Problem: car veers sharply right when braking hard

[johanaxelson]

and then pops back left.

Unfortunately it would not go through inspection today because of it One thing they do there is take it up to 50km/h and step on the brake.

Not a major issue for me since it stops well but I am not the guy with the badge.

Everything else was fine though. And the brakes are strong and distinct otherwise.

Tried to find another thread on this but did not see one so it may not be a common problem?

The brake system is pretty well serviced:
- Main brake cylinder was renovated 4-5 years ago
- Front brakes renovated 10 years ago
- Not sure about rear brakes
- Hoses changed up front about 6 years ago
- Disks seem OK, no wobbling that I can feel
- Just bled the brakes fully. Not just the top bit. Got some black oil and air out from the top nipple on the front brakes. Seems my shop "forgot" to do them all last time. Rear were OK.
- Pads seem OK but could they do that? Pretty easy to swap them and not too expensive.


I am running out of ideas on this, anyone have any thoughts?

Brakes were bled with a machine, someone once told me that was inferior to manual pumping. Would it really make a difference? Will try and bleed again tomorrow.
Also have some faint memory about reading that this could be fixed by adding something to the right front brake line?

 

[HB Chris]

It could be that the right front caliper is working and the left front is not due to a frozen or dragging piston or plugged brake hose. With nose on jacks can you turn the left wheel with brakes applied?

 

[johanaxelson]

Thx Chris,

the brakes did pass the normal brake test with the rollers so it seems the calipers are OK or it would have shown there. Problem seems to be only when you make an emergency type stop.

The hoses are also pretty new. I had two of them "implode" so I replaced all maybe 4 years back.

Can jack it up and try though, see if I feel any difference at all.

/Johan

 

[61porsche]

Caliper piston orientation

Check and see if the angle of the cut out at the outside edge is correct. Not bearing full on the pad at first; hence the snap. See the manual.

 

[Sven]

Would loose of worn suspension components cause the car to veer?

 

[61porsche]

Snappy Steering

Valve going bad in the power steering pump can do it. But not effect brakes.

Don't think worn suspension would snap. Wander; yes.

 

[cdavie2002]

Double check caliper pistons. Unbolt calipers, apply brake pressure and visually check that they all move freely.

 

[johanaxelson]

Thanks all, will go check the pistons now and bleed a 2nd time to see if there is any new air in there for some reason.


61Porsche - "Check and see if the angle of the cut out at the outside edge is correct."

Am not sure what that means, sorry. Will see if I can find a manual and have a look. I am ashamed to admit I don't have one...

 

[61porsche]

Online

Here you go-http://www.e9-driven.com/GeneralInfo.asp

Click on the repair manual.

The pistons have an particular orientation. By that it means that the edge of the piston has to meet up with the pad in a particular angle to prevent rocking in place. There once were even a tool to measure the position of the piston. from the vertical edge of the caliper. If my memory serves me- 30 degrees from the horizontal edge of the caliper- but pls. check.

 

[johanaxelson]

Thanks again but at the risk of looking like even more of a fool; I can't find that in there. Looked through the brake section in detail but did not find that bit anywhere.

 

[Bwana]

Try here

http://www.e9-driven.com/Public/Library/BMW-E9-Manual/pages/en/34212720.html#refertoc

http://www.e9coupe.com/forum/showthread.php?p=35046

But I don't think this is your problem. Brakes are important! Just rebuild them.

 

[MMercury]

Not aware of any specific brake caliper piston orientation in the front brakes. The two piston rear brakes have a 20 degree orientation. Per Bwana's post this has been addressed before: http://www.e9coupe.com/forum/showthread.php?p=35046 and http://www.e9coupe.com/forum/showthread.php?t=3471 How this would strongly impact front braking (as suggested in the thread) is puzzling.

To the extent I fully comprehend the symptoms, any number of things may cause the erratic braking you describe. As others described, a sticking left caliper may make the right caliper appear to overcompensate - when all it really doing is functioning normally. There are other easily overlooked things to consider. These include contaminated friction surfaces, loose or worn parts such as forward strut (aka braking rod) bushings, control arm bushings, wheel bearings and even tie rod ends. Misalignment, odd ball tire combinations and different tire pressures might also contribute to the mix as might a loose steering box.

