Seized up master cylinder

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LEONIDAS
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Trying to put my old 270Ge ( 460- ) through re commissioning  and MOT after some time  lying idle and stored . Just finished  reconditioning  all the calipers  and  repalced some corroded pipe lines. The technician now tell me that all brakes are locked due to a seized up master cylinder. Does this make any sense ???

In any case, could anyone pls suggest a supplier who could either recondition  If possible or supply a new master cylinder???

Thanks

Pistonhead
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Re: Seized up master cylinder

LEONIDAS wrote:

........ The technician now tell me that all brakes are locked due to a seized up master cylinder. Does this make any sense ???.........

No, If the master cylinder were to be seized (a condition I have never heard of nor come across) the brakes simply would not apply so how come is your mechanic's claims that the brakes are locked? 

The master cylinder could have been left in a dry state when other work had been done or during storage.

In order to ascertain if the brakes work the master cylinder firstly has to be applying pressure to it. If the master cylinder can apply pressure then I do not see why the pressure can not be relieved when the pressure is removed unless the brake pedal does not move freely to a rest position. Furthermore, the rubber hoses could be internally collapsed preventing return of brake fluid hence locking on the brakes; now that is a condition I have come across. 

You should be able to get a repair kit from the dealers, or factors but you will need to arm yourself with information about the make and possibly internal bore size of the master cylinder if there are variants on size.

mgrays
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Re: Seized up master cylinder

I would have said never seen a seized master cylinder.. but that is what happened 6 months ago on my JCB. It was dragging the brakes (and wearing out) the £500 wet brakes) because of local corrosion where you push the external piston was stopping the piston from being pushed back by the internal spring. This was on a master cylinder that lived outside all it's life but it was on mineral oil. So it happens in rare occasions.

 I would slack off the bolts on the master cylinder first - sometimes the servo goes wrong and can hold on the brakes. If it still holds on the brakes then crack a bleed nipple to release the pressure to check his theory. So it might just need a strip, wet/dry paper and reassembly with silicon/brake grease but it seems unlikely as that part is inside the servo and so does not corrode normally. I have seen a few master cylinders where contamination has swollen the seals (brake fluid is vegetable oil and the seals do not like mineral oil) and that holds a little pressure on.

LEONIDAS
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Re: Seized up master cylinder

Pistonhead,

I wish I had your knowledge  of these things to challenge my  so called mechanic. Now he tells me ( having replaced the master cylinder of my GE280 (460) , that the brakes still don't work and the  problem  is the servo unit. Furhermoret the  original  MB part cost something like £900 !!!

It looks  to me like he is trying to sort things out alphabetically. What comes after S for servo?? V for vacuum??

I recall that that the Gs share quite a few parts with the MB Spinter vans.Looking at these parts they cost only a fraction of what it was quoted to me for an original Ge280 part..

Any idea if a Spinter van's servo brake unit is compatible , or if can be modified to fit  the 460??

Gavin's bible may be of help here

Thanks

Arnie
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Re: Seized up master cylinder

 

It's unlikely to be the servo-unit, if you have jammed-on brakes. The most common servo unit failure is that of its diaphragm and when that goes, you need to apply a lot more force to action the brakes. However, it's easy to unbolt the master cylinder from the servo unit and test it manually (as suggested by MGrays, above). if the brakes release when the master cylinder is unbolted from the servo drum unit, you have your answer (a new servo is required). But test before you buy.

For locked-on brakes, at the rear, I would check the pressure- hold valve in the rear brake circuit.

panzer
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Re: Seized up master cylinder

£900 for just a brake master cylinder - are you sure or did I miss read it?

I could have been remanufactured for about £150

Arnie
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Re: Seized up master cylinder

Well, they were around £400 some 25 years ago - the last time I tried to buy one.

davidb
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Re: Seized up master cylinder

Just make sure the brake pedal hasn't seized on the cross shaft and is returning fully to the stop, You my have to physically pull the pedal back and then see if the brakes are free.

jdring
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Re: Seized up master cylinder

When my 460 had binding brakes, it was simply the mechanics of the brake shoe and the spring was not returning the shoe to rest position - the whole mechanism just needed cleaning and/or replacing.  Quite common I think with rusty metal parts.

I did also replace the master cylinder because the plunger in there was worn and also sticking - keeping the brake fluid at pressure and not relieving fluid back to the reservoir.  

Never had a problem with the servo - surely that would affect the application of brake pressure, not the release.