bleeding brakes

Post by **grumpygrandad** » Thu Oct 30, 2008 6:40 pm

well had the drums off today clean check for leaks and put back so didnt need to blead thankfully,,,grandad

Post by **Kevin** » Fri Oct 31, 2008 11:34 am

I dare you to try a crocodile clip!

Ouch think I will stick with chocolate

Post by **bmcecosse** » Fri Oct 31, 2008 1:23 pm

Grumpy - bleeding brakes isn't about what you see inside the drums - it's necessary when you have a soggy pedal! Also a 'good idea' to bleed some new fluid through the system at each nipple once a year - the old fluid absorbs moisture and that's what starts the rot inside the cylinders.

Post by **rayofleamington** » Fri Oct 31, 2008 1:47 pm

Thinking about it there is no reason why it wouldn't work. As long as you (like BMC says) have a bit of juice in the jar and keep the cap off the master cylinder and keep it topped up. Gravity does the rest, a push of the pedal will start the syphon. Looking forward to trying it.

I'm yet to hear from anyone who's managed to bleed air out this way apart from BME - the minor brake reservoir is so low it gives insufficient pressure to do gravity bleeding - the flow will be FAR too small to push air bubbles past a high point in the pipe.
I'm not saying that it doesn't work - just that I really don't expect it to.

Gravity bleeding should work on cars that have a bulkhead mounted reservoir and a poor return valve in the master cylinder. Therefore with a Minor with disk conversion (including bulkhead reservoir and removed NRV) it's a distinct possibility.

Post by **jaekl** » Fri Oct 31, 2008 5:11 pm

It doesn't take much elavation change to run a syphon. Remember is the difference in height between the high and low open fluid level that pushes the syphon. A jar on the ground will be at least a foot below the master cyllinder, even more if you are on jack stands. The trick of course is to get fluid up and over the high point in the line. Depending on where you opened the system, you may need to push the pedal some. So it will work terrrific for a fluid flush but will not passively work on an empty system. The hoses are the highest point so if you work on something downhill from there it will work great. If you replace the hoses, a pump with an open nipple should work great.

Post by **bmcecosse** » Fri Oct 31, 2008 6:09 pm

I think what DOES make it work on a Minor is that residual pressure valve - there is ~ 5 psi in the sytem and when that bleed valve is opened there is a spurt of fluid followed by any air - and then it just keeps running if need be! But I agree - it works well on cars with high mounted reservoirs and no 'residual pressure' too!

Post by **grumpygrandad** » Fri Oct 31, 2008 8:28 pm

bmcecosse wrote:Grumpy - bleeding brakes isn't about what you see inside the drums - it's necessary when you have a soggy pedal! Also a 'good idea' to bleed some new fluid through the system at each nipple once a year - the old fluid absorbs moisture and that's what starts the rot inside the cylinders.

i only ask if there is away to bleed brakes IF I NEEDED TO DIDNT MENTION soggy pedal,,,grandad

Post by **MGFmad** » Sun Nov 02, 2008 11:42 pm

I didn't have any luck with the gravity bleeding - on re-reading the instructions, is it important to push the pedal down slowly?

Post by **bmcecosse** » Sun Nov 02, 2008 11:47 pm

Not too slowly! Usually the pent-up pressure in the system makes it work. Maybe the gravity in Fife is a bit less than in darkest Lanarkshire! I can see i'm going to get lots of folks saying 'it doesn't work' - I can only say - it works for me !

Post by **MGFmad** » Mon Nov 03, 2008 8:16 pm

I will try again as I like the theory. Perhaps I am having bother as its an entire new braking system, possibly not any pressure in the system until I get rid of the majority of air.

Post by **rayofleamington** » Mon Nov 03, 2008 10:08 pm

I didn't have any luck with the gravity bleeding

Sorry you've wasted your time - this method is well known not to work on Minors. I'm not saying nobody has had it work, just that it's very unlikely and the only person I've come across in 18 years in Minor circles who seems to have had success is BME. Most of the pipework is level with the reservoir so there is NO gravity pressure in a new system. The flexis go much higher than the reservoir and fluid won't run up hill without a good push.

Perhaps I am having bother as its an entire new braking system

That will need a fair bit of pumping with the brake pedal. Rear cylinders may take a bit of priming if they have the (common) ring seal design not the original (flat dish) design seal.

To bleed a complete new system it can be worth to prime the circuit in parts, by opening the T-pieces until you get fluid pumped through.

Post by **bmcecosse** » Tue Nov 04, 2008 8:41 pm

Worked ok for me earlier this year when I changed a rear cylinder - and swapped one set of W front brakes for a new set with Minor cylinders. They all bled out easily - by gravity. A syphon is set up - so the fluid and air (within reason) WILL flow up and over 'high set' flexi pipes. I suppose if the master cylinder is allowed to run completely empty it could be difficult to get the syphon started again. I always seal the master cylinder cap with a plastic bag when doing any work on the system - thus preventing all the fluid running out!
It's hardly a 'waste of time' to try gravity bleeding - if it doesn't work then just immediately set to with the pedal, and at least you will have enjoyed a short break and a nice cup of coffee !

Post by **MGFmad** » Tue Nov 04, 2008 11:08 pm

I have not tried the gravity bleeding again but will do soon. Instead I drilled out the cap of my old master cylinder to accept my pressure bleeder and did it this way, along with pumping the pedal in between bleeding to get all the air out of the rear cylinders.
Pedal feels quite good, I will let the system settle and give it another go manually with a reluctant helper and a hose/jar.