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E30 (1982 - 1993)
God's Chariot. The E30 was produced primarily from 1982 through 1991. The cabriolet was the one exception which was produced through 1993.

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  #1  
Old 10-11-2007, 05:55 PM
NetTechie NetTechie is offline
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Is it bad to spin wheels in gear up on blocks?

Is it ok to spin the rear wheels by putting the car in gear and revving the engine while the car is up on blocks? Putting it in say 5th gear and revving to 3k rpm?

I just did this, and I broke something. But maybe it was about to break anyway? Or was my revving a bad idea?

Thanks.
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  #2  
Old 10-11-2007, 06:31 PM
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Well, um, i wouldnt really recommend it at that high of a speed, maybe 2nd gear at 2500 is ok or 5th at idle.

should i even ask what you broke
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  #3  
Old 10-11-2007, 06:50 PM
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My Questoin Is...why?
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  #4  
Old 10-11-2007, 07:10 PM
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Originally Posted by downhiller View Post
Well, um, i wouldnt really recommend it at that high of a speed, maybe 2nd gear at 2500 is ok or 5th at idle.
Why not 5th gear?

Last edited by NetTechie; 10-11-2007 at 07:12 PM.
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  #5  
Old 10-11-2007, 07:28 PM
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Quote:
Originally Posted by NetTechie View Post
Why not 5th gear?
Because if your blocks broke, you'd be SOL?
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  #6  
Old 10-11-2007, 07:33 PM
NetTechie NetTechie is offline
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Yeah, I was worried about that so I put it up on cinder blocks with wood. put cinder blocks in front of the front wheels. then I pushed on the car hard from both sides, from the front, and from the back (tried pushing in all directions). it wouldn't budge. I would rather not have a bmw shaped hole in the back of the garage.

after the test I examined the blocks, and the car had not moved at all.

sounds like whatever it is that broke it would have broken anyway, that this test did not cause it to fail prematurely.

Last edited by NetTechie; 10-11-2007 at 07:36 PM.
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  #7  
Old 10-11-2007, 08:08 PM
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did you have the rear axel on the blocks or did you have them more towards the body and frame?

if you had them on the axel, then it would simulate a flat road with the suspension compressed.

if you had it the blocks on the frame, then your suspenion would be unweighted, and a ton of stress would of be on your u-joints.

and from your other thread, "my assistant saw sparks, and told me to shut the engine off," the u-joints makes pretty sparks as they explode and send shrapnal everywhere. might take a look at them, and send pictures
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  #8  
Old 10-11-2007, 11:30 PM
NetTechie NetTechie is offline
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Originally Posted by downhiller View Post
if you had it the blocks on the frame, then your suspenion would be unweighted, and a ton of stress would of be on your u-joints.
oh-oh. I mighta fried the u-joints with this test.

I had the blocks on the frame, as that seemed more secure. Maybe I made the u-joints fail prematurely.

Last edited by NetTechie; 10-11-2007 at 11:33 PM.
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  #9  
Old 10-12-2007, 01:13 PM
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wait a minute... isn't the differential bolted to the frame? If the differential lowered with the rear wheels when they got suspended by jacking up the car it would make sense -- but the differential doesn't move. how would jacking up the car put the u-joints under stress?

Last edited by NetTechie; 10-12-2007 at 01:15 PM.
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  #10  
Old 10-12-2007, 02:34 PM
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With the car jacked up and the tires and suspension unsupported the shocks/struts allow the suspension to extend to their fullest limit. That limit is within normal operating parameters, and while not optimal it also should not cause damage. If that were the case we would see broken u-joints every time a car unloaded it's suspension over a large bump in the road. BMW's engineers would not design the suspension to self-destruct under these conditions.

It sounds like your center support bearing (or maybe the gubio ?) failed. If that component failed the other rotating parts of the drive-line would also warrant inspection, as they might not be far behind.
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  #11  
Old 10-12-2007, 03:25 PM
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Quote:
Originally Posted by wag-zhp View Post
With the car jacked up and the tires and suspension unsupported the shocks/struts allow the suspension to extend to their fullest limit. That limit is within normal operating parameters, and while not optimal it also should not cause damage. If that were the case we would see broken u-joints every time a car unloaded it's suspension over a large bump in the road. BMW's engineers would not design the suspension to self-destruct under these conditions.

It sounds like your center support bearing (or maybe the gubio ?) failed. If that component failed the other rotating parts of the drive-line would also warrant inspection, as they might not be far behind.

