Rear master cylinder rebuild kit

[Rich205]

Morning all,

Does anyone know where I might be able to buy a rebuild/repair kit, with new seals etc. for the rear brake master cylinder?

I've searched eBay, Wemoto, M&P and other regular parts suppliers along with hours of googling, to no avail.

Is there a specialist parts supplier for the CBF 1000?

Bike is an 07 ABS model.

Any help on this one would be great, thanks.

[Art]

Could not believe a rear cylinder repair kit was not stocked by Wemoto but surprise, surprise they don't list one
May be worth a phone call (01273 597072) if you're up for some old school IRL conversation 

An ebay search for 'cbf 1000 rear master cylinder repair kit' found these and this rear master cylinder repair kit for Honda CBF 1000 A7 2007

[Rich205]

Thanks, yes they might be worth a call just in case.

I did find those you link to on eBay. But I was under the impression, from the service manual, that on the ABS model the piston and the pushrod are integrated, and had assumed that these on eBay were for non-ABS.

I'm not that familiar with these bikes though and have not yet disassembled the master cylinder to check. Wanted the parts before I do so.

Am I right in thinking that the CBF1000 A7 is an ABS model from 2007?

They're not expensive though so might be worth ordering one in any case.

[Art]

Well spotted you may be right. I assumed the listing was for an ABS model because it was listed for CBF 1000 A7, the A should denote its for an ABS model.

This one listed by the same supplier (A W Motorcycles) appears to be for ABS model, it doesn't say as such but is listed as CBF 1000 A, as above the A should denote that its an ABS model, other than that the listing doesn't specifically mention ABS. A W Motorcycles of Doncaster may be worth a call (01302 338600) to clarify.

A W Motorcycles appear to list the same part and specify it for "CBF 1000 A7 (ABS)" and others at £24.95 its £5.00 more than their ebay listing link here

edit: Just realised A W Motorcycles of Doncaster is like 20 miles from Sheffield, happy days

[Rich205]

Ah yes, didn't notice they were local to me... that's handy!

Will give them a call when they're open tomorrow and ask them to measure the diameter of it. Should be easy to tell them apart; 17.5mm or 14mm for ABS or non-ABS respectively.

Also stripped a master cylinder today and the piston and pushrod are indeed joined with a tiny circlip. Perhaps this one is sold as piston only...Either way if the seals are the correct diameter it should do the job.

Cheers

[Rick]

Just wondering how many miles your 07 bike has done when the rear master cylinder failed ? Was it just a slight fluid weep from the failing seal ?

[Rich205]

Hi Rick

The bike has around 35000 miles on it.

However I should clarify that the master cylinder has not failed.

I have been trying to fix a fault with the rear brake whereby it sticks on and drags after application. This only happens perhaps once in a ride though and is impossible to replicate in the workshop. The brake can be unstuck by flicking the lever up with your toe, however it is course not ideal!

I was certain that the fault was not mechanical, in the linkage, and have stripped cleaned and regreased the pedal linkage many times, including radiusing the sharp edges on the clevis to eliminate this as a problem.

Therefore, I figured that the issue could be hydraulic, and it just felt as though the master cylinder may be sticking internally as it released with a definate click which just from the feel I assumed to be the master cylinder.

I decided to rebuild the calliper first as previously when changing brake pads the pistons had been difficult to push in. It was extremely difficult to remove the corroded pistons, and it became clear that this was the likely cause of the problem. Calliper was rebuilt with new seals and pistons and the full system front and back was bled and fluid changed. At this stage I did not touch the master cylinder as I prefur to change just one thing at a time when diagnosing faults.

On riding the bike, this appears to have totally fixed the problem of the sticking rear brake. The brake also has so much more feel now and I can modulate it much better (unsurprisingly considering the state of it on dissassembly). As it stands I don't think I need to do any work on the master cylinder as it seems the problem lay with the rear calliper all along.

Thanks all for the help on this one, and hope this is useful to anyone with this issue.

[Rick]

Thanks for your detailed reply Rich, good news you have sorted the problem. My question was to try and establish if there is an average mileage for the life of the rear master cylinder. Great that yours is still going without problem. cheers, Rick

[Art]

It always helps to hear the whole story. With the symptom of rear brake drag the first thing to check is the ring of grime that builds up around the caliper pistons caused by road fling. Normally this can be sorted in situ by washing with soapy water, agitating with a tooth brush and a final spray down with brake cleaner, its half an hour and £5 well spent. Prevention is better than cure you should be checking the caliper pistons for any build up of grime as part of the 'every 4,000 mile service schedule', if you can't see the shining ring of the caliper piston behind the brake pad backing they need cleaning. Whether they appear to need it or not also give the caliper pistons an in situ clean as part of the annual service or whenever the pads are removed for inspection or replacement. Best plan now would be to give the front caliper pistons an in situ clean although they don't get as dirty as the rears they will benefit from regular cleaning.

What is the service life of a master cylinder? Under normal working conditions a master cylinder will not fail. I've only ever known of a few master cylinder failures and they've been due to two things. 1) Corrosion because they've been left displaced or unused for many many years. 2) Corrosion and wear caused by contaminated brake fluid. Prevention is again better than cure inspect the brake fluid by bleeding a little off at the caliper as part of the annual service, replacing the brake fluid every two to five years according to condition, moisture content etc.

[Rich205]

Thanks, that's good advice. I'll definately be making this type of cleaning and inspection part of a regular maintenance schedule.

Rick, if you're ordering a master cylinder seal kit, it may be worth noting my comments earlier about the size difference between ABS and non-ABS. A few suppliers I tried had listed these parts incorrectly. A W Motorcycles in Doncaster though were very helpful and able to supply the right parts once we both understood this. Worth trying them if you need a seal kit.

Cheers, Rich