Brake Pedal Nearly goes to floor, intermittent - Page 3 - Kia Forum

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post #21 of 37 (permalink) Old 05-04-2019, 05:42 PM Thread Starter
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Originally Posted by rejesterd View Post
Then it's the pedal. ABS wouldn't cause the pedal to go to the floor like that (as far as I understand).

Kia Sorento: Brake Pedal Inspection - Brake System - Brake System - Kia Sorento XM 2011-2019 Service Manual
Kia Sorento: Brake Pedal Adjustment - Brake System - Brake System - Kia Sorento XM 2011-2019 Service Manual

edit: I know your model is older, but it should work the same way.
But the pedal felt fine when the master was plugged. I will have a look at the pedal, but I don't think it is the pedal.

I am back to thinking there is air trapped in the lines somewhere..

I am going to try a new brake bleeding technique today. Attach a long piece of tubing (5m) from the bleeder valve, all the way back to the reservoir on the master cylinder. Fill the reservoir then pump it until the cows come home..

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post #22 of 37 (permalink) Old 05-04-2019, 05:51 PM
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I've been thinking it might be the brake servo or vacuum system. However, I have a diesel which has a slightly different system with a separate vacuum pump on the back of the camshaft. On mine the brake pedal will be hard/high with the engine off, but on starting the pedal will slowly sink (say midway). This is normal and brakes are very efficient.

Setting up new servo/master seems complex: (attached for earlier model with vacuum pump on alternator)
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Last edited by gee6; 05-04-2019 at 05:55 PM.
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post #23 of 37 (permalink) Old 05-05-2019, 02:48 AM Thread Starter
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I've been thinking it might be the brake servo or vacuum system. However, I have a diesel which has a slightly different system with a separate vacuum pump on the back of the camshaft. On mine the brake pedal will be hard/high with the engine off, but on starting the pedal will slowly sink (say midway). This is normal and brakes are very efficient.

Setting up new servo/master seems complex: (attached for earlier model with vacuum pump on alternator)
I think you might be on to something.

I have bled the system to the nth degree, pedal is hard as a rock with the engine not running. As soon as the engine is turned on it becomes quite soft (more-so than just the brake booster should produce). Still also getting the strange 'fading pedal' under feathered light braking pressure...

I am quite certain there is no air in the system at all, I have replaced all 4 calipers and bled the system to death. Thoroughly checked all areas for leaks or ballooning lines, all seems fine..

Another thing I have noticed now is that when turning the wheel a long distance (ie when turning in to my driveway), the pedal will depress further. This is consistently reproducible, unlike the brake fade under light braking which seems to be only intermittent..

I don't quite understand how the vacuum and brake booster interact, but I suspect that possibly the booster is losing vacuum pressure intermittently or under heavy turning? Would the power steering being activated cause a potential loss in vacuum pressure?
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post #24 of 37 (permalink) Old 05-05-2019, 07:03 AM
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ahh.. it's one of the calipers.

When you're turning, either the hose to the caliper is too short, or the caliper is hitting the frame.. Have someone turn the wheel while you look at each caliper. Maybe the banjo bolt on the caliper is hitting a strut.. whatever it is, you should be able to spot it.
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post #25 of 37 (permalink) Old 05-05-2019, 05:14 PM Thread Starter
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ahh.. it's one of the calipers.

When you're turning, either the hose to the caliper is too short, or the caliper is hitting the frame.. Have someone turn the wheel while you look at each caliper. Maybe the banjo bolt on the caliper is hitting a strut.. whatever it is, you should be able to spot it.
Hmm, OK I will have a look at the calipers (front ones only right?) when the wheel is turning to see what they are doing.

Still not sure how that would explain what's going on with the fading pedal in a straight line though?

Anyway, will have a look-see tonight and report back.
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post #26 of 37 (permalink) Old 05-05-2019, 05:31 PM Thread Starter
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Hmm, brain wave. Just did some more reading on the fading pedal when turning issue. Few suggestions are for a bad wheel bearing in either front wheel causing the wheel to lock and the hub to cock slightly when turning (and possibly at low speed), thus pushing back the pistons and increasing brake pedal travel.

I have been getting really bad fuel economy, so that could also be explained (at least partly) a bad wheel bearing (or bearings??).

Thoughts?

It looks like the whole hub needs to be replaced when replacing the wheel bearings, is that right? Can't replace just the bearing itself?
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post #27 of 37 (permalink) Old 05-05-2019, 06:42 PM
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Yep, they sell just the bearings. Easy test is when you jack it up and there's play when you grab the tire and try to wiggle it. It shouldn't wiggle at all.

Could certainly be a bad hub, but see how the front calipers do when you turn the wheel.

The bad fuel economy is probably due to something else.
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post #28 of 37 (permalink) Old 05-07-2019, 05:01 AM Thread Starter
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Sigh.. I jacked up the front end and turned the wheels, both calipers seem fine, aren't hitting on anything or getting puled out of shape when turning. Both hubs seem tight and don't wiggle at all.. Guess it's not that after all.

I have found that if I hold the brake pedal down slightly and drive along a bumpy road, the pedal consistently go towards the floor. Seems like something is pressing back the pistons when the wheels are bumping around and then allowing the pedal travel to increase. Doens't seem like the front wheels though, so I guess it could still be the back wheels? I'll have another look at them tomorrow..

Any other ideas?
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post #29 of 37 (permalink) Old 05-07-2019, 11:08 AM
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Could be a rear hub then.. the correlation with bumping points toward that.

Tough one.

The only other thing I can think of would be the booster.. I know you already did the tests for it, but maybe try to find some other ways to isolate it. I'm sure someone out there is more creative than me.
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post #30 of 37 (permalink) Old 05-07-2019, 04:40 PM
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Shooting in the dark ..... check the flexible hoses between the body and rear axle.


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