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Mk1: How much friction is "normal" on front brakes?
by
ldeikis
on 15 Oct, 2010 05:03
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Hi all.
My 81 rabbit had a front caliper drag/lock up bad enough to reek of brakes and smoke when I stopped. Long story short, after snapping off a bleed valve, sucking a bubble into the MC and back flushing that out, I flushed the whole system out, replaced both front soft lines, and replaced both front calipers with reman'd units (when 180psi of air couldn't force out the piston I gave up on rebuilding). The car hadn't had any brake work in 20k+ miles since I replaced the vacuum pump with a mk2 unit, and has driven fine that whole time. When I got everything back together, I was suprised by how much friction is still on the disc when the brakes are released. I can spin the rim by hand, but it won't "freewheel" at all, and though I can spin it with just one hand, I have to grip the tire to do so, I can't just give 'er a slap. I don't remember ever paying attention to how much friction was present before, though. It seems like the anti-rattle clips would hold the pads in some contact with the disc, so maybe this is normal?
Related question: If the brake booster goes bad and I disconnect the vacuum line, should it totally release? And is there a way for a sick MC to cause the brakes to not quite release?
I finished swapping on the new calipers Tuesday night at 1am and tried to take a shortcut by not rebleeding the rears, which didn't work. I had to leave to drive 150 miles to work at 4am, so I ended up taking a train rather than roll the dice on it... so I can't confirm if it is or isnt' misbehaving again.
Thanks for any guidance.
Luke
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#1
by
theman53
on 15 Oct, 2010 05:09
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Not really normal. Should be easier than that. If you released the bleeder it should freewheel like no brake is on. The rubber lines you replaced would be my next guess as they can act like a checkvalve, but you have that covered. Just from what you describe I would guess caliper being bad. See what you find when bleeding it.
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#2
by
rabbitman
on 15 Oct, 2010 11:04
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A disk squeezes to stop and just "relaxes" the rest of the time. So the pads are still slightly rubbing since nothing actually pushes them back.
Squeeze the piston back and make sure the caliper slides good enough.
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#3
by
ldeikis
on 18 Oct, 2010 18:31
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Piston seems to move in the caliper fine, and the caliper pins are well lubed and happy. I rebled everything and took it out for a shake down. Nothing's getting warm. I suspect it was an ailing caliper to begin with, and my concerns about friction were a combo of paranoia and the small amount of rust that appears on the disc when the car isn't able to be driven for a couple weeks. I'm running down to the city with it tomorrow, so here's hoping it's all good.
Thanks for the reassurance.
Luke
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#4
by
8v-of-fury
on 24 Oct, 2010 19:56
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How did this turn out? wasn't a failing wheel bearing was it?
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#5
by
ldeikis
on 08 Nov, 2010 14:55
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It's turning out fine so far. Car has almost 2k on the new calipers. I think my concerns about friction were just paranoia coupled with some slight surface rust on the rotor from sitting around for weeks. Nothing's getting warm, even after city driving where I'm on and off the brakes a lot, and I can give the wheel a good spin (on jack stands) and it'll spin a revolution or so before stopping. As far as push/pull tests, wheel bearings seem ok.
I'm now onto new demons--the battery died while working on the brakes because the door was open all evening with the dome light on. I didn't get it charged back up for a couple weeks while I waiting on parts. Now all of a sudden it doesn't want to hold a charge. Replaced an iffy negative clamp and thought I had it nailed, but this afternoon it wouldn't even turn over again.
Car will run for hours and hours with the lights and blower on once jumped, and will start if it was run decently the day prior, but even 2 days sitting and it turned up with a whopping 8.4v. And my brand new rear hatch seal leaks. But I guess that's another thread.
Luke
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#6
by
rabbitman
on 08 Nov, 2010 19:46
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The friction sounds normal to me, the front wheels also have the driveshafts so it's never gonna spin as easy as the rears.
It kinda sound's like something is draining your battery, it seems like they can sit forever without going down to 8.4v. Is it charging good?
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#7
by
ldeikis
on 18 Nov, 2010 12:50
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Way off topic now, BUT:
I believe the charging system and cables are up to snuff now that it's got a new negative clamp on: If the car is totally 100% dead and I jump it, I can hop on the road and run 3 hours with lights and heater blower on, and when I arrive the battery posts meter 13+v.
It kept running down to nothing, though. It would die dead after sitting even overnight in mild weather. The car has a mostly broken analog radio from the 80s with no electronic memories, and no other accessories.
I pulled the battery positive off and hooked up a multimeter in line to look for a parasitic drain. The only circuit that showed anything was my analog clock, which hopped from 2milliamps to 10mA each second. Kind of funny to watch it jump as the clock tried to tick. This was with a full 13.4v in the battery after putting in on a charger. I popped that fuse out and it reads NO draw at all, as you'd expect. All the same, I don't think 10mA is enough to drain out a battery overnight. New cars run 20-30 with their fancy stuff. The clock is broken anyway, though (it ticks and keeps time for a day or two very accurately, then you'll look down and it'll be 6 hours off all of a sudden), so I wondered if maybe it was intermittently having major issues and running the battery down?
I left the fuse out of the clock circuit for now, which also kills my dome light, which is annoying. That was a few days ago. I haven't metered the battery but it's starting up ok. It doesn't sound as aggressive turning over as I remember, but maybe I'm being nuts. If it holds up a while I'll pop the cluster and cut/unplug the clock so I can get my dome light back.
I have to admit, though, that I still suspect the battery. It ran to dead and sat there, whereas I didn't touch the clock.
Thoughts? I'll try to remember to update if I ever figure it out conclusively. My girlfriend's dad is a mechanic and we're going out of town to visit them for the holiday, so I could ask him to check the battery at the shop. Not sure if it'll be inappropriate at a family visit though.
Luke
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#8
by
clbanman
on 28 Nov, 2010 19:18
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I suspect the battery is toast. Try charging it up like you were and then disconnect the battery cables overnight, reconnect in the morning and try it. (Or do it on the weekend.) If it starts fine, then you have electrical issues, if it does the exact same no start - your battery is toast.
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#9
by
smutts
on 17 Dec, 2010 02:45
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As you probably now know, leaving a lead acid battery dead flat is the quickest way to kill them, especially in cold weather. The modern ones don't give much warning of impending death either.
