General notes on bleeding hydraulic systems in Spitfires.
Here is my experience with overhauling my brake system. It may not totally
apply completely to the clutch but there are always questions about brakes,
bleeding and stuff. I'll try to keep this as concise as possible. Keep in
mind I am thinking of a single circuit system, although it should work for a
double.
1. New seals on Callipers and M/C, new disks and pads.
2. Bench bleed M/C.
3. Bleed brakes, nice firm pedal.
Then I take a look at the rear, and discover that I need new cylinders.
4. Replace cylinders, snap brake line.
5. Drain and replace brake lines with copper ones, the whole system is now
dry (inc. MC) apart from fluid still left in callipers.
6. Clean up the running tracks for RW cylinders and use red rubber grease on
them.
7. Sort out hand brake linkage and adjust rear drums. (Note: I did have to
tidy up the new rear brake shoes the sides of which catch on the backing
plate and the drum)
8. I had heard about a trick that means you don't have to bench bleed a MC
no matter what angle it is at, so I tried that.
9. Bled the air out of the system, and also did the trick on the callipers
and the RW cylinders.
10. In the end I had a perfectly working brake system, the car brakes
evenly very hard to lock a wheel, and it stops very fast.
I use Gunsons Easy Bleed, and I have one person bleeding down to a fine art.
Easy Bleed is a clear plastic pipe, with a rubber pipe and clip on one end
to go over the bleed nipple. On the other is a one way pressure activated
valve, which lets fluid out but no air in. Loosen off the nipple with brake
spanner, put the easy bleed on, open up the nipple with normal spanner 1/2
turn do the bleeding thing and then lightly tighten the nipple with normal
spanner, remove easy bleed and finish with a proper brake spanner.
Now for the trick.
Why do you need to bench bleed or use the trick?
The MC is angled and designed such that the fluid exit point is lower than
some parts of the cylinder. Thus are gets trapped in there. This applies
to the rear wheel cylinders as well. Normal bleeding won't that air out so
you have to resort to different methods.
Bench bleeding you angle the MC such that the exit part is higher than the
rest of the cylinder so you get all the air out. This is messy and a pain
to do, it also doesn't work on the rear.
What is the trick?
Open the nipple so there is nearly no resistance to the pedal, then stamp
quickly and violently a couple of times in fast succession. This gets the
air out of the MC. Then bleed as normal, then go round each nipple in the
system and stamp on the pedal again.
How does it work.
Normally when you bleed slowly the fluid gets up to the level of the exit
and goes out. When you are violent it all becomes turbulent and the surface
brakes up and the air goes down into the fluid to be carried away through
the exit. A couple of stamps on the pedal and you have got rid of all the
air. It's a bit like filling a glass with water, a slow stream of water
will fill it completely to the brim, but try filling a glass with a jet of
water, it can't be done unless you get the jet down into the glass.
Other hint's on bleeding.
Buy a 1L container to fill the system, you will need it.
If you bleed the system slowly or pause the air has time to flow back up the
brake lines to the highest point. Aim to completely bleed one line in one
go don't stop, get someone else to top up the MC.
The quicker you get the fluid through the less fluid you waste in the end.
Go round the system about three times to be sure to get all the air out.
Well I say it's a trick but wasn't me who taught of it it's been used for
years I just heard of it and sort of got carried away describing it to you.
It's not a trick as well it's sort of common sense.
Sorry it's a bit long and all that, but I am quite pleased with this I may
put it on my web page as soon as I work out crosswinds ftp thing.
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