Urethane FILLED Subframe bushings

[Russell]

BACKGROUND
I filled/injected my old cracked and possibly separated subframe bushings with black 3M Windo-Weld super fast urethane. 8609. It is available in 10.5 fl oz cartridges that fit in a standard caulking gun. NOTE: I did not remove the bushings or drop the subframe.

Found the urethane at Advance Auto Parts. I understand it is available at most auto parts stores in the US. Many performance-oriented enthusiasts use this product to fill motor mounts and suspension parts to stiffen up the suspension. There are no photographs as I did not think any are necessary as there are many posts in the archives or other forums with photos of subframe bushings particularly http://www.bmwe34.net/e34main/Mainte...ameBushing.htm

NOTE: There are several postings about using pourable polyurethane on this board and other boards. This is not that product.

TECHNIQUE
Rather simple. Raise the car, place on jack stands, ramps or lift. Whatever technique you use, make sure you are high enough to allow a fully extended calk gun to fit vertically. Otherwise, you are trying to force the urethane into the subframe bushing at an angle. More later on injecting the urethane.

I think it is optional to remove the wheels. However, it gives you a bit more working space. Remove the two small bolts and the large nut on the subframe-bushing pin for each bushing. I used a breaker bar on the large nut. It is not necessary to remove the pin. This will expose the bottom of the subframe bushing. Clean the rubber surface with Acetone. I used a Q-tip. You can also purchase and apply a single step primer from 3M 08682 which may help adhesion. Then tape up the bolt/pin to keep the thread from coating with urethane. Note: I wanted to inject the urethane from the top as well as the bottom. However, there was not enough clearance (about 1/2inch) from the top even with the side jacked up. There may be other ways, but I did not have a lift or other tools.

Note: use heavy rubber or nitril gloves. This stuff is stick and messy. I then pushed the caulking tube into the voids as far as I could and injected the urethane as far up into the bushing as I could. There appears to be a membrane about ½ ways up in the voids. It was torn on my bushings, so I just pushed beyond it and filled. Even so, I am sure a substantial amount of the void above the membrane was only partially filled. I continued filling the bushing until flush on the bottom. The material did not sag or flow. I used my fingers to level out and clean up. Acetone or denatured alcohol will clean. Then as they say, I reinstalled the cover plates. Not sure of the correct torque. However, I retightened the large nut to about 80 ft-lbs. You could cover the bottom of the bushing with duct tape or similar until the urethane sets up, then reinstall parts. I just went ahead and installed the parts as I use Bruno’s subframe inserts, which fit almost flush against the subframe bushing acting as a barrier. NOTE: I reinstalled the wheels and set the car on the ground before I did the final torque of the large nut. Have no idea if that makes any difference. Nevertheless, I wanted to urethane to set in normal road situation.

IMPORTANT: Do not drive the car for about 48 hours. It takes that long for the thick urethane to cure. On a sample 3/4 inch, thick ribbon only the outer 1/8 inch had fully cured in 12 hours during a wet 45-55 degree temperature.

FINAL RESULTS/THOUGHTS
To be determined. I will not be able to drive my car until Monday at the earliest. I will later report with my initial thoughts. Even so, if there are improvements to what I think is "rear steering" creating wandering, the “fix” may not last. I really think that my subframe bushings are “toast” as they are original with 134,000 miles and appear to be cracked and partially separating.

I have heard that harder polyurethane separates after a few months. However, this material is supposedly softer than most pourable urethane and flexes more with the original bushings. We shall see. I also wonder if I have created a nightmare when I decide to replace the subframe bushings and they will need to be cut out.

[Russell]

If your garage is cold, I would suggest some sort of heat to speed up cure time. If you do use a space heater, I would put out a long thick bead of the urethane material and cut off a piece every 12 hours or so. That way you will have some idea how fast it cures.

