FredR

JP,

No idea what you have on your example but on my reservoir there is a plastic strainer insert that as I can tell sits around the max liquid level, maybe slightly below it. The reservoir cap has a rubbery flexible insert that fills this volute and can thus expand or contract as the liquid level changes. My presumption [but not an established fact] is that this insert can compress if the brake fluid expands when hot and it can also in-breath when the level drops.

There is a small amount of air "trapped" between the fluid surface level and the insert that also gives a degree of compressability but this is probably of no consequence as the minuscule amount of moisture in this small volume of air will be absorbed but presumably not replenished because of the flexible diaphragm type barrier.

Whether a small amount of air can migrate across this "barrier" in more extreme circumstances I have no idea but I consider it a good idea to keep the reservoir topped to full as the pads wear [and the level drops to accommodate the piston travel needed to engage the pads on the disc]. Thus one has to be careful when opening the pads prior to removal to ensure the brake fluid does not exceed the breathing capacity. Recent experience suggests this is not a problem opening one set of pads at a time but if you did all of them at once on a well worn set of pads/discs the reservoir might overflow [I suspect].

This type of arrangement I have seen on all my vehicles with hydraulic brakes so I would expect yours to have these features unless a PO inadvertently lost the cap insert?

Rgds

Fred

jpitman2

Fred,
As you can see mine is an 83. Now I will have to go and check what I have in my m/cyl ! Yellow plastic screw on cap with a centre prong ~25mm long, 2-3mm diameter. Under this is a nylon filter insert in the reservoir throat . The fluid level is just above the level of the filter mesh. Thats it.
I understand what you speak of as an air isolator, but I have never seen such a thing in any of my cars up to 2009 models.

jp 83 Euro S AT 56k

FredR

Stan.

Confirms my suspicion that I had read different versions of "how to". Tried to reason out in my head why it should make a difference- I failed miserably!

You raise an interesting point about seal failure. This happened to my wife's old Mitsubishi Pajero [Montero or Shogun depending on where you are in the world]. A very reliable vehicle that she had for over 18 years but then one day the brakes failed- replaced the master and slaves but the damage was done in her head so she had to have a new one. My only regret is that I sold the old one- should have kept it for myself! No problem with the brakes after the repair. Sounds as though it would be a good idea to use one of the single handed techniques and avoid pumping the brakes- that or limit the pedal travel on each pump stroke assuming such is possible. JP raised an interesting suggestion about simply releasing the nipple and let gravity take care of things [over time] - never heard of that one before - the beauty of this list!

Regarding humidity we can get spells of high humidity but as long as the can is sealed and cannot breath then the fluid should not degrade and as I stated earlier the ATE can has a plastic soft seal but of course without analysis one has no idea whether this is holding other than the fact that there are no signs of fluid seepage. I will take a look on the local market to see what brake fluids are available and possibly use the blue as a pre-flush to see colour change and then a fresher fluid for security.

Regards

Fred

FredR

JP,

Took a look at the WSM to see what you might have- seems earlier models had a pokey looking plastic tank with Tupperware lid! Does not look like the later models at all. Also picked up that it seems dual circuit master cylinders were introduced around 84 so presumably a step change there.

As I now understand, the 84+ as well as the later models like mine, have dual circuit brakes wherein the front brakes are on one circuit and the rears on the other circuit. Thus if you lose one circuit the other still functions. Seems this feature has no bearing on the bleeding operations other than possibly the circuits are bleed in sequence.

Rgds

Fred

Martin's928

Got a Power Bleeder about 8 years ago when I put new master cylinders in and couldn't recommend it highly enough. Huge time and labour saver and works great every time. I like doing my brake fluid changes every 2-3 years now! I know, get a life….

Don't forget to bleed both sides of the callipers (inner and outer halves have their own bleed nipples): some idiot didn't realize this the first time he did it and spent a couple of weeks trying to figure out why the pedal was soft…...

FredR

Martin,

I have a "power bleeder"- married her 37 years ago and she is still bleeding the power out of me- bless her!

I attempted the bleeding this afternoon and despite managing to bleed too much of the original reservoir oil, I managed to get the job done with less than 1 litre of hydraulic fluid. That of course assumes I have none of the air I let into the system still in there- pedal feels reasonably firm.

Initially I tried to do the job with the Mityvac but quickly gave up with that one as I could not get it to work- probably because I initially used the wrong connector on the bleed nipple.

I defaulted to the two man method and for the very first time in married life my nearest and dearest did a sterling job with the brake pedal. Just a question of disciplined coordination really. Started at the front [as per Stan's note] bleeding the inboard nipple first and then the outboard progressively working further away until the job was completed. The initial undoing of the nipple took a bit of effort and I used an 11mm deep socket to do that- no sweat. I also used the Mityvac kit vacuum bottle to collect the fluid and keep a hydraulic seal. although this vessel is relatively small it is useful in that the small volume makes it easy to see the accumulated amount and thus keep top up the reservoir when this vessel is fullish.

On another note, one of my earlier statements was incorrect. I said that the reservoir lid had a diaphragm in it- that is not correct- it has a sort of top hat that goes into where the strainer basket sits when the cap is engaged but that has vent holes in like JP said- my apologies for that. Other vehicles of mine have a bellows arrangement there.

