Problem: car veers sharply right when braking hard

OK, brake discs are changed as well as pads and the steering is realigned.

And guess what? Problem is still there.

So I am down to the main brakecylinder as last thing to change but since both front brakes go on the same chamber in it I don't see how it could affect it. Unless it is losing pressure into the secondary chamber and the different lengths of the brake lines affect it.

Another thing could be that my hydraulic brakeservo pushes too hard or quick on the main brakecylinder and that affects it. In relation to the original vacuum one that is.

I also checked that primary and secondary circuits are hooked up the same on both front brakes and they are.

Granted I have only driven it like 80km so far so the new parts are not worn in yet so I did not do any real hard braking. It started snowing so I had to head back to base. Brakes are generally noticeably better though.
But it still seems to veer left.
 
Brake issues

I think you should re-confirm the integrity of the brake lines. Without x-ray vision, no telling. But your symptoms are classic for this. Maybe money ahead if you score a set of the stainless lines and give it a go. Nice upgrade anyway.
 
Probably not a pinch, not one I could feel. I could of course put the autobleeder on and remove them one by one at the calipers to see how the fluid flows but that would still not tell me 100%.

If I change the main brake cylinder I could blow pressurised air through them in both directions as I need to rebleed anyway.
 
OK, these may be stupid ideas but inspector Cluseau is a big believer in black box testing.

1 - If the pull is brake circuit related, it should not be directional. One could test by driving fast in reverse and then braking hard. The car would pull in the same direction (left) as it does going forward. If it doesn't pull at all, it may be steering/suspension or rotation related but not brake circuit.

2 - Is it possible to swap the left and right brake lines connections and see if it pulls in the same direction?

Neighbors may speak behind your back after repeated backward braking drills. You are always welcome in Cupertino.
 
Sounds like it is time to take a closer look at the rear brakes, even though it seems unlikely that they could affect the symptoms you have.
 
johanaxelson said:
OK, brake discs are changed as well as pads and the steering is realigned. And guess what? Problem is still there.

. . . .

Granted I have only driven it like 80km so far so the new parts are not worn in yet so I did not do any real hard braking. It started snowing so I had to head back to base. Brakes are generally noticeably better though.
But it still seems to veer left.
Click to expand...

Given what appears to be an improvement, I would consider putting more mileage on the car before proceeding with more work. Still, assuming the issue is pronounced enough to prevent passing an independent (or your own) inspection, here are some followup thoughts.

Given all that you have replaced, could it be that the issue is being magnified by something not specifically related to the brakes. I know you have relatively new suspension bushings, but a a bushing can be new or even look new and still be cracked, torn or distorted. No, I am not saying replace the bushings, just reexamine them. This includes the upper strut mounts.

One thing you did not mention was the road or road condition upon which you experience the issue. When it happens, does it happen on one particular roadway? (One that has the high speed -30 degree- banked turns? lol)

You stated tires are new, but that does not mean automatically ruling them out as possible suspects. We expect speed-rated tires to be perfect, but that is not always the case. Imperfections and tread irregularities can and do occur. This may not result in the tire being out of round, but it can result in a tire with less-than perfectly flat tread. Depending upon the area (inside or outside tread) where the tread is taller or shorter, this could alter alignment and ride/braking characteristics. It may be that any tire irregularity goes unnoticed until you stress the tire/s at just the right road surface and angle. After all - you said the braking problem occurs on one out of every ten stops. Uneven air pressure likewise can affect a tire's diameter and footprint. You seem extremely methodical, but could it be that one front tire has a substantially different inflation pressure than the other? Might not hurt to rotate the tires to a different position and see if this affects things. (I suppose even unidirectional tires could be briefly moved to the opposite side - for a brief period - just to eliminate this as a a possible contributing factor.)
35788d1270641056-uneven-tire-wear-defective-tire-image60.gif
tire_wear_pattern.jpg


The fact that you noticed an improvement after you did some caliper work and swapped pads begs the question, what exactly did you affect? Sorry to bring this up, but given the plastic remnants you found behind the caliper pistons, one has to wonder if you didn’t free something up enough to cause an improvement. However, maybe there is even more debris in the system. Again, all of the above are only wild guesses on my part.

Before incurring more expense and changing brake lines or the master cylinder, consider that some shops will actually put pressure gauges on the brake lines to test for any hydraulic line inequality. (I doubt this procedure is all that common today and unless the operator is familiar with this procedure, there could be a lot of spilled brake fluid.)

