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Go Back   Madabout Kitcars Forum > Mad Build Area > Marlin Sportster, Cabrio, Berlinetta and Roadster builds

Marlin Sportster, Cabrio, Berlinetta and Roadster builds Enthused or Confused about your vintage Marlin build? Ask away here or show off your build.

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  #201  
Old 7th December 2011, 00:45
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Mike. Some thoughs about your forum post #195

1) While researching a brake upgrade for my classic (front drums to discs) I have found that the braking ratio for road cars is usually set at 65% Front / 35% Rear.

2) Unless the front / rear ratio was way out at original build then the improved servo should not worsen the tendency for front /rears to lock first, only get it to happen with less pedal effort / sooner?

3) When Jason did his road tests did he notice any tendency for fronts or rears to lock first?

Re your post #197: I will be using my car (Hunter) through the winter but due to other planned jobs it will likely be end Jan before I get to test the servo on the road. Peter.
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  #202  
Old 7th December 2011, 08:59
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Quote:
Originally Posted by Mike View Post
Jason

Is your PM working?
Yes. Saw it last night, but SWMBO decided I needed to do other things. Done now.

As for questions on locking, I don't know which wheels locked first... All I know is I started to slide.

That said, I know that at IVA, on the rollers the fronts locked before the rears, so she passed. The master cylinder hasn't changed, and neither has any of my brake lines or routing - so the bias will be exactly the same. Only the level of assistance has increased.

If people want me to do further testing, I may need to ask for contributions to a new set of boots when I flat spot them.
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  #203  
Old 7th December 2011, 09:09
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Quote:
Originally Posted by Grey V8 Pete View Post
Mike. Some thoughs about your forum post #195

1) While researching a brake upgrade for my classic (front drums to discs) I have found that the braking ratio for road cars is usually set at 65% Front / 35% Rear.
Quote:
2) Unless the front / rear ratio was way out at original build then the improved servo should not worsen the tendency for front /rears to lock first, only get it to happen with less pedal effort / sooner?
This makes a lot of sense to me, and is quite reassuring that we should not have bias problems.

Quote:
3) When Jason did his road tests did he notice any tendency for fronts or rears to lock first?
Jason - did you hang your head out the side and have a look ??!!


Quote:
Re your post #197: I will be using my car (Hunter) through the winter but due to other planned jobs it will likely be end Jan before I get to test the servo on the road. Peter.
Oh no! Who is going to be able to give the first corroboration of Jason's findings? I know several of the other guys plan / have their cars on SORN over winter.
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  #204  
Old 7th December 2011, 10:48
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Quote:
Originally Posted by GreatOldOne View Post

As for questions on locking, I don't know which wheels locked first... All I know is I started to slide.

That said, I know that at IVA, on the rollers the fronts locked before the rears, so she passed. The master cylinder hasn't changed, and neither has any of my brake lines or routing - so the bias will be exactly the same. Only the level of assistance has increased.

If people want me to do further testing, I may need to ask for contributions to a new set of boots when I flat spot them.
Does THE STIG make such demands?
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  #205  
Old 7th December 2011, 10:53
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Some say that he keeps lists of brake components up to date for fun... And that he like the smell of burning rubber in the morning. All we know is he called The GOO.
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  #206  
Old 7th December 2011, 12:36
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Default Another order

Quote:
Originally Posted by GreatOldOne View Post
Some say that he keeps lists of brake components up to date for fun... And that he like the smell of burning rubber in the morning. All we know is he called The GOO.
OK "The GOO"

Another update.
Can you add Alan Hogg, who has confirmed an order, to the list for a complete kit.

That now means the initial order for 2 + 18 is all allocated. So that is good news - Thank you all for committing - it now makes placing the main order very easy, and safe (commercially).

If we get any more interest I would like to keep it in multiples of 6, as the more people who have them, the less others there will be to take up any spares.

Unless of course MBM will send some more "samples"...........?
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  #207  
Old 7th December 2011, 12:53
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Alan added to the list.

And on that bombshell...
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  #208  
Old 7th December 2011, 18:51
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Default Master Cylinder Diameter

Quote:
Originally Posted by Mike View Post
Guys

I don't know if any of you looked at the specification figures for the boosters, or are even interested in the numbers, but I have made some calculations based on the data given by MBM, which show a very interesting result: see if you agree with the following;

My brake details are:
Pedal centre to pivot centre 32cm - excuse mixed units - it does not matter
Pedal connection to servo to pivot - 8cm
Therefore my pedal ratio is only 4:1
My master cylinder bore = 22mm = 7/8" = 0.6 sq inch
Now assume 23” of vacuum and 100lbs of applied foot pressure for comparative purposes.

