Unstable roadholding
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Author:  Jaco Naude [ Mon Apr 16, 2018 2:24 pm ]
Post subject:  Unstable roadholding

I am new to this forum. Having problems keeping my 356C 1962 on the road. Imported the car from New Mexico to the Netherlands. Replaced the worn 195/60R15 Bridgestones Ecopia with new ones, same size. Rebuild the front suspension, new king&link pins, adjusted the tow-in to 1mm as per driver's manual. No play on the steering system.
On the freeway, anything over 60mph the car begins swaying. When passing a truck the car is pushed laterally by the displaced air. The swaying is even more noticeable when driving in slow/right lane where trucks groove the road.
Are the tyres too wide? Should I try 155/80r15 or 165/80r15, and if so' would fitting narrower tyres to the front only ( like later 911's) solve this problem?
Haven't checked the steering shock yet. Would it make a difference?

Author:  C J Murray [ Mon Apr 16, 2018 2:36 pm ]
Post subject:  Re: Unstable roadholding

Check the rear toe adjustment and camber.

Author:  Jaco Naude [ Mon Apr 16, 2018 2:49 pm ]
Post subject:  Re: Unstable roadholding

Thank you. And how are these adjusted?

Author:  steven mclean [ Mon Apr 16, 2018 11:32 pm ]
Post subject:  Re: Unstable roadholding

Try lowering the air pressure in front tires first to see if it changes.

Author:  Edwin Ek [ Tue Apr 17, 2018 12:13 am ]
Post subject:  Re: Unstable roadholding

Could very well be more than one cause. How wide are your rims? For a 1962 car, a 165 tire is the original size.

I am a fan of wider rims and tires in the rear, but you have an underlying problem to fix before exploring that setup.

Author:  Erik Thomas [ Tue Apr 17, 2018 1:10 am ]
Post subject:  Re: Unstable roadholding

I think it best to take the car to a good alignment shop, and check the rear end out carefully on a modern machine. Sometimes when the transmission mounts are changed, the position of the gearbox can shift. Once the rear is confirmed good, the front can be done. Be sure you have the rear camber set to factory specs. Some say you can run 1 degree negative. Check the steering damper while you are under there. I prefer the original size 165 x 15 tires on 4.5" rims. However there are many that diverge about this . I use 28psi front, and 32psi rear.

I had a large project doing alignment with my 1960 356 B coupe. But after careful adjustment, it drives like a new car.

Author:  Vic Skirmants [ Tue Apr 17, 2018 7:50 am ]
Post subject:  Re: Unstable roadholding

What tire pressures are you using?

Author:  Martin Benade [ Tue Apr 17, 2018 7:53 am ]
Post subject:  Re: Unstable roadholding

The rear toe is adjusted by loosening and sliding the axle tubes, not hard at all. Rear camber is not something a regular alignment shop could do, its quite a chore. If it is equal on both sides, I could live with anything between -.5 and -2 degrees, although that is a matter of taste, not everybody would agree with me on that. Another matter of taste, narrower rims on the front- not many people do that, and it certainly will handle nicely with all four matching. Also your current tire size is not a problem, that size is commonly used, including by me.

Author:  Norm Miller [ Tue Apr 17, 2018 9:14 am ]
Post subject:  Re: Unstable roadholding


I suggest tire pressures of Front 24, rear 32 PSI for the 195's.
You will be close given there are no major suspension abnormality's.


Author:  Al Zim [ Tue Apr 17, 2018 9:29 am ]
Post subject:  Re: Unstable roadholding

