> 944 Spring Plate Bushing Replacement project
944 Spring Plate Bearing
to Polybronze performance
Put the car up on jackstands, or a lift.
At a minimum you need both rear wheels up in the air, but the
job is easiest with all 4 wheels up.
Remove both rear wheels.
Remove 2 bolts attaching spring plates to
the trailing arm. Remove
the sway bar drop links.
Popular wisdom says disconnect the brake
line flex hoses, remove the exhaust, and drop the torsion bar tube. I found this wasnít required.
It is possible to tilt the torsion tube down, one side at a
time, and gain the required clearance.
Do remove the spring clips that hold the
brake line flex hoses to the trailing arms and the tub.
Pulling these clips off affords a couple extra inches of
slack on the brake lines.
Pull the trailing arm clear of the spring
will need to remove the bolt that secures the trailing arm to the
torsion bar tube. On
the driver side you will need to remove one side of the axle to
avoid interference with the muffler.
Your goal is to have the spring plates hang free without
interference from the trailing arms.
Lifting the trailing arm with a jack will help.
You want the spring plate to hang free so
you can create a reference line marking its angle relative to the
torsion bar tube. This
mark will be extremely valuable when you re-assemble to avoid
repeated attempts at re-indexing the torsion bars.
Draw a pencil line as shown:
Again, be sure the trailing arm is not
interfering with the angle of the spring plate.
If you plan to re-install the same torsion bars, your goal
will be to re-install the spring plates with the same angle.
If you are installing stiffer torsion bars, you will need to
install the spring plates a bit higher than the reference angle.
The amount will depend on the stiffness of the torsion bars,
but at least you have a staring point to reference.
Remove the rear bolt that secures the torsion
bar tube to the chassis.
Remove 4 bolts surrounding spring plate,
1 bolt from forward bushing, and 1 bolt from the rear mount.
You will need to pry the forward bushing down
to free it from the bracket.
You should now be able to tip down the
torsion bar tube, one side at a time.
Be sure you are not putting
excessive stress on the brake flex hoses.
Remove the spring plate cover.
Remove the rear section of the rubber rocker valence.
Pull the spring plate from the torsion
tube and remove. The
torsion bar sometimes sticks in the spring plate.
Usually it can be freed by rocking it back and forth while
With the rocker valence removed and the
torsion bar tube tilted down you should be able to fully remove the
spring plate and the torsion bar.
With the spring plates on the bench, the
deterioration of the factory rubber bushings is obvious.
The factory rubber cold flows over time from the weight of
the vehicle such that even low mileage bushings deform after 15
years or so. In this
case the car is 18 years old with about 80k miles, fairly fresh as
These pictures tell the tale; the digital
readout is partly obscured but one side of the bushing is 16mm the
other is 20.22mm. It
is supposed to be round.
These measures are taken on the bench, but with the weight of
the vehicle in the difference would be even greater.
Next step is to remove the bushings.
The bushings are vulcanized to the spring plates and they are
very secure. Removal is
rumored to be a very difficult job, and if done incorrectly it is a
difficult job. Iíve
done this many times for 911s and have developed a technique that is
easy. Follow my
instructions here and you will have it done in no time.
Secure the spring plate in a bench vice.
Use a propane torch to heat the metal tube of the plate from
the inside. Your
goal is to get the metal hot enough to melt the contacting rubber.
Heat it for several minutes.
While it is still hot, work a flat blade
screwdriver between the rubber and the metal tube.
Work all the way around to separate the rubber.
Use a razor knife to separate the rubber from the flat part
of the plate. The
bushing can now be easily pried off.
This will remove 90%+ of the rubber in one big
donut. Next use a razor
knife to cut off remaining large chunks.
Cut away the thin layer that covers the tube portion of the
spring plate. Small bits of rubber will remain. These can be removed easily with some medium sandpaper.
Be sure to get the tube portion of the
spring plate very clean, any residual rubber here would interfere
with the fit of the new bushings.
Next I recommend having the plates
them plated along with the hardware with yellow zinc dichromate.
Shop around and you can get this done for $40-$50, well worth
it. You may have
some other parts youíd like to throw in the batch too.
Not only do the plates look like new, the acid
bath used in the process will clean off any remaining rubber bits. Donít rely too much on this for rubber removal
though, give the plater clean parts.
This really gives the project a finished
appearance. Do it
once, do it right and be proud.
Next step is to install the Polybronze
bearings. Polybronze is actually a bronze bearing that rides on a
steel race fitted to the spring plate.
The bronze on steel provides a precisely machined
low-friction bearing action that never squeaks and can be
This picture is of the prototype set that has
been adapted from 911 parts. Four
of these are used. Production
parts will look the same, except the grease grooves will be sized
properly for the part.
The bronze is surrounded by a
polyurethane jacket. The
polyurethane is not part of the friction surface, its purpose is to
accommodate irregularities in the factory mounts. Because the bronze
core is rigid, the poly jacket can compress slightly for
irregularities without pinching the bronze friction surface.
