I have an Edwards lab vac pump and was thinking that I could use it to bleed my disc brakes. Just wondering if anyone has had any success with this method and if so I am trying to work out the exact steps to doing it.

So far I have concluded.

1. Connect the vac pump line to the bleed nipple on the lever, with a catch pot in between pump and lever.
2. Connect the hose to the caliper and into the glass jar of brake fluid.
3. Switch on the pump and draw the fluid up through.
4. Pinch off the tube on the caliper which will create a full vac in the brake system.

It’s after step 4 that I am unsure what to do?

Maybe this is all in vane as it is not possible to seal the system back up with allowing air back in just by design of the nipples and the fact you have to disconnect the hose from the caliper/lever to put the bleed nipples back in.

Ta

My initial though that the volume of fluid in the system will be way too small and you’ll suck it all out almost instantly.

My initial though that the volume of fluid in the system will be way too small and you’ll suck it all out almost instantly.

I’d have to agree with that and was thinking that I could get around it by controlling the air flow at the vac pump.

Too much, even for car brakes I reckon. Even the small robinair VPs I have used can pull 700″HG in quick order on systems much bigger (50x and more) than a hydraulic brake.
Interested in trying a mityvac though.

On reflection and based on the feedback here I think I’ll pass with the pump. Was just looking on ebay and you can buy a mityvac style pump for £12

No matter how many times I try the syringe method the lever always has a ‘spongey’ feel to it. I suspect that although you reduce air from the fluid by creating a -ve pressure the actual pressure level reduction isn’t that great.

If I put a pot of mineral oil in the vaccuum chamber and reduce it to 29″ Hg the stuff will most likely boil, showing just how much air is contained within the fluid.

I’ve found a fix for many customers and mates “spongy brakes” that always need bled is simply to centre them correctly over the disk….and I don’t mean squeeze the lever and tighten the bolts !

is simply to centre them correctly over the disk

By eye or using a special centering tool?

That does also raise the question regarding how many new frame / forks need to have the mounts faced so as to get the vertical alignment between the pad and the rotor aligned correctly.

I think you could get the OP’s idea to work, the flow of fluid would be limited by the smallest aperture in the system, so if you only just cracked the bleeder nipple on the caliper, you could limit it to a very low flow.

However, what’s the point. It’s just another way of feeding fluid into the system through the caliper. If your brakes are still spongy after bleeding, then you’re either not getting all the air out of the system or something else is flexing.

If you start by drawing some fluid out of the caliper and into the syringe, you can check that there are no air bubbles in the caliper. Then force all the fluid in the syringe through to the lever, use a container to catch the extra fluid that will come out of the lever. This will ensure that you have flushed all the old fluid out of the system along with any air bubbles in the hose.

Why?

Brakes can be bled perfectly without using a pump. I’m not convinced that this would remedy the most common fault – that of leaving air trapped in the system.

need to be careful as too much vacuum can knacker the seals. They are designed to seal under pressure not vacuum. A simple vacuum pot with a bleed type arrangement should be fine though if you take it easy. Planning on setting something up myself for the cars and the bikes.

In the end I degassed the fluid in the vac pot and then used the syringe method but this time with the lever and caliper off the bike and clamped so upper nipple was highest point and lower caliper nipple was the at the lowest.

Pushed through the fluid and did see a few small bubbles. Used the negative pressure on the syringes to remove air from caliper and lever.

End result is a less spongy feel, but if I pull really hard the lever still flexes. I cannot deduce whether this is air still in the fluid being compressed or just the lever assembly.

As I have no other bike to hand I cannot do a meaningful comparison.

Try reading trail rats post again, that’s probably your answer. Hydraulics really aren’t that’s hard and I assume you’re not testing them when they are boiling on the trail so that means you configured them wrong or you have faulty brakes. Given the description, I’m going with you setting them up wrong, I recently had this issue and straightening the calliper fixed it completely after trying bleeding, pads, rotors. Lucky for me I had spares of all of those so it wasn’t an expensive lesson.
Align the calliper to the disk, not the frame and you’ll be fine. You don’t need to face the mounts, that’s what the dome washers are for.