Plus 2 front brakes

[worzel]

Hi all

Apologies again on this one. Fitted system about 8 weeks ago but still vaguely "edgy" about its performance. Originally I used (incorrectly) plus 2 pads but realised these were servo spec so fitted GT6 non-servo spec ones and these improved matters. Later fitted EBC (about 150 miles ago) but am still not convinced about the stopping ability.

I'm still using the original master cylinder but am considering switching to a 5/8 inch one to reduce pedal effort. I've worked out this smaller unit represents a 25% bore reduction so does this reduce pedal effort by 25% for a given braking distance.

I'm puzzled as to why the system doesn't seem as good as I expected- I'm sure it's not that I'm too used to a servoed system and as I've mentioned before on this subject I used to have a S4 non servo model over 30 years ago and never noticed the brakes so I guess they worked ok.

The car stops but doesn't exactly inspire confidence- the pedal somehow seems "squashier" (technical description eh) but I'm 100% convinced there is no air in the system, the hoses are not ballooning, the bulkhead isn't flexing, the wheel bearings have correct float etc. I am using silicone fluid (have used it for 20 odd years without issue) and some suggest this is more compressible than std stuff but my understanding is that fluids don't compress so this can be ruled out. The master cylinder is fine- I've checked it by bleeding it separately from the rest of the system and there is absolutely no pedal movement with a bleed nipple substituted for the outlet pipe.

Am I being disappointed too early and should I reserve judgement until I've covered more miles?

On a possibly related note- the discs are brand new and I'm always careful about cleanliness when fitting new ones. I've noticed that an element of steering wheel judder has appeared recently but a mot failed to reveal any oscillation on the rollers. On wednesday I noticed the front tyre (driver's side) was showing scrub on the outside shoulder so I checked the tracking and toed-out that wheel by about 1mm.

Since then the steering wheel vibration has definitely worsened (from about 50 mph- at lower speeds it disappears).

There is defintely nothing amiss with the suspension or rubbers/dampers/springs/chassis etc so how can altering toe-in produce this effect.

Your ideas welcomed.

Regards

John

[rgh0]

John

In an unboosted Plus 2 system the extra "compressibility" of sythetic fluid was noticeable in my car. Not noticeable with the booster connect due to the "softness" of feel introduced by the booster itself. All fluids (and solids) are compressible to some degree it is just that they are very hard to compress compared to a gas. Synthetic Dot 5 silicone brake fluids are more compressible than DOT 3 / 4 / 5.1 fluids and this difference can be felt in real life under the right (wrong ? circumstances).

Rubber hoses even in perfect condition also expand under pressure more than teflon / stainless braided hoses.

Racers like a solid pedal feel for confidence which is why they use braided hoses and DOT5.1 fluids.

cheers
Rohan

[gjz30075]

Could be a slightly warped disc, which will cause several of the symptoms you mentioned. I had a brand new Brembo disc that was badly warped and had the symptoms mentioned. Once cut, the car was fine.

Greg Z
'72 Sprint

[GrUmPyBoDgEr]

You mentioned driving your S4 over 30 years ago; I wonder if you have the same problem as me, that being used to driving modern cars with highly efficient servo brakes?
I've actually put +2 brakes on my non-servo S4 to get over that feeling you're encountering.
Initially I was not impressed with the "improvement" & have actually invested in a pair of Wilmore 4 Pot Calipers with matching slotted & cross drilled disks. These will be fitted this Winter.
I must add that after quite a number of miles driving the +2 brakes have really improved & I now question my wisdom on spending all of that money on those gorgeous Alloy Calipers.
Nevertheless they're going on now the money's spent
Your choice of a smaller master cylinder will reduce the pedal effort which, it seems, is what you're really looking for.
For the spongy feel you should start looking further. Are you sure that all of the air has been bled from the system? A bit more new brake fluid & a re-bleed may do it & be a cheap fix.
How old are your brake hoses? Maybe those need replacing.
Braided hoses have been proven to give a firmer pedal.

Good luck
John

[Foxie]

Initially I was not impressed with the "improvement" & have actually invested in a pair of Wilmore 4 Pot Calipers with matching slotted & cross drilled disks. These will be fitted this Winter.

Good luck
John

John,

Do you mean Willwood ? In any case, what are the piston diameters, the part nos. and what supplier ?

I've not been happy with the +2 brakes over the years. I changed to a 5/8 MC, but changed back due to excessive pedal travel. Steel lines were a big improvement.

A few things to check:

There are two different servo bore sizes used in the Elan and Plus 2, but the servos are identical on the outside. A well known supplier even sent me the wrong one.

Pad knock-back is often a cause of excessive pedal travel. Check for excessive front bearing play. Check for minimum disc run-out, the rear discs is often the culprit. New anti-squeal shims, 4lb piston helper springs, spotless pistons, new seals on a regular basis, all minimise pad knock-back.

Triple bleeding, using both pedal operation AND Eezi Bleed, (To be sure, to be sure )

Sean Murray

[denicholls2]

...and the contradictions are possibly related to DOT-5.

