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Old 12-12-2021, 06:57 PM   #1
Radtap
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Default Brakes go to floor after lots of troubleshooting

My brakes have been going to the floor after converting the front to vented disks. I have installed new master, booster, front and back rebuilt calipers, have fresh fluid coming out of all 4 calipers. Have pressure and vacuum bled as well as old fashion 2 man brake bleeding. I was able to get as much air as possible out of rear calipers but I believe I have air stuck in the rear valves. I’m getting good strong flow out of the right rear and left calipers without problem. New rotors and pads up front. I did try swapping back to the original non vented calipers and rotors and that didn’t solve the issue. I was having a leak at the octopus junction but have since fixed. Haven’t been able to locate any leaks. I saw someone else mention just opening the rear bleeders and stomping on the pedal to get the fluid moving quickly and that didn’t seem to help. The pedal feels like there’s air somewhere in the system but I simply cannot find it or get it out for the life of me.
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Old 12-12-2021, 07:09 PM   #2
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Did you bench bleed the master before everything else?
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Old 12-12-2021, 07:55 PM   #3
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Yup
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Old 12-12-2021, 08:04 PM   #4
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I’m 99% sure it’s the rear valves above the axle trapping air, in the last half inch of travel the system will build enough pressure to stop a little and I’ll hear a clicking noise coming from the rear end, doesn’t sound like the calipers and when bleeding I can hear those valves click when building pressure and when opening the bleeders.
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Old 12-12-2021, 08:37 PM   #5
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Raise the rear as far as you can and leave it for a day. Always follow the diagram when bleeding.
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Old 12-12-2021, 08:59 PM   #6
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If you do have air caught in the valves. Tap on them with a small hammer to jar them bubbles to move past the valves to come out with bleeding. If you have a pedal that pumps up and gets better then you have air in there. If it doesn't pump up and get better there isn't any air left in the system. It is normal to have a bit of a soft pedal with new rotors and pads all around. However, also do the pressure bleed down test by holding your foot on the brake pedal if it gradually sinks to the floor after a couple of minutes your master is probably bad.
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Old 12-12-2021, 09:07 PM   #7
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I've done a pressure bleed down and the master is good, I'll try tapping the valves when I try bleeding again tomorrow. I understand soft pedal with new rotors, not pedal to the floor car barely stops lol. I've been making sure to bleed in sequence too. With the car off the pedal goes about half way and feels somewhat spongy but alright to drive. With car running it just goes to the floor and barely builds pressure within last half inch of travel.
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Old 12-12-2021, 09:51 PM   #8
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One time long ago on my friends 242 flathood it still had a low pedal after all the effort as you have done. So he drove on it for a week and then we bled it again with the classic manual pedal method and it pooped out that last bit of air and was great after that.
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Old 12-12-2021, 09:54 PM   #9
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When manual bleeding today I pulled quite a bit of air out of the rear calipers and figured that was the air in the valves and then it turned out wasn't all of it.
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Old 12-19-2021, 06:39 PM   #10
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Bled a lot of air out of the two rear calipers but still hasn’t seemed to make a difference. This is getting extremely frustrating chasing air I still can’t find. No damage to any of the brake lines hard or soft, no more leaks anywhere. Pedal goes to floor when car is running, pedal feels spongy but doesn’t bottom out while car is off. New booster and MC
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Old 12-19-2021, 07:00 PM   #11
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Had a similar problem when I did the brakes on my 240 earlier this year. New rotors, rebuilt calipers and a new master. Couldn't get a firm pedal, even after 4 complete bleeds.

Swapped in another new master (ATE) and things were back to normal.
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Old 12-19-2021, 07:18 PM   #12
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I have an Oreilly's (BrakeBest whoever makes that) master. Just swapped it in to replace another BrakeBest master thinking that was the issue, should I try an ATE master at this point?
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Old 12-19-2021, 07:35 PM   #13
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Get some M10-1.0 bubble flare brake plugs and plug the master cylinder. If the pedal gets hard as a rock, the master isn't the problem. FYI, you can also bench bleed the master this way.

https://www.ebay.com/p/20017010553
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Old 12-19-2021, 08:16 PM   #14
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Okay I'll try that. I did bench bleed both masters before installing. I've made sure I'm doing the entire system bleeding process properly after having to do it 6+ times now.
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Old 12-19-2021, 09:47 PM   #15
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Get the back of the car up as much as is safely possible and have someone tap on the proportioning valve with the handle of a big screwdriver while you power bleed the corresponding rear caliper.
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Old 12-19-2021, 10:24 PM   #16
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I was tapping on the rear valves while bleeding today but had the car on level jacks, I'll try angling it though as well.
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Old 12-19-2021, 10:58 PM   #17
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Best to start in the back one at a time when swapping components and thoroughly bleed each corner twice before moving onto the front corners, and then thoroughly bleed each front caliper twice starting with the top bleeder since air rises before moving onto the reccommended order which simply uses the least amount of fluid per flush, but other than that it's nothing special in and of itself.


NB:

If it's just a soft line swap leave the downstream fitting cracked and gravity bleed until it weeps so you're injecting the least amount of air possible into the caliper.

Cliffs:

The whole point of the exercise is to figure out how NOT TO SEND AIR OUT BACK TO BE TRAPPED IN THE PROPORTIONING VALVES.

