Liquid urethane filled subframe bushings

[BigKriss]

I filled them up using Flexane 80A. It takes up to a week for them to set at room temperature.


I first did the bottom side and there was a break in one of the bushings rubber meaning the urethane poured into the other half of the bushing when it was upside down.

not so good bushing with urethane slowly went down. I didn't bother putting new urethane over the 12 hour old set stuff.


better bushing

[nuclearfusion]

We used this technique on four E28s in 1999. Devcon Flexane 80 with FL-20 primer, left cure for a few days before installing, etc.

All four cars belonged to local club members and all are driven pretty hard quite regularly. One E28 M5, two 535i's and one 533i. As far as I know all of them are still using these bushings 7 years later and none have worn out so far. That's saying a lot given these guys and how they drive their cars.

I didn't notice any very great increase in harshness or differential noise, etc. and believe overall the urethane fill was a good improvement. I'd recommend it.

Enjoy!

Fusion

[BigKriss]

Yeah I used the FL-20 Primer, I put that on after I first cleaned the surface with acetone and a cloth. They fl-20 stayed on for 1/2 an hour then I made up the mixture. I have Bruno's delrin rings to install also. It costs aud$35 for the primer and aud$80 for the Devcon Flexane 80 (1 pound - 450grams).

[nuclearfusion]

Yeah I used the FL-20 Primer, I put that on after I first cleaned the surface with acetone and a cloth. They fl-20 stayed on for 1/2 an hour then I made up the mixture. I have Bruno's delrin rings to install also. It costs aud$35 for the primer and aud$80 for the Devcon Flexane 80 (1 pound - 450grams).

OK, I dragged out my invoice from '99 on these parts. (!) The FL-20 was $CAD 17 and Flexane 80 was $CAD 47. Probably more expensive now.

My strategy was to cut out the mold pouring flash from the centre of the bushings, tape the bottom of them and pour them full of urethane all at once from the top. A bit of agitation with a stiff wire all around the edge surfaces to ensure good adhesion and remove bubbles seemed to help.

In all the time I had the bushings in my E28 (7 years) I never saw the urethane delaminate from the rubber substrate of the bushing shell. We were careful to prep the rubber surfaces really well, much as Kriss did, and apply the FL-20 primer well in advance. I think we painted it on and let it dry per instructions before pouring the flexane.

It's a messy job as I recall, and urethane cleanup is a total bear so I'd advise elbow-length nitrile surgeon's-style gloves for this one.

Enjoy!

Fusion

[BigKriss]

Nice comments there mate. I didn't use gloves though. The taping of the bushes sounds better to do all at once. Maybe that way is better but it shouldn't matter too much.

[BillionPa]

so, im gonna do this soon, wondering if there is any logic to go to a thinner or thicker version of the liquid urethane. its available in 60A and 94A hardness.... 94 is the thicker one.

[BigKriss]

No idea, I could only get 80A or 94A.

so, im gonna do this soon, wondering if there is any logic to go to a thinner or thicker version of the liquid urethane. its available in 60A and 94A hardness.... 94 is the thicker one.

[neil_004]

Let us know your opinion on how they feel when you get them in.

[jjdickm]

What is the benefit of using a liquid urathane on a subframe bushing? does it last longer or does it make the car more ridgid? also where do you pick up this stuff?

[Brandon J]

What is the benefit of using a liquid urathane on a subframe bushing? does it last longer or does it make the car more ridgid? also where do you pick up this stuff?

The benefit is to fill-in the holes/open space of the bushing with something durable. By fillin-in the open space, there will be less flex and less fatigue on the bushing. BMW dials in the flex to smooth out the ride and harshness from abrupt acceleration and braking. The liquid urethane is easy to work with so it is commonly used.