Based on my brake's details:
[edit: it will not hold spaces to make figure line up below]

Booster size “Manual Pressure” “Free Pressure” Total Brake Pressure
7” Metro 666 psi *1 587 psi *2 1253 psi
7” Dual 666 psi 815 psi *3 1481 psi *4

*1 = (100lbs x 4:1) / 0.6sq.inch = 666psi
*2 = Metro booster constant 352lbs / 0.6 = 587psi
*3 = Dual booster constant 490lbs / 0.6 = 815psi
*4 - The dual offers an increase of 18% of the total over the Metro. This does not sound too impressive.

I then considered if I reduce the distance of myservo connection to pivot by 1.6cm to 6.4cm

The new figures are:
New pedal ratio is 32/6.4 = 5:1
Same master cylinder bore = 22mm = 7/8" = 0.6 sq inch
Same 23” of vacuum and 100lbs of applied foot pressure.

Proposed brake's details:
Booster size “Manual Pressure” “Free Pressure” Total Brake Pressure
7” Metro 833 psi *1 587 psi *2 1420 psi
7” Dual 833 psi 815 psi *3 1648 psi *4

*1 = (100 x 5:1) / 0.6 = 833psi
*2 = Metro booster constant 352lbs / 0.6 = 587psi
*3 = Dual booster constant 490lbs / 0.6 = 815psi
*4 - The dual offers an increase of 16% of the total over the Metro, appears not so good

However, if we turn the calculation around to how much foot pressure is required to achieve the same total as with the original Metro, we see a significantly different result:

Original foot pressure to achieve 1253psi was = 100lbs
New foot pressure to achieve 1253psi = 52.4lbs *5

*5 = 52.4lbs x 5:1= 262lbs / 0.6sq.in = 438psi + 815psi = 1253psi
ie almost only HALF the effort

This has got to be worth a try!!

What master cylinder bores do you have?
What brake pedal ratio do you have?

Does anyone have a view on the calculations?
Not looked inside my master cylinder to check bore but raised number 23 on casting maybe 23mm? From Google I found the following DLJ website link
http://www.dlj-autoparts.com/eng/pro...e=list&cid=485
which lists several master cylinders including one of 23mm bore which is for a Mondeo! Peter.
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  #209  
Old 7th December 2011, 20:53
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I have a set of spare seals for my BMW master cylinder.
From measuring those seals, the BMW master cylinder is 19mm or 3/4" diameter.
I think that makes it better than the Ford version?
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  #210  
Old 7th December 2011, 22:41
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Default E=Mc2

Quote:
Originally Posted by Grey V8 Pete View Post
Not looked inside my master cylinder to check bore but raised number 23 on casting maybe 23mm? From Google I found the following DLJ website link
http://www.dlj-autoparts.com/eng/pro...e=list&cid=485
which lists several master cylinders including one of 23mm bore which is for a Mondeo! Peter.
Peter

I suspect your master cylinder is a part of your brake issue. Peterux has said his MC is 19mm. If you calculate the surface area of the two you will see his has 30% less area than yours, therefore the same pedal pressures in your two cars will produce 30% different psi at the brakes, assuming the pedal ratios are the same. The servo will be diluted in your car too.

I am not too happy either, as my Cabrio has a 22mm MC, which means 25% more effort than Peterux pedal pressure. This may well explain why Peterux says he could lock his brakes up.
I believe Jason has a Ford type MC, so it would be interesting to know what size MC he has, as he says he could not lock his brakes up, prior to fitting the Dual servo.

try dropping your own numbers in to the calculations I have made and see how the different sized MC makes a big difference.

Of course the flip side of a smaller MC is that the pedal will travel further to get the same brake pad movement. So it will be a play off between pedal effort and pedal travel.

Do you currently get very limited brake pedal travel?