After 36 hours and no heat, there is still a lot of material not cured in my samples. Only the outside 1/4 inch is cured even with temperature of 40-55 degrees and is rainy. IMO that means the material deep inside the bushing is still uncured! Because of this situation, I do not plan to move my car until at least another 24 hours, which is 72 hours more or less. Even so, I may fire up a small ceramic heater and see what happens.

[billy]

I am doing this and after 36 hours, there is still a lot of material not cured. Only the outside 1/4 inch is cured even with temperature of 40-55 degrees and is rainy. IMO that means the material deep inside the bushing is still uncured! Because of this situation, I do not plan to move my car until at least another 24 hours, which is 72 hours more or less. Even so, I may fire up a small ceramic heater and see what happens.[/FONT]

if you use some sealent from a gun then leave the rest in the gun - what happens...the end of the nozzle sets the rest doesnt - i think you will find that when you squeeze out that sort of thinkness of the stuff that the middle may never set.

[Russell]

Intresting. This product is moisture cured with a 500 psi overlap shear strength after 48 hours at 75 degrees F. That is once exposed to the air it begins the curing process. Even then, I expect, the thicker the material and cooler it its, the longer it will take to cure. But it will cure. My 3/4 inch samples are almost comletely cured after 40 hours. Also, I have had silicone caulk or RTV cure completley in the tube after it has opened.

[Russell]

Well, I drove to work (30 miles of smooth city streets and undulating two lane roads) this morning after filling the subframe bushings with Windo-Weld urethane.

Note: I did not move the car for 3 days to facilitate curing. However, I am not sure the urethane has completely cured. Even so, subjectively I feel a “change” via the butt-meter. The car did not thump (in the rear) over bumps, seem tighter and had a bit better directional control (wandered less). It seem especially more stable when changing lanes or cornering. Seemed more planted. I did not notice any increase ride harshness, perhaps even less harshness. I think this is the desired goal.

Now, how long will it last???? If and when they fail, I will have my Indy install new bushings. I think I will replace the rear struts before replacing the subframe bushings. Hey- it never stops.


Below is the old bushing cleaned up with acetone before filling. Notice the cracks and possible separation especially just below the bolt..

[Russell]

Wandering is reduced. Cornering is different. Very little if any corrections needed as you corner. It used to be that a big correction was needed after starting a sweeping corner until the bushings (or something settled) settled. Turn in feels quicker...

Only one potential issue. Per my samples not all the urethane has cured even after over four days of setting in my cold garage. The center core is still uncured. Do this in warm weather! I suspect this will be a bit firmer after all material is cured. Even when cured, it is very firm and elastic. Very pleased.

However, I have found it interesting there seems to be limited interest in this process.

[brick8]

I am very interested, however, it is too cold outside here (below 0 degrees fahrenheit last two nights) now to even think of starting this project.

[Dash01]

Wandering is reduced. Cornering is different. Very little if any corrections needed as you corner. It used to be that a big correction was needed after starting a sweeping corner until the bushings (or something settled) settled. Turn in feels quicker...

Only one potential issue. Per my samples not all the urethane has cured even after over four days of setting in my cold garage. The center core is still uncured. Do this in warm weather! I suspect this will be a bit firmer after all material is cured. Even when cured, it is very firm and elastic. Very pleased.

However, I have found it interesting there seems to be limited interest in this process.

If you have a trouble lamp/work light, why not set it right next to the uncured stuff to add some heat: By tomorrow morn, it should be cured.

[Russell]

Good idea but my trouble lights are flourescent-not much heat. I did use a 1500 watt ceramic heater for about 30 minutes a side to get the bushings hot to the touch on Monday while I was around to check on it I am sure that helped the curing process a bit. Thanks.

[Russell]

Performace properties of Windo-weld for those interested.

Data is from 3M document Library data sheet. I believe this material is softer than some of the pourable poly urethanes some have used.

Tensile: 1200 PSI
Elongation: 700%
Hardness (Shore A) 55-60
Overlap shear strength (50% RH, 75 degree FH)
6 hours 65 PSI
48 hours 500 PSI