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#472393 - 13/09/17 12:57 PM Plus 8 brake issue
howard Offline
Talk Morgan Addict

Registered: 01/01/09
Posts: 3035
A friends Morgan Plus 8 of 1970s vintage had a brake problem following the replacement by his garage of shoes and pads and a rear slave cylinder. The rear brakes are drums of the non self adjusting sort and have been adjusted correctly _ I have checked the adjustment myself..

The problem is that the first application of the brake pedal goes almost down to the floor though the braking is still good enough to lose front wheel grip on a damp road. An immediate second application gives a harder pedal feel and much less travel of the pedal.

In neither case is the pedal spongy when you push hard on it so I doubt that there is air in the system . What do these symptoms suggest to you? Servo problem / leak? Master cylinder seals?

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#472403 - 13/09/17 01:56 PM Re: Plus 8 brake issue [Re: howard]
SteveT Offline

Talk Morgan Expert

Registered: 22/05/14
Posts: 2364
Loc: Forest of Dean, Gloucestershir...
I'd first put a pipe clamp on each the hoses in turn to see if the pedal improves and so isolate the issue. Remove the possibility of it being air before going further, if it was ok before the system was broken into it could still be air.
Also is the travel excessive regardless of whether the engine/servo in use?
_________________________
Steve

1967 Austin Healey 3000 Mk3

Wild Mogs – It’s a right carry on!

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#472404 - 13/09/17 01:59 PM Re: Plus 8 brake issue [Re: howard]
Graham, G4FUJ Online   content
Salty Sea Dog
Member of the Inner Circle

Registered: 03/07/07
Posts: 19249
Loc: Cheltenham, Glos. UK
Didn't these have a two way / shuttle valve in or just after the master cylinder?
If so it sounds as though that valve is not centred.
(Sorry, not a great explanation - can't remember the details)
_________________________
Graham (G4FUJ)

D8921 L44FOR '93 4/4 Sunny yellow 2 seat smile
'99 Z3 1.9; '90 LR 90 SW

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#472413 - 13/09/17 03:03 PM Re: Plus 8 brake issue [Re: howard]
DaveW Online   content
Roadster Guru
Member of the Inner Circle

Registered: 11/12/08
Posts: 13827
Loc: South Yorkshire
The MGB of the same vintage had the split master cylinder with the shuttle for the warning light which Graham is recalling. The master cylinder was integral with the servo.

The pedal on this arrangement was always on the soft side, but when pumped with the engine off, became hard very quickly. Start the engine and the pedal would sink and soften.

This isn't what you describe, but if that's the set up don't expect a hard pedal. My gut reaction is its the master cylinder seals. If they were time expired before the work, they will have travelled down the bore when bleeding the system, and may just have worn enough, or picked up some crud which is preventing a perfect seal.

It might be the servo - but just blank off the vac pipe and see if it makes a difference.
_________________________
DaveW
2005 Corsa Red Roadster S1
2016 Saffron Yellow (Narrow) Plus 4

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#472420 - 13/09/17 03:41 PM Re: Plus 8 brake issue [Re: howard]
Stringers Best Mate Offline

Charter Member

Registered: 16/10/13
Posts: 5109
Loc: Northamptonshire UK
My money's on master cylinder..
_________________________
Steve


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#472428 - 13/09/17 04:24 PM Re: Plus 8 brake issue [Re: Stringers Best Mate]
howard Offline
Talk Morgan Addict

Registered: 01/01/09
Posts: 3035
Originally Posted By Stringers Best Mate
My money's on master cylinder..


So is mine TBH. Cant see how air would affect the distance travelled in this way - surely it would be the same all the time. Nor can I see it being the servo - if that failed surely the brakes would be harder not softer. And if it was a balance valve issue would the car stop straight as it does?

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#472432 - 13/09/17 04:49 PM Re: Plus 8 brake issue [Re: howard]
MOG 615 Offline
Talk Morgan Regular

Registered: 24/09/14
Posts: 948
Loc: London
Howard

As others have said this is almost certainly the master cylinder seals , and as they are not sold separately these days , you are probably going to have to change the entire unit. Not a difficult job in itself , just take you time bleeding the brakes thoroughly until you are really happy that all the air is out , and then do it again about a week later just to check. A pressure bleeder will help , but it is not essential , and the old small length of runner tube and a jam jar will work just as well.

The 1970 +8 did not have a brake servo at all. But I think it was the first at MMC to feature split circuit brakes and hence the more complex master cylinder with an outlet pipe to each circuit.

What happens to cars that are not used regularly (and especially to those laid up over winter) is that the central rubber seal "relaxes" and then gives the impression of a long pedal even when everything else is adjusted correctly. I don't think it is worth trying to re-set the seal (although I am told some do it) because you really do want your brakes to work and inspire confidence when travelling at +8 speeds.
_________________________
Andy G
1999 +8 , Indigo Blue.
Ex-John McKecknie/Mike Duncan 1955 +4 racer.

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#472440 - 13/09/17 05:12 PM Re: Plus 8 brake issue [Re: howard]
Graham, G4FUJ Online   content
Salty Sea Dog
Member of the Inner Circle

Registered: 03/07/07
Posts: 19249
Loc: Cheltenham, Glos. UK
Originally Posted By howard

So is mine TBH. Cant see how air would affect the distance travelled in this way - surely it would be the same all the time. Nor can I see it being the servo - if that failed surely the brakes would be harder not softer. And if it was a balance valve issue would the car stop straight as it does?

I had the servo fail on my 90 Howard. Increased pedal travel for any brake application. Felt as though the pedal was reaching a bottom end stop. Not nice and while brakes worked, efficiency was definitely reduced.
_________________________
Graham (G4FUJ)

D8921 L44FOR '93 4/4 Sunny yellow 2 seat smile
'99 Z3 1.9; '90 LR 90 SW

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#472445 - 13/09/17 05:26 PM Re: Plus 8 brake issue [Re: SteveT]
Richard - Aus Offline

Member of the Inner Circle

Registered: 15/01/12
Posts: 14370
Loc: Perth, WA, Australia
Originally Posted By SteveT
I'd first put a pipe clamp on each the hoses in turn to see if the pedal improves and so isolate the issue. Remove the possibility of it being air before going further, if it was ok before the system was broken into it could still be air.
Also is the travel excessive regardless of whether the engine/servo in use?


+1

When I had this pedal was rock hard on the rears, fronts took a bit more bleeding.
_________________________
Richard
1976 4/4 4 Seater

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#472451 - 13/09/17 05:59 PM Re: Plus 8 brake issue [Re: howard]
SteveT Offline

Talk Morgan Expert

Registered: 22/05/14
Posts: 2364
Loc: Forest of Dean, Gloucestershir...
Originally Posted By howard
Originally Posted By Stringers Best Mate
My money's on master cylinder..


So is mine TBH. Cant see how air would affect the distance travelled in this way - surely it would be the same all the time. Nor can I see it being the servo - if that failed surely the brakes would be harder not softer. And if it was a balance valve issue would the car stop straight as it does?


I'd still clamp off the system first, if in doing so there is no real difference then I agree it's probably the m/cyl. If the pedal goes hard then you know where to look and you haven't wasted time and money on a new cyl. A Yorkshireman ought to appreciate that.
_________________________
Steve

1967 Austin Healey 3000 Mk3

Wild Mogs – It’s a right carry on!

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