Mike
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  #211  
Old 7th December 2011, 23:01
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Mike. From memory I don't think pedal travel was noticably short but the pedal effort required to stop was very noticable! I am thinking that the larger master cylinder diameter was fitted at POB because I have discs all round which theoretically may need more fluid displacement with eight large pistons? Can't do any practical checks at present as car on stands for smaller 24mm dia front ARB fitting (which has been on my 'to do' list for ages). Will do some measurements with and without engine vacuum when I can and let you know. Hopefully with a large master cyl bore I should get much improved braking with less tendency to lock the wheels. Peter.
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  #212  
Old 8th December 2011, 08:53
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I have a ford master. According to this site:

http://www.autopart007.com/product/f...id1470?lang=en

It's 7/8" in old money, which is 22mm in metric.
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  #213  
Old 8th December 2011, 20:22
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Quote:
Originally Posted by Grey V8 Pete View Post
Mike. From memory I don't think pedal travel was noticably short but the pedal effort required to stop was very noticable! I am thinking that the larger master cylinder diameter was fitted at POB because I have discs all round which theoretically may need more fluid displacement with eight large pistons? Can't do any practical checks at present as car on stands for smaller 24mm dia front ARB fitting (which has been on my 'to do' list for ages). Will do some measurements with and without engine vacuum when I can and let you know. Hopefully with a large master cyl bore I should get much improved braking with less tendency to lock the wheels. Peter.
Ah ha! Just realised I have the Teves type calipers with one piston on a floating carrier per wheel. So for eight pistons read four pistons total. Peter.
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  #214  
Old 9th December 2011, 10:32
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Code:
Pedal centre to pivot centre 32cm - excuse mixed units - it does not matter
Pedal connection to servo to pivot - 8cm
Therefore my pedal ratio is only 4:1 
My master cylinder bore = 22mm = 7/8" = 0.6 sq inch

Now assume: 
23” of vacuum
100lbs of applied foot pressure for comparative purposes.

Based on my brake's details:

Booster size  “Manual Pressure”  “Free Pressure”  Total Brake Pressure 
7” Metro       666 psi  *1	  587 psi *2	  1253 psi
7” Dual        666 psi 	          815 psi *3	  1481 psi *4

*1 = (100lbs x 4:1) / 0.6sq.inch = 666psi
*2 = Metro booster constant 352lbs / 0.6 = 587psi
*3 = Dual   booster constant 490lbs / 0.6 = 815psi
*4 - The dual offers an increase of 18% of the total over the Metro.
Mike - Where did you get the 'constant' figures in the calculation?

I've tried to do the sums my self, but as a bear of very little brain, what little there is is now smoking.

Taking all the figures as stated, I got as far as:

666 psi Manual Pressure.
Metro Boost Ratio is 1:1.9, so total brake pressure is 666 * 1.9 = 1265 psi
Free Presure is then 1265 - 666 = 599 psi.

Then I get confused. I don't know the boost ratio of the dual 7"...
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  #215  
Old 9th December 2011, 11:12
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Quote:
Originally Posted by GreatOldOne View Post
Code:
Pedal centre to pivot centre 32cm - excuse mixed units - it does not matter
Pedal connection to servo to pivot - 8cm
Therefore my pedal ratio is only 4:1 
My master cylinder bore = 22mm = 7/8" = 0.6 sq inch

Now assume: 
23” of vacuum
100lbs of applied foot pressure for comparative purposes.

Based on my brake's details:

Booster size  “Manual Pressure”  “Free Pressure”  Total Brake Pressure 
7” Metro       666 psi  *1	  587 psi *2	  1253 psi
7” Dual        666 psi 	          815 psi *3	  1481 psi *4

*1 = (100lbs x 4:1) / 0.6sq.inch = 666psi
*2 = Metro booster constant 352lbs / 0.6 = 587psi
*3 = Dual   booster constant 490lbs / 0.6 = 815psi
*4 - The dual offers an increase of 18% of the total over the Metro.
Mike - Where did you get the 'constant' figures in the calculation?

I've tried to do the sums my self, but as a bear of very little brain, what little there is is now smoking.

Taking all the figures as stated, I got as far as:

666 psi Manual Pressure.
Metro Boost Ratio is 1:1.9, so total brake pressure is 666 * 1.9 = 1265 psi
Free Presure is then 1265 - 666 = 599 psi.

Then I get confused. I don't know the boost ratio of the dual 7"...

Hi Jason

The servo generates a pressure by creating a vacuum on one side and allowing normal atmospheric pressure on the other. Therefore assuming your engine generates the 23" of mercury pressure (sorry about Imperial units, but just using the MBM assumptions), then the servo will always give the same amount of boost. It is not a ratio relative to pedal pressure, but a constant relative to diaphragm surface area - for a constant vacuum).

I calculated the constant from MBM's figures.