Maintenance performed years ago, is no guarantee that some of the installed items haven't developed issues. It may not be likely, but this malady afflicts even new cars with factory installed new parts.

20 Degree measurement on Porsche:


hth.

Good luck.

 

[johanaxelson]

Yeah, brakes are important

But mine are fine and strong except for when I do an emergency brake and lock the wheels. Then it veers sharp right and after 1-2 seconds back again. So yes, it does seem like the left one lags a bit.

@MMercury - tires are brand spanking new and made no difference to the problem. The inspection guys do check all struts, bars etc so they should be OK.

It was raining all day today so not a good day to be out testing brakes, will try to work on it tomorrow.

 

[MMercury]

Yeah, brakes are important

But mine are fine and strong except for when I do an emergency brake and lock the wheels. Then it veers sharp right and after 1-2 seconds back again. So yes, it does seem like the left one lags a bit.

@MMercury - tires are brand spanking new and made no difference to the problem. The inspection guys do check all struts, bars etc so they should be OK.

Did not intend to single out any one component as the culprit. A few additional things come to mind when reviewing the information you provided. We have no way of knowing exactly what type of inspection your car is subjected to and more specifically, the caliber and exactitude of the inspectors. If they are human, your reliance upon them to locate worn parts or badly installed components may be misplaced. Even the best inspector could hardly be expected to be familiar with each and every car on the street, and probably would catch only the most obvious of issues. Someone who works on cars similar to yours -on a regular basis- would be more apt to locate a less-than-obvious, but still potentially serious, problem.

Given the years since the last major maintenance on your braking system, you may be overdue for at least a thorough examination. This might include pulling the pads and inspecting them for glazing or contamination - which might impair braking performance. At the same time you ought to be able to check that each caliper piston is free moving and not leaking any fluid. Same goes for related components such as flex hoses and rotors. Remember that even new parts occasionally fail. While on the subject of routine maintenance, you should be aware that BMW recommends changing brake fluid yearly.

"The brake fluid must be renewed every year. The reason for this is that the brake fluid absorbs moisture through the vent hole in the reservoir. This moisture gradually reduces the boiling point of the brake fluid from 240° C to 160 ÷ 180° C. If this precaution is not taken, heavy use of the brake can lead to steam formation and failure of the brake system."

It bears noting that not all brake fluid is the same, nor are brake pads.http://forums.bimmerforums.com/forum/showthread.php?t=1553395 And even if the best components are used, if they are installed in a sloppy manner, this may not usually result in problems such as yours, but that doesn't mean it can't happen, given your description of the shop that neglected to bleed the brakes. :wink:

 

[johanaxelson]

MMercury -

Oh, I know they can screw up but are pretty meticulous here generally. I went to a garage today and they did not find anything obvious with the struts and bars either.

I also re-bled the system and checked the calipers which did move freely. Pads looked OK too as well as discs.

So I ordered a restoration kit from W&N along with new hoses, should have that in a few days and then we will see. They were unfortunately out of the replacement calipers.

I did try some more breaking today, maybe 20 times, and this happened every time.

Thanks again

 

[gwittman]

I had this problem a few years ago. It was the flexible brake lines. They had swollen on the inside and restricted the flow of the brake fluid. It got so bad that it would not release as quick as it should after stepping on the brake hard. That is when I figured out the problem and replaced the flex brake lines. Stopped as true as could be after that.

Recently, I replaced my rear brake slave cylinders. They were leaking and getting brake fluid on the shoes. This would cause pulling to one side at times. All is well again after the new slave cylinders.

 

[johanaxelson]

Arrgh dammit...

OK, front brakes restored. Bought kits from W&N. All hoses up front changed. Rear were only 4 years old.

Hoses took way longer than planned since they very really stuck and the heads on the bolts soft so now I have 4 round ones. Blowtorch loosed the most damages ones. Ran out of time so I could not change the lines. Next year....

Brakes themselves had to be taken apart in halves as pistons were pretty stuck. Taking them apart was a bitch. Had to use the blowtorch on every single nut. But they were pretty much OK on the inside. No rust at all and just a little bit of plastic loose behind two of the pistons.

