How to: Lowering the Rear End

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Greg Scallon
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How to: Lowering the Rear End

#1 Post by Greg Scallon » Mon Dec 06, 2010 12:00 am

All,
Awhile back I posted a how-to on lowering the front end of an A car.
http://porsche356registry.org/356talk/1/15122.html

Considering that's usually only half the job, I thought I'd post the steps involved with lowering the rear. Like the front, I read all the books and manuals, studied the old e-mail and talk posts, but nothing really explained the full process. Hopefully this will help others. If you have any questions, or if I missed anything, shoot me an e-mail.

Regards,
-Greg

The Goal: To lower the rear of my car to match the front.

The Car: '58 speedster

The How-to:

- Figure out how much you want to lower each side of the car. Measure to the top of your wheel wells, or the side trim, or whatever.

- Jack up the car with the rear axle's and wheels hanging free

- Remove the rear wheel on the side you're going to start with.

- Unbolt and remove the bottom of shock from spindle. (If necessary, compress the rear suspension a bit by lowering the car while you have something like a 4x4 under the rear brake drum. This can put some slack in the shock/spindle interface such that you can push the shock off.

- Unbolt upper shock mount and completely remove the shock. (remove the 4x4 if you used it to jack up the drum)

- Unbolt three rear bolts that mount the spring plate to the spindle. (Leave front-most bold in place. This is a camber-positioning bolt.)  

- Remove and set aside the rubber bumper that is held on by one of the bolts mentioned above.

- Release parking brake from inside car

- Push the drum/axle unit rearward and out of the way. Use a tie-down strap to hang it from the upper shock mount and the rear bumper bracket to keep it out of the way.(see photos)

- Finagle the spring plate out from around the axle such that it hangs free and isn't obstructed by the axle. (this is tricky but you'll eventually get it. Keep trying.)

- Put your digital protractor on the top of the spring plate and take an initial measurement of the angle of the spring plate while it's relaxed and hanging free. Write this number down.

- As a double-check, measure the distance from the bottom of the spring plate's rear most point to the ground. Write this down too.

- Unbolt the four bolts holding the spring plate front cover plate on.

- Remove the cover plate and then slide the outer rubber bushing off the tube.

- Before removing the spring plate, scribe a mark along it's top, on the inside of the wheel well, showing where the arm is positioned naturally. (while slightly pushing up on the spring plate to take up any slack) This can help you if you ever want to go back to the way it was.

- Do another angle measurement to double-check that removing the cover plate hasn't changed anything. It'll probably be the same as it was with the cover plate on.

- Remove the spring plate and inner rubber bushing. Leave the torsion bar in place.

- Use a sharpie to mark the end of the torsion bar with the mark pointing straight up. This will help you should you need to know which inner spline the torsion bar was positioned on originally.

- Remove the torsion bar by sliding it out of the tube and check for damage or rust.

- Clean everything and reinstall torsion bar into tube and get spring plate in place.

- Calculate how many degrees you have to remove from the spring plate angle to get the height reduction you're looking for. I have a table for this. Email me if you want a copy.  In my case the spring plate started at 11.5 degrees.  I wanted to lower the car by 24mm so I had to remove 3.3 degrees. So, I needed to set the spring plate to a final angle of 8.2 degrees.

- Get your digital protractor out and position it on the top of the spring plate.

- Rotate the torsion bar one inner spline and then slip the spring plate on to see how your angle looks. You're basically slipping the spring plate onto the outer spline that gets you closest to the correct angle.  If it's not good, rotate one more inner spline, slip the spring plate on and check again.  And again, and again, etc. Rotating the inner spline and then slipping the spring plate on such that it gets you close to the angle you're looking for is how I did it. You should be able to continue rotating the inner splines to eventually get really close to the angle you're looking for.

- When checking the degrees of the spring plate, push up on it slightly just to take up any slack. In my case this was about half a degree or so. My protractor only went down to half degree increments so I ended up at 8.5 with it hanging and 8.0 with it pushed up a bit. This was close to the 8.2 that I wanted so I went with it.

- Note: You can also ditch the protractor all together and just make sure you rotate the spring plate such that in it's new position it's rear most point is raised by the amount you're looking for(based on the measurement to the ground you took above). This does the same thing as the protractor method.

- When you get it as close as you're going to get it, slide the torsion bar in, reinstall the spring plate cover plate, and tighten everything up.

- Note that it's a really good idea to install fresh new rubber bushings if yours are old and worn out.

- Reinstall everything else and you're good to go.

- I set my rear shocks to one full turn in from being fully backed out.  This seems to be a good setting for street use.

