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E34 (1989 - 1995)

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  #1  
Old 10-22-2014, 12:20 AM
capricornbmw capricornbmw is offline
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Tighter brakes after hard stop/ABS stop

Hi Everyone,

My brakes are ok but they become tighter during normal braking after a hard brake from speed, often a hard brake involving the ABS. After some time, the brakes seem to go back to normal.

What does this indicate? If it indicates a particular type of failure, is there any other type of check that I can do without removing it, to confirm that it is faulty?

Fixes :

Calliper seals are new, rotors are new and pads are 2 years old redstuff still good wear, new Dot4 Bosch oil, 2 yr old oem booster and 4 year old oem master cylinder (both were new), system fully bled with calliper pistons squeezed during bleeding as well. New stainless steel brake hoses as well. Rear pads and discs are 4 years old. No uneven braking, no brake judder (fixed that with new upper arm bushings and new front disc rotors). No brake system leaks. No brake system codes.

The one way valve near the intake manifold is new, as are the two vacuum hoses, their clips, the plastic fitting at the brake booster, and the rubber grommet there as well. I've also silicone sealed the rubber grommet and the plastic fitting good, and have siliconed sealed each vacuum hose at its end even after the new clips were used and properly tightened.

I'm well aware that it is possible to buy a new part that is defective, or fails too quickly. Learn that the hard way here. But before I go doing something I need your advice on what is the cause of this strange behaviour. Thanks.

p.s. Brakes have never been ABS bleeded. Was told that ABS bleeding does not apply to our car. However it seems the later 5 series cars require carsoft to be hooked up and the ABS cycled or something. Is this a factor?
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Last edited by capricornbmw; 10-22-2014 at 09:10 PM.
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  #2  
Old 10-22-2014, 01:20 AM
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I would be servicing the calipers AND the MOUNTING PINS correctley before spending real money
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  #3  
Old 10-22-2014, 04:38 AM
capricornbmw capricornbmw is offline
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Originally Posted by BMWFatherFigure View Post
I would be servicing the calipers AND the MOUNTING PINS correctley before spending real money
Ok, I believe I have done that too. Anyway FF, how would unserviced callipers and unserviced mounting pins lead to the symptom I've described in my op ? Thanks.
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  #4  
Old 10-22-2014, 09:58 AM
capricornbmw capricornbmw is offline
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Quote:
Originally Posted by capricornbmw View Post
Hi Everyone,

My brakes are ok but they become tighter during normal braking after a hard brake from speed, often a hard brake involving the ABS. After some time, the brakes seem to go back to normal.

What does this indicate? If it indicates a particular type of failure, is there any other type of check that I can do without removing it, to confirm that it is faulty?
Could this be a problem with ABS bleeding? I've never done any ABS activation to bleed.

Could this be a problem with the master cylinder?

Is this actually normal behaviour?
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  #5  
Old 10-22-2014, 10:17 AM
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Doktor Bert Doktor Bert is offline
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Greater/larger piston surface area or pad surface area is not what increases braking performance. The use of multiple pistons and/or larger diameter caliper pistons result in a multiplication of mechanical force. To move the larger pistons, more brake fluid volume is needed. In my experience, this will result in more brake pedal travel, but no increase in pedal effort...FWIW
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Old 10-22-2014, 10:18 AM
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Quote:
Originally Posted by capricornbmw View Post
Hi Everyone,

My brakes are ok but they become tighter during normal braking after a hard brake from speed, often a hard brake involving the ABS. After some time, the brakes seem to go back to normal...
Need a better description of this...
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Old 10-22-2014, 05:06 PM
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The pedal firming up after a hard stop is normal. It's from a combination of factors involving shock loading of a hydraulic system (bulk modulus, seals, etc.), but suffice to say entirely not unique to the OP's car.

OTOH, if the brakes continue to drag after a hard stop, that would be a problem.

If there's any doubt regarding the bleed job, take it to a reputable indi or the dealership to have the ABS cycled while power bled. Worth every penny for the piece of mind the next time you're required to drop anchor.
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Last edited by Radian; 10-22-2014 at 05:13 PM.
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  #8  
Old 10-22-2014, 06:10 PM
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There is a DIY floating around here for bleeding the ABS on the E34, i just went on a dirt road an locked the brakes up a few times and re-bred, repeated it 4 times.
I blew a driver rear line when i drove my car home for the first time.
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  #9  
Old 10-22-2014, 06:18 PM
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Read this and the following
http://www.bimmerfest.com/forums/sho...d.php?t=616295
I know the following is E36, but should be applicable to the E34
http://forums.bimmerforums.com/forum...w-to-Cycle-ABS
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  #10  
Old 10-22-2014, 07:22 PM
capricornbmw capricornbmw is offline
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Thanks guys !! Lemme read through the links and stuff first and reply in detail in abit.
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Old 10-22-2014, 07:37 PM
capricornbmw capricornbmw is offline
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Can someone confirm that the ABS solenoids in our E34s are by default open, even while driving, and when the abs is activated the solenoids actually close valves and thus control braking to individual wheels ?

