Scott Turnbull

This thread is a continuation of my previous brake problem thread:

https://rennlist.com/forums/928-forum/223364-squishy-brake-pedal-even-after-major-power-bleed.html

The only change made to this system after the auto-to-manual conversion was cutting the tip off the plugged blue hose fitting on the brake reservoir and attaching a new blue hose, and changing all four brake lines from stock to braided stainless steel.

Since the last posting:

* Bleeding the slave and master has fixed the clutch system and clutch feel is solid as a rock
* Bled three full quarts of ATE Super Blue thru the brake system
* Used both the farthest point (RR) method and the new master, fronts, rears, method
* Use the power bleeder four times, used the wife pumping the brake pedal once.
* Have installed new brake pads (because I needed to anyway)
* Power bled all four corners again after pad install (fronts then rears)
* Used the tap on the lines and pound the calipers with a rubber mallet trick to dislodge trapped air bubbles
* Checked the adjustment of the actuating rod. Seems to be adjusted properly and has a very small amount (~1mm) play before actuating the piston so should not be depressing the piston at rest.
* Looked (visually) for vacuum leaks/disconnected lines (found none)
* Drove the car around neighborhood, brakes STILL Squishy!! Pedal travel is excessive before engaging brakes and not solid at time of engagement.

I am at a loss here. I don't know what to look at next and I am out of ideas. Please help!

Kevin in Atlanta

BTDT. You have no vacuum to the brake booster. You really need to check the vacuum at the brake booster. BTW, did you change the vacuum manifold at the rear of the engine? An Auto has more vacuum lines than a manual. If you left one unpluged, you would lose vacuum. Trace all you vacuum lines from the brake booster back to their source to look for leaks or uncapped lines.

GlenL

No, or low, boost is a good check.

With or without boost it should get firm after several pumps.

Does the pedal continue to sink with firm pressure?

Are you getting both of the bleeders on those calipers?

Jfrahm

Worst case, put the power bleeder on and bleed at every fitting instead of just the bleeder screws.

You might also try a trick I use on motorcycles. Put pressure on the system and leave it overnight. In the AM, bleed the brakes as normal. On a bike this is pretty easy, in the car it might take a few days. The theory is that the trapped air bubbles get smaller when under pressure, and find their way to a place where they can be bled out more easily.

Did you bench bleed the master?
http://superchevy.com/technical/chas.../0509sc_bench/

You can do this on the car too, that's the way I do it. Maybe it's not neccisary on a 928 with a MC bleeder screw though.

How is the Master? People often damage the MC piston seals when bleeding brakes on an older system, as the piston can travel farther than it does during normal operation. The piston moves into an unused, gunked-up area and the seals get damaged as a result.

-Joel.

Mark

I think 86_5 & Glen are on to something! I'd put a MiteyVac or some other vac gauge on the vac line going to the booster and check it 1st.

John Veninger

Sounds like a bad master cyl.

Scott Turnbull

The manifold at the back of the engine was a 5 or 6 port. I noticed there was one port open when I reassembled the air box. I plugged the open port with a screw and zip tie. I have visually followed all lines (I think) and can see no brakes or open connections. I will put the mighty vac on the system this morning and see what I get.

I have had low/no vacuum at booster before on other cars and yes the pedal would firm up after 3-8 pumps. However this situation does not seem to do that. In my other cars it was like you could feel the system pressurizing. With each pump of the pedal it would get firmer. Now it does not seem to ever get firm and any perceived improvement in firmness seems to be random. Yes, I am bleeding both screws at each caliper each time I have bled the system.

Master is only a couple years old and was working perfectly when I pulled it into the garage for the conversion. I have bled it several time at the bleed screw. Bench bleeding does not apply as it was not a new install and the system was never dry. Seal damage should not be the issue as the MC is so new and the first 4 bleeds were with the power bleeder and not using the pedal. But there is a slim chance I guess. Want to rule everything else out before I change out a relatively new MC. The pressurizing the system over night thing is an idea.

Yeah, me to.....at least I hope.

I agree. With the "it doesn't pump up" issue it does point to the master. I just don't understand how given the age and steps I have outlined. But can't rule it out as yet.

Thanks to ALL for your ideas and support. It was 3:30 am when I posted this and I was very tired and frustrated. Your ideas and a new morning bring new perspective. I will keep you posted.

AFARR

New enought to the 928 that I probably don't know what I am talking about...

However, my Clutch had issues in my 1994 Ford Exploder (Air in the clutch line...likely a trans problem, also, but that is another...long....story).

Two things come to mind with any hydraulic system...air in the lines (I know you can bleed the system, but in the Explorer, there is an arc in the clutch line (not quite a loop, but an area where the line angles up, then down, leaving a high point). This is a known problem.

Another thing (fortunately not in my car) that was recommended is to check the attachment points to the frame/body of all the components. In some cases there is cracking of the metal at the firewall where the master cylinder attaches--everything looks fine, but when someone observes while the brakes are being checked, they can actually see the whole clutch master cylinder move....And, in my wife's old (long since sold) Honda CRX, I couldn't troubleshoot the clutch issue--then I dislocated my back and shoulders to look at the "Cage" that the pedals pivot on--turns out that the sheet metal there was torn (same thing in the end--the pedal felt like it was moving properly, but with the metal giving way, the clutch wasn't moving like it should). For that one--Honda part $150 or small home welder $99 (and, as the part wasn't visible, the crappy looking weld didn't matter, so I now have a small welder floating around).