- Now do the other side. (keep in mind that many people like to have the drivers side of the car sit about 1/2 inch higher than the passenger's so that the car is dead even with the driver in the seat.)
Attachments
LoweringSpeedster02.jpg
You can see one of the bolts removed here. The upper bolt and rubber bumper haven't been removed yet.
LoweringSpeedster04.jpg
Side angle showing the strap mounting points.
LoweringSpeedster05.jpg
Another shot showing the way the strap holds the axle back.
LoweringSpeedster06.jpg
This shows the rear axle and spindle being held away from the spring plate such that it won't interfere.
LoweringSpeedster07.jpg
The protractor I used. Purchased at Sears for about $30.
LoweringSpeedster08.jpg
Removing the cover plate. Don't loose those washers.
LoweringSpeedster09.jpg
Spring plate and outer bushing.
LoweringSpeedster10.jpg
The torsion bar. Rusty I know.
LoweringSpeedster11.jpg
The spring plate sitting on the workbench. You can see the inner bushing installed on it.
Last edited by Greg Scallon on Wed Mar 09, 2011 9:13 pm, edited 3 times in total.
'58 Speedster
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Vic Skirmants
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Re: How to: Lowering the Rear End

#2 Post by Vic Skirmants » Mon Dec 06, 2010 8:29 am

PLEASE, don't forget that you are not only lowering the car, you are changing the camber.
3.3 degrees sounds fine for a race car, but be careful for street cars.

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Greg Scallon
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Re: How to: Lowering the Rear End

#3 Post by Greg Scallon » Mon Dec 06, 2010 1:29 pm

Photos of the car after lowering.
Attachments
Speedster4.jpg
Speedster3.jpg
Speedster2.jpg
Speedster1.jpg
'58 Speedster
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Vic Skirmants
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Re: How to: Lowering the Rear End

#4 Post by Vic Skirmants » Mon Dec 06, 2010 2:12 pm

Greg,
Your car is gorgeous, and your write-up on how to do it was great.
I just don't want some newby deciding to drop their car a ton, without considering the end result.

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Re: How to: Lowering the Rear End

#5 Post by Greg Scallon » Mon Dec 06, 2010 2:45 pm

I hear you Vic. I didn't drop the car a ton, and while the rear camber has been increased, it's not too drastic. The car rides and handles great.

Thanks for your comments.
-Greg
ps: My car is running it's original transmission which you rebuilt a number of years ago for the previous owner. It looks and performs like it's brand new. :-)
'58 Speedster
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David Baugh
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Re: How to: Lowering the Rear End

#6 Post by David Baugh » Mon Dec 06, 2010 5:22 pm

I love your articles, Greg! And the photos are great, showing a pristine undercarriage. That's a really sharp looking car.

Good point, Vic. When I bought my 58 coupe 40 yrs ago, it was really high in the rear, with an ugly bow-legged stance. I decided to lower it without the assistance of any knowledge. My e-brake cables were too short to get the axles out of the slots in the spring plates, so I disassembled the rear brakes and removed the anchors. The torsion bars were frozen to the interior anchor, so I simply raised both sides a single spline tooth on the outside. The result dropped it nearly to the ground, and left me with a severely decambered rear.

I found an old manual (can't tell who wrote it, because the first 8 pages are now missing), and tackled it again. It had a good description of the process. The chassis end of the torsion bar has teeth that are 9 degrees apart. The trailing arm end has teeth that are 8 degrees, 10 minutes apart. The example shows that to raise the arm 1 1/2 degrees, you'd rotate the torsion bar up (CW on driver's side) 8 notches, and the arm down (CCW on driver's side) 9 notches from the factory setting. I had to drive the torsion bars out with a sledge hammer and lots of Liquid Wrench sprayed in with an air gun, but finally got it adjusted satisfactorily.

Dave
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Gene Choin
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Re: How to: Lowering the Rear End

#7 Post by Gene Choin » Thu Jul 07, 2011 3:16 pm

Good job, just two issues I notice.
My torsion arms always are sitting against the cover nut (stud) and not "at rest". I always have to pull them out a bit to get it off the "stop" and then it comes off the torsion bar spline (usually inside) and the number is lost. A bit of more work to get the "original setting angle".
and since the coupe weighs a few hundred pounds more than the speedster, the angles will be more to get same height.
In the little spec book, it refers to 13 degree setting for SC. This seems quite low even with Camber spring.
Eugene H Choin

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Re: How to: Lowering the Rear End

#8 Post by Bruce Caswell » Thu Jan 24, 2013 9:29 am

Excellent Post ,both front and rear , my car is a bare shell now but by the time I finish this post this will help me getting my car to sit right when finished . Your Car looks really nice ,a real beauty. , Thanks ,Bruce

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Re: How to: Lowering the Rear End

#9 Post by Steve Harrison » Thu Jan 24, 2013 11:14 am

Good process post Greg. The only thing I'd add is to coat the entire tortion bar with a smearing of grease before putting it back. It was one of the eeriest feelings when I took mine out for the first time in their life...I could see the pristine finger trails of the worker who did it oh so many years ago.

