no pressure In rear brakes

[Red Herring]

Just goes to show you're never to old to learn. I've just read up on the various Mityvac kits you can get and they are certainly a useful tool to have, and if I was running some kind of commercial operation I'd almost certainly buy one. Unfortunately at upwards of £80 for the suck/blow models they're quite an investment and given I probably only drain, flush and refill brake systems half a dozen times a year probably not worth it for me so I'm going to stick with my £2 syringe as it seems to do exactly the same thing, although admittedly it's a bit more of a fiddle.

[SV650rules]

When I bought my Mityvac suck and blow years ago IIRC it was around £40 to £50 - since then I have used it for brakes on quite a few cars and bikes, it really is a nice bit of kit - proper mechanics also use it for finding leaks and various other stuff. I use a Sealey TP696 vacuum extractor for our cars oil changes via dipstick hole ( I measure what comes out and it is 99% of what should be in there ) and also for quick fork fluid changes, it got over 90% of the fork oil out of my AL7 without taking anything off except getting it up on ABBA stand and removing fork top caps, also use the Sealey for draining stuff when doing plumbing work, getting oil of of lawnmower etc. https://www.ebay.co.uk/p/1150857996

[SV650rules]

Originally Posted by embee

I have a suck/blow Mityvac too, a very useful tool. They also do suck only versions, quite a lot cheaper. I empty the reservoir of old fluid first using it, refill with fresh stuff, then bleed at the caliper. The big advantage is that you can get a continuous flow to draw the fluid through the system to hopefully purge all the air.
As said, air does get in past the nipple threads while bleeding, but in reality this doesn't matter because while you are pumping it the low pressure in the bleed line is always drawing fluid out of the brake system so no air can get back in while it is still flowing. Make sure you tighten up the nipple while the flow is still coming out.
I've never had any issues getting a firm brake using it. Just make absolutely sure you don't empty the reservoir while using it as this will take air directly into the system and you'll have to start again.
It makes the process so easy it means you tend to do it more often, keeping the fluid fresh.
There are alternative very similar items to the Mityvac, I don't have any experience of them so can't comment, but it's not rocket science so they're probably perfectly good. Mityvacs are used in industry and are good quality tools, well worth the money IMHO.
The one niggle is the small plastic vac bottles which come with them are very light and always fall over with the vac tubes attached. I made a steel holder for it using a square plate (old scaffold tube foot) and a slotted tube welded to it, the slot lets you see how much fluid is in it so you don't overfill and pull fluid into the pump.

One thing I like about the Mityvac vacuum bottle is that it holds a bit less than the brake master cylinder reservoir on most cars ( when reservoir filled right to top of thread ) so I know when bleeding car or van brakes that when the Mityvac bottle is getting full it is time to tighten the bleed nipple, release the vaccum, empty the Mityvac bottle and top up the master cylinder reservoir again - saves you from sucking air into system, which you could easily do if vacuum bottle larger. I am not so refined as you and just wedge the Mityvac bottle between a couple of house bricks.

[aburamjan]

Originally Posted by NedSVS

You could try taking the caliper off and elevating it a little and rotate it slightly so any air bubbles will find their way to the bleed nipple. Just put something between the pads so you don't pump the piston out too far.

okay so I tried this, and after making a huge mess. it worked. however, by the time I had screwed the caliper back on and torqued it all down, it went back to the way it was before. am I right to suspect a leak somewhere? bare in mind it was 100% working and fine before I took it apart

[SV650rules]

Are the seals in master cylinder OK, if the fluid can get past master cylinder seals just goes straight back into reservoir and not the the actual brake cylinder, and no / or very little pressure can be achieved ( long shot because you said brakes were OK before bleeding ). How far back does the brake cylinder retract when pedal is released ? Try wiggling the pads when brakes are released, too much movement between caliper and disc is a bad sign. If something was assembled wrong and cylinder moving back then it will need more fluid from master cylinder to reach the disc and apply pressure, and pedal / master cylinder may bottom out before enough fluid supplied. Another reason, as Bibio said is if shims are wrongly assembled pads may jam and never reach disc.

