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View Full Version : Front eng thunk when going over small bumps



pshirley
04-05-2005, 10:09 PM
I did a search and couldn't find an exact match to my problem. I have a 95 525i with 69K miles. When going over small bumps in the road, like the curb in front of my driveway, it sounds like a solid thunk. Here is what I know.

I installed new Bilstein touring shocks all around.
Factory springs are installed (all suspension is factory).
I have crawled under the car and looked for loose fittings.
I have double checked all the bolts/nuts that I had off for the shocks.
I have tighted the strut housing nut (holds strut in housing).
Top nut on shock is tight.
Both wheels do it the same.
Car drives straight down the road (recent alignment).
Rear upper shock mounts were replaced with shocks.
Pushing on the front fendors the car responds as it should, smooth and responsive.
New Toyo Proxy TPT tires.

Almost seems like something isn't right with the front to back motion of the front suspension (which should be almost zero movement). The up and down is smooth.

One question: Besides getting a shimmy at 50mph (which I haven't noticed), what is the symptom of bushings wearing out?

I would like to hear your best guess on what my problem is. Thanks

bjl4776
04-05-2005, 10:21 PM
Sway bar links are your best bet. Does it happen going into turns sometimes too? If it is then that is probably your problem, get under the car and check the boots and give them a good shake. Its a cheap part if thats the problem, like $20 a pair.

pshirley
04-05-2005, 10:24 PM
The sway bars seem okay. When I jerk on them they don't seem to move much, if at all. I like the idea of them being cheap, maybe I will try them. thx



Sway bar links are your best bet. Does it happen going into turns sometimes too? If it is then that is probably your problem, get under the car and check the boots and give them a good shake. Its a cheap part if thats the problem, like $20 a pair.

Kalevera
04-05-2005, 10:33 PM
Two thoughts:

1) If one of the fasteners for a sway bar link is even remotely loose, it will cause the bump-thunk problem. Before I installed my Sachs kit, I slightly loosened my pass side sway link at the bar, promptly forgot to tighten it back up, then spent a few days riding around CONVINCED that one of my (new) u/l control arm bushings were gone. When I pulled the wheel off again to do the sachs install, I realized that the nut wasn't completely tight and felt like an idiot. I suppose the sway bar bushings could be shot, but you'd have some weird handling and other noises (stop/go) going on, I think.

Edit: sway bar ball joints could also be bad (any cracked rubber boots?). I can't wiggle mine when the car's off the ground. They've got to be quite rigid as that part of the suspension functions as the solidifying link between the two sides on the bottom end.


2) The steering box mounting bolts (to the subframe) can loosen up over time and cause a clunk in low speed turns (check bmwe34.net)

best, whit

Mobius
04-06-2005, 12:57 AM
Sway bar links will be under heavy stress unless both sides of the front suspension are at equal positions relative to eachother. If you jack one side of the car up, the links will appear stiff as hell.

Given how the problem is described, there's not much it CAN be aside from the endlinks. It's remotely possible that a strut collar nut (which holds the strut insert in place) has become loose; but this is a bit more of a longshot than the endlinks.

As has been said, the bolts on the endlinks must be tight. For whatever (dumb) reason the shaft on the endlink ball joints doesn't match the bore of the holes on the swaybar. This little bit of play is more than enough to make noises.

BigKriss
04-06-2005, 02:54 AM
yep, check the swaybar links, Your getting excellent advice from intelligent gentlemen.

pshirley
04-06-2005, 06:06 AM
After work I will crawl back under the front end with 15mm wrenches in hand and check the swaybar links. I might go ahead and get a new set coming. Give me some time and I will send out an update. thanks for everyone's advice. Paul


yep, check the swaybar links, Your getting excellent advice from intelligent gentlemen.

632 Regal
04-06-2005, 06:35 AM
to check them correctly get the front on ramps, go under each swaybar end by the link and push straight up and down. It will be obvious if something is loose or worn.

as for the rest of the steering if you get shimmy is is not nesessarily from old bushings but can be caused by any play in the tie rod ends, drag link or idler arm bushing. This is a lot harder to check for as I had to get mine on a hoist and it was a 2 person job to locate any play. Sure enough I have a loose tie rod end and play at the pitman arm.

Good luck

pshirley
04-06-2005, 09:25 PM
I jerked on the sway bar links the best I could while lying next to the car. I know this isn't as good as being underneath with the car up on ramps, but they sure felt solid..... Tomorrow I will have more time and will put the car on ramps. Either way, I ordered sway bar links from BMA, great price, slow delivery estimation (next week).

