Brake talk again.

[craigb]

I  had a good day yesterday at Mallala - sort of a come and try family day as MSCA had drawn the short straw of a Father's day allocation and were worried we wouldn't cover costs if it was a normal competitive day. I didn't get that many laps in, with focus on all the new people (total entries almost 100 so it was a big day) but I did do some with a very experienced racer that had some good advice with minor changes to lines (a bit deeper into corners before turning in as a secret for Mallala and allowing power to get down earlier). Also did quite a few laps tutoring some first timers. I didn't have my SEC ready so I pressed the old W116 back into track service.

But on to brakes - It was the first time I had the lucas/TRW pads in on the track. I reckon they were no better than the textars I had in before (possibly worse) so looking forward to the qfm's and bigger brakes on the SEC. I will also run the Motul fluid and rebuilding all the callipers, new ATE lines and the RDA slotted front discs. But my brother was there in a WRX and he did have qfms 750 in it with RDA slotted discs and they were unF**##believable. Lap after lap he just stood on them at the last second, no fade, no pedal issues. Maybe I am just too hard on mine for the weight of the car (scotts pads are bigger and car is lighter) but I can't help feeling something could still be wrong with my system and maybe something has been replaced with a mismatched bit, but they work perfectly on the road so I am not going to mess with it and hopefully the old girl will stay in retirement from racing now.

I could clearly identify 2 different issues, one being pad fade, where the brakes just felt dead, like no matter how hard you pressed or released they just don't seem to work and the other being the soft pedal, that takes about one lap before it goes spongy. The fade was solved with just a little bit greater braking distance and not getting quite so hot. The sponginess never seems to be a real issue and still enough force there to lock the brakes (ie. Still able to apply the max force you need).  If I was staying with it, the higher temp pad would fix the fade but not sure if it would fix the heat transmission. I had a receipt for new brakelines shortly before my purchase, but was there a dodgy line, what brand were they or maybe they lied about replacing them?

If the transference of heat was causing some softness and stretch in the lines, that would give a soft pedal. I tested and it doesn't take long before the pedal comes hard again without any bleeding or anything. My guess is that if I came back after a run and quickly jacked it up and removed a wheel, I would be able to see physical stretch in the line that would disappear on cooling. As I write this I am talking myself into just replacing the lines anyway even for the street. I would perhaps go to braided brake lines at about $70 a piece from power brakes at Norwood If I was still doing track work.

I was thinking about you Oscar and the issues you have been having. I was always disconcerted about this spongy pedal, but with the freedom of better spaced cars on this training day I was able to muck about a bit and prove to myself that no matter how that pedal feels, if you can still lock the brakes (which of course you don't want to do) this indicates that you have more than enough pressure, and maybe you don't need to worry too much. As I recall it is the pedal sponginess that is your problem and not necessarily the brake performance?

And with the earlier post of mine about the K750 QFM's having to be made in the DB143 was wrong. In the end they were actually on the shelf and got to me in about a week and only around $140 something. Was tempted to put them in but wanted to see how the Lucas performed.

[oscar]

What!  A track day report without photographic or video representation!  Shame on you 

if you can still lock the brakes (which of course you don't want to do) this indicates that you have more than enough pressure, and maybe you don't need to worry too much. As I recall it is the pedal sponginess that is your problem and not necessarily the brake performance?

I haven't touched them since Winton but it's fair to say that yes they worked well enough to stop me without trouble, or even lock the wheels up if asked to, but the sinking pedal remains if I press hard enough whilst the engine idles away.  The dummy grid at Winton is on a slope and whilst waiting to hit the track, the car would edge forward, I'd apply more pressure on the brakes, then eventually the car would inch forward again, more pressure, then eventually the pedal was to the floor and I'd have to pump the pedal.  Yet the day before the race,  I isolated the callipers by putting bungs on the ends of the flex hoses.  The pedal would be rock hard.

Anyway, it's still a puzzle.  Braided hoses are something I was aiming for eventually, but based on that bung test, the flex hoses are fine.  Who knows what they are like when they are hot but my probs exist when they are cold too. 

Wish I could report more about the NOS OEM pads and new rotors.  Truth be told my braking was conservative and my early retirement prevented me from learning the track and braking later and harder.

but I can't help feeling something could still be wrong with my system and maybe something has been replaced with a mismatched bit, but they work perfectly on the road so I am not going to mess with it and hopefully the old girl will stay in retirement from racing now.

Even when my brakes were good last year, I didn't seem to have pedal problems after the race day let alone after a lap or two during a session.  The old pads on the other hand would fade at certain sections with prolonged hard braking.

There's one more thing to try though.  So far I've tried a few master cylinders including a new one of which none made a difference and replaced everything else with new except booster and steel lines plus all callipers have been resealed again.  There has been mentions on here and elsewhere about not letting the pedal hit the floor whilst bleeding brakes so when I get a chance I'll block the pedal so it can only move halfway and bleed the system again.  I've tried power bleeding too without success and every other time has involved forceful depression of the pedal to the floor.  There's suggestion that doing this will stuff up a seal but I'm not so sure, especially since I get a hard pedal when I put the bungs on.  So I'll try this other bleed method and if I have success I'll definitely let you know.  Pedal spongyness or sinking only occurs for me if the callipers are included in the circuit.

