RyanPerrella

Does the clutch master cylinder get its supply of brake/hydraulic fluid from the brake reservoir because of gravity, or does the pumping action of the clutch pedal also act as a pump to draw fluid from the reservoir? I cant really see the MC acting as a puller pump to dray fluid from the reservoir, if it did that it would be doing so everytime you hit the pedal and if it has no place to go then it would probably pressurize the line, which i don't think it does.

In either case it seems the line should be almost like a vacuum in which case the blue hose isn't just under low pressure, but none at all. I would think this makes a clamp unnecessary. Maybe someone familiar with hydraulics can comment on how the MC is fed.

I cant think of any real negatives for having clamps on the MC other then 1) you could potentially crack the feed tube on the (20 year old) reservoir by over tightening. 2) It could make hose removal even more difficult for the next guy in 2028 and 3) well the factory didn't see any need to do it (perhaps because of my theory above)

I'm not sure a clamp is a great idea, i don't think its really a problem either.

I would like to know how the MC is fed, wether its by a type of suction from the MC pumping or if its just gravity that feeds it.

Mrmerlin

I`m going to go out on a limb and and say this.
I think this is the best procedure to use to fix your clutch system, it saves time and will result in a trouble free/airless operation . It takes about 2 hours to complete and if you have helper to hold the clutch master in then it takes even less time, its easy to follow as one of our word perfect Rennlisters took the time to put things in a cognitive sequence , thanks for that, so here goes, Oh please dont put any clamps on the blue hose, all you will be doing is trying to crack the hard plastc fittings that connect the resivour and the master , then you will eventually damage your system SO NO CLAMPS the New Blue hose will hold over 30 PSI once its slid into position--------------------------------------------------------------------------------

In the past week I've submitted an NIH grant, revised a manuscript, and graded a bunch of midterms from my graduate students' immunology course. Here's my edit of what Stan said: (I only did this 'cause I will need these instructions soon and I really appreicate you writing it out, Stan! )

I am working on a 86.5 and part of the job was to replace the clutch master and slave and blue hose.
Given that its usually pretty hard to get out all of the air from the system easily, and not use a whole lot of blue fluid to boot, I removed the whole system from the car:

1. Disconnect the battery, cut the blue hose from just under the reservoir and catch the fluid that comes out.

2. Remove the 2 bolts that hold in the master cylinder.

3. Remove the pushrod from the clutch pedal and also the rubber boot from the master(This is important as keeping the bellows on will make removal difficult).

4. From under the car remove the line holding connection at the swaybar mount , the heat shield at the left exhaust header and remove the 2 bolts on the oilpan that secure the line.

5. Remove the slave-to-bellhousing bolts, remove the starter. The pushrod for the slave should be able to be pulled out of the slave

6. The whole clutch hydraulic system can now be removed from the car.It may take a bit of maneuvering and the top hard line may need a slight bit of bending, not much to get it out.

7. On the work bench refit the new master and slave to the old lines. Pay attention to the orientation of the hoses to the respective cylinders.

8. After this, open the bleeder on the slave and put the master in a vice. Hold the slave so it’s higher than the master. Using an oil pump type can filled with fresh brake fluid, begin filling the master thru the new blue hose till the fluid comes out of the bleeder.

9. Try to move the lines around so as to make sure that any air pockets are moved to the slave. All of the air should purge from the system.

10. Secure the bleeder, and plug the blue line with a clean bolt. Remove the rubber bellows from the new master cylinder and add some tape to the exposed end so dirt doesn’t get into the end when refitting,


11. Refit the whole system into the car starting with the Master. Once the bolts are installed, the blue line should be connected and the reservoir refilled.

12. Secure the swaybar mount, followed by the starter, then the slave to bellhousing.

13. Refit the master pushrod and bellows, adjust so it is not pressing on the master leave about 1 to 2 mm of play .


14. Bleed the clutch with your favorite power bleeder or helper, you should find that the clutch will be high and hard with little or no air , so you will use about 1 oz to bleed it. Don’t hold the bleeder open for more than about 3 seconds as the reservoir may drain, since it’s a smaller reservoir.

15. Reconnect the battery, Done, and no wasted fluid and no skinned knuckles from trying to remove the fittings on the cylinders.


16. As a side note now is a great time to clean out the reservoir. To do this I pulled out the reservoir, drained out the old fluid and sprayed brake cleaner into the res. After doing this I took Simple Green and sprayed this followed by a hot water flush of the reservoir. Then I took isopropyl alcohol and sloshed it a few times, followed by a blow dry with compressed air. Now the reservoir looks like new and all of the old dirt is removed from inside.


If this were for credit, I'd give Stan an A+.
__________________
1990 928GT #278, Black/Black, C03 048 418 474 498 538 570 850 691 935 980. 110K miles

hacker-pschorr

I'll never put a blue hose on my clutch again without a set of norma clamps.

I have never seen a blue hose rupture, but with age I have seen them work themselves lose.

Lizard928

Has anyone thought of seperating the clutch system from the brake resevior and running it with hydraulic fluid which is far less corrosive?

