Lotus Elan

Plus 2 Braking No Servo

PostPost by: gerrym » Thu Feb 04, 2010 9:13 pm

I see that there was a thread running in the racing section about braking etc, some of which includes a reference to using a split circuit tandem cylinder, without servo.

This has me thinking: split braking (front/rear), handbrake efficiency requirement reduces to 16% from 25%, got to be a good thing for MOT passes. Servo sticking on problems eliminated (more reliable braking). No chance of sucking the brake fluid into the intake manifold via failed servo seals (more reliable braking). Easier bleeding (thats good). Better braking modulation and feel, especially in the wet.

But downside, higher stress on bulkhead due to higher brake pedal force - so I will have to reinforce the bodyshell further - but that can be done on the inside of the body.

First some calcs. See Racetech spreadsheets. Target deceleration of around 0.87g. This gives me a target pedal force of 40 kgf (simple test rig with bathroom scales tested by me and my small wife shows this can be achieved). Need to measure or guess the COG height so used US SAE paper comparing sportscars, sedans and SUVs with their measured data (very few cars significantly below 0.5m)

Need some street suitable brake pad compound with reliable coldish friction coefficient: seems Ferodo DS2500 are quoting 0.5 across all temperatures (actually they have a whole lot of test data to show slight ratcheting with repeated brake applications.

Next measure all the vehicle brake system parameters such as caliper piston sizes, wheelbase, tyre sizes, brake pedal mechanical ratio etc and input into spreadsheet.

Results are that using a master tandem cylinder of 0.813" diameter, target of front wheel with non-race rubber lockup with less than 45kgf seems entirely possible. (Note Nokia publish a whole series of data on tyre effective friction against various slip ratios).

What tandem cylinders are available? Well the nice guys at AP racing manufacture a special for Caterham with the above 0.813" diameter. They OK'd publishing on this site. Same vertical bolt pattern and spacing so should mount direct to existing Plus 2 pedal box (but Plus 2 pushrod would need to be correctly spaced to give correct clearance/backlash or replaced with a new item).

So, obvious question, anyone been down this route before. Anyone not running a Servo in a Spyder Zetec and if so/ whose master cylinder?

Regards

Note BG Developments are the distributor retail) for this AP Racing Product.

Gerry
cp4627-2prm100cd[1].pdf
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cp4627-2prm100cd[1].pdf
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Race-Tech-Braking-model%20for%20Lotus%20Elan%20Plus%202(1).xls
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PostPost by: mikealdren » Thu Feb 04, 2010 9:46 pm

Gerry,
Last time I looked there wasn't a suitable master cylinder. I'm definitely interested, I was intending to run a Spyder setup is less servo anyway. I haven't loooked at the maths at all yet but you should get enough pressure with reasonable pedal pressures.

Mike
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PostPost by: gerrym » Thu Feb 04, 2010 10:17 pm

Hi Mike, yes I've checked with AP Racing and their tandem master cylinder (drawing posted) is available. The fit length-wise is OK, but will be tight up against the side of the engine bay because the outlets are on the "wrong side" for RHD applications. However, I'm hopeful that banjo fittings would gain enough space.

The calculations indicate lockup should be achievable at quite modest (for unboosted systems) brake pedal forces, but selection of pad compound will be as ever, important.

0.813 gives a little less hydraulic gain than the 0.7 stock but provides some additional volume. I need to do the calcs to check that in the event of rear circuit failure, there will still be enough volume displacement to operate the front calipers. My spreadsheet indicates that a rear bias valve might be a good idea: I've included the curves if you want to play around with what could be tuned on the car.

AP Racing told me to contact http://www.bgdevelopments.co.uk/ re sourcing of the tandem master. Looking at their website, they have a passing interest in braking components for classics, eg Jaguar calipers etc

For the pushrod, AP Racing provide as standard a threaded pushrod. However there's not enough room (initial measurements) for this. A trial fit with the existing pushrod would indicate if this would be suitable. However mine is worn on the pivot holes so will need replacing anyhow. I'm assuming that the master cylinder can be shimmed on it's mounting flange to provide correct clearances?

Regards

Gerry
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PostPost by: gerrym » Thu Feb 04, 2010 11:31 pm

Alternative for US owners?
Anybody know the bore and stroke?
http://www.lbcarco.com/mgb-brake-clutch ... linder.htm

MGBGT tandem cylinders approx 1969-1974 (non servo) with vertical flange
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PostPost by: bengalcharlie » Fri Feb 05, 2010 5:08 am

Gerry,

You must be able to find a suitable alternative for the plus two. I have removed my servo completely and in order to have enough stopping power changed the brake pads to a softer grade. I am still able to lock the front wheels with a completely bog standard setup with a single master cylinder.
I know this is not whatt you are intending to do but just to let you know that you can discard the servo in my opinion. the lancia fulvia is another car that came out without servo and then later in the production they added a servo.
I used to drive a series one fulvia without servo with no problems. you also add some lightness :lol:
cheers
Robin
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PostPost by: gerrym » Fri Feb 05, 2010 6:40 am

Robin, thanks for feedback. I guess you are confirming what the calcs are telling me. What compound are you using?

