How to: Spring plate bushing replacement, part 2
07-23-2004, 02:49 PM
#1
Former Vendor
Thread Starter
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. Click here to see part 1 Part 3 covers installtion. Click here to see 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, I’ve 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 you’d 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. Don’t 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 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 ½ 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 here to see 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, I’ve 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 you’d 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. Don’t 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 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 ½ 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 here to see part 3
Last edited by Elephant Chuck; 08-07-2005 at 03:22 AM.
07-23-2004, 08:23 PM
#2
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DO NOT PLATE THE PARTS WITH ZINC!! use cadmium because they are in direct contact with the aluminum trailing arms, and cad has a lower portential for galvanic corrosion. The price will be roughly the same. I did all of the spring plates and hardware for $125. Definitely give the job a totally pro look. I wish I had used these polybronze bushings instead of delrin!
07-23-2004, 08:44 PM
#3
Former Vendor
Thread Starter
The factory used CAD and it is a better choice. Unfortunately CAD plating has been regulated into virtual non-existence. If you can find a plater that does CAD for a reasonable price, by all means use them. However, platers who still perform this process are extremely scarce.
Yellow Zinc Dichromate is the commonly accepted alternative, the process is affordable and readily available. The appearance is similar to the factory parts and it provides good protection.
Yellow Zinc Dichromate is the commonly accepted alternative, the process is affordable and readily available. The appearance is similar to the factory parts and it provides good protection.
07-26-2004, 08:26 PM
#5
Former Vendor
Thread Starter
Skip,
Yes I am preparing a production run of these as well as complementing components for the trailing arms, control arms, etc. I sorta touched on this in part 1 here. Everything will be rolling out in the next couple months and will be on display at German Autofest in September.
944 Spring plate bearings will be priced similar to the 911 spring plate bearings which are $295/set.
Yes I am preparing a production run of these as well as complementing components for the trailing arms, control arms, etc. I sorta touched on this in part 1 here. Everything will be rolling out in the next couple months and will be on display at German Autofest in September.
944 Spring plate bearings will be priced similar to the 911 spring plate bearings which are $295/set.
Last edited by Elephant Chuck; 07-26-2004 at 08:49 PM.
07-29-2004, 01:20 PM
#6
Hey Man
Rennlist Member
Rennlist Member
Chuck,
This 3-part series is one of the best write-ups I've seen. You've provided a great alternative to an up till now difficult repair procedure. I'll hold off on the 951 until your package is ready for resale.
Good call on the cadmium. You may want to consider metallizing those parts using an Arc-Sprayed Metallizing Wire process, ASTM B833-97. The wire is 85%Zn/15% Al. It's a relatively inexpensive shop applied coating and will outlive every other exposed part on the car. Impact resistance is second to none. We've used this for years in corrosive full submersion service on massive structures with great results; for atmospheric service like this application it truly is bulletproof. Nearly all tank plated products will break down due to poor bonding and impact damage. The metallizing process virtually pounds the new coating into the target surface as a molten metal.
Steve
This 3-part series is one of the best write-ups I've seen. You've provided a great alternative to an up till now difficult repair procedure. I'll hold off on the 951 until your package is ready for resale.
Good call on the cadmium. You may want to consider metallizing those parts using an Arc-Sprayed Metallizing Wire process, ASTM B833-97. The wire is 85%Zn/15% Al. It's a relatively inexpensive shop applied coating and will outlive every other exposed part on the car. Impact resistance is second to none. We've used this for years in corrosive full submersion service on massive structures with great results; for atmospheric service like this application it truly is bulletproof. Nearly all tank plated products will break down due to poor bonding and impact damage. The metallizing process virtually pounds the new coating into the target surface as a molten metal.
Steve
07-29-2004, 02:37 PM
#7
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All these writeups and new product comes a week after I buy a set of Delrin bushings for when I do my torsion upgrade...ahh well. It may be more of a pain in the *** but I'll get them in somehow...with as stiff as my suspension already is (and is going to be moreso) and I don't really care too much about the noise, they should be fine.These writeups will definately help make the job of getting everything off and on a lot easier though...
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07-30-2004, 05:48 PM
#8
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You may want to consider metallizing those parts using an Arc-Sprayed Metallizing Wire process, ASTM B833-97
What does the finish look like with this process? flat, gloss, mirror, color? Any pictures?
07-30-2004, 06:08 PM
#9
Hey Man
Rennlist Member
Rennlist Member
It comes out looking like a very finely peened surface of bright aluminum with a semi-matte sheen. It can be topcoated with a clear finish if a shinier look is required. I'm not at work today but will try to get you some photos on Monday. I can't attach photos to PM's so if you want to shoot me your e-mail to sburke45@comcast.net I'll pass some photos on to you. It really is a bulletproof surface treatment, maybe overkill but much better than zinc dichromate plating. It can be done in chromium, Zn, Al, stellite, and many base metals and alloys. I've never seen it powder up like some zinc or aluminum plating jobs.