If your are using a boosted M/C, then it has a larger bore than a non-boosted one and will require more pedal effort when unboosted.

If you then switch to a non-boosted M/C, your pedal will by definition become squashier, as the greater leverage afforded by a smaller bore comes with the price of a softer pedal from the longer travel required to make up the same volume as the larger bore.

My unboosted 54, I believe with rebuilt boosted M/C bore, requires a very high pedal effort relative to my other cars, but the pedal is rock-solid. What matters to me is that a) I can lock the brakes in a panic stop, guaranteeing all braking is available to me, and b) It requires very large effort to lock them, meaning I am unlikely to lock them up unless I intend to.

Except for fears of breaking off the pedal, one learns to love the unboosted feel. Your complaint of squishiness combined with unboosted bore size concerns me.

Seemingly dumb question: Do the bleeders on your brakes point to the sky or to the road? If they point to the road, then you have the calipers on the wrong sides and will find that putting them right solves your problem nicely. Air rises relative to brake fluid and will be trapped in the caliper with the other orientation and cannot be bled out regardless of your diligence.

Best of luck in any event.

[1964 S1]

After reviewing this entire discussion, I gotta go with the bleeder position conclusion. "... point to the sky or the road..." In a +2 go with the sky position and the road will seem like the sky. I think you've got an air prob. Do you have enough confidence to jab the brakes on at fifty mph and hold the pedal hard as the car comes to a stop? Eric

[worzel]

Hi

Thanks for all of the input.Firstly, the bleed nipples are uppermost on the calipers so this eliminates the possibility of air being trapped and unable to rise- got caught out on this one once!.

Could possibly be the hoses slightly expanding- they've been on a few years so I'll try a switch to braided/stainless to see what that does.

The mot rolling road test didn't reveal any "pulsing" on the fronts but I'm not sure just how sensitive the machinery is to such faults- perhaps it only reveals severe problems. As I said the discs are brand new reputable makes and as the brakes (before I changed them) didn't show any problems of judder the new components must be the problem (probably). The calipers are as new with new seals/pistons etc and each piston moves in its bore so a "sticker" can be ruled out- maybe the discs are not as good as they should be and have warped slightly. I'm sure the mounting faces on the hubs are not a problem- as I said I've changed the discs twice in the 30 years I've owned the car so I think I know the necessity for cleanliness.

Pedal feel- maybe its my faulty recollection of a non boosted system that's the problem. I did expect the pedal effort to be higher without a servo but the progressiveness of the new system is not there- by this I mean that exerting more force on the pedal at say around 40 mph doesn't seem to be retarding the car as much as a lower initial pressure applied at say 20 mph or so- in other words braking effort seems to be tailing off in proportion to the effort applied rather than the other way round.

Frre play at the pedal with the car stationary seems about right and I've checked how much travel is required before the brakes start to grab (with all wheels off the ground) and this seems ok.

I'm also happy with the wheel bearing free play so pad knock back can be ruled out.

I'll have to try some of your suggestions before I reach for the tablets!

Thanks for your ideas.

John

[GrUmPyBoDgEr]

Hi Sean,

sorry, just one of my "senior moments"; Wilwood they are
Piston Dia. = 35mm
Part Nr. BK23M
Powerlite Pads Part Nr. 155-8813KJ
Disks are part of the Kit 265mm Dia 10mm thick. Extra cost for slotting & cross drilling 26 GBP / Pair
All of the necessary bolts & adaptors for mounting onto the Elan back plates are included.

All supplied as a kit for "Caterham / Spitfire" from "Rally Design Ltd"
Tel. 01795 531871. Well informed salesperson & helpfull.
(Google them)
They don't have dust seals which worries some people; unfounded in my oppinion.
e.g. My 1959 Mk14 Elite had Girling AR / NR racing calipers without dust shields.
I put some new seals in them during my ownership in the early 70's (preventative) & found all of the bits to be in very good condition..

Ref. the mention of if the bleed nipples are pointing up or down; the Wilwood calipers have nipples at both ends & 1 each side.
(Thats a total of 4 to avoid or add confusion).
A "one size fits all" sort of solution.

Cheers
John

[steveww]

My S4 fitted with +2 unboosted breaks took a while to bed in when I fitted them from new. Even today I find the EBC pads work better when warm and have more bite then.

Compared to a modern car the pedal effort required is much larger but I can lock them up if required. I am using Castrol SRF brake fluid. The pedal is solid with very little movement. It has braided brake lines and the original master cylinder.

[kstrutt11]

Hi,

My +2 has the set up you describe and a rock solid pedal, the differences from yours are:

- I use DOT 4 fluid (and change it every 2 years)
- I have the smaller master cylinder, without this the pedal had no initial bite and generally gave poor confidence.
- I have goodridge braided hoses.

I would sugest yiou start with the m/cyl as in my opinion the standard one is unnacceptable, with respect to synthetic, yes all fluids are pretty incompressable comparred to gasses but they are not equal I don't know how much effect this will have though.

kevin