The product has been available for 911s
for about a year and is extremely popular.
The product has none of the troublesome fitment issues and
squeaking that have made regular polyurethane bushings infamous.
The races are fitted to the spring plates.
Springs plates vary slightly in diameter (one reason regular
polyurethane bushings are so hard fit properly).
To accommodate the variation, shims are fit between the race
and spring plate to make it good and tight.
The shims are included with the product.
The race provides a precisely machined surface for the bronze
bearing to ride upon.
Above pic shows the spring plates with both
races installed and bearings slipped on.
Press the bronze bearings into the spring
plate covers using bench vice or press.
Liquid soap is used to lubricate the polyurethane to ease
Once pressed in, drill a hole for the
grease fitting. A small
pilot hole is first drilled fully through one side of the bearing.
A large hole is then drilled and tapped in the aluminum cover
plate to accept the grease fitting.
Pic above shows the grease fitting and
installed in the assembly.
And the back side of the assembly.
Next install bearing in the torsion tube.
Clean up the ID of the torsion tube using
sandpaper and scraping tools. The
ID tends to have hard residue from the rubber bushings, this must be
removed to get a good fit.
Lube up the bronze bearing with liquid
soap and insert it into the cleaned up torsion tube.
Then use the spring plate cover plate and a block of Ĺ wood
to press the inner bearing into place.
Tighten the 4 cover plate bolts in sequence to push the
Next drill the torsion tube for the grease
fitting. Again, using a
small pilot hole through the bearing then a shallow larger hole
tapped for the grease fitting.
Start by assembling the spring plates.
The large eccentric bolt provides a height adjustment
capability. Position it in the center of its range. This
will give you +- .75 inches of range to make final adjustments.
Next install the spring plates
Apply a good quality grease to the bearing
surfaces. Try to fill the grease grooves.
I recommend doing a dry run, installing the
spring plates without torsion bars to ensure the plates are moving
freely. Pull the trailing arm back so it does not
interfere with the spring plate. Slip the spring plate into
place, install the spring plate cover and torque it
The spring plates should move freely without
binding or friction. If they are tight, inspect the bearings
to be sure they are full seated. With the plates moving
freely, remove the spring plates covers and
Grease up the torsion bars. It's a good
idea to grease the entire bar for corrosion protection and the
splines for easy installation. Slip the bar into the torsion
Slip the spring plate over the torsion
bar. Carefully compare the scribed line to the edge of the
spring plate. You will note that indexing the torsion bar one
spline makes a large change in the angle of the spring
plate. Not to worry.
The torsion bar has a different spline count on
each end. This makes it possible to make very fine
adjustments in spring plate angle by rotating both splined ends
simultaneously. I'll leave it as a homework assignment for
anyone who wants to compute the affect of rotating each
end. I find it easier to simply pull the torsion bar
out, rotate the inside a spline or two, then do another test fit.
Repeat until you get the desired angle. It usually only
takes a few attempts to dial it in.
If you are re-installing the same torsion bars
and want to maintain the same ride height your job is relatively
easy; make the lines parallel.
If you are installing stiffer torsion bars and
/ or are adjusting ride height, you need to install the spring plate
at an angle different than scribed line. Stiffer torsion bars
will droop less under the weight of the car. The stiffer the
torsion bar, the less droop. You will need to take a guess at
how much to compensate for the new torsion bar stiffness and / or
ride height. Fortunately the spring plates offer some
adjustment for ride height, so you just need to get close.
Careful here, too far off and you will be pulling this apart again
to re-index the torsion bars.
Install the spring plate cover. Attach
spring plate to trailing arm using two bolts.
You may need to lift the trailing arm with a
jack to get the rearmost lower spring plate cover bolt and
spacer into place.
Install the inner trailing arm link. The fit is tight, tap it
into place using a mallet.
Next attach the front bushings to the
tub. Use a jack to raise entire torsion tube assembly up into
position. It is helpful to have two jacks, one on each
Once the bushing lines up, slip the bolt
in. It probably wont go through the backside yet, you'll come
back to this.
While you are raising the assembly up, make
sure it aligns properly with the little hooks on the torque
tube. A little pushing and prodding should be all it takes.
Attach the rear mounting bolts.
With the rear mounting bolts in place, the
front bushing bolt hole should now line up better and the bolts
should be fully installed.
Now it's just cleanup. Reinstall the sway
bar, lower shock bolts, driver side axle, and spring clips for the
brake lines. Go through and check all bolts for proper
torque. Give a couple squirts of grease to each of the grease
nipples for good measure.
All put back together, it looks like this:
To finish off the job you'll need to fine-tune
ride height using the spring plate height adjusters. This is a
straight forward process of loosening the bolts and turning the big
eccentric nut. You will need the special 36mm wrench made for
this job. Then get a good four wheel alignment and corner
Then go out and drive. Appreciate your
car's new-found handling precision.