Injecting suspension bushings.....

[George M]

no secret that urethane suspension bushings have been popular with tuners
to create a tighter suspension for track use etc at some detriment to NVH.
I have read sometime past that some have injected front thrust arm bushings with RTV or equivalent in an effort to create firmer bushings. Have stumbled on a product used by Saturn autocrosser's that I thought I would share with the BMW community...its called 3M Windo-weld which is sold in many chain autoparts stores in a caulking gun cartridge form and used to bond windshields into place. It is a urethane that maintains a level of compliancy when cured. I removed and injected the dogbone engine mounts in my Saturn as many others have to firm them up a bit as Saturn mounts are deliberately postured for NVH which is problematic for aggressive driving with 5 speed cars because of greater driveline lash. Stuff is really good...firmed the mounts up nicely and still maintains reasonable NVH. Am considering removing the bottom plates over my subframe bushings and injecting Windo-weld into them and seeing the net result. As long as the subframe bushings aren't too far gone, i.e. button holed, this may be the ticket. The subframe bushings appear to have an air gap not unlike the front thrust arm bushings which like many large bushings is there to quell the vibration wave length transmitted from the road to the car's chassis. Any experience out there injecting either thrust arm or subframe bushings?
George

[AllanS]

No, but if you do go through with this, please post a write up with pics! It'd definately be interesting to take a look at it.

[MikeV]

Haven't tried it, but I have used pourable polyurethane to beef-up engine mounts - works well. The advantage of the pourable stuff is it's available in many different durometers (e.g. at mcmaster-carr).... the advantage of WindowWeld is, of course, you can inject it while parts are still on the car.

Last time I was in Home Depot I noticed there are now several brands of polyurethane caulk out there, it could be worth experimenting to find the right durometer.

Hmmm, now you've got me thinking....

[George M]

a good point Mike...there are a number of different durometer urethane's out there.
The pourable stuff is of course less viscous when not subjected to oxygen as compared to Windo-weld which doesn't neccessarily equate to stiffness when cured. Beauty of Windo-weld is what you said...you can inject it while on the car...almost jell like..quite viscous and hence won't run without having a mold like boundary. Always best to inject off the car...what I did with the Saturn mounts but when injecting one side and then turning it over...the stuff held up in well against gravity...a major plus when injecting subframe bushings which is penpendicular to gravity and hence would have the highest chance of falling out prior to curing. A good technique is prior to injecting...what I did with the engine mounts...is make a small cardboard barrier. Inject it and then tape the barrier up against the mount to prevent the urethane from falling. May give this a go. If you study the subframe bushings which I believed are clocked to contend with subframe loading...there is quite a bit of gap between the bushing and the steel retaining shell.
The thing about bushings is visually it is hard to tell the status of a bushing because failure or degradation is generally due to micro-tearing of the rubber material which degrades its durometer. Only visual tell is either lack of concentricity or button holing or a dynamic test inducing unwanted deflection under typical load. Windo-weld may be a perfect adjunct to worn bushings...perhaps better than Windo-welding fresh bushings because the composite stiffness may be more desireable. Other thing is...if it doesn't work...or is too stiff...no foul...bushings have to come out anyway.
George

[MikeV]

PL Premium Polyurethane Construction Adhesive
http://www.stickwithpl.com/products...?PLProductID=14

$2.54 at Home Depot...

I'm told this is "Shore 90A" durometer (although I always thought if you were in the 90's, it's automatically Shore D.... but then, as you can tell I don't know much about urethanes other than what I own in bushings, motor mounts and rollerblade wheels).

[Unregistered]

If Window Weld works well as a buffer between the old rubber bushing and its steel retainer, why not use Window Weld for the whole shebang?

In other words, remove the rotten old rubber bushing (knife, propane torch?), fix the stabilizer bar (or whatever else you're trying to reinforce) in its correct position/orientation, install cardboard or plastic dams to keep the wet Window Weld from draining out, then inject it into the cavity. Call it "in situ" injection molding.

If you want to get fancy, spray the steel parts with WD40, sililcone, wax, or whatever else as a chemical barrier between the Window Weld and the steel parts. That way, WW won't stick to those parts as it solidifies.

When the stuff dries and hardens to final consistency, you'd have a whole new bushing ready to go, with perfect fit.

Now, how 'bout some response to my dumb question?

[Unregistered]

Does Window Weld come in CLEAR & TRANSPARENT form?

If so, one might make some decent stone guards for fog lights, etc..

[George M]

anonamous:
Reason why Windo-weld is more effective as a filler as opposed to the whole
enchilada is due to overall flexure modulus and yield strength. The beauty of a composite bushing, i.e. two different modulus materials is you can tune the overall balance of stiffness and NVH. Having composite materials naturally truncates noise frequency mostly due to density differences changing speed of sound propagation. NVH is highly tied to isolator stiffness which generally equates to strength. High durometer rubber is relatively strong but the stiffer you go, the harsher the NVH. Filling a rubber bushing with a low durometer urethane like Windo-weld, though not as effective as air to break the vibration signature from the road into the cabin is more effective than stiff rubber. The reason why it works so well is it is essentially incompressible in a captured environment like a filled bushing...not unlike liquid yet has an elasticity that allows flexure...what you want for good NVH levels....overall volume of material is conserved..just displaced as the bushing is loaded.

As to making your own bushing with Windo-weld...issue is it would be too weak because of its low flex mod and yield strength. Now you can opt for a solid high flex mod urethane but then you chase your tail back to high NVH levels which all report with solid urethane mounts.

As to putting Windo-weld over fog lights...lol...two issues:
- High heat...will challenge temp boundary/material melting point.
- Reduce lighting efficiency...even a clear urethane would be at best be translucent and counterproductive to light transmission.

HTH,
George P.S. Mike...I am a big blader and like 82A durometer for outside

[Unregistered]

3. WTF is "NVH?"

4. Being called Window Weld, it sounds like this stuff would be pretty good to hold the rear hatchback window in, say, a Porsche 944 or other fastback style car, which gets solar heat buildup, vibration, torsional stresses, etc.. Under those circumstances, how well does it hold up to UV/ultaviolet/sunlight degradation?

5. When you discuss durometer in the 90s, and in the same post mention rollerblade wheels of 90+ durometer hardness, is a layman to assume that Window Weld hardens to the consistency of a rollerblade wheel?

[Hector]

It's not going to hold up well because most polymer-based materials don't react well to UV light. It well degrade with time and become even more translucent.

4. Being called Window Weld, it sounds like this stuff would be pretty good to hold the rear hatchback window in, say, a Porsche 944 or other fastback style car, which gets solar heat buildup, vibration, torsional stresses, etc.. Under those circumstances, how well does it hold up to UV/ultaviolet/sunlight degradation?