HOW TO DO AN ADVANCED SEARCH.

Mon Jul 08, 2013 3:56 pm by Admin


For the benefit of 944Hybrids users there are two search functions available for you to use.
The purpose of this sticky is to explain the "Advanced Search" function because it is much more powerful and is the best choice when researching information.

When you log on to the site a list of options is shown in a line at the top of the page. One option is labelled "Search", use this option (NOT the search box lower down on the right).

After you click on the upper search option, a drop down box appears. At the bottom of this box is a radio button marked "Advanced …

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Wheel vibration

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Wheel vibration

Post  948inVA on Mon Oct 22, 2012 3:49 pm

Hey guys, need some help with this one. Since completing the swap I've been having pretty bad vibration through the steering wheel at highway speeds. I had the alignment done, no change. Had the front wheels road force balanced, no change. Installed new front bearings, new rotors and tried a different set of wheels+tires, no change. Everything on the front end is tight - bearings, ball joints recently replaced and there's no slop in the steering shaft that I can see. I haven't done the caster blocks but they look fine. At this point I'm wondering if it could be a bent hub, the front left rotor (which is new) has a bit of runout. Or maybe they screwed up the alignment. Any thoughts?

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Re: Wheel vibration

Post  Porch on Mon Oct 22, 2012 7:25 pm

I didn't see you mention the tie-rod ends, are you certain those are in good shape?

I also think it's worth upgrading to the 968 caster blocks, they're pretty cheap on ebay, and it's not going to be a waste if it doesn't fix the problem.
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Re: Wheel vibration

Post  948inVA on Mon Oct 22, 2012 9:07 pm

Tie rods and ends are new.. I tried adjusting toe out 1/8 turn on each side and it seemed to help, I'll have a better chance to test it tomorrow. I was able to get one of the inner tie rods to click if I rock the tire, but there's no noticeable movement.
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Re: Wheel vibration

Post  Vorsche944 on Mon Oct 22, 2012 9:16 pm

Wheels, are they Porsche or after market. I found that spacers can affect hub centric wheels as well as after market wheels are not always hub centric and that can cause some serious vibration too.


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Re: Wheel vibration

Post  948inVA on Tue Oct 23, 2012 12:38 am

I've tried both.. one set are replicas with early offset, the other set are oem cup2s and I used adaptec wheel adapters which are hub and wheel centric.
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Re: Wheel vibration

Post  Admin on Tue Oct 23, 2012 8:00 am

Change the rack, The inner gear has gone out on my car and it has a shake at about 60, Couldn't find anything wrong. Everything was tight , until I jacked up the car I could move the inner part of the tie rod up and down about a 1/4". I guess there is a bushing that wears out in there.

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Re: Wheel vibration

Post  Rich L. on Tue Oct 23, 2012 11:03 am

I'd suspect that left front hub. "A bit of runout" with a new rotor sounds like a smoking gun. A bent hub was the cause of my vibration that only showed up in hard left hand corners. You could start by swapping the hubs only and see if that runout is fixed.

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Re: Wheel vibration

Post  948 on Tue Oct 23, 2012 11:43 am

The 944 is known to have a slight resonance in the steering at about 60-70 mph, supposedly one of the reasons why power steering became standard after 84'. I have experienced it after converting my Turbo to a true manual rack.....
It is possible that worn items or maladjusted items could amplify this phenomena and/or change its point of occurrence....?

As already mentioned, I would continue to look for worn components and check your alignment specs again.

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Re: Wheel vibration

Post  948inVA on Tue Oct 23, 2012 2:08 pm

Thanks for the ideas, after setting the toe out a bit the vibration is still there. At 60 it's smooth, 65 to 75 it shimmies pretty bad, then it smooths out again by 80. Weird thing is that if I drive on fresh pavement I can almost get it to smooth out if I keep constant speed. Seems to feel worse when accelerating or coasting.

The rack is tight.. I took it apart and rebuilt it before installing on the car, and the bushing was fine. I suppose I should have this second set of wheels balanced just in case - just going on the word of the seller that they were good. I'll also check out the hub, but I would have thought I'd be getting brake pedal vibration from the rotor and I'm getting nothing. Only other thing I can think of is that the tech who did my alignment mentioned one of the struts having some movement when he was checking things over.. I wasn't quite sure what he meant but he didn't seem to think it was an issue. I'm using bilstein inserts on early strut housings and they're only a couple years old.

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vibe

Post  kevin924kevin on Tue Oct 23, 2012 2:15 pm

Just my 2 cents, but my car is manual from factory, it has a little over 100 000k on it and i have never had any sort of vibration, this car has beeen maxed out and all has been good.This sounds like a speed wable, which means there is a worn out part some where in the front end.on other types of vehicles they used to run steering dampers to correct this issue. Like i say my 2 cents worth. Good luck.
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Re: Wheel vibration

Post  87-944S on Tue Oct 23, 2012 9:24 pm

Strut movement, possibly strut bearing?
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Re: Wheel vibration

Post  948inVA on Wed Oct 24, 2012 3:14 pm

Strut bearings are same age as the shocks.. replaced with new 2 or 3 years ago and not many miles on them. I was not able to replicate the strut movement myself, just going on what the alignment tech told me. The only parts on the front end that I haven't replaced are the control arm bushings and castor blocks. Just doesn't seem likely that they could be the problem if they feel tight with the wheels off the ground. I inspected the rotor/hub again and I think the hub is fine, the rotor was just catching on the pads where there was a pad imprint and it wasn't a warped rotor. No visible runout on my wheel spacer either. I still find it hard to believe it could be a suspension issue unless there were some seriously worn parts.
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Re: Wheel vibration

Post  944convert on Wed Oct 24, 2012 3:37 pm

A few years back I developed a bad shimmy problem. Turned out my control arm bushings (which were aftermarket & had a lot less than 10k miles on them) were shot. I replaced them with Weltmeister "reds" with no more problems.

