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Front end Shimmy ???

Now that I've got the rear end pretty much in order (bearings, springs, shocks) my biggest handling issue is a shimmy or vibration in the front end that only seems to happen at certain speeds (maybe 50-60 MPH). What could cause this ?

I'm not sure, but I don't think it's "bump steer", cause it just wobbles at a fixed rate, not really in response to the road.

Could this be an alignment issue ? Car tends to track straight when I let go of the wheel.

I've bought (but not yet installed) front shocks. Is there anything that I can easily check while I'm in there ?

Thx,
Jeff
Old 09-10-2005, 03:48 PM
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My bet would be the tires need balancing.

I just went through something like this. Had a front end shimmy, so I replaced the wheels and tires but the shimmy was still there. So then I slowly replaced just about everything related to the suspension. Fast forward 2+ years and probably 3000 miles of driving and my shimmy is still there.

Out of desperation I took the wheels in to get balanced again. When I got the wheels back, you could tell that the weights were moved around. Not just a little either. I had one wheel that had like 8 of the sticky weights moved 180 degrees on the wheel. Whoever did the original job really screwed it up. When I drove the car it was so much better as the shimmy was almost gone.

I still need to get my alignment done.....again.
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Old 09-10-2005, 05:40 PM
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I had the same tire issue but on my truck. About 4 months later My 914 had this vibration at speed (50 - 60 mph) so I thought maybe a weight fell off one of the wheels. That was not the case
I found that if I pull on the tire itself I could feel a silght click on the passenger side. I was thinking great, maybe a tire rod end was going. Took it to my mechanic and he said that all that was need was to repack the wheel bearings and make sure the retaining nut was on good and snug, not to tight, but not to loose. That seem to have fixed my problem. YMMV
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Old 09-10-2005, 07:40 PM
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This can be caused by the wheels being out of balance, by the tires having internal problems or external flat spots, by problems with the steering linkage (including the tie rods, the steering shaft, the rack and pinion, etc.), with the struts, with the ball-joints, with the A-arm bushings... In short, everything having to do with the front wheels, the front suspension, or the steering. You need to check them one at a time if you want to eliminate this kind of problem.

Having the wheel balance checked is pretty easy and relatively cheap. Cheaper yet to check all the parts you can visually inspect yourself.

--DD
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Old 09-10-2005, 10:03 PM
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The primary cause of front end wheel shimmy at about 60 mph, but not above or below about 60 mph, is out or round tires. Sometimes in the case of rotors having been drilled for the five bolt conversion, it can be caused by the entire wheel being slightly out of round due to a slight misalignment of the newly drilled roltors.

Phil
Old 09-11-2005, 02:22 PM
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Wow, lots of possibilities. Philinjax, I think the wobble is right around 60 MPH (not sure, as my speedo cable isn't hooked up yet...). And my car did sit w/out being driven for a number of years. So the out-of-round tires sounds like the prime suspect.

Unfortunately, this is probably the last thing I'm gonna get around to changing. I have front shocks on hand already, and to change them I'm gonna have to undo & repack front bearings. While there, I'll have a good look at other stuff, and I'll almost surely booger up my tie rods. And I've already learned once that you should never buy new tires when your alignment has been srewed up...
Old 09-12-2005, 09:00 AM
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You don't have to undo the bearings just to change the shocks!! You don't have to touch the lower end of the strut at all. Just swing it into and out of the fender a bunch of times (out to get clearance to remove stuff like the dust shield, back in to get leverage to remove fasteners like the shock retaining gland nut). No problems!

--DD
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Old 09-12-2005, 09:11 AM
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What Dave says.

Phil
Old 09-12-2005, 09:37 AM
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Wow, that's news to me. I read Haynes backwards and forwards trying to figure out how to change the shocks. Also read the PP Tech Note. But both were about replacing the struts themselves, not just the insert. Glad I asked here first.


I'm still a little confused though. Are you saying that if I undo the top nut and push/pry down on the A-Arm, then the strut will lower enough to swing out and clear the fender ? Do I need to separate the tie rod ?

Also, the Haynes manual talks about fabricating a tool to dissasemble the strut. Is this neccesary or is there any other way ?

I must admit that the shock replacement was sounding pretty daunting; now it sounds like it will be a whole lot simpler. Maybe I won't have to rebuild the whoe front end at once...
Old 09-12-2005, 11:30 AM
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I've changed front struts several times.

The first time, I removed everything - But, I have since learned that you don't have to do that.

Just undo the top nut of the strut/shock (in the trunk). Then, you will have to compress the shock to get it to clear the fender. Just pull down with your hands until it is compressed enough to clear the fender. It's a little harder if you have gas pressurized shocks but can still be done by hand. Once compressed, you can tilt the strut housing so that the top is outside the fender and the strut can be removed.

There's probably a special tool to remove the top screw-on nut that holds the strut in place but I have always used a pipe wrench.

Replace the strut and re-install. I would recommend an alignment but check around to make sure the shop can co it. I initially took my car into Firestone and they told me that the rear wheels cannot be adjusted (which is flat out wrong). Also, if you plan on replacing other parts (like the tie-rods), do this before the alignment.
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Last edited by Tidybuoy; 09-12-2005 at 12:04 PM..
Old 09-12-2005, 11:40 AM
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Okay, thanks to all for the help. Man, I would have done it yesterday if I knew how easy it was...

