Failed Master Cylinder?

[beatnavy]

Lost almost all brake pressure on my '72 daily driver yesterday evening. If I pump the brakes I can build pressure temporarily to stop the car, and I'm convinced all four calipers are working. No evidence of fluid leaks anywhere, and there is brake fluid in the reservoir. Anything to suspect OTHER than a failed MC?

I've a 19mm ATE in the shopping cart here at Pelican ready to buy. I guess I would need the two rubber grommets as well. Anything else? Also, I saw one reviewer "complain" that the new 19mm has a one pole pressure switch instead of the two pole. I haven't looked at mine recently, but it's probably the "old" one, so is there a solution there?

TIA!

[Dave at Pelican Parts]

I'm not sure how you would absolutely confirm the MC as the source of your troubles, but it sounds likely. You might try bleeding the system to see if the pedal comes back that way--but then the question is how did air get in?

The solution to the one-pole switch is to not plug the brown wire in and to tape it out of the way. The two-pole switch grounds through the brown wire, while the one-pole switch grounds through its threads.

--DD

[beatnavy]

Thanks, Dave. Got the car up on jacks and was somewhat disturbed to find that the right front caliper was loose and that the brake pad retaining pins had partially worked their way out. Not good! After tightening up the brakes are still very squishy. I suppose I could try bleeding them and see if that helps, but a loose caliper wouldn't necessarily allow air into the system, would it? I checked the bleeder valves all the way round and they were tight, and I didn't see any evidence of loose brake lines or leaking. Hmmmm....

Thanks for the tip on the two pole switch. THAT I can handle.

Last question (for now): I don't seem to have that belly pan that protects the steering gear and the MC. I know I took one off my project car, but I can't even tell where the bolt holes are for this one. Did early cars not have that or is this just a "PO Upgrade?"

[etcmss]

there are 4 bolts--look back around the tie rod back covers for front suspension.--big ones and little ones close by.

closest picture I have to this area

[beatnavy]

Master cylinder is on order from Pelican. Hopefully get it installed this week.

I removed the belly pan off of my '75 teener as part of a disassembly, so I generally know how and where it connects. But on the '72 it's not there. If it's supposed to have one, I'll find where the bolt holes are. I guess I need to find a belly pan, too.

[Dave at Pelican Parts]

I believe all 914s had the belly pan. Two of the bolt holes are also bolts that hold the steering rack (or maybe the crossmember?) to the chassis. I think two of them have their own bolt holes, but my memory of that area is now foggy.

--DD

[beatnavy]

Received my new 19mm master cylinder last night and took the old one out without any problems. The new one, as is well documented here and other places, is a bit of bear to get in, especially the supply lines (at least for the first timer like me). No worries, I have the tank out anyway for other things, so I should be able to drop the brake fluid reservoir and lines so I can do this with it on the floor.

Here's my exceedingly stupid question, however: during this process I've lost confidence in knowing which supply line goes to which inlet on the MC. Is there a difference? I notice in the reservoir there are sort of two chambers but I don't get the purpose or design. I haven't been able to find a reference anywhere. I don't want to get this thing hooked up to find I've put the supply lines on reversed....

[The Glademister]

Originally Posted by beatnavy

Here's my exceedingly stupid question, however: during this process I've lost confidence in knowing which supply line goes to which inlet on the MC. Is there a difference? I notice in the reservoir there are sort of two chambers but I don't get the purpose or design. I haven't been able to find a reference anywhere. I don't want to get this thing hooked up to find I've put the supply lines on reversed....

That had me a little concerned also but the parts diagram kinda shows which hose goes to which compartment on the reservoir. There's a little divider in the reservoir and it appears that one side would run out later than the other should there be a leak. I think basically the supply lines cross before passing through the pan. The front line becomes the rear at the MC and the rear becomes the front (position wise).

[beatnavy]

I agree, I looked at the reservoir, and there does appear to be a difference. I did get confirmation, however, that because they are redundant circuits in the MC, it really doesn't matter which tube connects to which inlet port.

Now get back to your project

[jonbjornclark]

Ironically, I just replaced the MC on my '71 914 with a uroparts unit, and after 20 minutes of driving, the pedal went to the floor. it would come right back to firm pedal, then fail again. This made for some sketchy driving in traffic back home. On the rack, all four corners were re-bled with a fresh liter of super blue, no improvement. Turns out, the brand new MC was bypassing the brake circuit and simply raising the level in the reservoir. I ordered a new ATE 19mm unit from our host and installed it with no issues(other than having to relinquish the Super Blue for Gold). Check the reservoir level as your pedal is failing to engage.