steering and suspension 2002 front suspension torque specs

[Kuntacharlie]

I'm new here so I hope this the right way to ask for help.

 

I am finishing a front suspension rebuild on a 71 2002.  I am down to tightening the nuts on the rubber bushed joints.  The lower control arm is attached to the sub frame by a large bolt and nut and the control arm pivots around the bolt when the suspension moves up and down.  The BMW manual says the torque for the nut is 123 ft- lbs.  

 

My concern is that this is a bunch of torque (even for a half inch torque wrench)  and I cannot see how the control arm can freely pivot around the bolt with that much squeeze on the steel bushing in the control arm pivot point. The nut didn't have a hugh torque on it when I took it apart.   This doesn't make sense to me.   Can someone help me out with this?

 

Charlie

[TobyB]

The bolt should clamp tight.  You don't want that thing moving, ever.  It'll rattle loose and THEN where will you be?

 

The pivot function is provided by the bushing in the lower control arm.  As in, the rubber deflects.  All 

of the metal parts should be, in effect, one piece.  No movement.  Ever!

 

That's why, as it says in the manual, you're supposed to snug them with the car sitting on its wheels,

so that the rubber's not preloaded up or down.   It only has a certain range of motion...

 

hth

 

t

[Kuntacharlie]

Thanks Toby.  I agree, the rubber bushing will take all of the flexing if the required torque is applied. That's what bothered me. Seems like an odd way to design a suspension joint. 

 

I have the car on its wheels ( ramps in front and jack stands in back ) and will torque all the rubber bushed joints that way.  The manual says to load the car up with weight, presumably to simulate a full load condition.  Is that necessary?  I never drive this car with a load and am always alone in the car.  Only load is me and fuel.

 

Charlie

Hansville,WA

['76mintgrün'02]

You are not putting stress on the rubber when you tighten the bolts.  The stress comes when the suspension changes position, relative to where it was when you tightened the bolts.  

 

The rubber bits are like torsion springs, in that they 'want to return to center'.  

 

Set the car on all four wheels before you tighten the suspension bits.  

 

Also add your weight to the driver's seat and possibly a passenger (people make good sand bags).  Is the tank full, or empty?

 

You may not have to  do this, but it will make the new rubber happy.

 

Rubber 'bushings' are like ligaments in the suspension joints, as opposed to poly, which are actual rotating bushings.

 

The rubber vs poly debate is not part of your initial question, but I just found a link which discusses that comparison in some detail.

(See the part on Friction)

http://www.iwsti.com/forums/gd-suspension-handling-and-stiffening/206293-bushings-rubber-vs-polyurethane.html

[Kuntacharlie]

Thanks 76mintgrun.  I'll take your advise and add weight before torquing the joints.  Charlie

[peterschop]

I recently replaced the rubber bushings on the front of my car. I dropped the car down on all four wheels, then I put four 40 lb salt bags in the drivers seat and a couple of tool boxes on the floor of the passenger side and then tightened the bolts. I figured that the majority of time I drive the car by myself so I weighted the drivers side more. What ended up happening, the car now sits a little lower on the drivers side unloaded. This is with new springs, shocks and rubber bushings. So in hind site, I should have weighted both sides the same.

[Dev02]

^ Ditto. Though I used sand bags, not salt, I wish I'd done it exactly as the manual said. Mine sits off a little also.

[Kuntacharlie]

I ended up putting 150# in the drivers seat and 100# in the passenger seat and 50# in the trunk ( I also replaced my rear shocks ). I have not noticed/checked to see if the car is noticeably lower on the drivers side.  I hate to think about doing that bolt tightening evolution again.  It was a pain to get the bolts torqued and the cotter pin holes to line up, especially the lower control arm to sub frame joints.

 

Thanks for the responses Dev02 and Peterschop.  

 

Charlie

['76mintgrün'02]

Hey Charlie, I see that you have added your location to your signature.  We're neighbors!  

 

You should to stop by and say hello      PM sent.  Tom