I read this somewhere and if it is true then would there be a need to cycle through the ABS during bleeding, since the brake fluid passages are always open as ABS is not activated ?
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Old 10-22-2014, 07:40 PM
capricornbmw capricornbmw is offline
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Quote:
Originally Posted by E34ZombieHunter View Post
Read this and the following
http://www.bimmerfest.com/forums/sho...d.php?t=616295
I know the following is E36, but should be applicable to the E34
http://forums.bimmerforums.com/forum...w-to-Cycle-ABS
Zombie, I encountered that bimmerforums thread a little earlier while reading up. It seems to have certain features unique to cars which have automatic stability and traction control (ASC/T). Most of our E34s only had ABS and not ABS with stability and traction control.

Could the ABS cycling procedures be different for non ASCT cars?

Could the ABS unit itself be a different construction between both types?

Could ABS bleeding be unnecessary for ABS-only cars?
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  #13  
Old 10-22-2014, 07:45 PM
capricornbmw capricornbmw is offline
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Quote:
Originally Posted by E34ZombieHunter View Post
There is a DIY floating around here for bleeding the ABS on the E34, i just went on a dirt road an locked the brakes up a few times and re-bred, repeated it 4 times.
I blew a driver rear line when i drove my car home for the first time.

Er....blew a rear line ie rear brake line ? Does that mean your brakes were too good? Apologies, I'm not really following you here.

What happened immediately after you dirt road braked and bled the brakes 4 times ? Was your normal braking better each time? Was your normal braking better, ultimately tighter, the after the 4th post braking bleed?
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  #14  
Old 10-22-2014, 08:14 PM
capricornbmw capricornbmw is offline
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It looks like cars with stability and tractions control have a separate ABS pump filled with brake fluid, but cars with just the ABS do not have an ABS pump. Can someone confirm this ?
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  #15  
Old 10-22-2014, 08:16 PM
capricornbmw capricornbmw is offline
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Originally Posted by Doktor Bert View Post
Need a better description of this...
Ok after hard braking, my brakes are tighter during normal ordinary braking. The pedal response seems quicker, there is less sponginess, its seems there's more bite at the wheels although i could be imagining this and its just that i get to the usual biting point more quickly, it is harder....its what I want my brakes to be all the time sigh.
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Last edited by capricornbmw; 10-22-2014 at 08:17 PM.
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  #16  
Old 10-22-2014, 09:02 PM
aalpine1 aalpine1 is offline
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I would check the brake booster's one way valve.

This valve on my car look good, no hissing sounds, no cracks; however, the idle was not always steady and the brake pedal was lower than normal. After I changed this part I had better brakes and I did not experience any idle issues.
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  #17  
Old 10-22-2014, 09:08 PM
capricornbmw capricornbmw is offline
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Originally Posted by aalpine1 View Post


I would check the brake booster's one way valve.

This valve on my car look good, no hissing sounds, no cracks; however, the idle was not always steady and the brake pedal was lower than normal. After I changed this part I had better brakes and I did not experience any idle issues.
Good point aalpine1 and yes that is the first thing I went for. I forgot to mention in my op, the one way valve is new, as are the two vacuum hoses, their clips, the plastic fitting at the brake booster, and the rubber grommet there as well.

That said, I join aalpine1 in encouraging everyone to get this changed. It is a cheap part like under $10, can be diyed easily...the only thing to remember is to shut off the engine and pump the brakes a few times to bleed off vaccum if not it will be difficult to remove this valve from the lower hose that leads to the booster.

I'll update my op with this info. Thanks.
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Last edited by capricornbmw; 10-22-2014 at 09:12 PM.
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  #18  
Old 10-22-2014, 09:17 PM
aalpine1 aalpine1 is offline
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How did you bleed your brakes ? When was the last time that you did this ?

To my best knowledge, for an e34 when you are bleeding the brakes you are also bleeding what it is also in the ABS lines. However, to be sure you can go and do some hard braking and re-bleed the brake system to be sure that you changed also what was in the ABS unit.
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  #19  
Old 10-23-2014, 12:28 AM
capricornbmw capricornbmw is offline
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Originally Posted by aalpine1 View Post
How did you bleed your brakes ? When was the last time that you did this ?

To my best knowledge, for an e34 when you are bleeding the brakes you are also bleeding what it is also in the ABS lines. However, to be sure you can go and do some hard braking and re-bleed the brake system to be sure that you changed also what was in the ABS unit.
Hi Alpine let me quote what I posted in the other thread I think it is relevant :

Quote:
Originally Posted by capricornbmw View Post
I have studied the matter and these are my preliminary conclusions about the differences between abs only and abs + asct systems.

