rear caliper hydraulic piston seal

[esray]

Dear Forum,

HBOL says that "A new seal must be fitted to the hydraulic piston and so placed that the smaller diameter of the seal is nearest to the pointed end of the piston".

I realise I am being slow, but obviously the diameter of the seal is the same at both ends...But please, do they mean the smaller end of the chamfered end of the seal ( I hope that is the right word) or do they mean the other end (sort of sleeved)?

Also, the 'stop washer' for the piston appears too small; it rocks on the end of the point of the piston? Is this correct, please?

I am going to attempt to attach a picture:

http://i861.photobucket.com/albums/ab17 ... 309b62.jpg

 

[harveyp6]

If you look at the outer diameter of the seal it's tapered. The smallest part of the taper goes at the top, the largest at the bottom. The top of the piston is the end with the point on it. The stop washer is held by the allen screw that screws into the caliper body.

 

[esray]

If you look at the outer diameter of the seal it's tapered. The smallest part of the taper goes at the top, the largest at the bottom. The top of the piston is the end with the point on it. The stop washer is held by the allen screw that screws into the caliper body.

Harvey,

No wonder this caliper has failed again after only a year or so...When I refurbed it last time, I placed the seal with the smallest diameter (i.e. the end opposite the taper) at the top!

Harvey, I am so glad I checked!!

The stop washer I am referring to is a washer which fits over the top of the point of the piston - It seats sort of halfway down the point, not at at its base - I just wondered if this was right?

Ray

 

[harveyp6]

If you look at the outer diameter of the seal it's tapered. The smallest part of the taper goes at the top, the largest at the bottom. The top of the piston is the end with the point on it. The stop washer is held by the allen screw that screws into the caliper body.

Harvey,

No wonder this caliper has failed again after only a year or so...When I refurbed it last time, I placed the seal with the smallest diameter (i.e. the end opposite the taper) at the top!

Harvey, I am so glad I checked!!

The stop washer I am referring to is a washer which fits over the top of the point of the piston - It seats sort of halfway down the point, not at at its base - I just wondered if this was right?

Ray

If you fitted the seal with the smallest part of the taper at the top, you had it the correct way around.

The washer doesn't fit over the pin on the piston, it's screwed to the caliper body to prevent the piston popping out. I'd say it was the most safety critical part in the whole caliper.

 

[esray]

If you look at the outer diameter of the seal it's tapered. The smallest part of the taper goes at the top, the largest at the bottom. The top of the piston is the end with the point on it. The stop washer is held by the allen screw that screws into the caliper body.

Harvey,

The washer doesn't fit over the pin on the piston, it's screwed to the caliper body to prevent the piston popping out. I'd say it was the most safety critical part in the whole caliper.

Harvey, this is the washer to which I am referring and this was how I had the piston seal:

[/URL]

 

[quattro]

That's the wrong way up, think of the piston like a little lady with a pointy head. The seal fits her like a little skirt :shock:

The piston stop does NOT fit over the top of the piston. It bolts onto the caliper with an allen bolt and just overlaps the bore so the piston cannot come out.

I'll see if I can find a piccy

Richard

 

[quattro]

Here you go

You can see the piston stop under the plate, held on by the allen bolt



Here are the pistons fitted, and you can see the mark where the piston stop fits onto.

 

[esray]

Harvey, Quattro,

Firstly thank you for your help - I now have my piston seal the correct way round - Probably why I find myself engrossed in Harvey's favourite job yet again after only a year or so!!

We are at cross purposes here; I am relying (perhaps foolishly) on what I have and what HBOL says I should have? The stop washer you both refer to is called a Location Plate in HBOL. I have that Location plate; however, in addition the washer that I have (which appears to fit badly) is shown in HBOL and in my photo?

Ray

 

[Tom W]

There are some photos of when I dismantled my calipers here

viewtopic.php?f=21&t=7453&start=30

There shouldn't be any washers between the piston and the strut. The points of the piston and of the handbrake pin act directly on the strut (601926) which in turn operates the lever (601927). The washer Quattro and Harvey refer to is 601935 in the attached photo.



Tom

 

[quattro]

I really don't know what you have there, but you should have a black pressed tin plate which you can see in the top photo, and underneath that, there is a washer which you can just see under the black plate.

You can see a mark in the lower picture where the washer (piston stop) fits and overlaps the bore slightly. There is a threaded hole in the centre of the mark where the washer fits.

Richard

 

[esray]

There are some photos of when I dismantled my calipers here

viewtopic.php?f=21&t=7453&start=30

There shouldn't be any washers between the piston and the strut. The points of the piston and of the handbrake pin act directly on the strut (601926) which in turn operates the lever (601927). The washer Quattro and Harvey refer to is 601935 in the attached photo.



Tom

Tom,

Thanks for your reply - look at your picture, in the drawing the washer is 601935(2)

 

[Tom W]

That's the same part Harvey and Quattro are referring to. It fits under the Allen head bolt, between the tin pressing and the caliper body. It's not concentric to the cylinder. The (2) at the end of the part number means there are 2 required per car, i.e. one per caliper.

 

[esray]

That's the same part Harvey and Quattro are referring to. It fits under the Allen head bolt, between the tin pressing and the caliper body. It's not concentric to the cylinder. The (2) at the end of the part number means there are 2 required per car, i.e. one per caliper.

Tom, Harvey & Quattro,

Thank you - I've got it at last! 10 out of 10 for your patience!!

The washer in my caliper was just lying on top of the piston - I did wonder why it was needed there - It did not seem to fit very well - Which is why I brought the matter up in the first place! Probably explains why the tin pressing is slightly distorted where it fits over the piston - Being forced down without this quite substantial washer underneath it?

Ray