Poor ride quality 75S

[RetroSC]

My new to me 75S suffers from what I consider a harsh ride. Small impacts such as expansion joints feels like the car sort of crashes over them with no compliance. Larger bumps don't seem to be any worse.

Suspension is totally refreshed with new rubber bushings everywhere and Bilstein HD's front/rear. Everything is stock including the ride height.

For comparison, my former 67S with Koni's and uprated suspension for autox was much more compliant. It had 21/26 torsion bars with 22mm sways and just didn't suffer from the "crashiness" I'm getting on the 75.

I've read threads on digressive valving for Bilsteins, or may consider trying Koni Red's all around. Not sure what else to do..

[2.7RS]

If you don't track it try street tires

Lower your tire pressure

That's how I deal with my car with polybronze and MCS all around

[RetroSC]

I'm running street tires now, Vredestein Sprint's. Tried another set of street's I have on different wheels, no change.

[Flat6pac]

Probably someone put bigger torsion bars all around.
I had a 76 930 that had to run about or over 80 so the road seams didn’t seem like rumble strips
Bruce

[John Ashford]

In my experience, shocks make more of a difference than torsion bars.

[RetroSC]

Originally Posted by Flat6pac

Probably someone put bigger torsion bars all around.
I had a 76 930 that had to run about or over 80 so the road seams didn’t seem like rumble strips
Bruce

Thought that too, but they're stock. I actually changed out the rears with adjustable spring plates and upped them to 26's. No difference in ride, but I'm going to do a bit of autox with it and like the combo of stock front with more rear bar, turns in better.

Anyhow, I'm going to take the front apart to make sure top mounts and such were installed correctly and rubber is in the correct places.

[Trackrash]

This is a long shot, but I believe that year came with the raised suspension that used the doughnut spacers on top of the front shocks. Worth a look, I guess.

[RetroSC]

Thanks Gordon, I'll check that out.

Running 25psi in 70 series street tires shouldn't feel like this..

[KNS]

Originally Posted by RetroSC

Running 25psi in 70 series street tires shouldn't feel like this..

That should be down right "cushy".

[fanaudical]

I think stock t-bars on a '75 is 19/23. I've got 21/26 on my '75 with digressive shocks and it's certainly "firm" but not "crashy".

Are you sure you've got some suspension travel and it's not just bottomed out somehow?

[racer]

That's not stock USA ride height. Might be closer to Euro ride height.

Also agree that larger torsion bars dont necessarily contribute to "crashiness".. My SC ran 22/31 bars and was firm, but not crashy.

It does sound like a shock valving issue, alignment/caster or even bumpstop issue. I wondered if it is actually "too low" and limiting the shocks effectiveness. Or perhaps there has been a shock failure. Do you have an old receipt with alignment settings?

While it likely won't matter, I think stock tire pressures were staggered, likely 26F, 29R

[RetroSC]

Originally Posted by racer

That's not stock USA ride height. Might be closer to Euro ride height.

Also agree that larger torsion bars dont necessarily contribute to "crashiness".. My SC ran 22/31 bars and was firm, but not crashy.

It does sound like a shock valving issue, alignment/caster or even bumpstop issue. I wondered if it is actually "too low" and limiting the shocks effectiveness. Or perhaps there has been a shock failure. Do you have an old receipt with alignment settings?

While it likely won't matter, I think stock tire pressures were staggered, likely 26F, 29R

It was at stock ride height when I got it, lowered it to euro after a few months. It was just as harsh when higher.

I've changed Tbars on several 911's over the years, never really noticed much change in ride harshness, just less body roll really.

Guess I'll pull all the shocks and check things closely.

[ab1752]

This sounds like alignment issues, same as i had after doing the full suspension. Not everyone understands how to align these cars. One trip to turn 3 who understood what was necessary and it is a different car.

[Bigtoe32067]

Alignment isn’t going to affect ride quality. That’s typically a shock issue or a suspension stiction in rare cases.
My vote is shocks or possibly shock spacers if it has them.

[icarp]

I'll bet it is bump rubbers as trackrash said.
Mark the outer dust shield height on the inner tube at ride height .
Then undo the lower mount and compress the shock to the ride height mark , then measure how much more you can compress the shock until it hits bottom or the bump rubber .
I look for about 1.25- 1.5"
I usually have to cut off 1 or 2 doughnuts to get the right length for compression
Ian