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syspig

4rt rear brake bleeding "trick"

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I wasn't looking forward to bleeding the rear brake on my 4rt after reading some of the posts here. Especially since an empty brake line was going back on with plenty of air to disperse.

Came up with a trick I've not seen before that worked great, not only for ensuring all air gets out - but it's easy to do single handed and addresses the difficulty in filling the reservoir.

Remove rear fender and muffler. Remove reservoir and two bolts holding the master cylinder. Pass the master cylinder through to the other side around the shock (yes, there's room - barely) then suspend it up high with the rear fender bolt in the right rear fender hole. This keeps the master cylinder well above the rest of the system and makes it easy to fill as you bleed.

I started using the pull method (large syringe/tube to bleeder valve), draining/refilling the reservoir 4-5 times. I then switched to the push method, compressing the piston in the master cylinder while opening/closing the bleeder - and since it's removed from it's normal location, a small screwdriver was used which works far better than the short foot pedal plunger.

Picture/thousand words...

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With that setup if you had a reverse bleed setup it might have been a one shot setup... Ether way, I will have to remember this if I ever need to do a complete bleed on ether of my 4RT's.  Thanks!

Edited by jonnyc21

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I've never had luck with reverse bleeding, but it's likely just tools/technique. In theory, it does sound like it would work really well. There are certainly plenty of people who are successful with it.

For me, I just can't get an adequate seal on the bleeder with the tube/syringe. I've tried zip ties and safety wire and can't get either to grip adequately. So, invariably when I start to apply pressure in sending the fluid up - it shoots out the side and I spew brake fluid on the caliper/disc/shoes.

The lack of tight seal isn't a huge deal when pulling the fluid with the syringe from the bleeder, but that's why I finish the job with the master cylinder plunger. I get "fake" air bubbles when pulling with the syringe due to the bad seal, but finishing up with the plunger shows whether any air is actually still in the line.

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 Having the reservoir at the high point does nothing. You need the caliper at the high point. Actually you can remove this whole system and hang it by the the caliper to make it easier. The air bleeding from the caliper is the main result desired.

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23 minutes ago, lineaway said:

 Having the reservoir at the high point does nothing. You need the caliper at the high point. Actually you can remove this whole system and hang it by the the caliper to make it easier. The air bleeding from the caliper is the main result desired.

To my eye, it appears the reservoir is lower than the top banjo bolt on the master cylinder. Many folks, here and elsewhere, have suggested that elbow at the master cylinder can trap air when bleeding towards the caliper. That was my primary reason for raising the reservoir - to eliminate that elbow as a high point, allowing fluid going through it to more easily push the air down.

Regardless, while I'll not claim to be a master mechanic - the setup I described worked quickly and perfectly when there was tons of air in the line. It resulted in a rock hard pedal in minutes.

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3 hours ago, syspig said:

I've never had luck with reverse bleeding, but it's likely just tools/technique. In theory, it does sound like it would work really well. There are certainly plenty of people who are successful with it.

For me, I just can't get an adequate seal on the bleeder with the tube/syringe. I've tried zip ties and safety wire and can't get either to grip adequately. So, invariably when I start to apply pressure in sending the fluid up - it shoots out the side and I spew brake fluid on the caliper/disc/shoes.

The lack of tight seal isn't a huge deal when pulling the fluid with the syringe from the bleeder, but that's why I finish the job with the master cylinder plunger. I get "fake" air bubbles when pulling with the syringe due to the bad seal, but finishing up with the plunger shows whether any air is actually still in the line.

It can be tricky for sure.  Tell I got a kit I was not able to get a good seal and bleed it correctly in reverse.

Even when I revers bleed a system I double check everything with a forward bleed and have even had to use a suction setup on an old BMW I used to have that I just couldn't get completely good without doing so. 

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How do they do this at the factory? My Montesa is all cable but I have a Triumph Speed triple and that has all the same problems you are having here. I fixed the SP3 the same way as you describe here. Got to be an easier way.

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5 hours ago, bigshineybike said:

How do they do this at the factory? My Montesa is all cable but I have a Triumph Speed triple and that has all the same problems you are having here. I fixed the SP3 the same way as you describe here. Got to be an easier way.

Front or back on the Triumph?

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I'm having a nightmare trying to bleed my 2014 Repsol 4rt. I have no pedal pressure whatsoever, have tried "little bleeder" tool but was unable to get any pressure from the pedal. I do get a reaction in the tube when pressing pedal but very limited. No visible leeks and I was able to stop the wheel with the pedal on stand with my hand before attempting the bleed. Pads look okay and did work. Read all of the above and more! Did undo the banjo at the caliper and heard and saw air bubbles, mistake I think as it's worse since doing that. Tried to reverse bleed but only managed to cover workshop floor, bad seal. Could it just be an air lock? Others say syringe and draw it through, what size of syringe? Tips would be most welcome, loosing the will to carry on!

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 Best way is to take it completely off the bike. People are just too lazy to do it right. You can hang it by the caliper and use a phillips to pump the m/c. This works the easiest because the trapped air can go straight up. Otherwise the air stays trapped at the banjo bolt. You can also take a 3 foot clear hose up and over the rear fender. You will still have to crack the bolt at the m/c.

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Thanks lineaway. The lack of success is taking me to that eventuallity. On looking at the rear caliper pistons, the movement is hardly noticable. Should the pistons come further out of the caliper than this? Could they be stuck?Pads are between 3&4mm.  Bled again and at m/c. Thanks for any suggestions you may have.

image.jpg

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I would expect them to move a lot more than that... You also look like you have a great deal of fluid inside...  Might have a bad seal?  

Edited by jonnyc21

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The fluid is WD40 residue, I sprayed the caliper in the hope of freeing the pistons. It was dry before doing so. Like you, I think they should move out more than this. Any tips on freeing them?

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