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Rusty rear brake pistons. Again..... #656052
13/08/20 08:52 PM
13/08/20 08:52 PM
Joined: May 2012
Posts: 1,050
Sumerset
Rog Offline OP
Has a lot to Say!
Rog  Offline OP
Has a lot to Say!

Joined: May 2012
Posts: 1,050
Sumerset
Fantastic drive across Exmore yesterday in the oh so hot summer heat but a bit of a surprise on the way home. A few miles from home I put my foot on the brake pedal and it went to the floor (and my foot taking the accelerator pedal with it). Fortunately a quick grab of the hand brake was enough. Turned out to be the near side rear wheel cylinder semi-seized on and I guess I boiled the fluid so a slow limp home after that. It must have seized over the journey as I had been pushing the car around in the garage the day before and didn’t notice anything.

Everything too hot to strip down last night but started at 6:00 this morning and had it freed before breakfast. I was expecting a fight with the seized drum but it came off and all looked nice and clean apart from the external rust on the pistons lurking under the dust covers. Fortunately the pistons freed up with a few shots of silicone spray and all has been well today.

So I guess the moral of the story is to get some brake lube on those pistons to keep the external surface rust at bay woohoo


Roger
2011 Plus 4
Re: Rusty rear brake pistons. Again..... [Re: Rog] #656122
14/08/20 10:53 AM
14/08/20 10:53 AM
Joined: Nov 2015
Posts: 2,663
Yorkshire
CooperMan Offline
Talk Morgan Expert
CooperMan  Offline
Talk Morgan Expert

Joined: Nov 2015
Posts: 2,663
Yorkshire
When I service my rear brakes I peel back the dust covers & wipe some red (brake rubber safe) grease around the end of the pistons

I've recently swopped to Mintex Ceratec as it's more resistant to heat


Jon M
Re: Rusty rear brake pistons. Again..... [Re: Rog] #656188
14/08/20 03:13 PM
14/08/20 03:13 PM
Joined: May 2012
Posts: 1,050
Sumerset
Rog Offline OP
Has a lot to Say!
Rog  Offline OP
Has a lot to Say!

Joined: May 2012
Posts: 1,050
Sumerset
Yes an important little job I think. When I peeled back the dust covers about a quarter teaspoon of red oxide dust fell out of each. Considering the car has had many services in it 5k miles of life its obviously not on the service schedule. My dust covers now have a high temp grease inside too.

But the odd thing was only the part of the pistons behind the dust covers were covered in rust, the portion of the pistons that pokes out through the dust covers was still bright and shiny. Odd that.....


Roger
2011 Plus 4
Re: Rusty rear brake pistons. Again..... [Re: Rog] #656195
14/08/20 04:08 PM
14/08/20 04:08 PM
Joined: Nov 2015
Posts: 2,663
Yorkshire
CooperMan Offline
Talk Morgan Expert
CooperMan  Offline
Talk Morgan Expert

Joined: Nov 2015
Posts: 2,663
Yorkshire
Trapped moisture / condensation that can't dry out ?


Jon M
Re: Rusty rear brake pistons. Again..... [Re: Rog] #656197
14/08/20 04:13 PM
14/08/20 04:13 PM
Joined: Dec 2008
Posts: 18,725
South Yorkshire
DaveW Offline
Roadster Guru
DaveW  Offline
Roadster Guru
Member of the Inner Circle

Joined: Dec 2008
Posts: 18,725
South Yorkshire
I think the brake fluid attracts condensation, cylinders are usually like that. It's certainly a hot spot for corrosion, but then again I got 15 years out of my original Roadster rear cylinders.


DaveW
2005 Corsa Red Roadster S1
2016 Saffron Yellow (Narrow) AR Plus 4
Re: Rusty rear brake pistons. Again..... [Re: Rog] #656200
14/08/20 04:21 PM
14/08/20 04:21 PM
Joined: May 2012
Posts: 1,050
Sumerset
Rog Offline OP
Has a lot to Say!
Rog  Offline OP
Has a lot to Say!

