Front Master Cylinder question

mn5587

RMS Regular
Messages
702
Location
Near Coleraine
Drives
CLK 55 AMG
Hi All,

I am upgrading the front end of my bike (on a budget, all eBay stuff).

I have come to the last bit, the brakes.

After getting everything bled, the lever caused the brakes to work (all the pistons moved); however I could pull the lever all the way in and it didn't seem to get any harder.

I stripped the MC, both seals in good condition; I couldn't see any issues. I put it all back together and gave it a test on the bench (covering the brake line hole with my finger and trying to create a bit of pressure). This bench test resulted in no pressure build up and the fluid squirting back up into the resevoir.

Has anybody experienced this before? Will an MC rebuild kit do the job?

The upgraded front end is all from a 2008 GSXR750.
 

Chris666

RMS Regular
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7,432
Location
Larne
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Often
Would be worth doing imo, not overly expensive and on a K8 pre ABS bike it's maybe due a refresh
 

Apis

RMS Regular
Messages
4,074
Location
NW
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various
What exactly did you replace, was it a whole new/secondhand mastercylinder? Just saying in case the diameter of the replacement MS is bigger than the old one then you will have too much movement at the lever. ie you don't get enough fluid into the callipers before the lever hits the bar.
Or same thing if you got bigger pistoned callipers and didn't change MS to suit.
 

mn5587

RMS Regular
OP
mn5587
Messages
702
Location
Near Coleraine
Drives
CLK 55 AMG
What exactly did you replace, was it a whole new/secondhand mastercylinder? Just saying in case the diameter of the replacement MS is bigger than the old one then you will have too much movement at the lever. ie you don't get enough fluid into the callipers before the lever hits the bar.
Or same thing if you got bigger pistoned callipers and didn't change MS to suit.

I had kept the previous MC with the new calipers but it was very soft. After some googling, I discovered the calipers were matched with an 18mm MC (I was originally using a 17mm). I then bought the matching MC for the calipers.
 

Apis

RMS Regular
Messages
4,074
Location
NW
Drives
various
What exactly did you replace, was it a whole new/secondhand mastercylinder? Just saying in case the diameter of the replacement MS is bigger than the old one then you will have too much movement at the lever. ie you don't get enough fluid into the callipers before the lever hits the bar.
Or same thing if you got bigger pistoned callipers and didn't change MS to suit.
I mean MC not MS, lol. Senior moment.
 

hannakournikova

RMS Regular
Messages
12,217
@mn5587 check you haven't flipped any seals. Rebuild kits are about £40 iirc but you may find a cheaper complete unit?
 

mn5587

RMS Regular
OP
mn5587
Messages
702
Location
Near Coleraine
Drives
CLK 55 AMG
@mn5587 check you haven't flipped any seals. Rebuild kits are about £40 iirc but you may find a cheaper complete unit?

It did occur to me last night to check the seals weren't in backwards but unfortunately they were fine!
I went for a rebuild kit, hopefully that solves it; if it doesn't I'm really perplexed as the MC has no other moving parts!

If the rebuild kit sorts the MC but not the poor lever action then I'll be back onto eBay to get a 19mm MC before I lose all patience lol.

I'll report back with the results
 
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