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Re: How to: Lowering the Rear End

#10 Post by Bernd Brix » Sat Sep 07, 2013 5:07 am

Issue: Parking brake cables interfering with pulling out the axle/brake assembly.

On a tour, following a nice A coupe I checked my car's stance and noticed it was much higher than the coupe and uneven in ride height (right > left).
So I followed Greg's post exactly and got the desired result, even stance, lower rear and a bit of negative camber. The spring plates are set at 8.5° now.

The only problem I encountered was that the parking brake cables did interfere with pulling out/ back the axle/brake assembly. They were plainly too short and got stuck under the spring plate and prevented me pulling the assembly far enough so that the spring plates were free.
After giving the central adjusting screw in the front all the slack possible I could pull the brake cables in the back out for approximately 2 ". This made all the difference.

I have added a picture of the result.
By the way, I used my IPhone to measure the angle of the spring plates - works perfect.
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IMG_3044.JPG
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Re: How to: Lowering the Rear End

#11 Post by MarkWade » Sat Sep 07, 2013 9:06 am

Greg: Thanks for the great in sight on lowering! I really want to do this on my C outlaw. I am really concerned on the amount of lowering that will look good and still have a nice ride! So with that said can someone out their add what's the best height to use?

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Re: How to: Lowering the Rear End

#12 Post by Geoff Fleming » Sat Sep 07, 2013 1:48 pm

Nice job! One bit of advice I have to add, is to coat the entire length of each torsion bar with a heavy grease, since they can crack if bare metal is exposed without this protective covering. I have had one break in two due to lack of sufficient grease on the exterior, fortunately it was at the curb and not while driving!

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Re: How to: Lowering the Rear End

#13 Post by Greg Scallon » Sat Sep 07, 2013 10:34 pm

Mark,
All I can say is that mine rides just as good as it did pre-lowering, and I probably dropped at least an inch. (but overall mine isn't that low) You do get some camber in the wheels/tires, but with mine it's nothing I would worry about.

If you really go low, the rear wheels definitely bow out, your tires wear out quickly, and your ride will suffer, but you have to go really low to have those problems. If I were you, I'd drop it an inch and see how you like it. If you want to go lower you can judge from that point how much lower you want to shoot for.

Good luck!
-Greg
'58 Speedster
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Re: How to: Lowering the Rear End

#14 Post by Laurent Clerc » Sun Sep 08, 2013 12:56 pm

Greg, a question for you: is there any predictive relationship between the number of teethes move and the final lowered height? Or is it possible to know that x degree will result in y inch lower?
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Re: How to: Lowering the Rear End

#15 Post by Charlie White » Sun Sep 08, 2013 2:46 pm

I don't want to hyjack Greg's very excellent post and write-up about lowering 356's. He has presented the nuts and bolts of doing this for everyone to try out. I wanted very much to lower my 65-C, but I'm not as mechanically inclined as some are. So I looked for an alternative method that didn't involve all the mechanical work. And it is a complicated subject for the not-so-mechanically inclined.

Having said all that, I solved my problem by switching to 14" wheels and low profile tires. In particular, 14" Fuchs which came on some early 900 series Porsches. I chose the Porsche factory Fuchs 5.5" x 14" wheels with 185/60R 14 tires. This dropped the car down about 1.5 inches all around. The good news is that the ride characteristics did not change one bit. The other news, good or bad, as you may decide, was the smaller diameter wheels/tires changed the effective rear end gear ratios, they are much lower across the board. It's great fun around town as all final gearing is much lower, very zippy in third and fourth, but on the freeeway at speed (I never go there) the top end is adversely affected. I swap these 14's for stock chrome 15" wheels back and forth as my mood indicates.

You can see a picture of the car with the 14 Fuchs. The Fuchs were repainted a "dull gloss" black with a 1" polished area around the edge of the rim. Also pictured is a comparison of the original 15" wheel and tire with the 14" Fuchs and low profile tire.

CW
Attachments
01t.jpg
01.jpg
Charlie White

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