[craigb]

that is so so wierd!  And no leaking from the system. Physically where is that fluid in the master going when the callipers are connected (not bypassing because of bungs fix). Not compressing? You tried different calipers too didn't you?

[oscar]

I slipped out to the garage before I posted that last one to double check the fluid level - definitely no leak.  It is weird and I can't explain it.  The bung test proves no bypass, rock solid pedal with engine running.  Different calipers from the red car were tried previously too along with its MC.  It's brakes prior to retirement were as good as the 350's but same issue remained when tried on POVO.

The only thing that's under question I suppose is that every MC I have tried including a new one, involved a bleeding method whereby the pedal was pushed to the floor.  I know of two other people that have experienced a "pop" kind of sensation through the pedal just before the pedal hits the floor whilst bleeding.  If that's caused damage to the MC's seals, then after the bleeding process, there may be a condition that now exists for when the pedal is released that tries to draw fluid back out of the circuits, creating a negative pressure or vacuum in the lines and more fluid than normal is returned back into the reservoir that would have normally resided in the MC to refill it. 

So if the MC is supposed to have a one way valve aspect to it, maybe that function has diminished.  Not entirely of course, otherwise bleeding would be impossible as the MC wouldn't refill at all, but if it has diminished, then the recuperating ability of the MC that koan has talked about in the past might be not effective.  I have no way to prove any of that unless I buy another new MC and bleed by not pushing the pedal to the floor.  But I'm not shelling out for another MC and besides, the issue only occurs when the calipers are included in the circuits.  So who's to say it's caliper and not MC related.  I don't know.   

[craigb]

Yep - you would think you have narrowed it down to calipers alone with those bungs. What about with the bungs in you take a while more gently pressing on the pedal?  My thinking is that you are going to have less fluid to compress, not that fluid should compress anyway, when the bungs are in, and maybe that gives you more pressure to force the master cups out. With a little less pressure if you can get the sink in the pedal, maybe your MC theory might come to be? But I wouldn't think so because I can't think where the seals could get damaged. I really am clutching at straws, but it there is no leakage of fluid, no stretching of lines, where is the fluid going unless it comes back into the reservoir. What about getting someone on the brake pedal to make it do the sinking thing and you watch carefully in the reservoir for movement? In our Datto the pedal was going straight to the floor with no leakage. I got Jo to press on the pedal while I did this and you could see heaps of movement in the reservoir. Dismantled it and the valve that blocks off that intake of fluid was clagged up. But you have a whole new master and it is ok with the bungs in.

[koan]

I've got the same thing as oscar but not quite as bad. I can detect the pedal sinking if I push really hard but there's no sink under normal pressure.

Rock hard pedal with engine off, rock hard pedal with clamped lines and engine running but spongy pedal any other time. I get the pedal drop when bleeding too.

Complete front and rear brake rebuild, calipers, hoses, discs and pads didn't fix it. New master cylinder didn't help. I've bled umpteen litres of brake fluid through the system.

There is something odd going on. I don't know if air can somehow get trapped between pistons in the M/C that can't be bled out. Even tried pre-bleding the M/C.

The car stops straight and can easily lock up all four (not that you want to).

I seems some people do the full rebuild and have a perfect hard pedal, others do the job and end up with spongy pedal.

koan

[craigb]

I agree Koan, it is like we are all missing something. I may have mentioned this already but it reminds me of when I was about 18 (nearly 30 years ago!) and had a V8 Falcon, rebuilt the front calipers but just couldn't seem to get the air from the system. Took it to a brake place that bled it, charged me, but I knew it still wasn't right. I thought about it and thought about it and ways air might get trapped and  finally the penny dropped that maybe I put the calipers on the wrong sides and the nipples were at the bottom. After minutes of work I had it fixed.

But unfortunately we have been there and Oscar has checked all that on his. And just repeating I don't have a rock hard pedal, like in a non booster situation, but it feels normal. At the track it does go spongy after a lap or so, but within minutes (say 10) of cooling, it is straight back to normal. You guys are dealing with something quite different though. I will keep thinking about it though.

[TJ 450]

I still have the spongy pedal... it hasn't changed at all. I can also lock up all four wheels if I so wish. There's no problems there.

I get into the 450 and its pedal is absolutely rock hard with no booster assistance. It certainly is a mystery.

Tim

[WGB]

Both my 450 and 6.9 have good pedals and the same pads but my 450 is much more savage and will lock the front wheels very easily - where the 6.9 is much more progressive.

Bill

[chinny4290]

I too have a spongy pedal and although I don't have an issue stopping the car, it only gets really hair when I'm maneuvering a parking move or sitting in traffic. It gets so bad sometimes that I find that I have to shift into neutral and floor the brakes. I get a stiff pedal when the car is off and I can most of the time lock the front wheels with no issue.

