Author Topic: How easily should my wheels turn? (Read 2693 times)

DesertEagle · « **on:** February 19, 2010, 06:22:22 PM »

I have a 1991 318is. It has a 4.10 LSD. I have it up on jack stands, so the wheels are off the ground. With the parking brake off, when I rotate either rear wheel I hear a noise that sounds like something rubbing/grinding on heavy, solid metal. I can rotate either wheel about half a turn with this noise until it becomes much more difficult to rotate the wheel further. When I removed one of the rear brake calipers, it was definitely contacting the rotor.

When I turned the rear wheel to test for an open or limited-slip differential, I expected the only resistance to be the weight of the parts in motion. However, in the bentley e30 manual on pg 1-13, it says "Operating the car in gear while the rear wheels are suspended will cause damage to the axle shafts." Also, on page 150 of "101 Projects for your 3 Series" it says to push back on the brake pads until the brake disc turns freely. In light of these statements, I don't know whether what I've observed is normal or if it indicates a problem. HELP!

Ryann · « **Reply #1 on:** February 20, 2010, 11:12:18 PM »

Although I've never checked for an LSD by turning a wheel, I do know that it's pointless to spin a wheel for the purposes of checking for wheel bearing noise/function without removing the brake calipers.
The reason it's not recommended to engage the drive wheels while the car is suspended is because of the severe angles of the driveshafts and cv's while the suspension hangs. Maybe what you're experiencing is a combo of pad/rotor contact and cv joints binding.. You could use some jack stands or jacks to support the rear suspension to prevent this.

DesertEagle · « **Reply #2 on:** February 22, 2010, 07:59:25 PM »

Ryann, thanks for your insight.

I have the car up on four jack stands. The back two are on the beam that goes the width of the car in front of the differential. Can I move those two to the rear axle or do I need two more jack stands?

Also Does the state of the ignition affect the caliper piston? IOW, when the ignition is in Off, On, Start, or Run is there a difference in the position of the caliper piston? I don't know if the engine vacuum would affect the hydraulics, especially if there is a problem with the brakes.

Ryann · « **Reply #3 on:** February 23, 2010, 01:03:45 AM »

I'd try moving your rearward jack stands to beneath the trailing arms as close to the rear hubs as you can get them (careful!) so that your shocks and springs are forced to bear the weight of the back half of the car. that ought to solve the cv/axle angle issue.

As for your other question, I'd say your brake system hydraulics should only be affected by pressure on the brake pedal. I see what you're getting at, but a vacuum booster should really only exaggerate the pressure you apply with your foot using engine vacuum, which is only present while the engine's running and only active while you're foot's on the pedal. eh? Best case senario would be to unbolt and hang the calipers out of the way.

DesktopDave · « **Reply #4 on:** February 23, 2010, 11:04:50 AM »

For test like this I typically load the axle by putting jacks under the suspension arm or shock mount. If I'm doing brake work I put them on the sub-frame beam like you did. I've also heard that the extreme angles of the half-shafts are why it's not recommended, but I've frequently ignored that advice as there isn't any weight on the drive line. As long as you're not spinning the wheels at 4k RPM it'll be OK...that's what the warning is about...giving a running car some throttle on a lift will break lots of stuff in very short order if you're not careful!

The rules I follow are never spin an unloaded suspension over idle speed and never spin a bearing that's not properly torqued down.

The brakes are supposed to drag on the rotors. It's inefficient, but the master cyl should retract the caliper pistons slightly & the rotor will kick the pads back. Make sure your caliper guides & slides are well lubricated with high-temp grease.

The parking brake assembly shouldn't drag at all, test & adjust it so that's not happening. I've noted that my LSD is harder to turn than my old open diff was when it engages. You should see the wheels turning in opposite directions as well. You're turning both shafts (and the drive shaft) at that point, so the effort should nearly double. Like Ryann said, pull the calipers & suspend them out of the way to verify.

Murdul · « **Reply #5 on:** February 23, 2010, 12:12:02 PM »

Is your car in Neutral? Probably is, but if it was in gear it would be pretty hard to turn those wheels.