[Red Herring]

Originally Posted by SV650rules

..... I use a Sealey TP696 vacuum extractor for our cars oil changes via dipstick hole ( I measure what comes out and it is 99% of what should be in there ) and also for quick fork fluid changes, it got over 90% of the fork oil out of my AL7 without taking anything off except getting it up on ABBA stand and removing fork top caps,..... https://www.ebay.co.uk/p/1150857996

Which is all very well as long as you are happy with just changing the fluid. Personally I like to dismantle things so I get all the sludge out that is sitting in the bottom clogging up the internals......

[Bibio]

Originally Posted by Dave20046

For clarification, that's rectal rubbing grease.

yes and all this talk of sucking and blowing is getting me excited


#4 in the parts below has to be orientated in the calliper housing properly. double check that it is.

[SV650rules]

Originally Posted by Red Herring

Which is all very well as long as you are happy with just changing the fluid. Personally I like to dismantle things so I get all the sludge out that is sitting in the bottom clogging up the internals......

Change fluid regularly with good quality stuff and should be no sludge there to suck out and clog up things, who would do an annual change ( or more regular ) when you have to take forks out etc ? So easy with Sealey vacuum extractor it can easily and quickly be done - about 2 hours including putting ABBA stand together and getting bike up in the air with front lift strap, removing fork caps, removing front lift strap, letting forks collapse and sucking fluid out and measuring carefully what came out of each leg, and then putting back in exactly what was sucked out of each leg, fit lift strap to unload forks and then put caps back on - no need to remove anything from bike. Leaving fluid in too long does the damage, ( just like brakes, where brake fluid absorbs moisture and causes corrosion in the system ) I find brakes so easy to do with Mityvac they get done every year..

[Red Herring]

Originally Posted by SV650rules

Change fluid regularly with good quality stuff and should be no sludge there to suck out and clog up things, who would do an annual change ( or more regular ) when you have to take forks out etc ? So easy with Sealey vacuum extractor it can easily and quickly be done - about 2 hours including putting ABBA stand together and getting bike up in the air with front lift strap, removing fork caps, removing front lift strap, letting forks collapse and sucking fluid out and measuring carefully what came out of each leg, and then putting back in exactly what was sucked out of each leg, fit lift strap to unload forks and then put caps back on - no need to remove anything from bike. Leaving fluid in too long does the damage, ( just like brakes, where brake fluid absorbs moisture and causes corrosion in the system ) I find brakes so easy to do with Mityvac they get done every year..

Like I said, if you're happy with that then I'm certainly not going to argue with you about it, to each their own. Different people have different ideas about how they like things being done and there is little merit in trying to decide which is "best" if in their individual experience they are both happy with the results they get. I just got into this discussion as I wanted to share a very simple technique that I've been using successfully for over thirty years with someone who I thought might have had use of it.

Out of interest when you replace the fluid in your brake system do you simply draw it through the system topping up the reservoir as you go, or do you remove the calipers and drain them before filling the whole system from scratch?

[SV650rules]

Originally Posted by Red Herring

Out of interest when you replace the fluid in your brake system do you simply draw it through the system topping up the reservoir as you go, or do you remove the calipers and drain them before filling the whole system from scratch?

Just drain reservoir, fill with fresh fluid and then bleed a decent amount of fluid from caliper bleed screw, done it that way on bikes and four wheelers for ever and never had a problem with brakes. My take on it is 'if it ain't broke or giving problems - don't mess with it', more harm is often done by taking seviceable things apart that don't need messing with. Only problems I have ever seen on brakes is when fluid has been left in way too long and caused corrosion inside the cylinders - brake fluid is hygroscopic and moisture is bad news inside brake system, regular fluid changes remove what small amount of moisture may have got into fluid.