I want to make clear that it doesn't feel like something is really out of wack, just on larger that normal bumps (pot holes and curb like heights) is when I feel the harder than expected noise/jolt. I might have mislead a few with my first description.

thanks again, Paul



I did a search and couldn't find an exact match to my problem. I have a 95 525i with 69K miles. When going over small bumps in the road, like the curb in front of my driveway, it sounds like a solid thunk. Here is what I know.

I installed new Bilstein touring shocks all around.
Factory springs are installed (all suspension is factory).
I have crawled under the car and looked for loose fittings.
I have double checked all the bolts/nuts that I had off for the shocks.
I have tighted the strut housing nut (holds strut in housing).
Top nut on shock is tight.
Both wheels do it the same.
Car drives straight down the road (recent alignment).
Rear upper shock mounts were replaced with shocks.
Pushing on the front fendors the car responds as it should, smooth and responsive.
New Toyo Proxy TPT tires.

Almost seems like something isn't right with the front to back motion of the front suspension (which should be almost zero movement). The up and down is smooth.

One question: Besides getting a shimmy at 50mph (which I haven't noticed), what is the symptom of bushings wearing out?

I would like to hear your best guess on what my problem is. Thanks

emw525E34
04-06-2005, 09:40 PM
It is *most likely* the 22mm nut that secures the strut to the mount is NOT tight. It looks tight when the car is set flat without ramps or jacks. But if you use a big wrench to turn it, the whole middle rod will turn. How to hold it ?.

Special monkey wrench below to hold it when you get a few turns in the 22mm nut. When new springs/struts were installed, this is usually the case. This nut need to mildly compress the springs a little during rest. If not, the rebounded spring will raise the front a little. The car, when loaded has about 3 to 6 mm play due to that "raised" REBOUND , so clunk. Then it stays there cos the car is loaded and that play is going. When you park and get off, it rebound and raises again!. This repeats and gets annoying.

Another possiblily is the steering link below the driver side, its about 2 mm lose (needs 2 or 3 turns more), this causes a minor clunk on bumps.

Kalevera
04-06-2005, 09:56 PM
Actually, you can just use a hex key and an open ended (or crow's foot if available) wrench to tighten the strut nut. Every strut insert I've ever seen made for the e34 has had a hex female machined into it.

And also: you do *NOT* want to hold any part of the strut insert's shaft with a monkey wrench...You don't even want to touch it, as it will remove any grease on it that's on there to protect it...Sticking a monkey wrench on it is a quick and easy way to destroy it: if it's correctly installed in the mount, there won't be anything to grab onto except for the shaft.

I still think it's the sway bar links. If the collar nut were loose, you'd be able to see and hear the problem when you jacked up that side of the car.

It may also be a bent dust shield. One of mine is still badly messed up from my front end rebuild. I keep on bending it so it doesn't bang against the rotor (which it does, over some bumps) because replacing it is a pain (have to remove the hub). You'll probably be able to see evidence of it ON the rotor if this is your problem. Mine sounds like a metal "clink" when it happens. Also, (I guess because of suspension geometry) it's much harder to reproduce when the front of the car is up in the air...I guess the shield is closer to the rotor when the sucker's on the ground. But again, this happened because I pulled the strut housing, then stood it up on the dust shield (which bent it).

best, whit

pshirley
04-06-2005, 10:02 PM
I think I understand what nut you are talking about... the nut on the very top of the shock shaft that connects it to the upper mounting bracket? If so, I used an allen wrench to turn the shaft while I held the nut with a gerry-rig'd socket and channel locks. How tight is tight? I was able to get a pretty grip......but maybe not enough.

You description discribes the problem pretty good. I will get the proper tools and try tightening it. thanks, Paul


It is *most likely* the 22mm nut that secures the strut to the mount is NOT tight. It looks tight when the car is set flat without ramps or jacks. But if you use a big wrench to turn it, the whole middle rod will turn. How to hold it ?.

Special monkey wrench below to hold it when you get a few turns in the 22mm nut. When new springs/struts were installed, this is usually the case. This nut need to mildly compress the springs a little during rest. If not, the rebounded spring will raise the front a little. The car, when loaded has about 3 to 6 mm play due to that "raised" REBOUND , so clunk. Then it stays there cos the car is loaded and that play is going. When you park and get off, it rebound and raises again!. This repeats and gets annoying.