Over the years Zim's has used as many alignment systems as we have changed our name. About 4 years ago we moved to the Hunter Elite system which leaves the car in a fully loaded position as it is aligned. The alignment rack is on a parallelogram style lift which allows the technician to work under the car while it remains level. If the car is not level, then the portion of the suspension that is loaded and the position that is not loaded will not be correctly aligned. We have weights to duplicate the weight of the driver. Normally (about 30% of the time) we find that the lower right front trailing arm is bent from hitting curbs. This allows the spindle to lose camber which cannot be corrected with shims. Each spindle must be checked with the Factory P69 tool. 356C/SC spindles require an adapter (which is a P69 C) I know this adapter exists but I have never seen a picture of one. Zim's has been able to successfully duplicate this tool.
SETTING THE REAR TOE IN BY MOVING THE TRANSMISSION: Since this method was posted over two years ago I have thought about the conclusion that have been drawn. FIRST: The rear axle is a full floating axle. SECOND: the with of the track on the rear is governed by the shims located between the clamping plate and the 6 bolt cover that holds the bell of the axle to the transmission. THIRD: Moving the transmission bends the spring plates which results in toe in change. I do not believe that Porsche and VW designed their vehicles to do this. Since the rear axle has the ability to pivot as the toe in is set it can somewhat compensate for the movement of the transmission. VW transmissions were affixed to the car with a more solid mounts and no shims. The suspension on the rear of the car is solid heavy material located on the chassis before the body is fabricated. This is paramount in its stability.CONCLUSION: Alignment in the rear is correctly done by torsion bar adjustment and movement of the axle on the spring plates. See your factory shop manual. At our shop this is usually a minimum of a 4 hour job for front and rear adjustment. More time is necessary if if other people have fixed the car. al zim

Author:  Adam Wright [ Tue Apr 17, 2018 9:30 am ]
Post subject:  Re: Unstable roadholding

Have the tires over inflated will make a 356 handle a little jumpy. The recommendations given here are good.

Author:  Jaco Naude [ Tue Apr 17, 2018 3:13 pm ]
Post subject:  Re: Unstable roadholding

Thank you ever so much for all the advise.
I think a few nails have been hammered on the head. The suspension has been lowered , to the extend that the back wheels are inclined ( same as if car is overloaded) . The car was delivered in this condition. It certainly gives it an " outlaw" appearance, but whether it's healthy is another question. The firm who did the wheel alignment recently corrected the front, but did mention that the camber and toe-in at the back is considerably out. Figures of 3-4 degrees were mentioned, but the firm didn't know how to adjust this or whether it would make a difference in road behavior. The measurements were done with an electronic computerized instrument.
Rims are build-out chrome versions that is often seen on 356's, width 5,5" .
I am fortunate to have a specialist Porsche service center close by, who has a keen interest in Porsches from the 60's into the 70's. Although I have done most of the rebuild, if not all, by myself, I think this matter is best adjusted by fundi as it most probably involves the torsion bar settings.
Please don't stop the stream of advise, it's always good to have as many opinions as possible. Much appreciated..

Author:  Doug McDonnell [ Tue Apr 17, 2018 7:18 pm ]
Post subject:  Re: Unstable roadholding

I hate to mention this but if your car has ever been wrecked and repaired it is possible that it is not close to spec. A factory service manual has all the measurements that could be checked. Here is a link to Greg Scallon's excellent write up of lowering the rear which will give you an overview of how to set the rear ride height. viewtopic.php?f=1&t=24968 If you decide to take the rear apart I would encourage you to use new rear torsion bar bushings-perhaps the slightly harder ones sold by Willhoit.

Author:  Geoff Fleming [ Tue Apr 17, 2018 7:57 pm ]
Post subject:  Re: Unstable roadholding

The rear toe position is very important, ( not that the front end is not.), and should show no 'toe-out' at all.
When the front was 'corrected', was the steering re-centered? If the steering box is not holding the true center while in the straight ahead position, the steering will wander. Very important to carefully set the center position after a front alignment. There is only one correct position, unlike cars with rack and pinion steering or the earlier VW steering boxes.

Author:  Erik Thomas [ Wed Apr 18, 2018 1:32 am ]
Post subject:  Re: Unstable roadholding

Years ago, I had a '62 VW beetle convertible. In those days, being young and foolish, I reset my torsion bars for about 2 degrees of negative camber, and reversed my rear wheels for more track. The car handled very poorly like this, and I returned it soon to stock specification. That and years of racing Porsche and other swing axle cars, including a pre war Mercedes, have led me to conclude that the rear camber should be kept so that it never goes positive, but not too much negative. I use straps and or special length shock absorbers to this end. With a set of nice adjustable Konis and a more or less "stock" or one or two degrees negative, if you swear off rear seat passengers, works best. Colin Chapman said that even a very poor suspension design can be made to work if you limit the travel. As Al Zim says, put a bag or two a sand in the drivers seat when making the alignments. I do not like sway bars, Z bars or camber compensators. I do not even like steering dampers as they make the car feel like a marshmelow to me. ( I am, however a heretic )

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