Last edited by Redwood Chair; 12-19-2021 at 11:14 PM.. Reason: Spelling
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Old 12-19-2021, 11:12 PM   #18
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Do you have a manual for your book? My book had a diagram telling me what valves to bleed in what order. Also is the master cylinder, brake booster rod the right length? I didn't have this problem with my car but I have heard of the rod coming out of the brake booster being too short because its a slightly wrong part causing you to loose a lot of your petal travel just making up the gap. correct me if/when im wrong.
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Old 12-20-2021, 01:13 AM   #19
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I have books and I know I'm bleeding in the correct order. I don't think the rod length is an issue? With the car off I can feel the rod pressing on the master, don't feel any play. I'd just have to unbolt & check
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Old 12-20-2021, 06:06 AM   #20
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Quote:
Originally Posted by hiperfauto View Post
Get some M10-1.0 bubble flare brake plugs and plug the master cylinder. If the pedal gets hard as a rock, the master isn't the problem. FYI, you can also bench bleed the master this way.

https://www.ebay.com/p/20017010553
Thanks!
Ever the wealth of info you are.

At this late date with all the china crap and sketchy 'rebuilt' calipers & the rainforest climate with lousy brake fluid much more an issue here than AZ, & age of the cars, I repair 240 brakes uh...very gingerly/cautiously.

I like to have some of the strut hard lines on hand, a spare known good decent brand MC & some quality flexible hoses on hand & a stick to keep the brake pedal depressed with the 'stop lamp' fuse removed or battery (-) disconnected should help eliminate as much fluid loss / air introduction as possible..if the master works/seals.

Overlooked some acid eaten threads on a replacement rebuilt caliper that I didn't test fit with something like those M10 plugs first...lost some fluid on a rear caliper that almost gave me a heart attack, but didn't suck air backwards into the prop valve...by some miracle.

Got the car bled and didn't send any air back into the prop valves...lord help you if that happens.
Still, I try to disturb as absolutely little as possible and drag old or unknown master seals or caliper pistons over ranges of motion that are no more than normal operation/where the bores are clear/not likely crusty or to rip a boot or damage a seal, if possible?

Often times, I do it corner at a time after a good flush (if the bleeders already co-operate/flow or can easily be made to), extend the rear caliper pistons onto 2 worn out pads as much as I dare and go about doing a corner, then bleed and so on and compress the rear pistons to push any stray air forward and up into the master reservoir with the now 'basically all clean' flushed fluid after the end of each bleed and gingerly check the pedal on the avg old used master. But I keep it all 'wet' like a sorta diesel engine/injection system manual bleed & don't introduce air to fragile old components.

If you're a poor sod that has to do an octopus or a rear prop valve, even more care, inspection and fussy bleed is required. Misery. For whatever reason, the -72 140 brake failure shuttle/sensors don't seem to fail as often as the '73+ 140/240, IDK why? They also don't fail as often in 7/9s that are non-ABS/dual diagonal, no idea?

Ignore the order, that's just for a quick flush if we all maintained our cars throughout to Swedish dealer manufacturer & master tech standards & our brake parts never rusted or had calipers with torn boots by some magic. This is TB, right?
I've seen TB borderline scrap-price field rat & molested roach coaches...

It is NOT to prevent introducing air, trouble shooting or to remove introduced air with the least risk possible on a crusty old car with a ??? master and assortment of calipers and ??? fluid with lord knows what kind of purity or ??? particulates???

When the calipers & their seals are all fresh, the pedal will travel a bit more than when all of the hydraulic system holds fluid fine/master is verified bench bled & dead-heads well without leaking internally, but the pistons & seals are reluctant to move as freely/easily, as it common with crusty ancient calipers with seals marinating in brake fluid for a quarter century, see cleanflametrap's posts on that...
...IIRC his theory is a good set of new calipers with appropriate anti-rattle springs and pistons that move freely the pads and pistons retract more each time, where as old crusty calipers the pistons don't retract especially willingly? Thus, what feels like more pedal travel, even if all is verified perfect with no air anywhere & no pulsing rotors etc?
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Old 12-20-2021, 10:50 AM   #21
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Looking at images the brake failure sensor on 140s appears to be similar if not the same plastic piece, on my original junction the rubber oring failed, on my new one the rivet that held the metal piece on was allowing fluid out
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Old 12-20-2021, 10:52 AM   #22
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I had this problem on a Jeep once, the issue turned out to be that I had inadvertently swapped the left and right side calipers, the resulted in the bleed screws being oriented on the bottom of the caliper. No amount of bleeding will fix that. I swapped the calipers sides and the brakes were perfect. Please don't get offended at the suggestion, it happened to me after 40 years of messing with cars and countless brake jobs.
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Old 12-20-2021, 10:53 AM   #23
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Rubber o-ring(s)...on the shuttle inside it, you mean?

'cause the plastique switch & little rubber dust boot isn't what's supposed to seal it.
No way that thing is supposed to seal brake system pressures!

Same problem on the old early dual diagonal circuit F100 fords. & half the guys on the ford foamer/nerd board misunderstand it too, so don't feel bad...
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Old 12-20-2021, 11:08 AM   #24
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I mean yeah a combination of both seals failing and don’t worry I’m sure my calipers are right side round
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Old 12-20-2021, 10:23 PM   #25
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Check the brake master cylinder 1st like my brother, hiperfauto suggested.

If the master cylinder check outs okay, then I would suspect the front brake calipers might have been assembled incorrectly when they were rebuilt which happens more often then it should.

At some point, Volvo/Girling started to put a small indentation on the bottom of each half of each caliper to help avoid this problem, so check your front calipers for these indentations.
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