Another possiblily is the steering link below the driver side, its about 2 mm lose (needs 2 or 3 turns more), this causes a minor clunk on bumps.

pshirley
04-06-2005, 10:13 PM
Thanks for the feed back everyone. I will double check everything you've mentioned tomorrow. I will update tomorrow. Paul


Actually, you can just use a hex key and an open ended (or crow's foot if available) wrench to tighten the strut nut. Every strut insert I've ever seen made for the e34 has had a hex female machined into it.

And also: you do *NOT* want to hold any part of the strut insert's shaft with a monkey wrench...You don't even want to touch it, as it will remove any grease on it that's on there to protect it...Sticking a monkey wrench on it is a quick and easy way to destroy it: if it's correctly installed in the mount, there won't be anything to grab onto except for the shaft.

I still think it's the sway bar links. If the collar nut were loose, you'd be able to see and hear the problem when you jacked up that side of the car.

It may also be a bent dust shield. One of mine is still badly messed up from my front end rebuild. I keep on bending it so it doesn't bang against the rotor (which it does, over some bumps) because replacing it is a pain (have to remove the hub). You'll probably be able to see evidence of it ON the rotor if this is your problem. Mine sounds like a metal "clink" when it happens. Also, (I guess because of suspension geometry) it's much harder to reproduce when the front of the car is up in the air...I guess the shield is closer to the rotor when the sucker's on the ground. But again, this happened because I pulled the strut housing, then stood it up on the dust shield (which bent it).

best, whit

Kalevera
04-06-2005, 10:14 PM
talking about this one:

http://img.photobucket.com/albums/v736/suzpectx/FrontStrutMount2.jpg

(center nut)

You want to use a hex key and a 19/22mm (depends on the car -- mine's 19mm, yours is probably 22mm) C wrench on the top. Also, be sure to use either a new nylocker nut or some red loctite on it so that it doesn't come loose. It'll be snug when set correctly.


best ,whit

Kalevera
04-06-2005, 10:17 PM
Hey Paul...also, check this out:

http://www.bmw4life.com/images/suspensionLowellPic15.jpg

there's me actually doing what I'm talking about here. read http://www.bmw4life.com for the whole shebang.


EDIT: the wrench I'm using is even the Heyco that's included in the trunk tool kit.

best, whit

pshirley
04-07-2005, 06:07 AM
Lowell, The 22mm nut I have is set down inside the upper mounting bracket making it difficult to access. I plan to get a spark plug socket that will fit it so I can run the allen down the middle and have some to put a wrench on to tighten it. I really think they are snug, but it has been difficult to get much leverage with my current setup.

Nice pictures! I headed to the link now.



Hey Paul...also, check this out:

http://www.bmw4life.com/images/suspensionLowellPic15.jpg

there's me actually doing what I'm talking about here. read http://www.bmw4life.com for the whole shebang.


EDIT: the wrench I'm using is even the Heyco that's included in the trunk tool kit.

best, whit

Mobius
04-07-2005, 11:14 AM
Lowell, The 22mm nut I have is set down inside the upper mounting bracket making it difficult to access. Bah.
http://home.comcast.net/~rjchristie2/SA/535i/0343s.jpg
I should mention that with that stupid hex key I could get nowhere near the torque I needed to break the bolt free. I later used a hex socket and adapted it to a nice long 3/4" ratchet. With a friend of mine holding the socket still, and me leaning on the 22mm wrench, it finally broke.

Torque spec on this bolt is pretty high - something like 90 ft-lbs, if I'm remembering correctly. I don't know how you're going to measure that, but going as tight as you can should be good.

pshirley
04-08-2005, 05:54 AM
I put the car up on ramps last night and checked, and double checked for anything loose. Nothing found.

I also bought cheap 22mm socket and grount to flat spots on the ratchet end that allowed me to get an 22mm open end wrench on it. I cranked as hard as I could hold the allen wrench with a long cresent wrench. These babies are tight, no movement.

I started to wonder if the upper shock mounts are shot. They physically looked okay (nothing broken), but they are extremely stiff/hard maybe even brittle. What are your thoughts? I know the new back mounts I put on were soft and actual flex when weight is put on the rear of the car. The fronts don't move, almost like hard plastic. Is this normal?

thanks again for your help. Paul

Bah.
http://home.comcast.net/~rjchristie2/SA/535i/0343s.jpg
I should mention that with that stupid hex key I could get nowhere near the torque I needed to break the bolt free. I later used a hex socket and adapted it to a nice long 3/4" ratchet. With a friend of mine holding the socket still, and me leaning on the 22mm wrench, it finally broke.

Torque spec on this bolt is pretty high - something like 90 ft-lbs, if I'm remembering correctly. I don't know how you're going to measure that, but going as tight as you can should be good.