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Brake master cylinder replacement guide 4th gen

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Bludge
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Brake master cylinder replacement guide 4th gen

Post by Bludge » Mon Apr 22, 2013 10:51 pm

Just a quick quide to replacing the BMC, i know its an easy job but it might help someone, so here goes:

You will need a 10mm flare spanner for the brake lines. its worth paying £8 or whatever one costs to save the headache of possibly rounding off one of the nuts.

so the BMC is circled here in green. it connects to the brake booster (the big black circular shaped thing behind it) with 2 bolts.
First, remove as much of the brake fluid from the cylinder as possible, i used a turkey baster. Make sure you dispose of it properly and keep in mind it will strip paint. its nasty stuff. i recommend getting some old rags or towels down under the BMC as you will get some fluid leak when you remove the brake lines.
I had to undo my strut brace to get to it. as you can probably tell on mine by the cable ties, my clutch cylinder (circled in orange) is just tied to the strut brace fixing. on the lude i removed the BMC from there was a little attachment under where the strut brace bolts to the chassisthat holds the clutch cylinder, (circled in yellow) its just a case of undoing the 3 bolts and popping it all off.

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Next i removed the bolt and unscrewed this connection on the fuse box and pulled it out by unclipping it at the back, there is still stuff attached, but you can move it enough to get to the bottom bolt on the BMC.

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Once that is out the way, crack the 2 bolts holding the BMC in place (you cant really seem them with the pics, but they are easy enough to locate), and then crack the brake line nuts (circled in green). undo the bolts holding the BMC in place fully, so as soon as the brake lines are off you can pull it out, as brake fluid will start dripping from the BMC.

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One thing to check for as i didnt notice it until i got a second master cylinder from ebay, is on the piston is a black ring that you can slide off, the BMC i removed from the car didnt have one and neither did the one i got from the scrap yard, im wondering if the absence of that part was what was causing my loss of pressure. circled here in green.

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Then pop the new BMC on, screw in the brake lines, tighten it up, refill it, refit the fuse box reserve cylinder and strut brace and bleed the brakes. job done.
Last edited by Bludge on Tue Apr 23, 2013 5:00 pm, edited 2 times in total.

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Post by Merlin » Tue Apr 23, 2013 12:04 am

Nice thanks. Its nice to see some pics ad I'll be doing this soon since I'm upgrading from a 15/16 MC to a 1" :D
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Post by Ted » Tue Apr 23, 2013 12:37 am

Bludge wrote:my little reserve cylinder (circled in orange) is just tied to the strut brace fixing.
thats the pot for the clutch master cylinder
Bludge wrote:on the lude i removed the BMC from there was a little attachment under where the strut brace bolts to the chassis, (circled in yellow) its just a case of undoing the 3 bolts and popping it all off.
that would be a brake stopper, it removes some of the flex you get in the bulkhead when you apply the brake
Bludge wrote:One thing to check for as i didnt notice it until i got a second master cylinder from ebay, is on the piston is a black ring that you can slide off, the BMC i removed from the car didnt have one and neither did the one i got from the scrap yard, im wondering if the absence of that part was what was causing my loss of pressure. circled here in green.
this is a seal that keeps the vacuum in your servo, are you sure this isn't still stuck inside the servo meaning you now have 2 in there?

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Post by Bludge » Tue Apr 23, 2013 7:31 am

tramroadmotors wrote:
Bludge wrote:my little reserve cylinder (circled in orange) is just tied to the strut brace fixing.
thats the pot for the clutch master cylinder
Bludge wrote:on the lude i removed the BMC from there was a little attachment under where the strut brace bolts to the chassis, (circled in yellow) its just a case of undoing the 3 bolts and popping it all off.
that would be a brake stopper, it removes some of the flex you get in the bulkhead when you apply the brake
Bludge wrote:One thing to check for as i didnt notice it until i got a second master cylinder from ebay, is on the piston is a black ring that you can slide off, the BMC i removed from the car didnt have one and neither did the one i got from the scrap yard, im wondering if the absence of that part was what was causing my loss of pressure. circled here in green.
this is a seal that keeps the vacuum in your servo, are you sure this isn't still stuck inside the servo meaning you now have 2 in there?
Thanks for the corrections, although what do you mean about the brake stopper? i was talking about the little fixing to hold the clutch cylinder in place. and not sure about the seal being stuck in the servo, im having some trouble bleeding all the air out of the system, could that be a cause?

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Post by Ted » Tue Apr 23, 2013 8:41 am

Bludge wrote:Thanks for the corrections, although what do you mean about the brake stopper? i was talking about the little fixing to hold the clutch cylinder in place. and not sure about the seal being stuck in the servo, im having some trouble bleeding all the air out of the system, could that be a cause?
my mistake on the brake stopper then,thought you meant one of these url=http://s1272.photobucket.com/user/tramr ... d.jpg.html]Image[/url]
there is no air in your servo its sucked out to create a vacuum by your inlet manifold, just bleed it again and you should eventually get it all out.
Last edited by Ted on Tue Apr 23, 2013 8:58 am, edited 1 time in total.

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Re: Brake master cylinder replacement guide 4th gen

Post by Bludge » Tue Apr 23, 2013 8:51 am

ah right, not seen one of those before!

so would having two of the seals cause problems? the brakes are working ok and i dont really want to have to take it all apart again! lol.

is the rest of the guide accurate? first time i have tried to write a guide.

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Post by Ted » Tue Apr 23, 2013 9:02 am

2 seals, only rubber may squash down tight.just check the cylinder is bolted tight to the servo and there is no gap.

yes buddy im sure you have covered it all.

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Post by 4th Gen Doug » Tue Apr 23, 2013 9:32 am

Bludge wrote:
One thing to check for as i didnt notice it until i got a second master cylinder from ebay, is on the piston is a black ring that you can slide off, the BMC i removed from the car didnt have one and neither did the one i got from the scrap yard, im wondering if the absence of that part was what was causing my loss of pressure. circled here in green.

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First of all - Brilliant! Nice one Bludge - I was going to do this as well, but couldn't, and still cant get the damn brakes working! (see this thread)

Secondly - I notice that black ring - I didn't have one of these on the one I removed or on the new one I replaced it with. I'll check in the servo over the week-end, but I'm pretty sure I would have noticed that!
Anyone know where I can get one of these from (the washer, not the MC!)
Cheers
Doug

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Post by rob quilter » Tue Apr 23, 2013 11:28 am

Nice write up

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Post by Bludge » Tue Apr 23, 2013 4:30 pm

Thanks guys, glad i could give a little something back to a community that has been massively helpful in helping me fix up my lude!

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