77 911 Very Twitching Handling
 

My 77 911S came out of a guy's garage with 270,000 miles having been parked for 20 years. It was a no rust worn out car. No evidence of impact other than a zillion rock chips. I've owned an 84 and 87 Carreras so i have a good feel for how these should handle.
I replaced shocks, suspension bushings and a lot of other items. Once the car was back on the road, the handling was noticeably twitchy. At straight ahead highway speeds, it wanted to pull which ever way you nudged the wheel. Very small inputs would make the car want to move more in that direction. I replaced the steering rack. I changed my tires to Pirelli P6000s - 185 in front, 195 in back. I replaced the inboard rear suspension bushings (the only bushings not previously replaced). A couple months ago i was driving in cross winds and the car was terrifying, not at all planted, very un-Porsche like

Last week my mechanic changed all 4 torsion bars and re-aligned the car. It's been aligned by two Porsche only shops. The 2nd shop confirmed the my regular shop did it right. I've discussed this with lots of Porsche people and have yet to hear an idea that i haven't already tried so I'm asking the greater Pelican community - any ideas?

Thank you

Post alignment sheet

Tires with soft sidewalls? I know they're new, but try pushing the car sideways with your leg against the front and rear bumpers and see how much body and tire movement you get. Shouldn't move too easily. Watch the tire sidewall at the road.

Maybe it just sat too long and needs to be driven? My '71 VW Bus had a similar problem. Its suspension was refreshed before it was parked but it was very twitchy after being off the road for 10 years. I replaced the steering box, tie rods, etc with no luck. I thought I had a defective steering box since I was all over the road and the car would veer unpredictably from one side of the lane to the next. I took it to the alignment shop where the mechanic confirmed it was ok. He told me just to drive it a couple hundred miles as a lot of these old cars develop a "memory" from sitting so long.

I took it for a mini road trip and after about 400 miles, it noticeably improved. Now, it handles as good as it supposed to. How many miles have you put on it since it sat?

Pulling could be a brake issue. Have you done any work on the brakes? Does it pull when you push on the brakes, or only when you touch the steering wheel?

Thanks for the feedback so far. 2nd set of P6000s. These are the Porsche rate tires. Brakes are all new and work perfect. This car has been on the road now for 5,000 miles.

Ok, that rules out my ideas! Interested to see what it could be though.

Did you use Elephant sport hardness in front? I've used these on several cars including my own. Feels a lot more composed.

Yes.

Ride height correct, front spoiler in place? Any different with a full tank of gas? Front end can get pretty wild in windy conditions if air is getting under the car, worse if you don't have any weight in the nose.

You say it's bad at highway speed, where aero comes into play. Does it drive normally at neighborhood speeds?

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Wheel bearings good and properly torqued? Try rocking the tops of your wheels side to side while stationary.

Loose wheel bearings is a good thing to check. Also if the struts/spindles have been apart, make sure the spacer between the inner race and the spindle is in there. A friend assembled some struts without that spacer and the results were bad.

Too much front toe out can make a car very twitchy and unable to track in a straight line. Is there a chance something is worn causing it to move to toe out while driving?

I know you say the alignment was done, but as Manbridge mentions, the post sheet would likely help those here on the board. What’s the toe front and rear? Ride height? Could it be bump steer issues?

Did you have the car corner balanced ?

Multiple alignments by knowledgeable shops makes me think it is not an alignment issue. Corner balance also would not lead to the problems the OP is describing. To me it sounds like a matter of CHANGING alignment while driving. That means something is loose. Big suspension pieces would likely have been caught by the alignment techs.

I had a very similar problem with my 914-6 years ago. Very unstable and skittish while travelling in a straight line, especially at higher speed. Yet very stable in corners. It turned out to be a loose rear wheel bearing. It was just loose enough to add an element of rear wheel steering to the car that would alter side to side depending on road crown, wind, ext. It made for VERY disconcerting handling. Yet the car was fine while cornering as it would load up to one side or the other and then be stable. Once I tracked it to the wheel bearing (by rocking the top of the wheel side to side as I suggested above), I pulled it apart and inspected it for damage, then reassembled and properly torqued it. Problem fixed!

Exactly my thoughts - loose rear wheel alignments. With the wheels in the air, see what you can move. If they won't move by hand, lever gently with a pry bar. In order to cause the described behaviour, I.e. exaggerated steering, either a pivot of the front suspension is loose behind the front wheels, or a pivot of the rear suspension is loose in front of the rear wheels.

Check all parts of the steering are bolted up firmly. Does it have power steering fitted? Also check all the steering linkage from the steering wheel to the front wheels for play. Can you rock the steering wheel without turning the front wheels?

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Good point about the rear steer effect with worn bearings.

Another possibility and thing I always do when aligning these is to push out on the front edges of front wheels while watching toe setting. This approximates road forces, when the car is moving the wheels toe out. So you don’t want to set toe at zero static but with some amount of press. I think the manual called for around 40lbs but would have to check. Strive for the most caster if stability is a goal and make sure they are equal side to side.

