The two bleeders Options

[emerygt350]

I just popped on my newly remastered rear brake calipers from PMB and was wondering if there was a point to the lower bleeder? I only ever bothered with the top bleeder before but now that it's bone dry I was wondering if that might be why the second bleeder exists? I will be bleeding the brakes tomorrow morning.

[technicalninja]

Dual bleed nipples of the 914 rear have nothing to do with handedness, the parking brake lever defines that.
However, I have found that when doing an annual fluid bleed it is often better to open both bleed nipples to fully drain the calipers before refilling. Forty years ago I had to start rebuilding the calipers to keep them fully functional; there was no PMB to send calipers to and there were no (!) parts available in any case. Taking the pistons out was a real eye opener since the outer pistons were always filled with more crap than the inners. The reason for this is simple. The fluid inlet is on the inner side of the caliper as are the bleed nipples. When you do a quick flush and bleed the fluid enters the inlet and heads straight for the open nipple. This does not flush the fluid inside the pistons, particularly the 914 rears with the adjuster mechanism inside, and it certainly does not do much of a job in circulating to the outer half of the caliper. The result is that old fluid is retained inside the pistons and most of the outer caliper half with a quick flush and bleed. Hence my method was to drain the calipers first, then do a complete refill and bleed. Every few years I would disassemble the calipers to thoroughly clean inside to keep them operating efficiently.

I do hydraulic system flushing all the time...
On almost all cars the entrance into the caliper and the bleeder is on the upper side of the caliper and a flush does not get ANY of the old fluid in the caliper. The fluid in the caliper is what goes bad first!
What I do, on normal appliance cars, is to apply my vacuum bleeder to the bleeder bore and push the piston back into the caliper clearing most of the bad fluid out.
After I get one collapsed, I'll feather the brake pedal, going no farther than normal pedal travel, and push the piston/pistons back out.
Do this twice (time consuming) and you get 95% of the old fluid out of the caliper.
The hardest ones to do this with are fixed calipers with opposing pistons like what we have on Porsches. Datsun Zs have the same set up but they don't have the two bleeders.
Having two bleeders makes this far easier to do.

Thanks to Davep for showing me a trick that I didn't even think about.
I've been doing this crap a long time and seldom do I have a "Eureka" moment any more.
Davep gets a (IMG:style_emoticons/default/first.gif) for that little tidbit

Now, I'll return the favor...

One thing I do after I'm finished with a flush job is to blow the bleeders out with a needle tipped blow gun. Brake fluid is hydroscopic and that little bit of fluid that get left in the bleeder draws moisture into the bleeder and IMO is the reason bleeders rust into their bores.
Don't breathe in the cloud of brake fluid that this will produce. Brake fluid stays in the human body forever and inhaling it is bad.
I'll put a tiny little blob of silicone grease in the rubber cap (most cars have this) to seal the bleeder from the outside atmosphere after I blow the bleeders out.