911SC rear end hop

gcrafty100 · 11-29-2006, 02:12 PM

I seem to get a hopping - a chattering when sharply accelerating in a corner in my newly acquired '80 SC. It seems to be there even if the road is smooth and the rate of acceleration doesn't warrant it. I nailed it on a sharp right-hander in first and didn't feel it, but skid padded it and it was there. It feels like it is going to come way out. Unknown condition of shocks. Tires good. Car has CamberMeister bar in front - is it unbalanced, does it need shocks, or am I just oversensitive. I am used to a smoother oversteer in these situations.

Thanks, George

johnsjmc · 11-29-2006, 02:32 PM

A 1980 is now 26 years old. Without knowing the service history if there are worn parts They are likely worn out rubber trailing arm bushings and or shocks. Alignment is adjustable and so is ride height which affects "corner balance" and steering feel.. It,s also possible you have a broken rear swaybar mount(common). Have you driven other SCs to compare? It,s also possible you are unused to the feel of a 911 which is tail heavy.More info would be helpful and you can search various threads on suspension rebuilds .

gcrafty100 · 11-29-2006, 03:52 PM

Well, John, I know it is 26 years old, but it replaced my 1972 which was even older and didn't hop. I have driven no other SCs to compare, and, frankly, was surprised at the symptom. I have owned all manner of Porsches (356, 912, 914, 911) and never experienced the hop. This car has 16' 225s on the rear and "only" 180 hp.

I am unsure of service history but have a stack of records, none showing any problems or work on the suspension.

Car has 170K miles.

Any other thoughts?

johnsjmc · 11-29-2006, 04:26 PM

Since you are an experienced 911 driver I would look at rear shocks and trailing arm bushings first. While under look at the rear swaybar mounts ,(I have even seen a car that the owner removed the stock rear bar instead of repairing a broken mount.

gcrafty100 · 11-30-2006, 06:50 PM

Thanks. So I asked the former owner if the car had the optional limited slip diff and he said "Yes." I suspect that may be what I am feeling. This being 1970's technology (and one with a lot of miles on it) it may be a little less smooth than the current versions.

What do you think?

johnsjmc · 11-30-2006, 07:23 PM

I would expect a limited slip to aid rear traction ,not cause hopping. It is also probably well worn with at 170 mi. You can get some chatter if the oil in it isn,t right.There is an additive from GM which is added to normal gear lube for a ltd slip. You can also jack up one rear wheel and measure breakaway torque on the unit by putting a torque wrench on the wheel and see what it takes to rotate. You may also detect the chatter if it is the diff causing it.I think it should be around 35 ft lbs.

dentist90 · dentist90's Garage

I had a limited slip rear end start to seize up in another vehicle once, to the point it almost became a spool axle. The inside wheel in a sharp turn would break free and one could feel it 'jumping' over the pavement. This was only evident in really tight turns, usually parking or making a U-turn. This was a multi-clutch type of LSD, I have to admit my ignorance in that I'm unfamiliar with the construction of the Porsche LSD system. Try making a tight (full lock)left hand turn while watching the your left hand rear tire to see if it is hopping. If the problem only happens at speed probably wheel hop from worn shocks.

gcrafty100 · 12-01-2006, 06:59 AM

Thanks. It seems to want to do it under acceleration but not at other times. We could be talking worn shocks here. I haven't had it out on the track so I don't know what it will do under really extreme conditions. When I get the chance I can also as someone to watch the inside wheel and see if it is hopping.