bmw e30 "crunchy" brakes

My 89 325i has a brake problem I haven't experienced before on any other car. Several times a day, when the brake pedal is depressed it feels (for the lack of a better term) crunchy,
a bit like the ABS is kicking in. For those of you who live up north, it feels exactly like stepping on snow that partly melted and then re-froze. This has been going on for several months and seems to be getting more frequent.
My mechanic, who used to own the car, couldn't find anything wrong, although we did replace one set of brake pads (and inspected the other), and that didn't help. He thought it might be the ABS controller, and so I tried a couple of used ones (new ones are outrageously expensive), and this also didn't help.
Any ideas of what else it could be? Is this a common E30 problem?
Thanks for any advice.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Nedavno dhs napisa:

I do not know if this is legal / safe, but you could try driving with ABS disconnected to find out if it is ABS related.
--
___ ____
/__/ / \ ** Registrovani korisnik Linuksa #291606 **
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Safe (and easy/cheap) would be the more important issues, at least for short-term trouble-shooting. Is this something I can do myself, or will I need to take it to my mechanic? I'm inclined to believe that at least one of the two used controller/computers that I tried was good, so could there still be ABS problems causing this? Could it be the ABS sensors or the hydraulics? When I deliberately engage the ABS (jamming on the brakes on a wet/dusty road), it seems to work normally.
And is this a common problem on E30s? I've searched with Google, and didn't find any mention of this type of problem.
Thanks,
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

You can disable the ABS by pulling the right fuse.
I've heard of ABS problems being caused by a chafed wire to a wheel sensor shroting out. But it's pretty rare.
When did you last have a brake fluid change? Maybe there's air in the system?
--
Who needs a life when you've got Unix? :-)
Email: snipped-for-privacy@unixnerd.demon.co.uk, John G.Burns B.Eng, Bonny Scotland
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It's possible the ABS is kicking in. Pull out the ABS relay and see if the problem persists. If it still happens, it's an ABS issue. There is no harm in driving with the ABS disabled for a while if you brake properly. --scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

OK, I yanked the ABS relay, and didn't see the problem see the problem in a 20min test drive.

I would have thought the opposite - that if the problem doesn't happen with the ABS effectively disconnected, that this points to an ABS problem?
If so, could this be the relay? The ABS light has been intermittently on in the last few months (and is, of course, on with the relay removed). The relay, unlike the controller, is cheap enough to buy new. Or maybe I have 3 bad controllers or ???
If not, I'm not sure when I last changed the brake fluid, as another poster suggested - would that be a good place to start?
Thanks,
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Sounds like an ABS issue, then. Drive it around for a week or two like that and see if the problem appears again. Intermittents are funy.

Yes, I posted that before having my morning tea.

Wait.... wait... the ABS light has been intermittently coming on and you did not associate it with your problem?
It could be the relay, but probably not. It could be an intermittent wheel sensor or a wiring issue, too.

I don't know, and I don't know if your ABS system is new enough to generate proper error codes for diagnosis. I do know that if you continue to swap parts out without doing actual diagnosis, it will cost you a fortune before you find the problem.
If you HAVE established that it's an ABS problem, you're probably going to have to take it to an ABS guru. I don't drive any cars new enough to have ABS so I don't work on the things much. I generally don't like the whole idea of ABS but that's another story.

It probably has nothing to do with the issue, but you need to change it out anyway to prevent other problems in the future. While you are at it, do you remember when you last changed your transmission and differential fluids? How about coolant? You gotta do this stuff. --scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

OK - I'll try that, but the 20min drive was probably enough, since the problem usually appears now every 4-5 stops.

For the first 2 months that I saw this problem, the ABS light wasn't coming on - it's just been the last few months and it's not 100% correlated with the perceived brake problems.

Any cost-effective way to check these? I have the Bentley manual and a meter.

Eventually (see above). But the two controllers cost me $50 and about 10min to swap them in, and sometimes swapping parts is cheaper than taking it to even a competent mechanic.

I don't either - this is the first car I've ever owned that had ABS, and it never kicked in until it started acting up. Figures.

I actually do - I just don't remember if the brake fluid was changed when we did the brakes earlier this year or last year. I change my oil every 3 months, and the other fluids at least every other year.
I think your advice about an ABS guru is probably the best course of action, but finding one is another matter. One of my complaints about mechanics is that they all charge by the hour, regardless of whether they solve the problem or not. So its often cheaper to just swap-in lesser components (used ABS controllers, ABS relays, etc) yourself - even if you don't solve the problem, you still have probably saved money because the mechanic won't need to try those simple things.
Any recommendations for ABS (BMW?) gurus in Austin TX?
Thanks,
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Bad form to follow-up your own posts, but I did want to note that I ordered a new relay and will try that - the old one had loose connectors that could cause signals that may have confused the controller. But if that doesn't work, are there computer diagnostics for ABS problems on an 89 325i? The sensors are $150/per. Before I replace one, I'd like to have some reason to believe that it's defective. A quick visual inspection didn't show any damage.
Thanks,

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.