I suspect the Servo was added at the Plus 2 "S" stage as part of the showroom specification appeal, as opposed to any fundamental design necessity. Overall, I see going split circuit and deleted Servo as a major reliability improvement.

Regards

Gerry
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PostPost by: bengalcharlie » Fri Feb 05, 2010 6:47 am

Gerry,

do not know what the compound is but the brand is Remsa partnumber DB525E used on morgan 8 and Vauxhall HP.
I hope that helps. Can not remember where the pads where made. Maybe you recognise it as a UK brand?? I bought these here in NZ
I forgot to mention that I reinforced the pedal box area with glass and I also added an aluminium flat sheet to spread the load so it is nice and strong.
Cheers
Robin
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PostPost by: kstrutt11 » Fri Feb 05, 2010 3:41 pm

I also have deleted the servo, I have a 0.7" single m/cyl, goodridge flexi hoses and greenstuff pads on the front with std pads on the rear,(it also had re-built frt and rear calipers at the same time). This set up works a treat, with a very firm pedal and little travel.
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PostPost by: Spyder fan » Mon Feb 08, 2010 3:57 pm

Gerry,
My zetec +2 doesn't have a servo, it's running XR4i calipers and ventilated disks on sierra uprights, I have greenstuff pads on the front and standard motorcraft items on the rear (also Xr4i items). The master cylinder is single line by Tilton, not sure of the bore but there's very little pedal travel and a very firm brake pedal. The pedal box and mounting area was reinforced by Spyder. There's very good brake feel and loads of stopping power, my brother's Ferrari 360 nearly rear ended me on the motorway recently when there was a big emergency stop scenario.
Kindest regards

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PostPost by: SimonH » Mon Feb 08, 2010 4:31 pm

Anyone tried this tandem master cylinder from The Elan factory? (Pics from their site, hope thats ok)

Looks the part and is a 0.7" bore so should feel much as the normal one without a servo?

mastercylinder.jpg and


mastercylinder2.jpg and


Looks to work out a bit cheaper than having a new single master cylinder and a servo rebuild, even after importing it, if its adequate without the servo.

Cheers,
Simon
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PostPost by: ppnelan » Mon Feb 08, 2010 7:34 pm

Was the +2 ever sold as standard WITHOUT a servo? It concerns me that removing it could cause insurance 'difficulties'... :shock:
I know the Elan was made without so I'm happy to run my S4 like that. But I wouldn't risk removing it from my +2 despite the awful pedal feel (Lockheed replacement servo). :x

:arrow: Matthew
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PostPost by: Spyder fan » Mon Feb 08, 2010 8:54 pm

Matthew,
It might cause a problem if the brakes were made unsafe by removing the servo, I can't think under what circumstances that might be though? Although it's worth pointing out if only to ensure that we think about safety when doing these sort of conversions or upgrades. Gerry knows what he is doing as do a lot of other people here, the rest of us get our wallets out and pay someone!

Our insurers in the UK for classics are usually a clued up bunch of people, I use RH Specialist cars and they recognise my car as a professional conversion by a known specialist, they also accept home brewed modified classics and very rarely ask for engineers reports, thank goodness that we are not restricted in what we do to our cars in this country unlike Germany, Holland and quite a few other places where type approval restricts you from even changing the wheels to a larger diameter or width from original let alone do engine swaps or suspension upgrades or any manner of other things that are discussed on this web forum.

I think you can't wash your car at home in Germany, you have to go to a special wash centre where the suds are environmentally disposed of (John Pelly am I right?)

Regards
Kindest regards

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PostPost by: gerrym » Mon Feb 08, 2010 11:30 pm

Kevin and Alan, thanks for replies. Both of you are using Greenstuff front pads which have a pretty high cold friction characteristic and "bite" that inspires confidence. I think this is the key to getting a non-servo setup to work.

Again, I'm sure that the Servo installation on the Plus 2 was put there by the marketing folk to match expectations of the spec sheet for the car. After, it is not by modern standards a heavy car. Also both of you are using calipers that hev been overhauled or are in good condition with presumably mininal run-out on the disks. This will minimise pad knock back and wasted motion in the hydraulics.

Between the positive feedback, the calcs and the advantages of ditching the servo in terms of safety and reliability, I think it is worth pursuing the tandem fitment.

So back to the options: Elan Factory?, MGB USA specification (1967 -1973?), Westfield?
(Only the Elan Factory has the hydraulics on the correct side)
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PostPost by: brian wilson » Tue Feb 09, 2010 2:54 am

Elan Factory master cylinder is a slightly modified Mitsubishi E300 van one.

I supplied them with the original as it was my idea to use one.

The reservoirs are simply lathe turned alloy tubing with original Girling caps.

It is my car on the web site (used without my permission) and also has 2 Lockheed servos.

The dual system works really well with no braking problems.

Brian Wilson
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PostPost by: mikealdren » Tue Feb 09, 2010 9:58 am

IIRC servos came into use with disc brakes and they were pretty much standard at the time, even my 1965 Vauxhall Viva had one. I later removed the servo and the brakes felt a lot better, the pedal loads were never a problem and it went through several MOTs.

Mike
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