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Chuck Moreland's Avatar
 
Join Date: Apr 2002
Location: Santa Clara, CA
Posts: 5,666
How to: Spring plate bushing replacement, part 2

This is part 2 and will explain the actual bushing removal and installation. Part 1 covered removal of the spring plates (and torsion bars) from the car. See part 1 here Part 3 will cover installation into the car Click for part 3

Click any picture for a larger view.

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 944s go.




These pictures tell the tale; the digital readout is partly obscured but you can read the scale. One side of the bushing is 16mm the other is 20.22mm. It is supposed to be round / equal thickness. 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 knowned to be a very difficult job, and if done incorrectly it is a difficult job.

Not to worry, Iíve done this many times 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 re-plated. Get 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.
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Last edited by Chuck Moreland; 07-26-2004 at 03:33 PM..
Old 07-23-2004, 09:55 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
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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 re-lubricated.



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 positioned differently.

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. They are the hot ticket performance wise and with none of the troublesome fitment issues and squeaking that plague regular polyurethane/delrin type bushings.




The races are fit 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 insertion.




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 bearing in.




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.




That's it for part 2. Part 3 will show re-installation of the spring plates and torsion bars. Click for part 3
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Last edited by Chuck Moreland; 07-26-2004 at 03:32 PM..
Old 07-23-2004, 10:03 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
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