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Re: Wheel vibration

Post  bp944 on Thu Oct 25, 2012 9:38 am

I had a similiar problem and it turns out my front right hub was bent. The only difference was that my wobble was scary enough that I never took it past 65 to see if it eventually went away. The only reason I knew the hub was bent was because the grease cap wouldn't go back on one of the hubs when I changed the wheel bearings. Both caps would fit in the left hub but neither would fit in the right. Its an easy check to see if your hub was as bad as mine.

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Re: Wheel vibration

Post  docwyte on Thu Oct 25, 2012 12:43 pm

I had this and it was unevenly worn brake pads caused by worn calipers. If I didn't put the pads back in where I pulled them from, with the exact same orientation, the pads would rub the rotors and cause vibrations.

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Re: Wheel vibration

Post  948inVA on Sat Oct 27, 2012 3:10 pm

Thanks for the ideas everyone. So I replaced the castor blocks yesterday with new 968 blocks. I pulled the control arm bolts and the front bushings are still tight - but for some reason the bolts holding each arm to the crossmember were really loose. Not sure if they just worked loose from the vibration or what, but I tightened everything up and got it on the road. And now the shimmy is worse.. can feel it up to 80mph. Obviously my alignment is off now, but it would seem that tightening those up has just amplified whatever is causing the vibration.

My hubs look fine - the dust caps go in easily and they don't have any visible runout. I don't know the age of the caliper seals.. I did pull the pads when I changed the rotors but I'm sure they went back in the same orientation, if that was an issue.

I did some closer inspection on the struts and the passenger side shock does move a bit when I rock the wheel at 12 and 6. I think the insert is moving very slightly inside the strut housing.

The other thing I noticed is that my steering rack seems to turn very easily. There isn't any slop in the movement but I'm wondering if I need to tighten the spring pressure on the pinion.

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Re: Wheel vibration

Post  948inVA on Sat Nov 03, 2012 3:20 pm

update: had the front wheels balanced today.. they were mostly fine, one wheel was correctly slightly but they were both already in spec. I also adjusted my caster blocks all the way out, and tightened the spring adjustment on my manual steering rack. After doing that, the shimmy seems to be mostly gone. Hopefully when I have the alignment redone they can get rid of it entirely. I also need to correct the front ride height, it seems to have risen about 1/2" since the engine swap.
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Re: Wheel vibration

Post  962porsche on Tue Sep 10, 2013 1:25 pm

?


Last edited by 962porsche on Sat Sep 21, 2013 2:09 pm; edited 2 times in total
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Front end alignment

Post  simon123 on Fri Sep 20, 2013 6:40 pm

After frustration with a rebuilt alloy arm and a ball joint problem I decided to fit steel control arms to my 88 948. Now I have inexpensive easily replaced ball joints. I had an alignment done today and have a question.

The Porsche Workshop Manual gives alignment in Degrees and minutes
( Toe is 10' +/- 5' ) (.166 degrees +/- .083 degrees)
My local alignment shop's computer rig uses Degrees and tenths of a degree

(This is not a problem as .1 of a degree is 6 minutes or vice versa).

A previous post mentions a Porsche bulletin setting toe in at 1/16"
Now i would expect Porsche to use Degrees and Minutes the same as the Workshop Manual but how do you relate 1/16" to Degrees/Minutes or Degrees/Tenths?

Anybody got a copy of the bulletin?



Last edited by simon123 on Fri Sep 20, 2013 6:52 pm; edited 1 time in total (Reason for editing : Added data)

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Re: Wheel vibration

Post  962porsche on Fri Sep 20, 2013 7:49 pm

.


Last edited by 962porsche on Sat Sep 21, 2013 2:10 pm; edited 1 time in total
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Re: Wheel vibration

Post  944-LT1 on Fri Sep 20, 2013 8:37 pm



Quoted from Pelican
1/16" toe in correlates to 0.15° or 0° 9' on a stock size tire diameter, so is spot on with Porsche`s published recommendations of 10' +/- 5'
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Thanks

Post  simon123 on Fri Sep 20, 2013 8:49 pm

Thanks LT1, yes I have that data sheet from the Service Manual.
My question relates to this "Porsche bulletin" changing the toe.

My alignment guys work with degrees/Minutes[tenths] (as per your sample) and the suggested 1/16"
does not work with their electronic rig.

What did Porsche actually suggest the toe be changed to? (In degrees/minutes)
I seriously doubt a German company would have issued data in Imperial units.

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Re: Wheel vibration

Post  944-LT1 on Fri Sep 20, 2013 10:14 pm

1/16" toe in correlates to 0.15° or 0° 9' on a stock size tire diameter, so is spot on with Porsche`s published recommendations of 10' +/- 5'

My bad. Thought you were asking for that page.
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Thanks

Post  simon123 on Sat Sep 21, 2013 6:57 am

Thanks LT1, that's great info.

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