Rgds

Fred

Petza914

Motive Power Bleeder is awesome and worth every penny. It can be used 2 different ways - 1 you can fill it with fluid and it becomes the bleeding resevoir or 2 you can just use it to pressurize the system and move the fluid in the brake resevoir through. Using method 2 keeps the Power Bleeder cleaner but means you have to stop every caliper and top up the resevoir, then repressurize to do the next one as you have to make sure you never run the resevoir fry.

Regarding ate super blue, it will permanently stain the plastic of your reservoir a blue color, which I'm not a fan of.

FredR

My 928 is Cobalt Blue so will go nicely with the tinted reservoir

I would not be at all surprised if I have to replace the master cylinder or the seals given Stan's cautionary warning. I am not convinced the pedal is as firm as it should be but the car is more or less ready for a test run now- bit more work to do tomorrow.

The Mityvac approach I could not get to work despite pulling a reasonable amount of vacuum so defaulted to the push/pull method.

I have never used the power bleeder type approach but it looks to be a useful piece of kit.

Rgds

Fred

Petza914

Another great tool or accessory is Speed Bleeder bleed nipples. They have a spring loaded valve inside so once loosened, the pedal down stroke will push fluid out then the valve closes to not allow air back in on the return stroke. I have these on all 4 of my P-Cars. Makes brake bleeding a 1 man job, even done the traditional way. The company also sells a length of clear silicone tubing that fits snugly but easily over the bleed nipple, and fluid catch bags with a tube just the right size for the tubing to also slip over. No mess, you can see any bubbles, and the bags can be reused multiple tones by emptying them into a larger catch container. Their website is www.Speedbleeders.com, though this is probably not their intention. Check them out.

Martin's928

I fill my power bleeder (well, put some fluid in it….it's quite big so filling it would be a bit expensive!) and use it as a reservoir from which to bleed the brakes. For changing the brake fluid as recommended every couple of years it's just so easy. I was using ATE Blue alternating with Gold (pour in a can of fluid; open the bleed nipple 'till the new colour comes out!) but I can't do that any more. I have heard it's not that hard to tell the difference between fluid which has been in your system for 2-3 years and new fluid though. I'll find out this winter.

Having said all that: I have heard from several sources that Speed Bleeders work really well. I think for a fluid change the Power Bleeder is just so darn easy but Speed Bleeders would be great for bleeding air from a system. I think if I ever have to replace any of my bleed nipples, it'll be with Speed Bleeders...

Martin

Shark2626

..

Jason89s4

I swear by SpeedBleeders. http://www.russellperformance.com/mc/speed-bleeders/
Makes one-man bleeding easy, fast and clean. I had a car restoration with a full brake system replacement (all hard lines included), and even after allowing gravity bleed, "traditional push-the-brake bleed" and vacuum bleed, we just could not get the pedal firm to my satisfaction--air was still present somewhere in the system.
Installed Speed Bleeders, bled it and did the trick. Just leave them in place of the original bleeders. Makes for quick bleeds at the track as well.
(Note that bleeder size listed on Russell website was not correct for the '83 928, as front bleeder were different size from backs on the car. Fronts are 639520, rears were 639570. Same as listed for '83 911)
Available on Amazon or Summit.
Jason

dr bob

Safest/easiest way is to use clear vinyl tubing that just fits over the bleeder nipples on the calipers. On your '89 car, there are two bleed ports on each caliper. You'll want to flush them in sequence inner then outer. Connect a hose to each nipple, and put the other end in a container placed BELOW the caliper. Note this is the opposite of a pedal or power bleed, where the container is elevated relative to the caliper so air bubbles will rise away from the caliper. You'll get to do that after the gravity bleed is finished. Anyway, hoses connected and routed, you can open the inner bleed valve on each caliper. Remove the cover on the master cylinder reservoir, and add fluid as needed to keep it at least above the min line. Then let gravity take its course.

You'll know when a circuit is purged when the fluid in the clear tubing from a caliper changes from not-clear to clear. When that happens, open the outer bleeder and close the inner bleeder, so the outer piston cavities will get new fluid. The individual calipers will "clear" at different times, as each circuit length is different. After all circuits have delivered clear fluid and the bleeder valves are closed, set the fluid level in the master cylinder and replace the cap. Only Then should you test the pedal to make sure it's firm and high. If it is and it doesn't sink with firm foot pressure, start the engine and test for firm high pedal again.


Gravity bleeding is pretty easy but it can take a long time. It's safe for the master cylinder since the bores aren't swept by the piston cups. You absolutely can not allow the reservoir to run so low that air is drawn into a circuit. The bleeder screws like to "seep" fluid around the threads when loosened, so be ready with a tray under each one.


----
I'm a religious brake fluid changer, and use a power bleeder to get the job finished the same day I start. At one session I allowed the power bleeder fluid level to drop, and I ended up with a little air passing into the system. That was not a good day. I got most of it out, but had a somewhat lower softer pedal in spite of some pretty aggressive power, pedal, vacuum, and gravity bleeding sessions over the next couple years. I ended up opening the system line by line after bench-bleeding the master cylinder. The vacuumed each circuit and system section before allowing fluid to be drawn back in. It was half a day of fun, mixed in with some other brake system resto work. Not something I recommend. Don't let the resrvoir run low.