Dual 7" Servo

[Mike]

MBM have used USPS to send the first two powder coated servo samples, as the UPS cost for this small package was horrendous.

(Stuart and John can follow progress on the USPS website: using the code I have sent PM - they have reached New York as of this morning)

Always looking to keep costs down, I have promissed to delivery some of the servos whilst out on my work/leisure travels.

May I ask you all to forward your addresses via PM, and I'll see if there are any others I can add to the list, or maybe double up by getting one of you in a group to take delivery, and arrange local dispersal.

As for cost, Thank you all, I would rather sort the cost out when I know the final total costs and can be fair to everyone.

[Mike]

Originally Posted by GreatOldOne

Another order - I've had an email from Ian Papworth saying he would like a full kit (servo, adaptor, clevis).

Goo

can you PM me Ian's contact details please?

Mike

[Mike]

Jason

Can you add Andrew Curtis (BMW M50 Sporster) to the list for a complete zinc kit, please? Thank you to Peter V8 for putting him in touch.

By my reckoning we now have firm orders for 18 including myself, as I have someone willing to buy my original zinc servo which Jason tested (not shown on Jason's list).

That potentially leaves only two unallocated zinc units at present. So if you know anyone who is interested they need to get their order in quickly!

[Grey V8 Pete]

No probs Jason. Mike. Please also see my PM about Andrew Curtis re further contact info re the servo “kit”. Many thanks. Peter

[Mike]

Originally Posted by Grey V8 Pete

No probs Jason. Mike. Please also see my PM about Andrew Curtis re further contact info re the servo “kit”. Many thanks. Peter

No PM

Mike

[jeremy]

hi mike, did you get my details on pm I sent? Jeremy

[Mike]

The two sample servos have landed in UK this morning.

C'mon!

[Sorton]

Hi Mike

PM sent with details

Sorton

[Grey V8 Pete]

Originally Posted by Mike

No PM

Mike

Mike. Just replied to your last PM. You have correct email for Andrew C. Peter.

[Mike]

MBM have sent me an article about the effects of a brake booster - christ I'm even talking like one now. Y'all hear!

Does anyone know how to post a pdf file, or copy of one on to here?

It has prompted my old grey matter in to action again, and I would like others thoughts too.

[peterux]

Not sure, but I think you'll have to ask one of the guys with 'real websites' to host the document. Jason, Robin or Patrick should be able to help?

[GreatOldOne]

Depending on how large it is, you should be able to attach it to the post. Max file size is 19.5K though.

If it's that size or under, just use the paperclip button in the post toolbar to attach the file.

[GreatOldOne]

I'll host it if neccessary...

[GreatOldOne]

I've managed to OCR the Doc that Mike sent me, and shrunk it down enough to attach here. I'll also put the original on my site and post a link later on when I get in from work.

[Mike]

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?

[Mike]

I've had a response from Terry at Marlin today ref adopting the Dual servo for future cars:

[Hi Mike
Mark has now read your email with interest and of course yes he would like to have a look at what you have found. A few points that may bear thinking about
1) That with your new servo installed and the mechanical advantage that it gives you may, on the one hand make you feel comfortable about the fact that less (personal)pedal pressure needs to be applied to cause the front wheels to lock ............ this situation is not necessarily going to result in a more safe brake situation.

2) With reference to the new servo & brake pedal pressure it is an IVA requirement that the brakes must operate correctly and effectively at 400 nm of pedal pressure. This stipulation would allow for a test range of 0-400 nm’s, if the wheels lock and say 200 nm’s you will only be left with half the range of brake application/feel.

3) In your pictures it didn’t look as if you had a very good vacuum seal face between servo and master cylinder. Maybe its not the case it just looked that way from the pictures.

4) £100 for a servo seems like a very reasonable price... if not a good one.

5) Mark was not sure from your email of exactly the situation i.e. are you having these servo’s manufactured for you and have you then ordered some stock or are you simply buying them through an EBay shop (or were you trying to say that the EBay source is you)?

In closing Mark would be very interested to take a close look at these servo’s and if you would like to send one we will be happy to pay the £100 cost and postage of course
ATB
Terry.]

I have replied that we currently plan to have two spare servos on order and that they are welcome to one of them for trialling.

It will be very interesting to see what price they want to charge for the kit?!

[Mike]

How many owners have registered cars that they will be running through the winter?

We will need you to give us all more feedback on the new servo!

[peterux]

Originally Posted by Mike

I've had a response from Terry at Marlin today ref adopting the Dual servo for future cars:


In closing Mark would be very interested to take a close look at these servo’s and if you would like to send one we will be happy to pay the £100 cost and postage of course

Mark must be really interested if they are prepared to pay for one and do some tests. ("Delivery will be in about 6 weeks...." )

[Mike]

Originally Posted by peterux

Mark must be really interested if they are prepared to pay for one and do some tests. ("Delivery will be in about 6 weeks...." )

Mike likes that..................

[Mike]

Jason

Is your PM working?

Can you add:
Andrew Curtis & now Marlin to the list.
I believe this only leaves one servo from the 12 zinc units unallocated.

They're going quickly............................