Steve
Steve
05-11-2005, 11:53 AM
#11
Nordschleife Master
I have a question about the platting...
What happens if you don't get them platted? since around here there is no one that will do the platting for less then $100 (min fee)
What happens if you don't get them platted? since around here there is no one that will do the platting for less then $100 (min fee)
05-11-2005, 08:44 PM
#12
Former Vendor
Thread Starter
You can just paint them if you want. But the plating holds up very well and looks great.
You could just ship your plates to someone with a reasonable minimum. Try Swift Metal Finishing (408) 727-5776, Santa Clara CA. I think they have a $50 minimum, you can through in all your spring plate hardware and small batch of extra parts for that min. You'll get hit for shipping, but it should still be under $100.
There are many plating shops that would do this for $50. Surely some closer to you than CA.
You could just ship your plates to someone with a reasonable minimum. Try Swift Metal Finishing (408) 727-5776, Santa Clara CA. I think they have a $50 minimum, you can through in all your spring plate hardware and small batch of extra parts for that min. You'll get hit for shipping, but it should still be under $100.
There are many plating shops that would do this for $50. Surely some closer to you than CA.
01-28-2010, 09:40 PM
#14
just a tip for future ppl reading this.
when you're drilling and tapping, there's going to be obviously alot of metal and urethane shavings. get ALL out before you put the grease fitting in.
these are the steps i did. BEFORE inserting the bushing
1) take measurements, with a caliper if u have one. the grease channel is 1/2" from the edge of the bushing. the bushing has a 1/16" lip. 8/16"-1/16:=7/16" is the distance from the edge of the springplate/torsionbar housing.
2) mark and drill 1/16" hole at 7/16" from the edge of the piece....be sure to go slow and not too much pressure or you'll snap yer drill bit. i've broken 2 tonite.
3) expand the hole to incrementally up to its final 13/64 (6mm) tap size.
4) tap the hole with yer m6x1.0 tap
5) clean out all the metal shavings. use towels, compressed air, or a liquid like wd40 or lubricating oil
6) inspect the bushing. look carefully where the two grease channels intersect, there's an area where it's more open. i call this the sweet spot
7) line up the bushing so that the sweet spot aligns with the hole u just drilled and tapped.
8) press bushing in and get it so it's flush.
9) redrill using 1/16 thru the red polyurethane and the brass, hopefully hitting the sweet spot. if close but no cigar, expand as needed.
10) feel the inside of the brass bushing at the drill point. if u feel a burr or a lip, use a blade or other instrument to clear the burr. maybe a sanding pen or some 100grit on a small screwdriver.
11) again clean out all the shavings. blow compressed air/lubricant OUTWARDS past the brass bushing.
12) thread on the grease fitting. i used a 9mm wrench...but i think i might be a 5/16 sae. make sure it's pointing "down"
then after everything's done, make sure your grease fitting is reachable from yer grease gun.
when you're drilling and tapping, there's going to be obviously alot of metal and urethane shavings. get ALL out before you put the grease fitting in.
these are the steps i did. BEFORE inserting the bushing
1) take measurements, with a caliper if u have one. the grease channel is 1/2" from the edge of the bushing. the bushing has a 1/16" lip. 8/16"-1/16:=7/16" is the distance from the edge of the springplate/torsionbar housing.
2) mark and drill 1/16" hole at 7/16" from the edge of the piece....be sure to go slow and not too much pressure or you'll snap yer drill bit. i've broken 2 tonite.
3) expand the hole to incrementally up to its final 13/64 (6mm) tap size.
4) tap the hole with yer m6x1.0 tap
5) clean out all the metal shavings. use towels, compressed air, or a liquid like wd40 or lubricating oil
6) inspect the bushing. look carefully where the two grease channels intersect, there's an area where it's more open. i call this the sweet spot
7) line up the bushing so that the sweet spot aligns with the hole u just drilled and tapped.
8) press bushing in and get it so it's flush.
9) redrill using 1/16 thru the red polyurethane and the brass, hopefully hitting the sweet spot. if close but no cigar, expand as needed.
10) feel the inside of the brass bushing at the drill point. if u feel a burr or a lip, use a blade or other instrument to clear the burr. maybe a sanding pen or some 100grit on a small screwdriver.
11) again clean out all the shavings. blow compressed air/lubricant OUTWARDS past the brass bushing.
12) thread on the grease fitting. i used a 9mm wrench...but i think i might be a 5/16 sae. make sure it's pointing "down"
then after everything's done, make sure your grease fitting is reachable from yer grease gun.
