The cheapest way to upgrade the brakes.

[johanvanboven]

As we all know, our cars don't have the best brakes.
Main reason for this is that it's a sort of standart brake system from Opel Kadet (or Vauxhall Astra for UK).
But why do the original brakes from the Opel work better than the Elan?
The answer is simple: Lotus chose for a short but heavy pedal feel, while Opel took a normal pedal feel.
Where is the difference then? : Lotus fits a master cylinder of 22.2 mm, while Opel fits one of 20.6 mm.
So last weekend I fitted a 20.6 mm master cylinder.
The result is fabulous. With a normal pedal pressure you can now block the wheels, even on a dry surface.
After a few emergency stops the system starts to smell like hell, but this means the brakes are doing their job now.
The master cylinder could be used for an upgraded brake system aswell, if a bit longer pedal travel is affordable.
A bit of data:
For the same brakeforce: pedalpressure 7 lbs, now 6 lbs.
Pedaltravel extended from 26 mm to 30 mm.
These figures don't look extreme, but it makes a world of difference.

Was used for this: master cylinder TRW PMF172, currently on sale at mister-auto.co.uk for about £50!

RHD drivers are the lucky ones, it fits straight to the 4 line brake system.

On LHD, one of the 4 connections has to be closed of. The problem is finding a M12 x 1 mm conical bleed screw.
So I made one myself. On the picture you can see a hollow bolt of M12 x 1 mm, this is localy sourced at a LPG workshop and is a standart connection of a 8 mm gas line.
The other bolt is a normal 8 mm filed of to a point in a drill.

Pictures say more than words.

If there are more questions, go ahead.

[HJ2]

Thanks for posting this on LEC as well!

[ovi]

[RayD]

Thank you for that Johan,

You've just confirmed something I suggested six years ago.

Did you find any other differences when comparing the two cars, particularly with the geometry of the pedal box and the diameter of the servo.

As regards the pedal travel ... I'd found it to be at least 37mm on standard calipers when operated by hand.

Ray

[johanvanboven]

Hi Ray,
I did not make any comparising of the booster servos.
Only calculated the differences between the cylinders.
Lotus 22,2mm (7/8"), smaller 20,6mm (13/16")
As the pressure is proportional to the surface of the piston, aswell as the pedaltravel, the data are just an example.
If you now have 37mm travel, then you will get 37:13 X 15 = 42,7mm travel. But you have to push 13/15 less hard.
But this is theory. In reality, the surface of the pistons are less, as other stuf travels along which does not create any pressure.
This means, in reality it might be something as 4/5.
The only thing I can tell you is that you feel the difference, and it is a simple and inexpensive job.
Why don't you give it a try now after 6 years, it is really plug and play on a RHD, and now for only £50 of parts.
Please post your findings to this topic.
BR; JVB

[nicowalker1]

I may well give this a try...

[maz_r]

And me.

However, mister-auto have no stock (they refunded my payment promptly) and neither did the next supplier I tried. Currently have a third supplier trying to get one from the factory...

Will let you know if they have any joy.

[epipete]

This is very interesting but it is brakes we are talking here and given the obvious implication of failure what are the potential negatives, and if none then why was this not specked by Lotus originally?

[johanvanboven]

Hi, why this is not done by Lotus, is because al setup is registered in all countries in the COC. (Certificate Of Conformity) For anything you want to change, you need a new COC or get the changes registred. And this is expensive and can take a long time.
Legaly in most countries it is forbidden to change anything to the car what is written down in the COC. Forbidden to change discs by bigger ones or even drilled ones. Forbidden to fit braided steel brake lines, forbidden to fit pad's with other compound, etc.
If I can see what is possible in UK, then you're the lucky ones. Cars in Belgium or Germany wouldn't pas the MOT for this.

[johanvanboven]

Some part ref. for TRW172:
Opel 558034 or 558040: no longer supplied.
Vauxhall 3488959
ATE 24.2120-1711.3 or 27.2100-0726.3
Bendix 132111B or 3613030
Bosch 0986480095
Delphi LM50014
Lucas 2676966085 , 32967226 , 32967365
Unipart GMC826

Goodluck finding it.

[epipete]

Hi, why this is not done by Lotus, is because al setup is registered in all countries in the COC. (Certificate Of Conformity) For anything you want to change, you need a new COC or get the changes registred. And this is expensive and can take a long time.
Legaly in most countries it is forbidden to change anything to the car what is written down in the COC.

No, I understand that, what I meant was that the car was designed back in the '80's when owned by GM with the Master Cylinder that we all have, it was designed with this at the same time as GM were producing the unit that you are suggesting is a direct substitution so it could have been COD'd with this unit at the time; you suggest that the choice was because 'Lotus chose a short heavy feel, while Opel took a normal feel' what I'm trying to understand is was that the only consideration or were there any other factors particularly safety and compatability?

[johanvanboven]

It is safe and compatible to change. As for being discussed for 20 years or more, they have chosen a wrong setup.
22.2 mm: short but to hard to push, 20.6: works well, if you would consider a 19 mm pump, then you would propably have to push to far, but able to stop with a finger push. Having to push the pedal to deep is not ideal with all our pedals so close to eachother.
Why did they not fit bigger brakes at first? or a bigger booster? We will never know.

