Lowering - Guys, I need some help.

[skidowntown]

Hello everyone, about a month ago, I shared this post about wanting to lower my '83 911 SC.

Wanted to lower my SC...ran into a challenge

i did a lot of research on this site, read the link about "how to lower the 911" and thought I was there (purchased some new high clearance oil lines, etc).

Porsche's been great, but I've ran into a challenge.

See Before and After photos:

The Porsche mechanic says that this lower height is the result of coming down only "one notch"...I checked to see if he also worked on the inside T-bar as well as the outside, and was told he had.

They said that my wheels being 17's and 9"'s in the back (255/40 x 17) on the rear were also the reason why it was showing too low, but I've seen others here with those wheels, yet don't have the sizing problem.

Am I stuck or do you guys think I should be able to get the height closer to ideal?

Art, over at Elephant Racing thinks this can be fixed pretty easily, but I need some help knowing how to explain this to the mechanic. He's awesome, great guy and mechanic, who works on all Porsche's, but he's dealing w/me (total novice).

Hope you guys can help me...thank you!

[ed mayo]

By moving the inner torsion bar end one spline, and the springplate on the outer end one spline in opposite direction you should be able to change heights in about 1/2" or less increments. Unfortunately he didn't do that.

[skidowntown]

Thank you for the feedback.

I'm going to be sharing this link with him, so that he can read it to. Please share whatever you can to assist!

Thanks again

[gtc]

You have adjustable spring plates, so he should be able to fine tune the height with those as well.

Also, I don't mean to be rude, but what sort of Porsche mechanic doesn't know how to reindex torsion bars?

[Rodsrsr]

Originally Posted by ed mayo

by moving the inner torsion bar end one spline, and the springplate on the outer end one spline in opposite direction you should be able to change heights in about 1/2" or less increments. Unfortunately he didn't do that.

this ^^^^

[Bill Douglas]

It might be time for a corner balance as well.

[Driven97]

Um, did he even try the spring plates? May have not even needed to pull the torsion bars at all.

[Arne2]

Originally Posted by skidowntown

The Porsche mechanic says that this lower height is the result of coming down only "one notch"...I checked to see if he also worked on the inside T-bar as well as the outside, and was told he had.

Nope, he didn't. Went one spline lower on either the inner or the outer, but didn't do both as he should have. IMO, time to visit a new shop that knows how to work on early cars.

[jons911]

This is exactly what I had happen when I lowered my SC. I only pulled the spring plate out with the torsion bar and moved one spline and put it back on. It was about a 2 1/2" height change. Initially, I couldn't figure out how to get the torsion bar out of the spring plate, so that was all I could do at the time. I've since fixed it. Either your mechanic only took the spring plate off and moved it one spline, or the torsion bar came out with the spring plate and he moved it one spline on the inner side. Either way, he did not use both.

If I remember correctly, there are few splines on the inner side than the outer. In that case, what you want to do is rotate the torsion bar one spline in the way you want the spring plate to be adjusted and then rotate the spring plate one spline in the opposite direction. The ratio of the inner and outer splines means you can achieve a less than one degree change, which is maybe 1/4" or a bit more. But then you can adjust the spring plate itself which pretty much bridges the gap.

From my experience with a similar ride height, I don't think adjusting the spring plate alone could have fixed either before or after setup. They do not have that much range. My first attempt left my rear ride height pretty much exactly the same as yours and maxing out my spring plate did not get the fender above the tire.

[Trackrash]

Maybe someone can find the link to the torsion bar angle calculator.

At any rate, the way I used to do it, was to measure the spring plate angle with the car at rest on a flat surface.

I then used some weights to lower the car to the exact height I wanted and re-measured the spring plate angle.

Then after I got the spring plate loose, I measured the angle again and then adjusted it the difference I originally measured with the car on the ground.

[obscene]

looks perfectly lowered to me ¯\_(ツ)_/¯

[Driven97]

Originally Posted by Trackrash

Maybe someone can find the link to the torsion bar angle calculator.

Oh neat, looks like Elephant is hosting a version now. That should stick around for a while hopefully. OP should use ~2700lb as weight give or take in this calculator.

For posterity in case this link dies, I Googled "Will Ferch spring plate calculator" as IIRC he was the person that did the original math and made the original site. The original site is gone. So if it disappears from Elephant, this is your best bet to finding another copy of it.

I've used the calculator a bunch of times, and it's worked pretty well for me. I typically split the difference between "euro" and "race." I set my spring plates to center of travel when I have them apart so I can tweak either way from there if desired. Note that it's measured with the spring plate fully disconnected from the trailing arm. And also the arm can't be resting on the spacer that's at the bottom rear spring plate cover position. Also, obviously, the car either has to be level or you can zero your angle gauge to the door sill. I use a free phone app.

Anyone know how much adjustment range is in the factory spring plates? I'd guess around 1", but that's a total guess. I still think the shop should know better than to think there's no option in between the "before" and "after" photos. That has to be multiple splines, not just one.

[skidowntown]

These guys are working on everything between a 356 and a 918, as well as all of the SUV’s, etc, so they are master mechanics, but I think it’s totally reasonable that they may not be up on how to do everything on every ride. There aren’t many classics where I live so he’s likely mostly working on newer stuff.

The mechanic is great to work with.

[David Inc.]

Maybe the guy has only worked with the early, early T-Bars? I think those only had splines on one end and that was all the adjustment you got. But hell, he should know better if he's an aircooled mechanic.

The factory spring plates allow for about 1/2" plus or minus.

[Driven97]

Do you know if you have the OE sized torsion bars in the car? If so, you can tell them to shoot for an unloaded spring plate angle of ~32°. Also let them know the two bolts at the front of the spring plate are for fine height adjustments, one is a "lock" the other is cammed. Have them set the spring plates to the middle height position so you can tweak without full disassembly.

Sometimes it's a PITA to re-index because the spline engagement is right about where the spring plate bushing engages into the body, so it's tough to do "one click."

[skidowntown]

Alright, adjustments made. Car looking good and will post pics later. Thx!

After ride height is set, alignment, toe-in, corner balance and I should be good, right? Thx!

[ADDvanced]

Adjustable spring plates are amazing.

[skidowntown]

Alright, here she is...the 5mm spacers/slims helped a lot...hope you guys like it :-)

[Rodsrsr]

Perfection!

[75 911s]

Beauty!