Russell
01-13-2007, 02:23 PM
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/Maintenance/Suspension/SubframeBushing.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.
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/Maintenance/Suspension/SubframeBushing.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.