Engaging in drive with driven wheels jacked up - Bad for CV?

**Z2TT** · 01-05-2010, 12:04 AM

Hello.

When having the car with the drive wheels jacked up and putting it into gear to drive the wheels to troubleshoot problems/noises whatever :

Is this bad for the Joints on the shafts on RWD cars and same goes for FWD cars, will this be damaging to the CV Joints?

I have vague memory of being told this should not be done, or maybe reading it in a manual somewhere.

Thanks.

**Billzilla** · 01-05-2010, 12:23 AM

Probably not, as there's no load on them. But yes the balls in the CV's are moving into places they normally wouldn't - except on a FWD/4WD as they get a workout from the steering anyway.

**TRD-12A** · 02-05-2010, 08:19 AM

I've seen a commodore jacked up (IRS) guys put it in drive and drove it and both sides the shafts pulled out of the knuckles he actually did a fair bit of damage to stuff around them so it's not a good idea FWD should'nt be too bad but still there is no load so the noise your chasing may not be there unless it's really bad.

**winnie_man** · 02-05-2010, 09:04 AM

What about axle dynometers? They take the wheels off and attatch a generator the the axle to measure the power output. They use these when troubleshooting and developing race engines. The only problem i can see is the shocks are fully extended meaning the maximum angle is placed on the drive shafts, not good. You would also have to brace the car solidly to stop it from doing all sorts of unforseen stuff like twisting, shaking, jumping and anyonther random movements which are normaly contained in the wheels.
I wouldn't personaly do it but If i did it would be done on a 4 post hoist and using spring compressors on the driven wheels

**Omegaman** · 03-05-2010, 05:25 PM

If i were to jack the car, i would place stands under the conrol arm, or somewhere where the load of the car actually compresses the suspension. This way your CV's are close to parallel to the road. This goes for RWD also, i place stands to keep the diff compressed,as not to let the tail shaft hang.

**Talasas** · 03-05-2010, 09:59 PM

The main reason you'll hear this is because of the lashing that CVs can do when they are exposed to high angles. This is usually only the case if they aren't attached to anything so I don't see why it would be a problem. I remember getting drilled by a guy at a CV joint place when I told him I ran the car in gear whilst on jack stands. "You'll expose then to really high angles" he barked. I don't see how the sagging wheels can give a CV more angle than steering can.

**SilverRA23** · 04-05-2010, 11:26 AM

Originally Posted by winnie_man

What about axle dynometers? They take the wheels off and attatch a generator the the axle to measure the power output. They use these when troubleshooting and developing race engines. The only problem i can see is the shocks are fully extended meaning the maximum angle is placed on the drive shafts, not good. You would also have to brace the car solidly to stop it from doing all sorts of unforseen stuff like twisting, shaking, jumping and anyonther random movements which are normaly contained in the wheels.
I wouldn't personaly do it but If i did it would be done on a 4 post hoist and using spring compressors on the driven wheels

Cars on a dyno as you describe are generally run at ride height.

**lexsmaz** · 04-05-2010, 06:40 PM

The main concern i believe is that the CV's actually bottom out in their housing, because as the lower arms drop down when the vehicle is jacked up the distance between the inner & outer CV actually reduces causing the cage & balls etc to bottom out & due the angle the shaft is now on the balls & cage go through hell ...