So, everything put back together and problem is still there

Not as much as before but still happens sometimes.
I.e. I break really hard at 50kph and the the car veers very sharply left (I wrote right earlier, my bad)
I should mention it does not happen right away but maybe 2-3 seconds after I hit the pedal as it is about to come to a full stop. So kind of like there is a pressure drop on one side after a while.
Now it happens maybe one out of 10 times. The other times it will stop as it should or cringe a little left and right as it is stopping which I guess is OK?

So what can it be? Master cylinder? It was restored maybe four years ago so it should be OK. And should it not happen more often if it was bad?

Pads? I did not change those but can it really be them? Are original BMW pads. They and the disks are pretty much perfectly smooth. Almost no wear. I have a spare set, maybe change to those. Or just swap sides and see what happens.

 

[MMercury]

Brakes themselves had to be taken apart in halves as pistons were pretty stuck. . . . No rust at all and just a little bit of plastic loose behind two of the pistons.

So, everything put back together and problem is still there :sad:

I should mention it does not happen right away but maybe 2-3 seconds after I hit the pedal as it is about to come to a full stop. So kind of like there is a pressure drop on one side after a while. Now it happens maybe one out of 10 times. The other times it will stop as it should or cringe a little left and right as it is stopping which I guess is OK?

So what can it be? Master cylinder? Pads? I did not change those but can it really be them? Are original BMW pads. They and the disks are pretty much perfectly smooth. Almost no wear. I have a spare set, maybe change to those. Or just swap sides and see what happens.

Sorry to hear about those continuing demons. The simplest thing for you to check on are the pads. The fact that they appear to be wearing smoothly is not particularly determinative of their quality or performance. I would wager that you could grease the rotor faces and everything would wear very smoothly too, although braking would be practically non-existent. :wink:

As noted before, different friction compounds have different personalities. All of the pads carry trade-offs including wear rates, longevity, noise, dusting and of course -resistance to fade and heat. Your panic stops may be demonstrating that your current pads may be decent for normal driving and not terribly good for the track or severe use. I would be inclined to try a different pad, and perhaps even an aftermarket version. (FWIW, my limited experience with the ceramic-based compounds used on Japanese vehicles has been pretty good.) Who knows, better pads, may actually cost more. But again, everything is relative and as the cliche goes, "your mileage may vary."

http://www.brakeworld.com/brake-pads.asp

It is curious you found both sticking calipers - and plastic debris behind some of the pistons. This could suggest many other issues - or none. Could it be that some of the debris was plugging the internal passages to the calipers and that some still remains? In any event, foreign material (especially hard plastic) couldn't be good for any seals. Naturally, if the plastic entered the system aft of the master cylinder, that could have resulted in decreased pressure as you hypothesize. Given that the weird braking issue does not present itself except for one in ten efforts, I would doubt that is the problem though.

Best of luck.

P.S.:

From: http://www.consumerreports.org/cro/...rake-pads-what-to-look-for/overview/index.htm

"Do you need new brake pads?
Usually, the first sign of excessive brake-pad wear is a high-pitched squealing. This sound comes from a soft-metal wear indicator that rubs against the brake rotor to alert the driver that a change is needed. Other symptoms can include the vehicle pulling to one side under braking, the brakes grabbing or vibrating, and the brake pedal feeling softer to depress. A grinding sound means that replacement is overdue and the worn brake pads may be damaging the brake rotors. Always check the owner's manual for any brake-related recommendations, including pad replacement intervals."

 

[johanaxelson]

Thanks MMercury,

I would not say they were really sticking but the place I was in did not have any kind of special tool to remove them so I had to make do with different types of pliers and with the limited amount of space "inside" the caliper it was difficult to get a good hold. But the guy who owns the place tried and said they were harder to remove than normal. Did not need excessive force to be removed though.
The bits of plastic were a little odd though, not sure where they come from. were bigger than the holes were the oil comes in but the gaskets were not really frayed. Could have been there a week or 10 years... I did clean out the channels with pressurized air and nothing came out. It was softish though.

Will swap the pads on Monday for my spare ones. BMW originals and maybe 10 years old. Will hopefully be OK. Should at least be different in some way. And pray to whatever deity is in charge of E9s that works and your last pasted text is correct.

 

[sfdon]

make sure sand your rotors and pads before assembly- nice and roughened up is the key..
Polished rotors are worthless.