1. ABS only has a chance to work when the driver consciously brakes the car (and the appropriate wheel slippage is detected subsequently). It does not apply automatically.

2. ASCT is always live and always in operation, as wheels may slip during normal driving over different surfaces, and as soon as a differential wheel slip is detected the asct system has to react instantly. It is independant of the driver. And it does not function to brake the vehicle, but to maintain control at perhaps just one specific wheel, so it needs its own dedicated pump to do this. And of course that pump is in a brake line circuit of its own and requires independant bleeding/activation by DIS for proper bleeding.

3. ABS's master cylinder system is all that it needs to be itself.

In fact, asct is not an enhanced braking system at all, it is a stability control system pure and simple and is dovetailed with the existing braking setup because it uses the same basic tools (callipers, pads, discs, oil, oil lines ) to achieve its task, so they can be intelligently shared.

As such, there is no such thing as ABS bleeding, it should be ASCT or ASC/T bleeding. And as such, on cars only equipped with ABS, there is no special bleeding method required.

On cars with ASCT, they need software to activate the asc unit while bleeding all 4 wheels, or they need to do heavy braking several times and then bleed, or they need to directly bleed from the asct unit's pump's bleeder, to get all the air out. Of these three methods, the third is the one I consider ideal, and in cases where such a car needs general brake bleeding, I would first bleed to four wheels with calliper bleeding included, then bleed the asct pump separately, then fill up the brake fluid reservoir, then test the brakes during driving. The brakes should be excellent, and there should be no difference in the normal braking before and after a hard abs/asct brake.

ndrzdad, can you confirm if my understanding is correct? Thank you.


rgds,
Cap
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  #20  
Old 10-23-2014, 12:30 AM
capricornbmw capricornbmw is offline
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Quote:
Originally Posted by aalpine1 View Post
How did you bleed your brakes ? When was the last time that you did this ?

To my best knowledge, for an e34 when you are bleeding the brakes you are also bleeding what it is also in the ABS lines. However, to be sure you can go and do some hard braking and re-bleed the brake system to be sure that you changed also what was in the ABS unit.
I last bled my brakes 3 months ago and I bled it three different times in the 3 months before that.

All methods were use for the bleeding...the manual pump method, the vacuum suction method, the calliper squeeze method (this led to a small but noticeable improvement in braking). But the main sponginess was unchanged and the phenomenon of better brakes following a hard brake was still there.
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  #21  
Old 10-23-2014, 05:18 AM
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Quote:
Originally Posted by capricornbmw View Post
Er....blew a rear line ie rear brake line ? Does that mean your brakes were too good? Apologies, I'm not really following you here.

What happened immediately after you dirt road braked and bled the brakes 4 times ? Was your normal braking better each time? Was your normal braking better, ultimately tighter, the after the 4th post braking bleed?
Yes a steel line blew in the rear near the wheel, it is a short section the connects the main line from the body to the rubber line, so it was easily replaced. I have another somewhere for the other side since the parts store gave me the wrong one but did not take it back when they refunded the money.
Now that i think of it my ABS setup does look different than some i see at the JY, and i do have ASC+t.

The pedal felt strange and after ABS activations and bleeding it got a bit more firm, and i did get more air after the activation the first time or two.
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  #22  
Old 10-23-2014, 09:09 AM
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Hey, since you all brought up the check valve, I can never seem to find it's replacement along with the grommet.

Best I've found so far, please help:

Valve - but it says for 1998

Grommet - but it says for 525i

Please share better solutions, and I'll delete these links to avoid potential confusion.
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  #23  
Old 10-23-2014, 11:10 AM
aalpine1 aalpine1 is offline
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here you go -> http://www.ebay.com/itm/BMW-e30-e32-...4dd47c&vxp=mtr
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  #24  
Old 10-23-2014, 11:29 AM
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Yeah, I've seen that one. Problem is, mine doesn't have that smaller nipple on it. The pieces I've referenced appear aesthetically correct, but I'm not looking to guinea pig this sort of thing.
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  #25  
Old 10-23-2014, 11:53 AM
aalpine1 aalpine1 is offline
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Probably yours is missing the little nipple and someone glue something else in (or is from a different model). When I looked on realoem to replace mine I was looking for one that would not have the useless nipple, but I could not find one for the E34. However, in this case it does not matter how it looks, or if it has the little nipple or not. The only important thing is not to leak!

I have on my `93 525i (m50b25tu) the part from ebay.

OP how is the brake fluid level after a hard brake (with ABS) and the pedal is behaving unusual ?

I cannot go to the car right now, but does the e34 brake pump have the little valve for bleeding ?
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Last edited by aalpine1; 10-23-2014 at 11:59 AM.
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