I haven't thought about it in years, but the twitchiness I had - came from the rear end. In that instance, it was a loose rear castellated nut to keep the wheel on. Someone forgot the cotter pin.

good luck,

I don't have the alignment sheet but this shop does only Porsche so i'm confident they got it right. The've aligned my previous four Porsches. I know front wheel bearings are good. I'll figure out how to check rear. I do know the front is very tight and without play.

I agree with the comments that this "feels" like something is loose but so far, all the wise people who looked at it say it's good. Thanks for the comments. I'll check the rear wheel bearings and wait for further wisdom

The easiest and fastest thing to do is get someone else to drive the car while you drive a second car and follow ..
Make your car go straight and you change lanes going to both sides of your car from behind and look for problems like "crabbing" where your car drives straight but the tires are not tracking in the same plane.
How many times have we all driven down the road and seen problems on a car just because we were in a dynamic where a bad shock on a wheel is jumping up and down or a wobbley wheel from hitting a curb.
Maybe it is just me, I spot all kinds of crap when I drive, wife thinks I'm nuts. She thinks I am looking at something too long and I will point out a bad part or bad paint match.

I got the car on the lift today and found the rear wheel bearings to totally solid. I really wanted that to be the problem. What's next?

what tire pressure?...

Did you do what I suggested in post #3? Need to get that off the list of possibilities.

Tire Pressure is 36psi all around. But we've played with other pressures.

As far as watching the side wall while i lean on the car; Sure, they have some give but if you are going to suggest tires, i'll ask what tires we are all ok with. As said, these are P6000 with the Porsche P rating. These tires were designed for this car. I'm on my 2nd set. So, should these tires work? Do we know they won't? Buying 4 more tires gets to be an expensive experiment.

What tires are ok?

Tire pressure is incorrect! please lower the fronts to 28 -29 lbs, all will be right with the car, there is a sticker in the engine compartment stating the correct pressure

Fitting Pirelli P6000s on my 1978 SC cured instability. Initially I had P6000s fitted to the rear only after originals delaminated and with different make tyres on the front the car was twitchy. So fitted P6000s to front as well and problem was solved.

Mixing two different construction/manufacturer tires front to rear is a recipe for bad handling. BIG nono.

36 is high, drop it and test as it is easy money. Check your alignment sheet to see what Toe is at. If its zero, then that will cause the car to be twitchy like stated above. I run zero toe, 31 rear, 28. Good luck.

I run ~7 psi more in the rear vs. front ('85 w/16" 7 & 8); this is the first time I've seen anyone here say they use same inflation pressure all around -- other tire pressure threads I've seen have posters here say they run 5-7 psi more in the rear than front.

Didn't see it in your post but sounds like you're running 15x6 all around? If so, I'd try ~3 psi differential. I know you said you tried different pressures but though this might help.

36 in the front????????????????
Oy!
You may want to check and also see if the alignment was done at 36.
If so, have it rechecked.
>83 29F/34R 84> 29F/36R (Non-turbo,non-M491)

too much air in the rears on my 930 makes it quite scary.
when I put new tires on it they inflated to recommended pressure I assume, (don't know what it is) the pressure was quite hi. I thought the tires just sucked. dropped it down and it was much better.
very hard breaking and the back end was everywhere. cornering was not too fun either.

I don't know where some of the posted tire pressures are coming from but while 36/36 cold is on the high side it is nowhere near being out there

I prefer 34/34 cold for street use myself but down to ~30/30 or so is fine too. For a track car you might start in the high 20s in the morning then adjust as temps come up w/ use but that's not desirable for street use.

was the car in question corner balanced? Wheels are stock Fuchs w/ no spacers or anything?

a look at the alignment specs and ride height would be really helpful

On one set of tires my 85 had very greasy handling when new. It took almost 100 miles for all the mold release to wear off. It was a very uneasy feeling.

My ‘77S had an odd high mismatch air pressures front and back set by PO for some reason when I bought it...P3000’s. I’ll agree with the tire pressure being too high for highway driving, think about the contact patch an overinflated tire has. Too low pressure and it should sway like a fish out of water essentially riding on both edges. As for the new tire theory, I recently put new tires, non OEM Toyos on my F150 and at highway speeds too, it was wandering all over the road, no crowns, no winds, proper PSI, no shimmy. Took it back to the tire shop and the alignment was spot on spec. They had no clue. After 200 miles it seems to have settled in better.

Like others have said, tire pressure. I think on a 1976 it calls for 29 front and 34 rear.

What speeds does this occur at?

Also, do you have any sort of duck tail or similar on the back and what is the front air dam? If they are not stock, they need to be a 'set'.

Edit: I just looked in the little spec book for 1976/1977 models. Pressure is: front - 2.0 bar, rear - 2.4 bar.

It is toed out in the rear.

Bump
Did you ever get this sorted out?

What steering wheel are you using? My car feels somewhat "twitchy" with a Momo 350mm vs. stock 370mm.

Steering shaft u-joint could be binding after sitting for 20 years.

Is there a difference in the struts left and right? Like if they are backwards the caster would be way wrong? Because I deal alot with lifted 4x4s and people screw up their caster all the time by clocking the front diff up to get the driveshaft better. And this is what happens. Very twitchy steering that doesnt self center anymore