Does the front Sub-Frame move on the frame and effect alignment

svx_commuter · #1 08-08-2006, 06:31 AM

Does the front Sub-Frame move on the frame and effect alignment?

I am looking for advice on this subject, let me explain. The front sub-frame is attached to the frame with four bolts. Each of the bolts go through the center of rubber bushings that are part of the sub-frame. The center of the bushings have metal sleeves and the outside of the bushings are pressed into the sub-frame. There is clearance between the inside diameter of the metal sleeve and the bolt outside diameter. This is clearance that might allow the sub-frame to move.

This clearance as I remember is about 1/8” total or 1/16” per side. I do not have the exact measurement right now.

The sub-frame is held to the frame by the clamping force of the bolts that goes through the bushings. The clamping force prevents the sub-frame from SLIDING on the frame. The clamping force of the bolts applies a friction force to the bushings and has to be higher than the acceleration force of the front wheels and also the braking force and cornering force of the front wheels. IF the clamping/friction force is lower then the tire forces or reduced such as when the sub-frame bushing are covered in oil, then the sub-frame can move when the tire forces are applied.

When the clamping force of the bolts is NOT high enough the sub-frame will move relative to the frame during barking, acceleration and cornering.

So the question is this: If the sub-frame moves around 1/16” or so will it effect the alignment?

If this “movement” is a problem can it be corrected with a metal stainless steel SLEEVE between the clamping bolt and sleeve in the bushing, something to take up the clearance between the bolt and bushing?

Is there a similar problem with rear sub-frame? I do not know much about that system of attachment, as I have not it apart.

Thanks

svxcess · #2 08-08-2006, 07:26 AM

Here is a quote from Harry Newman "newsvx" on the moving subframe issue:

Quote:

Originally Posted by newsvx

Not withstanding the previous thought about the "rattling" sound, I have found a solution to a "loose" frontend. I found that the bolts securing the front suspension subframe to the car become loose - not loose-loose, but needed tightening due to the rubber washer being compressed over time. The first time I tightened the bolts, some took as many as two full turns to tighten down. This applies to both the front end as well as the rear end suspension subframes.

A WORD OF CAUTION: Do NOT overtighten. These bolts have a shoulder on them, and if you run the bolt totally down (really compressing the rubber grommet), you will run out of threads on the bolt and can ring off the bolt. This was done on my car with an impact gun that was set too high. The problem: the bolt has a nut as part of the frame of the car. All of that has to be drilled out and a complete (high-strength) nut and bolt replace the old assembly.

BTW, the tightening of these suspension subframes really make a BIG difference in the way the car feels and handles. I also reduced front end noise by tightening the subframe.

The suspension subframes are a separate structure (both front and rear) that bolts to the underside of the car. In the front, the steering sector and anti-roll bar sit in this subframe. On the front, as an example, there are two large bolts just behind the lower "A" arms and two just in front that afix the subframe to the body of the car.

If you have the car on the rack in the air, they are fairly easy to see. You'll need a long breaker bar to get good leverage to turn the bolts - or an air impact tool. Again, be careful just how tight you try to get them. You DON'T want to ring the bolt off! A solution is to remove the bolts and add some washers to back the bolt up from the shoulder and to insure you have threads to work with.

.

DarknessofDeath · #3 08-08-2006, 08:00 AM

does anybody have a picture of where these bolts are? reading it is one thing but a picture always help out more

mbtoloczko · #4 08-08-2006, 09:18 AM

Here are some pictures of the rear subframe mounts:

http://www.subaru-svx.net/photos/use...toloczko|30914

I don't have any pics of the front subframe mount bolts, but they are pretty easy to spot. Look for the front subframe and look where it attaches to the underside of the car.

DarknessofDeath · #5 08-08-2006, 09:58 AM

that's very helpful. i'm sure i can get a good guess on where the front ones are.

Beav · #6 08-08-2006, 04:05 PM

John,

The center tubes of the bushings are serrated on their ends and 'dig' into both the bolt and frame when tightened. Add in the fact that the bushings allow flex to occur, the center tubes don't move - at all. If they did they would quickly chew through the sheet metal 'frame' and you would have a big problem. Like, "Why are my front tires rubbing against my back tires?"

So... no, the tubes don't move and allow alignment change but yes, the bushings do. This is all normal and tolerable and won't adversely affect your tire wear.

svx_commuter · #7 08-09-2006, 10:01 AM

Quote:

Originally Posted by svxcess

Here is a quote from Harry Newman "newsvx" on the moving subframe issue:
...........These bolts have a shoulder on them,.............
.

The bolts on my SVX are not shoulder bolts. The bolts on my SVX do bottom out when the center tube in the bushing is completely compressed between the frame(or call it the body) and the bolt head.

The rubber washers that sit between the top of the sub-frame and the body are not compressed by the bolts. IF this happens I think the bushings have moved in the sub-frame. I have compared the thickness of new rubber washers to the ones in my SVX and they are the same thickness. These rubber washers keep the sub-frame from boucing up and hitting the frame (body). Heck if the rubber washer is removed, and the sub-frame tightened, there is clearance between the top of the subframe and the frame (body) on my SVX. IS this normal?

So Beav, the ends of the tubes for the center bushings in the sub-frame are not serrated on my SVX as far as I can tell, the surfaces look pretty smooth. So IF the subframe can move 1/16" will it mess up the alignment? The only part not connected to the sub-frame is the the top of the strut that goes to the body. Everything else, lower control arm, stabilizer bar, rack N pinion are all connected to the sub-frame.