[Rusty Wishbone]

Is there a danger of the brake pedal hitting the floor under heavy braking?

[RayD]

The pedal will travel 16% further than it's doing now for the same amount of braking.

Ray

[inkitin]

There are a number of aftermarket equivalents to TRW PMF172. The only one I can find at an equivalent price is the Delphi (Lockheed) LM50014 (this is according to TRW's website cross referencing).

I'm no expert, so please check!

If you're relaxed about buying through Ebay, they're available here for under £45 inc P&P.

[Brit-Car-Nut]

Rock Auto US offers the Delphi LM50014 for $82.89

[RayD]

... you suggest that the choice was because 'Lotus chose a short heavy feel, while Opel took a normal feel' what I'm trying to understand is was that the only consideration or were there any other factors particularly safety and compatability?

Did you have something in particular in mind with regard to safety Pete?

From what I understand the MC is identical apart from the bore.

I can't imagine Lotus "choosing" a "short heavy feel" ... I think they ended up with a short heavy feel by choosing that particular arrangement of MC, pedal box and servo.

Ray

[dapinky]

Just as a thought on this (from a man who's just bought one of these to fit!) - it would be worth bearing in mind that by fitting this item, it may cause a few problems should you ever wish to go for a big brake upgrade(Hi-Spec, Wilwood or any others) at some stage in the future.

The chances are that with this master cylinder, there will not be enough fluid displacement to operate bigger caliper pistons - and a full pedal travel (to the floor) won't operate the brakes effectively (or even at all).

Now, whilst this may not worry you (as it doesn't worry me - I've got well-maintained OE calipers and cant see me needing anything other than this to 'perfect' my system) - please bear in mind that should you ever come to sell the car on, and the new owner is unaware of this change, then it may become a (potentially dangerous) issue if they then fit bigger brakes.

I would suggest putting something into the Service History to reflect the change - it is the sort of thing which, if overlooked in the future, could be a nasty surprise for someone else.

[RayD]

That's a good point Dave,

In theory only ...

The smaller BMC seems to increase the pedal travel by 16%.

The 4 pot 38.6mm HiSpec brakes increase the travel by approximately 10%

In round figures it would seem if you started with 1½” of travel ... the smaller BMC would take it to 1¾” ... and the addition of HiSpec brakes to 2”.

Or 38mm ... 44mm ... 50mm.

Try to remember to check yours before you start.

Ray

[dapinky]

Master cylinder arrived today - far too busy with the suspension swap to think about fitting it, though.

But i have done some measuring on the bench.....

...The new cylinder has a maximum piston travel of 28mm, and I'm basing my calculations on the OE cylinder having the same travel (as the ports are in the same places!)

I havent stripped it down (and I dont intend to!) - but I'm assuming that the design is such that there are in effect, 2 pistons within the cylinder, one pushing fluid through the 2 front ports, and one pushing through the rear 2 ports, as that is the only way to achieve a 'proper' split braking system.

Therefore, in effect, each mm of travel will push twice the fluid into the system as a single line brake system, split FOS & RNS / FNS & ROS, thereby we can sort of disregard the rear brakes as they are constant, whatever front callipers get fitted. (unless they are upgraded to the hi-specs as well!).

If I make an assumption that each brake pad needs to travel 1mm to contact the disc with enough force to apply maximum braking effect.

On the standard OE rear callipers, piston diameter is 35mm, so to move each pad by 1mm, the single piston needs to travel 2mm, and this needs to be doubled, as there are 2 rear callipers - this will require 3848mm3 of fluid.

At the front, piston diameter is 52mm, so to get the same movement will need 8494mm3 of fluid - a total of 12342mm3

Hi-Spec calipers have 4 pistons each - 38.6mm diameter, so with those fitted you need 9362mm3 - a total of 13210mm3 needed.

Wilwood use 2 different sizes of piston, depending on the caliper - 1.5" & 1.38"....

The bigger ones will need a total of 16290mm3
The smaller ones will need a total of 11589mm3

Now, onto the master cylinders.....

OE ones (22.2mm bore) will displace a MAXIMUM of 21676mm3 (if full 28mm of travel is used)

the replacement (20.6mm bore) will displce a maximum of 18664mm3 at full travel.

Basically, this means that any of the recognised brake upgrades COULD be okay, but assumes that the pad to disc travel isn't too much more than my guestimate of 1mm, and also that the brake pedal pivot point will allow the master cylinder to make full travel before the pedal hits the floor.


For instance, lets assume that you will only get 25mm travel before hitting the floor, all of a sudden, if you have the Wilwoods with bigger pistons, then it's getting a bit marginal (16664mm3 displacement) - so it only needs for the rear brakes to not be adjusted correctly before you potentially end up with no brakes

When I get a chance, I'll try and measure the brake pivot points and see how much 'spare' movement of the pedal is available, and equate it to master cylinder travel - it may give us a better idea of future possibilites/problems.