You might want to glance at this article. Perhaps it may suggest something you have overlooked.

http://www.tomorrowstechnician.com/Article/610/pulling_you_in_to_brake_diagnostics.aspx
 
@Arde -
I Will try the reversing thing, good idea. As for swapping the lines, it might work. They do seem long enough but it would mean rebleeding the whole system.
And no ideas are stupid ideas :)

@MMercury -
Yes, tires are new and problem was same before the swap. So it should not be tire related but you can of course never know.
The improvement I think is related to new parts, i.e. the brakes are a bit smoother and stronger but the pull to the left is still there.
But after a bit more trying today it does feel like the left caliper is stronger than the right and "closes" faster. When breaking a little harder the left wheel locks before the right. It was a bit slippery out today so I could get the wheels to lock pretty easily without stressing the new parts. And left locked before right nine times out ten.
And the left turn actually occurs more often now, maybe 8 times out of 10 but that I can probably attribute to having eliminated other kinks.

I normally try to make my tests on dry and flat asphalt.

And today I found a place with pressure testers so I can try that.
The little plastic bits do make me a bit nervous and since the lower and left brakelines are fairly short they should be pretty simple to replace but I will go for the main cylinder next I think. It has to be ruled out and is not too difficult to swap.

@Bill -
Yes, I will have to start looking there are some point. I was considering deactivating them for a bit to test. I.e. remove line from brake cylinder and plug hole.

But now I need to stop work for a few weeks, going traveling for a bit. Will post an update after I have changed the main brake cylinder.
 
John,

I know there has been a lot of comments...and I did not see comments for one element (or maybe I missed it if a comment is there)

Have you opened up and inspected the parking brake components within the disc hub?? Could something be binding when you get to speed from an over adjusted Parking Brake??
Jon
 
Maybe not the brakes but the front tension strut rubbers and mounting

I´ve had a similar problem on my E3. Wasn´t related to the brakes at all.

Instead, during heavy braking the wheel excerts quite a pull on the front tension strut that is mounted in a rubber bushing at the front end of the front axle support.
If the rubber bushing on one side is more worn / cracked / softer than the other side, under heavy braking the on wheel will get completly out of alingment during heavy braking causing the car to waeve strongly.

In my case, the cause was even more peculiar, since the rubbers had been changed recently: The washers on the rubbers (the big ones you can actually see from the from of the car were slightly different right to left. One was completely flat and the other convex. Under heavy braking they would make the rubbers flex differently causing the misalignement.

The part are cheap, but changing the rubbers is a pain in the...

parts are 4 & 5 on this picture:

http://realoem.com/bmw/showparts.do?model=4510&mospid=47239&btnr=31_0446&hg=31&fg=05&lang=en

worth checking
 
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Hah, I actually ordered those and the other rubber bushings above them only 2h ago :)

I found that one was soft and one of the washers was the other way around. All were convex though. I turned the washer right and it did not make a big difference but some. So I will swap the bushings.

Question, should all the washers be concave and the round side outwards? Like this () or like this )(. Mine are like () at the moment.



Also one of the rubber bushings above that one was a bit loose. The inspection guys, one oldtimer garage and two doing the steering geometry missed both of those. Idiots.....
I did not know how to look for it but they really should have. Now I know.


Just got back to working on this again, main brake cylinder is now replaced as well.

Will update after I swap those parts. Looks like it will take an hour or two... :)
 
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thx JWShark, that is interesting. I called back to Walloth and Nesch after ordering and they said ().

Sorry to ask but are you sure?

)( would make sense in the way that it puts more pressure on the bushings.
 
Jerry posted the pic which shows proper orientation. The manual also states the words I used. W&N should know better...
Thanks,
Jon
 
Thanks again and sorry for doubting you.

I actually had a quick chat with Peder and his where like () on the car he looked at. So they were the wrong way as well then.

This is odd. Would be interesting to hear from a few more.
 
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oooh, now I get it. You are talking about different bushings.

Look at the link from Tierfreund : http://realoem.com/bmw/showparts.do?...&fg=05&lang=en

4 and 5 are for the bushing at the very front of the trailing link connection. You are referring to the ones at the back.

The ones we were talking about are in 9.9 of your link.
But here it gets interesting again. If you go back one page in your link at look at 9.5 it looks like there is a flat washer up front and a convex one in the back. So like this |(
And on the next page in your link it does say "the convex outer sides of washers 1,2 and 3 shown in 9.11 must face the rubber bushes"
So the convex one does indeed have the convex side inwards.

On my car both were convex and "bulging" outwards. Like this (). Which then is wrong.

But I guess )( or (( would equal |( pressurewise due to the shape of the bushing?



Can some of you who read this please look at your cars? Would be interesting to see how it looks for you.
 
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