Plus 2 front brakes on a 2 seater

[worzel]

Hi all

I'm after info/opinions.

Last year I fitted plus 2 calipers to my sprint but- the result isn't quite as expected. Pedal pressure is obviously higher than the old system with a servo (I've removed the servo) and a mot test confirmed that they're within required limits and they do lock up on the rollers-but- they don't exactly feel "confidence inspiring".

Presently I'm using the std 0.7 bore master cylinder but have a new 5/8 one I could fit. I know that the smaller cylinder will reduce required foot pressure for a given retardation level but by just how much?

Am I correct in thinking that since the smaller cylinder is roughly one seventh smaller then the pedal pressure will reduce by a similar amount or is the "leverage" calculated in a different way.

Secondly, what difference to pedal travel would the smaller cylinder make ie would it be likely to produce a much softer pedal or because the pads are virtually in contact with the discs would there be virtually no difference in feel.

Finally-almost- I'm using non- servo spec pads from a Triumph GT6. Is it possible these are the problem- I don't know their age but they are of a reputable make but I suppose they might be new and use a compound with less friction than genuine old stock pads with asbestos content.

Lastly, I'm experiencing occasional odd symptoms- the car will stop in a straight line (no weaving/pulling) then occasionally pulls noticeably to one side. The caliper pistons are operating properly, there is no air in the system, the tyres match and are correctly inflated, wheel bearing clearances are fine. This has happened before and I've cured it by swapping one pad from each side.

What might be causing this- odd layers in the pads being revealed as they wear down? (I'm clutching at straws here).

Thanks in anticipation.

John

[GrUmPyBoDgEr]

Hi John,

I did a similar swap on my S4 & like yourself was expecting a radical improvement with reduced Pedal effort.
It is always difficult when climbing out of a modern Car & into an old Elan accustoming yourself to the the extra Pedal effort needed.
I'm not sure what you mean by "Soft Pedal" but a smaller Master Cylinder will reduce the amount of Pedal effort but that will be accompanied by longer Pedal travel, which is not necessarily a bad thing IMO.
I still wish that a "dab" on the brake Pedal would provide rapid retardation accompanied by sufficient "feel" & have a set of Willmore 4 Pot Calipers to be fitted sometime in the future. I wonder if the expense & effort will be worthwhile?
Oh by the way my +2 Brakes did take a long time to bed in but resulted in better braking than the originals.
Maybe refitting the Servo (with all it's inherent problems) is the answer?

Cheers
John

[paddy]

Am I correct in thinking that since the smaller cylinder is roughly one seventh smaller then the pedal pressure will reduce by a similar amount or is the "leverage" calculated in a different way.

It's the ratio of the surface area of the piston that counts - and the ratio is just about exactly 4:5. So it'll be 20% reduced pedal effort, 25% increased travel.

Paddy

[stuartgb100]

Hi John,

I fitted +2 calipers to my Sprint, same as you, and kept the original master cylinder too.
However, I also kept the servo.

Two years now and no problems - stops like nothing else I know, and will lock up if too heavy-footed
(but rarely).

Regards,
Stuart.

[GrUmPyBoDgEr]

Hi John,

I fitted +2 calipers to my Sprint, same as you, and kept the original master cylinder too.
However, I also kept the servo.

Two years now and no problems - stops like nothing else I know, and will lock up if too heavy-footed
(but rarely).

Regards,
Stuart.

Yup I'm sure fitting a Servo would be the answer but I put the bigger Radiator up in the nose where the Servo once sat.
Now the Engine bay is nice & tidy but plumbing in a Servo somewhere in the region of the Steering Rack would mess up the looks & reduce the present super accessibility to the Timing/Poly-V Belts etc.
A case of like it or lump it.
Cheers
(this) John

[bast0n]

Standard brakes - standard servo - standard master cylinder - Green Stuff pads - no expense - no problems!!

KISS

[GrUmPyBoDgEr]

[quote="bast0n"]Standard brakes - standard servo - standard master cylinder - Green Stuff pads - no expense - no problems!!

KISS [/quote

I knew I must be doing something wrong.

[bcmc33]

I'm using non- servo spec pads from a Triumph GT6. Is it possible these are the problem- I don't know their age but they are of a reputable make but I suppose they might be new and use a compound with less friction than genuine old stock pads with asbestos content.