AFARR

Scott Turnbull

vacuum test and no answers yet. Here is what I did:

* Bake booster vacuum system seems to be closed loop with the vacuum accumulation pod (under the drivers front fender) and the flappy system.
* My four-way connection has one to flappy, one to vacuum accumulator, one to check valve which continues to fitting going into the brake booster, and finally one that is plugged off.
* I removed the plug and mighty vac'ed till I showed vacuum. stopped pumping and the vacuum slowly decreased. did this three times while moving/holding fittings on and around the four-way to insure they were not loose/leaking.
* replaced plug and tested from the hose that is between the fitting leading into the brake booster and the check valve (disconnected hose from brake booster fitting and attached mighty vac. to hose leading to the check valve and then on to four-way) Held pressure solid for 5 min.
* tested line after flappy solenoid leading directly to the flappy. Held solid.
* the vacuum manifold at the back of the engine (under the air box) is only a five way. (main line coming from under manifold and four outlets) one outlet goes to fuel pressure reg., two outlets go to the front and rear inline fuel whatchamacallits (can't remember what they are right now) and the last outlet is the one I plugged. (believe it was connected to something to do with the auto tranny.
* I took the line off the front inline fuel whatchamacallit and mighty vac'ed line leading back to the manifold. Never built vacuum. I believe this is correct. I think that system uses vacuum from the intake or crank case while the engine is running and would not develop and hold vacuum under this test. (right?)

QUESTIONS:
* I don't have a fitting big enough to plug into the big lines leading from the intake to the brake booster. If I did and could vacuum the line going into the brake booster, would I expect to see the brake booster hold vacuum?
* could the symptoms I am seeing be related to the large lines and fittings coming from the intake and/or the fitting/rubber grommet that attach to the brake booster? How should I test?

I am going to keep trying to figure out a way to attach mighty vac to the line leading into the brake booster unless I hear different from anyone on the list.

Brake master is still a possibility, but will be my last option after I have ruled out everything else since the age and process minimize that possibility and it requires $$, delivery time, and installation.

Please keep those ideas/input coming!


Thanks for the suggestions. The front lines DO form an "S" shape creating a high and low spot in the line. The line comes out of the fitting on the firewall going straight down. It then curves up and then back down to the fitting that attaches to the brake caliper. This is how it was in the stock line as well. Interestingly, I installed the lines incorrectly the first time....In a downward "U" shape. Although this was wrong and rubbed the inside of the rims, it was the configuration I did my first power bleed on and should have been conducive to removing air bubbles. Your other firewall issue was interesting, but should not be a factor in this case as far as I can tell.

mark kibort

didnt have a chance to read all this, but i found the power bleader to not work, and leave the pedal bad. Tom C. helped me at the track once with the power bleeder and it didnt work. we ended up doing the ole, "open valve, push pedal, close valve, repeat".

that could be the fix, unless you have a bad master cylinder

MK

jorj7

By the way, did you test the check valve? I had a problem with my brakes being "soft", replaced the
check valve, and the problem went away.
http://sis125.berkeley.edu/928/wk-br...eck-valve.html

GUMBALL

A question for you, when you manually bled the system (pump, hold, open, down, close, pump...) did you bleed one caliper at a time?

I have found, that it is necessary to bleed a front and a rear at the same time, because all street cars have a limiting check valve, (it prevents loss of all braking if one corner is lost)
By bleeding one caliper at a time, this check valve sometimes restricts flow.

When bleeding a racecar system with dual masters, to prevent the balance bar from binding, it is necessary to follow same procedure.

John Veninger

Never done this and have manually bleed brakes on street cars and race cars for over 25 years with no problems.

I've used the manual method and also the power bleeder with good results.

When manually bleed it is a good idea to place a piece of wood under the brake pedal. This prevents you from going all the way to the floor and damaging the seal inside the MC.

Gnarly 928

Brakes are tedious. I've made dumb mistakes while bleeding mine and ended up with a soft pedal. Perhaps you just "missed something" during all your various attempts at bleeding and stuff. You may find if you go back to square one and do it all again, you'll have good pressure again...just an off chance, but there are so many possible mistakes or details you may miss..it IS possible you screwed up, repeatedly..and maybe not the same way each time. I bleed my brakes when racing a few times per week..I make mistakes with the whole process perhaps a few times per season...but I DO sometimes get it wrong and I have to start right over again, hate it when that happens..
A cross-threaded line? a sticking bleeder valve? One "Down pedal and hold......Release" done out of sequence? Good luck.
Don Hanson

Scott Turnbull

Thanks Mark. I think I will give it one more shot with the two person method using a strong right leg on the pedal and see what happens.
Yep. Checked both check valves (that's a little redundant). The little inline blue one and the larger one that goes into the brake master. Both were working perfectly.
That is interesting. I have never heard of this before. I, like John, have done my fair share of brake installation, maintenance and bleeding and have never done this, nor was aware of it. I will need to research.
Good idea. I usually just trust the person doing it, but it is usually another racer, friend or someone who knows. Since my wife is the only person presently available that is a good insurance policy.
Thanks for the ego check Don! I honestly appreciate it and I am definitely aware of my ability, lack there off, and the human factor. Shy of removing the new lines and reinstalling them I have repeated the whole bleeding process 7 times now and 4 different ways (power bleeder, two person pedal pump, starting at RR and moving forward, starting at Master and moving backward). I am actually COUNTING on it being my mistake/missing something rather than an actual mechanical problem.

All, Thanks again. I will keep plugging away. If this last attempt at the two person bleed does not work, I am going to remove and reinstall the lines (possibly the stock lines instead of the SS ones). If that doesn't work then I believe I am forced to look at the brake master. Thanks for everyone's help and perspective.