Top mounts knocking issue ?

MarkM535i · Post by **MarkM535i** » Tue Mar 11, 2014 9:32 am

Hi everyone, im new to this forum. I have an e12 that's been converted to 3.5 motronic, had the car 6 years now and trying to sort one of the last issues I have, there is a knock on the front right, ive looked at all the ball joints, compressed the spring on the car to take the load off and gave everything a good tug, nothing seems loose, im thinking it might be the top mount, any way to test these without taking them off. If I have to take it off, looks like I need a deep socket with a cutout in it to get to the shocker shaft hex. Cant find an FAQ on the procedure. Was wondering also in the top mounts are the same as an e28.
I see them for sale on line, typically $200 each, if anybody has one for sale would be interested.

Many thanks

Mark

JodyStevens · Post by **JodyStevens** » Tue Mar 11, 2014 10:03 am

It's hard to say what the issue would be without being there but it could certainly be the top mount. They are very expensive as you know. If you took it off it would be apparent if it was broken or not.

Easiest way is to take the strut right out. Undo the top 3 nuts on the strut mount and undo the bottom of the strut and take it off the car. To take the top nut of you'll need an impact gun and itll just zip off, dont worry about the hex socket. My method is to put it on the ground and put my foot on the spring and zip the nut off. Works well everytime. I know many people will say to compress the spring first but the nut won't zip off without the spring pressure on the top mount. There is a considerable amount of spring pressure there so be careful. In my experince (50 or so struts) the assembly has never flown apart or had enough power to hurt anything. A slight jolt and its apart.

You should do whatever you are comfortable with. You will need to use the spring compressors to re-assemble the thing though.

GripGreg · Post by **GripGreg** » Tue Mar 11, 2014 11:51 am

Good info, Jody!
Mark, the E12 & E28 chassis are completely different I've been told.
I would think that includes the top mount? I can't confirm that though.
Greg

JodyStevens · Post by **JodyStevens** » Tue Mar 11, 2014 12:40 pm

e12 and e28 top mounts are different.

MarkM535i · Post by **MarkM535i** » Tue Mar 11, 2014 2:36 pm

Thnaks guys, usefull to know. I have spring compressors so think I will whip the strut out and have a look, when you say its easy to see if it looks broken or not, will I see the rubber all falling apart, splitting etc. I know the top mounts have some give, they are a damper of sorts right, not sure how they are made/how they work if that makes sense.

Think I saw them for $44 at something like topgarage.com, if they really are $44 they might be poor quality. Will check my local BMW dismantler for availability on lightly used item

Thanks again, will post how I get on.

JodyStevens · Post by **JodyStevens** » Tue Mar 11, 2014 2:51 pm

Usually the rubber will be all cracked when looking at the top mount before taking it off the car. Thats a pretty good indicator that it needs to be changed. I suspect if your hearing it clunk(and it is in fact the top mount) then you'll have pieces falling apart or missing from the rubber etc. On a new set you wouldn't notice them flexing a whole lot; if at all.

I bought cheap top mounts for the e36 last year and a week later the nut/bolts all sheared off and the struts started banging around violently in the strut towers. I then went and bought the BMW ones for $80 a piece and all has been good. I would advise against the cheapies.

bizz · Post by **bizz** » Tue Mar 11, 2014 6:50 pm

Definitely use spring compressors, better to be safe than sorry.

First thing to check while the strut is in the car is whether the top nut is in fact tight enough - I had one work loose and had a 'clunk' sound. If you have the strut apart, might be worth replacing the top/bottom spring rubbers & bumpstops too.

Mike W. · Post by **Mike W.** » Tue Mar 11, 2014 9:00 pm

Have you checked the shock/strut itself? I had a bad one years ago on an E21 and had a hell of a time figuring it out. It was a definite knock, right side, but everything seemed tight. Well, everything I checked. Seemed there was a loose spot, right at ride height, where there was plenty of play. Uncompressed there was no play.