+1
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Old 10-12-2007, 03:36 PM
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Doesn't an open differential make one wheel turn in the opposite direction to the other, when not under load?
3000 rpm in 5th gear... that'd be around 90mph. I can't imagine how that wouldn't be bad on an unloaded axle.

No matter what, it was a stupid and dangerous thing to do.
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  #13  
Old 10-12-2007, 03:50 PM
NetTechie NetTechie is offline
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it has limited slip diff, both wheels go the same way.

as for your other comment, I've already addressed that above.
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  #14  
Old 10-12-2007, 04:04 PM
NetTechie NetTechie is offline
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Quote:
Originally Posted by wag-zhp View Post
With the car jacked up and the tires and suspension unsupported the shocks/struts allow the suspension to extend to their fullest limit. That limit is within normal operating parameters, and while not optimal it also should not cause damage. If that were the case we would see broken u-joints every time a car unloaded it's suspension over a large bump in the road. BMW's engineers would not design the suspension to self-destruct under these conditions.

It sounds like your center support bearing (or maybe the gubio ?) failed. If that component failed the other rotating parts of the drive-line would also warrant inspection, as they might not be far behind.
Thanks wag-zhp. This is what I needed to hear. *breathes sigh of relief*.

In that case I'm grateful it broke in the garage and not out on the highway. The test was a success. Now I have some work to do...
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  #15  
Old 10-12-2007, 04:11 PM
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Quote:
Originally Posted by JAKE325 View Post
My Questoin Is...why?
This thread explains why I ran the test:

http://www.bimmerfest.com/forums/sho...d.php?t=234640
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  #16  
Old 10-12-2007, 05:22 PM
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No problem. If you are going to be working under the car I would recommend you replace those cinderblocks with some jackstands. Cinderblocks are known to fail when used as car supports. I've seen it first hand, and fortunatly no one was under the car yet. After that experience I always make sure the stands are in good repair and in the proper location and usually leave the floor jack under the car too!!!
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  #17  
Old 10-13-2007, 08:13 AM
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Quote:
Originally Posted by wag-zhp View Post
No problem. If you are going to be working under the car I would recommend you replace those cinderblocks with some jackstands. Cinderblocks are known to fail when used as car supports. I've seen it first hand, and fortunatly no one was under the car yet. After that experience I always make sure the stands are in good repair and in the proper location and usually leave the floor jack under the car too!!!

+1million cinder blocks SUCK. I learned the hard way when I was younger(16) and luckily without bimmer. I had a jeep and was replacing the front spindel an leaf spring retainer I broke from 4-wheelin. I had it siting on cinder blocks. I was by myself(also bad move) and under the front when a cinder block broke completely...I almost died. The fender-well smacked me in the head and forced me into the ground face first. I saw my life flash before my eyes, but luckily since the jeep had a suspension lift and it flexed and the axle hit the ground and top of the frame with barely enough room for my head....never ever ever going to use cinder blocks again
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  #18  
Old 10-13-2007, 09:21 AM
NetTechie NetTechie is offline
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was the car sitting directly on the blocks? or did you have slats of wood in between the car and the block?
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  #19  
Old 10-13-2007, 10:30 AM
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They had wood on them but it didn't matter. the jeep was a beast and weighed a good bit especially in the front with a big V8 and PTO winch.
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  #20  
Old 10-13-2007, 10:31 AM
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Mine had wood between the floor and the block and between the block and the frame of the car. I thought the wood would have prevented a failure, but it didn't. (Of course the block was one that was left over from a foundation job several years prior to it being used to support the car. No telling what effect the weather exposure played into the failure, but I've never seen a jack stand crumble like that!)
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  #21  
Old 10-13-2007, 10:51 AM
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problem I've had with jack stands is the car can slip off of them very easily. I almost had the car fall on me with the jack stands not long ago. I was under and I noticed the car had shifted and was being held up by about 1/8" of metal on the stand. I got the hell out from under the car...

and they can tip over too.
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Old 10-13-2007, 01:30 PM
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I've since invested in a quality set of jack stands that are super heavy and have a wide footprint and large support bracket.
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  #23  
Old 10-13-2007, 08:48 PM
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A trick to help keep the jack stands in place is to put a newspaper or piece of cardboard between them, the floor, and the car. Either material will compress and provide a stable base that is also very slip resistant when under weight.
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  #24  
Old 10-13-2007, 10:58 PM
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I just tried that tonight. It does help. But I think I'm gonna have to get stands with bigger bases. Mine are the small ones, and they just seem like they are about to turn over looking at them holding up the car. I'm thinking to get ones at harbor freight and get the rubber fittings for the top of them.
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