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Posted by: florida 914 Mar 21 2015, 09:17 PM

Sorry, folks, for asking yet another question about bleeding brakes, but I can't find the answer to this specific question and am at wits end.

I have a 1971 914. I am only able to get about a quarter of a pedal, i.e. it is off the floor, but only just, and no more improvement no matter how much we go through the routine. What seems weird is this: when I open the rear bleed nipples, the pedal goes to the floor (as my assistant pushes), but nothing like that happens on the front. I don't see air being pushed through on any corner any more, but there is fluid moving on all four corners (though probably more on the back than the front). And the pedal never pumps up better than a quarter or so even with all nipples closed.

We have installed rebuilt calipers, new pads, new flex lines, and a new master cylinder (in fact, we tried a second new master cylinder on the theory that the first may have been faulty). As far as I can tell there is no clog in the fixed lines (we checked the front especially).

Any suggestions?

Thanks!

Posted by: stugray Mar 21 2015, 09:36 PM

Does your pedal cluster have the brake pedal return spring?



Item #41

Posted by: florida 914 Mar 22 2015, 12:52 AM

I am not sure; I will have to take the pedal board off tomorrow to see. Either way I am very curious as to what effect that has.....

Posted by: screenguy914 Mar 22 2015, 01:21 AM

Don't understand the need to confirm the existence of a return spring. If the pedal doesn't retract on its own, there's an issue. If it does, look elsewhere. Since it's a new MC, there's a chance it's faulty. If it was the existing MC, I would suspect a cup was torn when the pedal went to the floor during the manual bleeding procedure.

Confirm the MC is creating pressure at the front and rear outlet ports. Simply remove the appropriate MC brake line and depress the pedal with a finger (or equivalent) blocking the port. Don't get brake fluid in your eyes.

Sherwood

Posted by: rgalla9146 Mar 22 2015, 08:32 AM

The master cyl. can only take in more fluid if it comes back fully to the top of it's travel.
I don't think he would have gotten as far as he has if the there was no flow into the master.
But, the spring is certainly important and should be checked.
Any chance the front and rear circuits were switched at the master ?
New hard lines ?

Posted by: 76-914 Mar 22 2015, 08:55 AM

Who's Blake?

Posted by: florida 914 Mar 22 2015, 10:37 AM

Blake is my assistant! That master cylinder was hard to get in ....

There is no problem with the pedal returning.

This is the second new master cylinder I have tried with the same problem, though I suppose that could still be the issue. Back under there to undo ithe lines again.....

Posted by: 76-914 Mar 22 2015, 10:54 AM

Did you bench bleed the MC?

Posted by: florida 914 Mar 22 2015, 12:00 PM

No. I don't even know what that means.

Posted by: Johny Blackstain Mar 22 2015, 12:44 PM

It means filling the MC w/ fluid & capping it before you install it. One of the possibilities available to you. Same applies to the proportioning valve in the rear. However, you can address these while the items are installed. With your assistant there, crack the lines on the MC while he remains up top & makes sure the reservoir does not go dry as you let the MC drip a bit. You should do the same for the proportioning valve in the rear although it's not as easy to do as the MC; your assistant might have to run between the pedal inside & the reservoir up front, making sure it never goes dry. Check the bushings & return spring on the pedal assembly as someone previously posted. Lastly, have you used a .004 feeler/gap gauge to adjust your rear calipers to the proper gap yet? You can also try tapping things w/ a screwdriver handle as you bleed to get the air bubbles to flow/move out.

Posted by: einic Mar 22 2015, 12:44 PM

Have you adjusted the push rod? You shold have just a tiny play before pressing the mc.
( The MC must return completely to relief pressure)

Posted by: pilothyer Mar 22 2015, 12:45 PM

Watch this, you can see what you need to do:

http://www.speedwaymotors.com/Tech/how-to-bench-bleed-your-master-cylinder.html

Posted by: stugray Mar 22 2015, 12:48 PM

Exactly. The OPs original post sounded like the pedal was not returning.



Then he clarified it here


It sounded like the pedal was not returning which would not pull new fluid in to the MC on each stroke.

This sounds more like the classic bleed issue like this alleged "inability to purge the Prop valve".

http://www.914world.com/bbs2/index.php?showtopic=225728&st=0

Posted by: Tilly74 Mar 22 2015, 01:28 PM

My name is Blake.

Posted by: 76-914 Mar 22 2015, 02:21 PM

Well then florida914 has a question for you. He thinks your bleeding or something.

Posted by: florida 914 Mar 22 2015, 04:34 PM

Okay, I have now "bench bled" the MC, though I did it while it was on the car. That seemed to be getting lots of air out, so I thought I was on the right track. But I am still in the same situation.

Here is one thing I can't figure out: when we pump up the rear and then open the bleed valve the pedal goes to the floor. It also has a lot of flow on both sides of the rear. But that does not happen on the front. To the person pushing the pedal the pedal feels no different front from rear. It also does not have nearly so much flow in the front as the back (on either side). When I was bleeding the MC at the cylinder both front and back seemed the same.

It seems like the pedal should go to the floor when the valve is opened, no?

Posted by: florida 914 Mar 22 2015, 04:39 PM

Also, when I put a wheel on it seems I do have braking in the back, but almost none in the front.

Posted by: bigkensteele Mar 22 2015, 04:44 PM

Is it possible that you have the front calipers switched and the bleed valves are on the bottom? If this is the case, we have found your problem.

Posted by: florida 914 Mar 22 2015, 04:58 PM

Um, maybe....

I definitely have the bleed valves on the bottom. I did not know it was possible to have them on backwards. Feeling kind of silly...but thanks!

Posted by: bigkensteele Mar 22 2015, 05:21 PM

I don't think that the rears can go on reversed but you should check them as well.

Bleed valves have to be on top because that is where the air ends up.

Don't feel silly. Feel happy that you have found the problem and that you will never make that mistake again. Better yet, you will be able to help the next guy who is asking this question.

Posted by: florida 914 Mar 22 2015, 07:48 PM

That was it! I had taken the rear callipers off on this very theory, only to discover that they only went one way. Someone had told me the nipples had to be at the bottom. Anyway, it's fixed, and they are better than on my other car. Thanks!

Posted by: bigkensteele Mar 22 2015, 08:22 PM

Glad to help! Now go find the guy who told you they had to go on the bottom and beat him senseless!

Posted by: wndsrfr Mar 23 2015, 06:07 AM

Now that's what I call thinking out of the box.....clever insight......then again possibly you've btdt??

Posted by: Dave_Darling Mar 23 2015, 09:26 AM

We've seen it more than a couple of times around here...

--DD

Posted by: bigkensteele Mar 23 2015, 12:12 PM

Nope, never did it myself, but it is quite possible that I would have had I not been around here for a while. As Dave said, this is not the first time it has happened.