Surface area of a circle = pye x r2

1 1/8" bore - Sorry I need to convrt to decimal = 1.125sq.in

therefore (1.125 /2) x (1.125/2) x 3.14159 = 0.994sq.in.

Stated Free Pressure = 355psi.
Therefore the force from the servo was 352lbs
(352lbs / 0.994sq.in. = 355psi)

If you do the same calculation for the 1" bore and the 15/16" bore you will get a constant figure for the servo boost.


1" bore = 0.785sq.in
352lbs / 0.785sq.in = 449psi

15/16" = 0.69sq. in.
352lbs/ 0.785 sq.in. = 511psi

Therefore the servo gives a constant boost of 352lbs force. Note this is not psi, but lbs only. It is a force, not applied per surface area, until directed at the master cylinder plunger, and then it is affected by the bore size.

Hope this helps.

PS : The adaptor arrived in the post this morning - many thanks.

Mike
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  #216  
Old 9th December 2011, 11:13
denniswpearce denniswpearce is offline
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Thank heavens for all you mathematitions, I will leave that to the intelligencia.

All I know is from what has been written so far is that the brake pedal should require a little less pressure to stop the car. Not quite up to my every day car standard but never the less better than it was.

Thank you one and all.

Dohhhhh, my brain hurts !!!!!!!!!!!!!!!
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  #217  
Old 9th December 2011, 11:16
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Default Follow Servo Delivery progress

The servos are now in Lincoln, being held up due to a customs charge to be paid! This is despite asking MBM to send them marked as "samples" which should not attract a customs charge! One of them has got it wrong. But I beleive it is £28 which we should not have to pay on the overall delivery costs

I hope to sneak off early today and collect them this afternoon.

Keep your fingers crossed.
Mike
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  #218  
Old 9th December 2011, 11:26
Mike Mike is offline
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Quote:
Originally Posted by denniswpearce View Post
Thank heavens for all you mathematitions, I will leave that to the intelligencia.

All I know is from what has been written so far is that the brake pedal should require a little less pressure to stop the car. Not quite up to my every day car standard but never the less better than it was.

Thank you one and all.

Dohhhhh, my brain hurts !!!!!!!!!!!!!!!

Dennis

You are absolutely right!

Sometimes I wish I were not so inquisitive.

If you look at the ratio of boost between the 7" single and 7" Dual you also get a constant :
493/355 = 39%
624/449 = 39%
711/510 = 39%

And
The figures for the Dual are almost directly comparable to the 8" single
493 vs. 507
624 vs. 642
710 vs. 730

Put simply : The Dual offers almost 40% more assistance than the current Metro servo, and matches the Ford 8" servo as near as damn it, which we know from Chris Cussen, and Simon Gregory, works.
- All in all - it MUST be significantly better than before!
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  #219  
Old 9th December 2011, 12:16
atlantasportster atlantasportster is offline
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It will be interesting to hear if any of the cars experience that momentary feeling of the pedal being pulled away from your foot as the diaphrams "sequence", in responce to increasing vacumn as revs decrease.
This happens in a '33 Ford hot rod with a flathead V-8 I have driven.
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  #220  
Old 9th December 2011, 18:03
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Default Pedal Travel Check Marlin Hunter

Quote:
Originally Posted by Mike View Post
Peter

I suspect your master cylinder is a part of your brake issue. Peterux has said his MC is 19mm. If you calculate the surface area of the two you will see his has 30% less area than yours, therefore the same pedal pressures in your two cars will produce 30% different psi at the brakes, assuming the pedal ratios are the same. The servo will be diluted in your car too.

I am not too happy either, as my Cabrio has a 22mm MC, which means 25% more effort than Peterux pedal pressure. This may well explain why Peterux says he could lock his brakes up.
I believe Jason has a Ford type MC, so it would be interesting to know what size MC he has, as he says he could not lock his brakes up, prior to fitting the Dual servo.

try dropping your own numbers in to the calculations I have made and see how the different sized MC makes a big difference.

Of course the flip side of a smaller MC is that the pedal will travel further to get the same brake pad movement. So it will be a play off between pedal effort and pedal travel.

Do you currently get very limited brake pedal travel?

Mike
Engine off (i.e. no vacuum /servo action)
Free pedal travel = 13mm
Total pedal travel with fairly hard push = 63mm.

Engine running at tickover
Total pedal travel with fairly hard push = 90mm.

Handbrake off for all checks. Peter.
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