Joined: May 2012
Posts: 1,050
Sumerset
But the brake fluid is the other side of the seals, this is external rust. I did wonder if the dust cover elastomer was hygroscopic and saturating with external airborne moisture. It might then outgas some of that moisture internally whenever it heats up

[Linked Image]


Roger
2011 Plus 4
Re: Rusty rear brake pistons. Again..... [Re: Rog] #656216
14/08/20 06:57 PM
14/08/20 06:57 PM
Joined: Jun 2015
Posts: 633
North Somerset, UK
Deejay Offline
Talk Morgan Regular
Deejay  Offline
Talk Morgan Regular

Joined: Jun 2015
Posts: 633
North Somerset, UK
Is the cause somewhat similar to the infamous Duratech spark plug corrosion...metal body trapped in air within a rubber shroud?


Doug

2011 +4 in Rich Maroon
1972 750 “ComDom” sprinter
1958 Triton 650
1992 Triumph Trophy 900
Re: Rusty rear brake pistons. Again..... [Re: Rog] #656218
14/08/20 07:07 PM
14/08/20 07:07 PM
Joined: Dec 2008
Posts: 18,725
South Yorkshire
DaveW Offline
Roadster Guru
DaveW  Offline
Roadster Guru
Member of the Inner Circle

Joined: Dec 2008
Posts: 18,725
South Yorkshire
I think Rog that there is always traces of fluid on the piston, maybe at a molecular level, but the corrosion under the rubber boot defies logic. Unless it's simple condensation, but every car I've had has been the same. And the fluid from the rears is always badly discoloured, even at two years. In fact when I changed the fluid in the 2012, it came out dark grey.

[Linked Image]


DaveW
2005 Corsa Red Roadster S1
2016 Saffron Yellow (Narrow) AR Plus 4
Re: Rusty rear brake pistons. Again..... [Re: Rog] #656242
14/08/20 09:12 PM
14/08/20 09:12 PM
Joined: May 2012
Posts: 1,050
Sumerset
Rog Offline OP
Has a lot to Say!
Rog  Offline OP
Has a lot to Say!

Joined: May 2012
Posts: 1,050
Sumerset
Oh dear Dave that looks a bit grim. I guess I had better get mine out. Who knows when or if it was last changed frown

But the good news was at least I managed to spot the hand brake cable failing before it had gone too far smile

The plastic outer had just started to crack but the metal inner was still in good shape.
[Linked Image]

So a quick repair job and a chance to use some of that magic tape recommended by bmgermany from another post thumbs

Originally Posted by Rog
Originally Posted by bmgermany

My first choice for many purposes!

in my workshop I use this "rubber splicing tape" (offered by many comanies) very often. You can wrap it around tubes, cables, wires and so on!



Clever stuff. I think I need some of that in my toobox


Hopefully this will keep the wet out for a while
[Linked Image]


Roger
2011 Plus 4
Re: Rusty rear brake pistons. Again..... [Re: Rog] #656249
14/08/20 09:44 PM
14/08/20 09:44 PM
Joined: Nov 2011
Posts: 3,625
Australia - NSW North Coast
OZ 4/4 Offline
Talk Morgan Addict
OZ 4/4  Offline
Talk Morgan Addict

Joined: Nov 2011
Posts: 3,625
Australia - NSW North Coast
Originally Posted by Rog
But the brake fluid is the other side of the seals, this is external rust. I did wonder if the dust cover elastomer was hygroscopic and saturating with external airborne moisture. It might then outgas some of that moisture internally whenever it heats up

[Linked Image]

Pack the rubber cap with rubber grease, no problems then.


A Morgan Identified Fastidious Owner...
2011 4/4 Bespoke, 1981 Delorean, Auburn Boat Tail
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