Plus 2 front brakes

[worzel]

Hi all- and apologies for yet again bringing up this old one!

I fitted this system some time ago and initially made the (stupid) error of using servo spec plus 2 pads (clever eh?).

I switched to the non-servo spec Triumph GT6 pads and found these improved matters and gave the system the benefit of the doubt thinking that as they bed in they'd improve.

After2-300 miles or so they have improved but still don't feel quite "right".

I noticed yesterday that in heavy rain the initial bite was poor and this got me thinking about the function of the mild steel plates fitted behind the front discs- just what is their function?

In one of my more imaginative moods I conjectured that (maybe) these minimise water on the discs but cannot see how this would have any really noticeable effect since the outer face of the disc is not shielded.

Years ago I ran a std S4 that came without a servo. This was my 1st elan and I cannot recall ever giving the brakes much thought- they just worked very well. It was fitted with the std size m/cylinder.

My current car also retains the std size m/cyl and I've checked its functioning by blanking the outlet and bleeding it. This resulted in zero pedal movement and a rock hard pedal.

Overall, the pedal seems to have more travel than with the servo but since I'm using silicon fluid and this is supposed to be more compressible than the std stuff I'm wondering if this might be part of the problem and theorised that when the servo was on the car the servo masked to some extent this greater compressibility.

I'm 100% certain there is no air in the system and the pedal moves only a fraction before the pistons move (checked on a flat surface with a helper pushing the car).

I wouldn't say the overall pedal pressure is noticeably higher without the servo but the pedal seems somehow "softer" in feel (very subjective I know).

I was thinking of installing the 5/8th m/cyl (I've a new one) but wonder if this might increase the pedal travel to an unacceptable level.

Any comments?

One last point- the front bearings are spot on in terms of play so it's definitely not pad "knock-off" causing the problem.

Thanks in anticipation.

John

[elan_fan]

Hi John, I note you say you are using silicone fluid, has it always used silicone or have you used it in a partly renewed system?. I'm thinking that either the caliper and or master cyl seals have swolen and particularly in the case of the caliper, are gripping the pistons so when you put your foot on the brake the pistons are moving out and deflecting the seals which retract the pistons slightly when pressure is released. Or maybe the pistons are partially seized due to corrosion which I believe can occur with silicone fluid.

regards
Mark

[steveww]

EBC Green Stuff pads are nice and soft and give good initial bite in a non servo system.

The only I have had extra pedal travel is when the front bearings were not set quite right but you have covered that already.

Have you checked the run out of the front disks?

[worzel]

Hi

Quick responses eh!

I've had silicon fluid in for over 20 odd years (not the same stuff I should add- it has been changed once or twice) so I think seal problems can be ruled out.

Wheel bearings- definitely ok on runout.

Greenstuff pads- these keep coming up with good reports so I think I might have to try them.

The discs are new, correctly mounted and runout is within tolerances.

I'm sure the basic system is ok- as I said a std S4 I had years ago had the sort of brakes you don't think about- I was able to lock the wheels on a dry road. Not sure if my present car could do the same- but with larger front calipers it certainly should be able to.

I went for Triumph GT6 pads simply because that car is a lot heavier than a 2 seater elan so the pad spec should have been ok.

In the meantime- thanks for the input and keep putting in your comments.

John

[kstrutt11]

I have 9/16 m/cyl, Green stuff pads, goodridge hoses and mineral brake fluid (changed every 2 years) on my +2, the pedal is nice and firm with and far better than it was with the servo, so the set up can work very well, I did start out with the 5/8 m/cyl and the pedal feel was very wooden If I was in you position, I would firstly check the wheel disc run out (front and rear), try removing the anti squal shims, an also check the m/cyl is fully retracting.

Kevin

[CBUEB1771]

I have 9/16 m/cyl

Where did you find a 9/16" bore master cylinder? I have never found one smaller than 5/8" bore. Your smaller master would give a decent 1.23:1 increase in line pressure over the 5/8" bore.

[bill308]

John,

Liquids simply do not compress, so rest assured, that in not a problem. It is possible there is some water content in the fluid that is vaporizing, but with a silicone based fluid, this is not likely as it is not hygroscopic as far as I know.

There is something else going on. The last time my Elan was on the road, I had switched over to a silicone based fluid for some time and I also detected a little sponginess in the brake pedal. My feeling was there may be some seal swelling going on. With break application, the swolen seals might compress giving the feeling of sponginess. I don't know for sure, but when I get the car back on the road, I will return to a more traditional brake fluid.

So the question remains, what else might be happening?

1. In addition to the seal issue, there might be a bubble or two of air in the system somewhere?
2. Other possibilities are brake lines that are expanding a tiny bit?
3. Maybe the piston, bore, or pad geometry are a little defective?
4. Maybe the firewall is weakening and deflecting a little?
5. or the peddle box bushings are wearing a bit?
6. or .........

There are lots of possibilities on our old cars and maybe several things might add up to a slightly spongy pedal feel?

Personally, I think item 3 is the culprit in my case.

Bill

[Petter Hval]

AP Racing are doing master cylinders with bores from
14 mm up to 25,4 mm but at a prize, From ?73 to ? 109 +
VAT from Demon T.I hope there are others with a more
decent priZe.
Petter

[worzel]

Hi Bill

Thanks for your input.

I've checked the firewall for flexing with a helper and this is definitely not bowing under pressure.

Seals- could be. The front calipers are as new with new pistons seals etc plus new hoses. I suppose there is a possibility that the fluid might be reacting to the seals (which might be made of modern materials that are affected by this fluid) I've had the car since 1978 and have run silicon fluid for the last 20 or so without problems but this was using "old material" seals. I'm pretty sure the calipers are all ok- the back have stainless pistons and a check on the rolling road revealed no imbalance/grabbing/earlier application on one side compare to the other.

Mystery eh- before I start dismantling I've just fitted EBC green pads so I'll see how they work first.

Again, thanks for all the input.

John