Front master cylinder 06 Classic

[Gary]

High Guy's
Have just rebuilt my master cylinder but can't get them bleed. Have tried the old fashioned bleeding with the help of her indoors and also vacuum bleeding but nothing. I took the calipers off and fired the air line in to see if the pistons were siezed. A couple were sticky but all ok and still nothing. I noticed in the the master cylinder that when you press the brake lever and release the piston never comes back further than the small hole, you never it see come back past the larger hole!! is this correct or should it come back far enough to push fluid down the brake lines? have I screwed up rebuilding the master cylinder?

Cheers

Gary

 

[Boog]

My 2014 R3T needed the master cylinder and right caliper rebuilt at 72K miles. The dealer had a hard time bleeding the front brakes as well. At best they only got them to the point that I could pump them and they would work. My fix was to pump them tight at the lever and tie the lever closed over night. I did this two nights and got my full brake power back.

 

[barbagris]

Did you FLUSH the brake hose? - If it's be a while since it was cleaned out - Dot4 will allow verdigris to develop where there are unions - especially the T splitter on teh lower yoke. If there is crud in there it will always trap air.

Are you bleeding upright or on side stand?. Due to the hose and union angles. SIDE STAND - FULL LEFT LOCK. And Bobby's lever ties.
There is an old mechanics pumping trick, but it is hard to do on the R3 without jetting Dot4 fluid everywhere.

 

[Gary]

Hi,

Thanks for the replies. There has been so much fluid thru the system now I would guess there is no where for air to hide lol! I have tried back bleeding as well. I stripped it back down and put back the orginal piston and now have some brakes but they are very poor. Yes I am bleeding on the side stand but on right lock not left??? I have tried the cable tie lever trick over night but will try again that I now have some sort of brakes.

 

[Nat67]

Hi,

Thanks for the replies. There has been so much fluid thru the system now I would guess there is no where for air to hide lol! I have tried back bleeding as well. I stripped it back down and put back the orginal piston and now have some brakes but they are very poor. Yes I am bleeding on the side stand but on right lock not left??? I have tried the cable tie lever trick over night but will try again that I now have some sort of brakes.

The nature of the master cylinder is that it is excellent at storing unwanted air bubbles . Fill the reservoir and pull the fluid thru using the vacuum pump alternating between the calipers . When you seem to be pulling no more air thru , lock off the nipples , lay bin liners and rags around any exposed parts , pump the brake lever until you can feel as much resistance as possible , then whilst holding the lever in , crack the banjo bolt on the cylinder until fluid starts weeping . Then retighten the banjo and clean up any spilt fluid . Top up the reservoir and then give the calipers a final bleed in the traditional manner starting with the caliper furthest from the master cylinder . Only crack the bleed nipples enough to allow a slow flow under pressure . If air continues to bubble through the line non stop , there is likely to be a compromised seal somewhere allowing air in . It's hard not to build the master cylinder right , only mistake that could possibly be is a failure to clean the parts surgically before reassembly ?

 

[barbagris]

Hi,

Thanks for the replies. There has been so much fluid thru the system now I would guess there is no where for air to hide lol! I have tried back bleeding as well. I stripped it back down and put back the orginal piston and now have some brakes but they are very poor. Yes I am bleeding on the side stand but on right lock not left??? I have tried the cable tie lever trick over night but will try again that I now have some sort of brakes.

Left lock arranges all the holes so that air cannot stop going up'ards until they're in teh reservoir.

Ties the Mrs' pacifier to the hose and turn it on - that'll shake any tiny bubbles loose and they'll go up. So I'm told!.

 

[Gary]

Yes was convinced I did something silly when rebuilding hence I stripped it back but all looked fine. When I rebuilt it took a moment or so to get the master to pressure up with thumb over the outlet and get fluid to come out, obviously air locked a bit

 

[cootertwo]

I had to start with bleeding the master cylinder first, then go to the calipers.