Front caliper piston position

[peteyg 256 1 Vehicles]

Just refurbed my calipers. The pistons have a half moon raised bit which is in contact with the pad. Does it matter where the contact is? By rotating the piston it would be pressing on the front,back,top or bottom area of the pad.

Cheers,

Pete

[Simon350S 191 1 Vehicles]

Never seen that on a caliper piston before, unless there is a locating groove on the back of the pad.

Did your old pads have a matching recess that your new ones don't?

[rogerch 63 3 Vehicles]

Picture please, cause from your post it sounds like you've put them in back to front.

[peteyg 256 1 Vehicles]

Typical. Ive already put them back on the car. I hope they're not back to front as they've been that way for the last 12 years and were rebuilt at a well know Lotus specialist, The other end of the piston is domed and had a grey coating. No locating marks on that pads at all.

[Simon350S 191 1 Vehicles]

Doenst sound right at all mate, I'd not be happy with them like that, the pad should sit square on the piston face and not angled in any direction.

[peteyg 256 1 Vehicles]

Now you've got me worried!

How do I send out a plea for photos of what they should look like?

[rogerch 63 3 Vehicles]

Is the cup of the piston facing in, or facing out? is the outer seal sitting snug in grove around the circumference of the piston?

[peteyg 256 1 Vehicles]

Cup is facing out, Roger, and seal is in the groove....so it's definitey the right way round.

I feel really stupid now, it's such an obvious answer.

Still...hasn't answered the question about the position of the piston...anyone?

Pete

[rogerch 63 3 Vehicles]

That's good, it was just that from your first post it sounded like they were wrong way round, sorry for doubting you. Can you sketch it and scan it, just to give us an idea of where this half moon thing is?

[wookiecj 9]

Now you've got me worried!

How do I send out a plea for photos of what they should look like?

Alternatively, you could post a picture and people could tell you what was wrong.... I presume that it is still accessible?

[peteyg 256 1 Vehicles]

As I've put everything back together, I can't take a photo so you'll have to forgive my useless art skills!

The top view shows the raised section in bold. It stands proud about 1/8". The side view hopefully shows the raised bit too. The raised bit is a semi circular shape.

Pete

[red vtec 78 1 Vehicles]

Can you not look in the parts manual?

[peteyg 256 1 Vehicles]

The piston is not shown in the manual. First place I looked!

[rogerch 63 3 Vehicles]

I see now, actually no I don't, I haven't got a clue ? Having looked around the best I can offer is it some sort of locator designed to marry up with the pads, so unless there is a matching surface on the pads, at this stage my best guess is wrong pistons.

I have to say I'm no fan of these early style single piston calipers as I never seen one wear evenly yet. Someone with the same model year as your car needs to come in and confirm that the outer edge of the piston should be even, or that here has become available pads to match the step for some reason.

[peteyg 256 1 Vehicles]

I think you're right, Roger.

Anyone?

[ramjet 957]

Personally I would find it difficult to think that someone would have gone to the trouble of changing all the pistons in the calipers so that they all have this step on them. I tend to think that they are original and that the pads have been changed from a pad with a step in the face that the piston sits on to pads with a plain back.

Having said that, I agree with Roger that someone with the same model needs to weigh in and give their experience.

If pads can't be found that have this groove in them, it should not be a difficult job to get the lip machined off the pistons.

[Nelly 130 1 Vehicles]

Pete I will e-mail you to see if I can help

[Simon350S 191 1 Vehicles]

I'm certain that as already said, one or other is wrong.

You thought about calling Sj's or PNM and asking the question?

Where did you but the rebuild kits and pads from? I'm sure they'd give you a few minutes of their time.....

[peteyg 256 1 Vehicles]

SJ rebuilt the car when I first got her many years ago and the calipers haven't bee touched since. The rebuild kit just consists of the seals which all fit perfectly. That came from SJ along with the pads. Will drop Steve a live and see what he has to say.

Pete

[p1renn 0]

All of my front pistons had that step too. It's subtle and at first I thought it might be a recess for the anti rattle plate to fit into but then the anti rattle plate is too thin. My pistons were fine so I'm re-using them. I just bolted everything back together and not going to worry about it.

[Paul Coleman 378]

I replaced my S1 front pistons with stainless steel ones but the tops of them are flat? I don't remember any steps in the face that touches the pad. I've still got the originals in the garage so I'll dig them out later and take a picture so you can compare.

Paul.

Edited June 18, 2010 by Paul Coleman

[esprit s2 94 1 Vehicles]

I'll be taking my calipers off this week Pete (again) so I'll take some pics.

[Matt-watts 105 3 Vehicles]

Mine where flat on the top, I would be interested to see yours

Keep us posted on this one !

Matt

[esprit s2 94 1 Vehicles]

OK, got round to stripping my calipers today. Here are some pics of the caliper and the pistons. I take it to get the pistons out you have to undo the 4 bolts on the caliper? Is it then just a case of pulling them out somehow? The old seals have had it, they are all crusty.

[peteyg 256 1 Vehicles]

Good work Paul! Looks like you have the same pistons as mine so I can't believe that's just coincidence.

The calipers come apart easily, just keep an eye on the two little O rings when you separate the 2 halves. I didn't get replacements in my seal kit but they were in good nick so just put them back in.

You can just pull the piston out, just take out the bleed nipple and use a pair of mole grips to rotate the piston as you pull. It'll take a little effort as it's supposed to be a close fit.

Pete