John,

My advice is to use EBC Black Stuff pads as they will bed-in reasonably quickly and ideally suited to our very light cars. These pads may wear a little quicker but will be kinder to the discs.

I use these on my single pot calipers which are fed from a Girling servo.

I have given some thought to using a M/Cyl with a smaller bore just to see the difference. I like Paddy's calculations, and will use it as part of the analysis.

[RichardS]

Standard brakes - standard servo - standard master cylinder - Green Stuff pads - no expense - no problems!!

KISS

Depends how much of the front braking system needs renovating - I found it cheaper to swap to +2 calipers + discs than the expense of having the servo renovated!

Hi all

I'm after info/opinions.

John

John - I have fitted +2 calipers to my Sprint and kept the standard master cylinder. I am quite happy with the brake feel but hadn't driven the car with the original set up for 20 years so cannot remember what they felt like before! You are welcome to see whether my set up feels any different to yours. Took mine out for a good thrash around the back roads of Willaston when the sun was briefly shining last week. Send me a PM if you would like to compare notes on the brakes.

Richard

[Elanintheforest]

I?m with 'Baston' on this one, and surely the front / rear balance is affected by putting more powerful callipers on the front? With the stickiest of modern road tyres on standard rims you can still lock the wheels up with the standard brake setup, so what advantage do the Plus 2 callipers provide?unless you?re putting some pretty wide rims and sticky tyres on of course?
Mark

[memnon]

I think that may be the problem,

The front rear bias is too far to the rear on the standard setup... I am of course talking for 100% commited driving, so I'm not sure I'd do it.

In an opinion to the question asked, I'd blame the pads and get a modern performance pad in there EBC seem a good place to start. I am nearly at this point, but still a couple of months away yet! I can report back on my own findings then though.

Jason

[elansprint71]

Standard brakes - standard servo - standard master cylinder - Green Stuff pads - no expense - no problems!!

KISS

Presumably your rear brakes are partially siezed then?

[worzel]

Hi- again

Some interesting comments.

I should clarify- by a "soft" pedal I should have said pedal travel. I'm (probably incorrectly) comparing the feel of the current set up with the (rather foolish) time I tried the std sprint brakes with the vacuum to the servo blanked off and the pedal felt very hard with very poor braking effect (not unnaturally). Possibly the increased travel resulting from the larger calipers is fooling me into thinking the feel is softer than I expected it to be.

Possibly, as some have said, it's my perception that's faulty- many years ago I had a S4 that came without a servo. That was my first elan and I never really noticed the brakes at that time, the car just stopped so I'm guessing they operated perfectly well.

As for the pads- I first tried std plus 2 ones but wasn't too impressed- it stopped but not particularly well I felt. I then fitted green EBC but although improved again I still felt they weren't quite "right". Lastly I'm using Triumph GT6 non-servo spec. These are better. As I said the car locks on the MOT rollers so I suppose they must be working ok- maybe I'm expecting too much!

Finally, as to the reason why I removed the servo- I had two of these fail previously. Both were fairly new (less than 2 years old). One completely locked up at a junction without warning (I now know it was probably caused by the air valve under the filter). The other blew the seals suddenly and I suddenly noticed I was surrounded by what looked like fog on a hot day- it was the fluid being burned.

After that I'd had enough and thought that such a light car shouldn't need a servo anyway. I understand that various Elise models don't come with servos so maybe that backs up my idea.

Regards

John
OP

[miked]

Hi John,
Re S4.

I know this is not exactly the same, but I had servo problems and said B*locks to them. After going through all corners and replacing the rubbers, I went down to the 0.6252 MC and fitted green stuff pads. They got better and better and bedded in. I can say that I was driving my S4 with no servo and was not crapping myself. Forgot all about the brakes. The smaller cylinder gave me more travel but gave a definite servo type progressive feel. So, I can see how guys were happy with the early cars with no servo.
I don?t know how it works with the increase volume of the bigger pistons on plus two callipers. I was going to sart with the standard MC. I will find out shortly on the Hill climb car that I am still building. Bit more progress than when you called for the calliper plates.

Regards Mike

[RedS4]

My S4 coame with a servo but the previous owner disconnected it as he was tired of "putting himself through the windscreen" every time he braked!! He much preferred the brakes without the servo - I have yet to put the car back on the road to see how it is.
i have read that if you fit softer pads to a car without a servo the results are quite good with plenty of "pedal feel."