How to: Lowering the Rear End
Posted: Mon Dec 06, 2010 12:00 am
All,
Awhile back I posted a how-to on lowering the front end of an A car.
https://forum.porsche356registry.org/v ... =1&t=15122
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.)
Awhile back I posted a how-to on lowering the front end of an A car.
https://forum.porsche356registry.org/v ... =1&t=15122
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.)