissapate the necessary energy of a standard road car. Kit cars are generally much lighter and unless they are used 'on track' the brakes will normally have to dissapte a lot less energy.
There is a danger as Paul highlights that you can over brake a vehicle, increacing the likelhood that you cause the wheels to lock up, breaking their traction with the road surface.
Having said that there is the 'bling' factor and wheels filled with big shiny discs look so much better than many standard setups, but when fitted on a modern road car any overbraking is compensated for by the ABS, releasing the brakes till traction is regained.

[Mike]

Re: BRAKES

Andrew Curtis has just called to say how thrilled he is with the new Dual 7" servo in his BMW Sportster set up. He is another person who says it has transformed his car.

The difference this time is that Andrew has access to a disused airfield behind his farm, so he has been out and conducted some "semi-scientific" tests.

Travelling at a constant 70mph, he braked at a fixed marker point, and measured the travel distance before coming to a complete stop, braking as physically hard as he could.
The average travel distance of the 4 tests with the original Metro servo was 210 feet.

Braking hard, but under control, with the new Dual servo the average distance was 103 feet.
Braking as though in an emergency with front wheels beginning to lock up was 85 feet.
This was a one off test though as he did not care to waste his tyres, but felt he knew now there was a point at which the wheels would lock up at the front.

Not only is he thrilled with the improvement in stopping distance, but with the 'feel' that he now has. He feels he can brake hard in control without excessive pressure, and know that there is more left before the wheels begin to lock up, but in an absolute emergency it would be there if required.

These are the first empirical tests which actually prove the anticipated benefits of changing the Metro servo for the Dual 7" servo.

Another very satisfied adopter.
Good luck to all who follow.

Mike

[Mike]

Re: BRAKES

Hi Mike, sorry but no drop down box with icons across the top. Also sorry to mess up this thread with my computer problems!!

Hi Martin

I think I may be able to help you find the toolbar you can not see at the moment?

If you look at the very top of your screen/this page, there should be a line beginning Welcome - Martin - Notifications - Settings - etc

Open up a new tab and go in to MOC Forum again

Click on to Settings:
On the page now opened up, go to side bar menus, scroll down to
My Settings

Scroll down to General Settings
Tick the box which says WYSYWYG

Save Changes

Now open up a new message to respond, and you will have all the icons available to you.
regards
Mike

[HunterV8Spain]

Re: BRAKES

Hi Mike,
I think that I now have it, many thanks,
Martin

[Mike]

Re: BRAKES

Mike
If you have a Metro servo you can improve your brakes enormously, without spending a huge sum of money.#Over on the Madabout Kitcars forum around 20 of us have bought a Dual 7" servo that transforms the braking capabilities. Andrew Curtis proved it on a disused airfield. At 70 mph the Metro servo required 210 feet stopping distance standing on the brakes. The Dual 7" servo required only 103 feet under normal braking and 85 feet in an all out emergency.

Have a look at this thread:

http://www.madabout-kitcars.com/forum/showthread.php?t=3149&page=2

Regards

Mike

Hi Guys
Just caught up with this thread, which makes interesting reading. Since taking over ownership of my Hunter a couple of years ago, I have replaced all of the standard factory stuff: calipers/pads on front and slave cylinders on rear. I have left the original servo alone, which I think is Mini/Metro design.

Overall, I am pleased with the way the car stops, but no way compares with my Skoda Octavia (Volkswagen). There are the obvious weight differences, with my Hunter having larger size tyres/greater footprint - great on dry roads but lousy on wet/ice, plus my Skoda has ABS and other clever devices.

Has anyone fitted ABS? I imagine this might be a major task.

Cheers
Mike