Mrmerlin

If your blue hose is older than 10 years it should be replaced.
Any time the clutch system is worked on the blue hose should be inspected if either side of it is loose fitting it should be replaced.
You should NOT use any type of clamp on this hose fitting as you will be clamping onto a hard plastic tube that will eventually crack and leak (either the resivour or the master inlet)

hacker-pschorr

You should not use a cheap auto parts store hose clamp on any part of a 928 (I shutter everytime I see this on any car).

Using the proper norma band clap is not going to hurt anything and could prevent you from being stranded.

Mrmerlin

Hacker, A new Blue hose will hold more that 30 PSI of pressure once its installed, and it IS NOT under pressure as its a feedline, so once again I would strongly recommend that no clamps are necessary . The fitting of a clamp on a hard plastic part may be enough to either deform it or crack it, remember that the fittings run close to the exhaust manifolds.
I know that there are other fitted plastic parts that have hose clamps fitted to the rubber hoses but the Blue hose is a press to fit part, if your hose is sliding around, then its time to put the correct piece of Blue silicone hose back on. Stan

RyanPerrella

Mrmerlin,

Thanks for helping answer my above question as to the real purpose (and exact function) of the blue line. Seems my "hypothesis" was correct and that we also share the same concerns when the suggestion is raised about the clamps on this line.

I only state this because its being said that i have NO IDEA what i am talking about when it comes to the 928.

Mrmerlin

Ryan we both know the clutch is gravity fed and the only pressure on the clutch master cylinder feed line will happen when a pressure bleeder is applied.
That said I blew a brake master cylinder resivour off of the master cylinder, with an air line connection that wasnt below 14 PSI but was at 30 PSI, the new blue line that was connected to the resivour didnt move, so i have first hand experience with this, and yes brake fluid went everywhere, followed with a thorough rinsing/washing of the car with a water hose on the lift,
Have you ever been able to twist a blue hose off of its fitting?
The plastic will snap off first, cut the old hose off with a razor.

hacker-pschorr

FWIW my 81 has been wearing a clamp on the blue hose since around 1993 when the master was changed, and my 79 even longer.
I'm not going to take the chance that hose will come off. Sure you could snap off the fitting if you tighten the hell of it. There are a lot of fittings like that on the 928.

I'm willing to bet more people snap off the fittings going to the heater core on the firewall than the two fittings on either side of the blue hose.

YMMV, it's just my opinion.

shmark

I'm with you, seeing how loose it was on my master cylinder. Now I'm not talking about screw-down FI clamps here, but a properly-sized pinch clamp. Just enough to secure it without causing a problem on the plastic fittings.

Sailmed

1st - Well done That isn't a easy job no matter how you try to do it.
Now that you have a "fresh" master in hand - I'd go through the effort of restoring it with a $20 rebuild kit and stocking it in your "Geez, I hope I never need this again parts".
The Clamp? Heres a old school thought for everyone concerning the blue hose of death.
Way back when in A&P school - we learned the advantage of stainless seizing wire on everything - It is on my blue hose.
This is available at most Marine jewelry stores. Simply wrap tightly upstream of the barb, approx 3 times around, pull tension while twisting the ends together, cut and tuck the ends in. You are only trying to stop the hose from expanding over the barb, clamping is not necessary.
But then again, that might be too easy

hacker-pschorr

I use the same style clamp that is on the fuel injector hoses on the 16 valve's.

RyanPerrella

Yes the MC has a plastic feed nipple and it can very easily be pulled from the iron body of the MC. I do recall the hose being almost glued onto the fitting ends but this was just age and it was as if the thing had baked together. I think that when they leak, they are now hard, no longer supple and cracks develop and the seal is broken. It needs to be soft and supple.

I have about 4 feet of the BMW version of our blue hose of death. I had wondered when i did this job if it wouldn't be a better alternative to the Porsche stuff. It appears to be some type of rubber compound with a similar cloth weave around the exterior of it. As such its fairly firm which is the reason i decided not to go with it. But I do believe based on how the old blue hose had nearly disintegrated that it could be a longer lasting alternative. Again this was used for an auto to manual conversion and was used as the feed line to the clutch master cylinder on the BMW 540.

I had mentioned this point before but its worth restating. I if your installing a new MC, attach one end of the blue hose to it before installing the MC. I had originally just been in this area to replace the hose, but it was impossible for me to reattach the hose to the feed nipple on the MC with me sitting in the engine bay and the engine removed, I still couldn't get the hose onto the fitting. Thats the reason why i ended up replacing the MC so that i could fit the damn blue hose. So I just replaced it with a new one.

But I guess some of you guys are doing this repair by pulling out the brake booster. If your doing that then you wont have any issues fitting the line so its a mute point. Hacker mentioned he would alway pull the engine first to replace the line, it is a PITA and for those doing it with the engine pulled you may find the above to be helpful.

Mrmerlin

The other side of this is that you should try to get the correct hose.
Its made by ATE the blue hose is made of silicone and will last a long time, that said once its been installed it nearly impossible to remove.
So If your blue hose is sliding around on its fittings then you have the wrong size hose and then a clamp would be the only way to make it tight.
That goes back to what i saying , if its loose then you have the wrong hose or its worn out, I believe that Roger has the correct hose and you need about 14 inches IIRC,( some added for RnR ) No clamps are necessary. Im done..........Stan