Jeff
Old 09-12-2005, 12:18 PM
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You won't disturb any of the parts that determine the alignment if you use Tidybouy's method, above. If you're changing tie rods or anything else that does determine the alignment, then you will need to get yours checked after the swap.

The "special tool" that Haynes talks about is for removing the gland nut. I, too, use a pipe wrench. If I had an air chisel I would use that... Most new shocks come with new gland nuts, so you can shred the old one if you have to.

If you go with the pipe wrench, be careful not to chew up the top of the strut housing too badly.

It can help to have a second pair of hands to hold things steady while you loosen and tighten the various nuts and bolts (particularly that gland nut, and also the nut that holds the top of the strut in the trunk), but it is not strictly necessary. Not if you can use your feet to hold the roadwheel steady.

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Old 09-12-2005, 01:00 PM
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My shimmy was at 62 mph as well.
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Old 09-12-2005, 09:27 PM
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PROGRESS :

Last night I changed both front shocks (strut inserts) in about 2 hours. Much, much easier than if I had followed procedure in Haynes ! Handling was better, but the vibration is still there.

About the vibration, here's what I found. On the right side, the wheel felt solid when I grabbed it and shook from side to side, up and down. Tie rod end seemed solid, but boot was rotted and split. On driver side, wheel *did* move a little when I shook it. So, in addition to replacing the shock, I tried tightening the wheel bearings. Still some slop, and I noticed that at least some of the play involved the tie rod moving, and the tie rod itself had a little dent in it. So my guess right now is that ithe problem is where the inner end of tie rod joins the steering rack. My (hopeful) thinking is that if it was slop in the steering rack itself, then it would show up on both sides. Does this sound reasonable ?
Old 09-13-2005, 09:09 AM
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Definitely. If your tie rods have any looseness the front end can vibrate, pull, or shimmy or all three.

I would recommend getting the "turbo Tie Rods". I bought mine at Pelican and they are much better than the stock 914. It is very simple to change them and the steering feels great now.

On mine, I did one side at a time. I took the old one off and then adjusted the new one to be exactly the same (at least very close). Then install. This way, the alignment won't be tooo off. Another way is to count how many turns the ball joint turns to be completely screwed in and then do the same to the new one. I like to do one side at a time so I don't get mixed up and also make some markings on a piece of paper in case I get mixed up I can refer back.

There's also a main ball joint at the bottom of each strut. If these are worn out, that can also be the source of your problem. They are not as easy to remove and replace as they require a special tool. I found a tool at Pep Boys that fit the ball joint perfectly and it was only about $14. When I was done, I sold it on eBay for $20. The ball joints are not too expensive and they have them at Pelican too.

Lastly, don't forget to get your tires balanced. Interestingly, I had my old tires and rims balanced. When I finally acquired a set of Fuchs, two of the wheels did not require any weights and the shop (which is a pretty good shop) told me that they had never seen a rim that was so perfectly balanced.

Vern
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Old 09-13-2005, 02:46 PM
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Okay, so I caved and ordered the Turbo Tie Rod kit. Hope to get it installed before the Red Rocks Classic.

Nice tip on the ball joint tool, BTW.
Old 09-13-2005, 03:11 PM
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I'm fighting similar issue in my '74. I have recently installed turbo tie rod kit, new ball joints, bump steep spacers. My shimmy is very transient at ~60 mph and above, at other times is completely smooth. I also found that front wheel bearings had some play, so I tightened the nut.

Before this work, the shimmy amplitude was much higher; now it's significantly reduced but still intermittently present. It's the intermittent aspect that really puzzles me.

I've had tires rebalanced.

How does one tell if a tire is out of round, and what amount of eccentricity is enough to consider out-of-round? When I jack up each wheel, spin, and observe gap, I don't see substantial variation in gap as tires rotate. Does out-of-roundness increase as tire spins faster (ie: do I need highway speed for such a condition to manifest)?

By the way, I have a couple of tips/observations from turbo kit installation if you're interested.
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Old 09-15-2005, 01:39 AM
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Any tips/observations on TTR install are very welcome.

Since I've found that there *is* slop in my front suspension/steering, I have been ignoring (for now) the tire issue. But one idea I had for testing for tire problems was to borrow a known good pair of wheels/tires from someone and see if there is any difference.

Last time I bought a new set of tires (different car), I took them to a high-end shop for balancing, and was pretty shocked at the price (don't recall, that's how shock works...) Anyway, they said they do dynamic balancing where the wheels are spun at speed and also placed under a load. So maybe it really does depend how the tires are balanced. If the tires are old, or havesat for a long time w/out driving, that could be a problem - I'm assuming that mine are a little flat on the bottom.

Oh, and I noticed you didn't mention alignment. I assume you've had that checked since all the other work ?
Old 09-15-2005, 04:12 PM
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I've decided my vibration (at about 50 for me) is mostly tire (out of) roundness. That and having a car that is such a handling-intensive go-kart; combined with a driver that is all over that aspect make for "high sensitivity". I'm pretty sure a non-Porsche (at least) driver would say "what vibration?" I'm thinking it might be worth getting my next tires at a chain place where I can (maybe) get a replacement.
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Old 09-15-2005, 04:42 PM
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