I know most of you have worked on nearly the entire brake system, have any of you thought about it being the boosteR? I know boosters seldom have issues making it unlikely for ours to be bad, but maybe ours just tend to develop issues after age? And I know it's also intimidating to buy a new booster because of its astronomical price even at wholesale ($800+ US!)

I've read up on how a booster generally works and it got me thinking:

http://auto.howstuffworks.com/auto-parts/brakes/brake-types/power-brake2.htm

What if the booster is to blame? What if some how the one way valve that seals off the vacuum and allows outside greater air pressure in is some how malfunctioning and is not sealing off the vacuum properly and allowing too much vacuum boost to be provided? Or maybe the diaphragm is old and in bad shape?

To those who sealed off the calipers from the system, I'm guessing that most of you only pumped the brakes to make sure you got a stiff pedal. But did any of you apply foot pressure and hold the brake, like you were sitting in traffic or something and experience any sinking? If not, I would try this but I don't have clamps at the moment nor the time. But clamp the rubber lines and hold the pedal as if you were sitting in a traffic jam and in drive...see if the pedal sinks then. If that's the case then it may be the booster.

The only other logical thing I can think of is that there were rubber o-rings on the connections between the rubber and steal lines and maybe those aren't sealing properly allowing leakage of some sort to occur? But if that was the case I feel like we would altogether lose braking power completely over time, which is also having me rule out that air is leaking in, thinking that if that was the case I wouldn't be able to stop the car as well as I can sometimes, and it's been about 3 weeks since I last bled the system, maybe more and only the spongy pedal at low speeds exists.

But what do you guys think about my booster-is-to-blame theory?

[koan]

If the pedal sinks (as opposed to being just spongy) one of two things is happening, there is fluid leaking out somewhere or the master cylinder is leaking internally.

My pedal is hard with engine off and more spongy than I would expect with engine on. Initially I thought it was only spongy but over the last couple of weeks I've concluded that there is a bit of sinking happening too - but I might just be talking myself into that. Nothing serious, I don't ever after pump or slip in to neutral, I just feel with constant solid pressure on the pedal it slowly sinks.

A few of us have worked on this, complete rebuilds, new master cylinders and oceans of fluid but no answer.

Maybe the only way to get an answer is to plumb a pressure gauge into the brake line and see what's going on, some way to measure pedal force might be handy as well.

But what do you guys think about my booster-is-to-blame theory?

I usually consider pedal boosters about the most reliable bit of a car ever invented. Could be time to reconsider.

If the booster wasn't letting the master cylinder push rod return because the vacuum/air control valve wasn't working  properly it might prevent the master cylinder from recuperating  fluid.

koan

[another sad 280s]

I too have a spongy pedal and although I don't have an issue stopping the car, it only gets really hair when I'm maneuvering a parking move or sitting in traffic. It gets so bad sometimes that I find that I have to shift into neutral and floor the brakes. I get a stiff pedal when the car is off and I can most of the time lock the front wheels with no issue.

this sounds the same as an issue i was experiencing for a while. we were told to get a new master cylinder and it improved the situation. certainly can be scary though when the car in front is worth more than we earn in a year

[craigb]

But following Oscars case, there is definitely no fluid loss and master has been replaced twice. And as far as recuperating fluid, it sounds like there is a sinking pedal without movement so that fluid must be moving somewhere. Not making these comments in an antagonistic way, I just have been running through the situation trying to find an explanation and had crossed those factors off for the above reasons. But I say keep the thinking coming. Have you tried changing boosters for the hell of it Oscar?

[chinny4290]

But following Oscars case, there is definitely no fluid loss and master has been replaced twice. And as far as recuperating fluid, it sounds like there is a sinking pedal without movement so that fluid must be moving somewhere. Not making these comments in an antagonistic way, I just have been running through the situation trying to find an explanation and had crossed those factors off for the above reasons. But I say keep the thinking coming. Have you tried changing boosters for the hell of it Oscar?

Maybe not leaking fluid but is it possible for the booster to provide too much vacuum and overboost the brakes causing a sinking pedal because the one way valve in the booster isnt working right?

[WGB]

All this talk about brakes is giving me the urge to rebuild mine but the though of converting a perfectly good set of brakes into a soft pedal is scary.

Having spent several Uni Vacations bleeding brakes at the Ford Assembly Plant at Seaview NZ in the late 60's early 1970's the hardest car to get a good pedal on was the Mark IV Zephyr/Zodiac which had a system very similar to the 116 system with independant rear suspension and 4 wheel disc brakes.

The only way we could get a good pedal was to bleed in the usual initial manner and then starting at the rear furthest away nipple my partner would pump up a good hard pedal while I let off the nipple and then tightened it up at midstream so the pedal never floored.

Several pumps at the first nipple and then the opposite rear, passenger side front and lastly driver side front and the end result was usually a good pedal with all those little "bubblets" expelled.

I still do this when I change fluid but these days I use the partner I am married to. (To pump the pedal that is)

Bill