Confirming, E28 upper mounts are completely different. All the way to the diameter of the bearing hole. Others like E23 or 21 are a long shot but more likely. Just checked, Realoem says no, but E23 might be close. Closer than E28 at least. If it's the bearing, you might be able to peen the staking flat and replace it alone. If it's the rubber...

MarkM535i · Post by **MarkM535i** » Tue Mar 11, 2014 10:50 pm

Ok so got someone to stand on the strut tower, holding on to the open hood they were able to bounce the car pretty hard, knock every bounce, loud. Had a feel around underneath, bottom ball joints, sway bar, track rod ends, cant feel a thing, really does sound to be on the top mount. If I place a screw driver on the strut top, end in my ear (blunt end

you can hear the knocking.

Will check the nut tightness just to be sure, that would be good if it was only that, thanks for the tip.

I have checked the nut that holds the shocker in the strut tube before, rock solid, was wondering if the actual shock was loose in the tube, nut could be tight in a good way, keeping the shock in, or tight in another way, seized and shock is moving around. Next step is take out the strut and disassemble and see what I find. Might take me a week to get round to it way things are, but will post when ive had a look, thanks again everyone.

Mike W. · Post by **Mike W.** » Wed Mar 12, 2014 9:57 pm

I put the wrong shocks in a car one time, I think it was an E3 but I'm not sure anymore. At any rate, I had to use a small spacer to keep things tight, I think it was a ring of 1/8" welding rod between the top of the shock and the nut. I never had any issues, but I throw it out just for reference sake, you never know what a PO put in there or if he did it right unless you check everything.

MarkM535i · Post by **MarkM535i** » Sun Mar 16, 2014 12:15 am

Ok so my local BMW dismantler knew what I needed as soon as I talked to him, he has what he thinks are good ones on an e21 (pretty sure he said e21 and not e23), says they are the same. He should be able to get one for me by Monday.
I bought a 1" 1/16" deep socket (couldn't get 27mm) to get the top nut off, so I should be ready for when I get the top mount. More later.

Going to get put my new front sway bar bushes in Tomorrow, looks like its not too bad a job. It has 1" bar, got some red poly bushes.

MarkM535i · Post by **MarkM535i** » Tue Apr 01, 2014 12:24 am

So I finally got hold of a replacement used top mount, to cut a long story short, got it fitted yesterday, took me about 3 hours in total, and it knocks exactly the same. The old strut top looked ok actually, put the new one on anyway (I have to say it is used, but looks pretty new. While I had the top mount off I checked the locking collar that holds the actual shocker in the strut tube, looks like someone has had a go at it before with a drift/punch and a hammer, couldn't tighten it myself, but couldn't loosen it either. Im back to square one, im wondering if the shock itself is defective, moving up and down, or plain broke. a previous post talked about a 'bad strut', any more ideas on where exactly I could look. My shock 'shaft' is 1.570" diameter, don't know if that tells me anything, standard, uprated, manufacturer etc. It has a hex on the end for external wrench. Good thing is next time I should be able to strip down quicker, always easier the second time.

Mike W. · Post by **Mike W.** » Tue Apr 01, 2014 11:18 pm

When I had a bad shock causing a knocking, it was only loose when compressed, in the air it was tight, but on the ground I could move the top of the wheel. But we may be getting too far out, have you checked the sway bar mounts?

MarkM535i · Post by **MarkM535i** » Tue Apr 01, 2014 11:21 pm

Just used a ball joint splitter to drop the tie rod off, and took off the sway bar link to see if I could isolate the strut more to make sure it is that, still knocking. Almost sounds and looks like the piston is not sliding in and out of the shock evenly at a specific point, imagine if you took out the shock from the strut tube and put a small ding on the side of the shock body itself so the plunger has to 'ride' over a ding at a specific point. I think im going to have to use a big pipe wrench to unscrew the nut/seal that holds the shock into the strut tube, anybody ever done that, using pipe wrench.

JodyStevens · Post by **JodyStevens** » Wed Apr 02, 2014 7:36 am

Most everyone uses a pipe wrench for that job. If its rusty heat it up and use some penetrating oil because it will mangle that nut.