Jacking up rear

[Jack J.]

Maybe a dumb question, but is it OK to raise the rear end by placing a jack under the differential? Would like to raise both tires off the ground simultaneously, without using separate jacks on both sides as I have been doing. Thanks Jack J.

[Ed S.]

Re: Jacking up rear

You should not have the car resting on a jack alone - use the jack to raise and lower the car - once raised you still should place jack stands under the frame in the specified locations and then slowly lower the car down on to the stands. You say ...... "without using separate jacks on both sides as I have been doing". You don't have to use "separate" jacks or two jacks (one per side), you can raise one side, position a jack stand, then do the same on the other side. If you were to raise the rear by placing a jack under the diff then remove the tires - without having the car rest on jack stands you are doing a very risky balancing act - you may not like the outcome.

[William F.]

Re: Jacking up rear

Chassis service manual does not show the differential as a place to use jack.

[Joseph S.]

Re: Jacking up rear

Doesn't the rear spring bolt to the center of the differential?

[Don H.]

Re: Jacking up rear

Joe, Is this a trick question? Since I know you know. The rear spring bolts to the differential rear cover (I think). The camber strut rods bracket bolts up to the center of the differential. Before I got my lift, I used to like to lift the back of my car with floor jack, and a piece of 2x4 under that bracket. You just have to be super careful not to tear up your spare tire tub edge with the jack..

[Frank D.]

Re: Jacking up rear

You can jack the car up at the center spring perch all day long (and twice on Sundays), just be SURE to chock the front tires, remember that once the rear wheels are airborne the parking brake is bypassed and yes, jack stands are required. Just also be SURE you don't get the jack saddle on the front lip of the spare tire tub carrier - the number one cause of damage to the carrier tubs. I have a piece or ripped 2x4 I put on the jack saddle that just fits between the spring perch bolts. Also NEVER run the car in gear with the wheels airborne as shown, it stresses the U-joints on the half shafts big time.

[Joseph S.]

Re: Jacking up rear

Don, YES! A trick question if you like. My point being, if GM chose the rear end housing to support the car's rear weight, why would you doubt jacking the car at that point?

[William F.]

Re: Jacking up rear

Because the General says not to. Do it if you want to but I don't take a chance doing it.

[Jack J.]

Re: Jacking up rear

You can jack the car up at the center spring perch all day long (and twice on Sundays), just be SURE to chock the front tires, remember that once the rear wheels are airborne the parking brake is bypassed and yes, jack stands are required. Just also be SURE you don't get the jack saddle on the front lip of the spare tire tub carrier - the number one cause of damage to the carrier tubs. I have a piece or ripped 2x4 I put on the jack saddle that just fits between the spring perch bolts. Also NEVER run the car in gear with the wheels airborne as shown, it stresses the U-joints on the half shafts big time.

Frank, that was the point of my question. My engine builder wants me to raise tires off ground, start engine, shift into 4th gear and run engine for 10-15 minutes to bring the engine temp up to a normal driving temperature in order to wear/seat rings under load. Also checking for leaks, unusual noises,vibration and brakes. After that, then drive the car close by. All this is done AFTER I replace the engine brake-in oil using a pressurized container. Make sense?? Jack J.

[Patrick H.]

Re: Jacking up rear

Frank, that was the point of my question. My engine builder wants me to raise tires off ground, start engine, shift into 4th gear and run engine for 10-15 minutes to bring the engine temp up to a normal driving temperature in order to wear/seat rings under load. Also checking for leaks, unusual noises,vibration and brakes. After that, then drive the car close by. All this is done AFTER I replace the engine brake-in oil using a pressurized container. Make sense?? Jack J.

No, it does not make sense.

As already noted it puts a lot of stress on the u-joints and half shafts.
OK on a solid axle car, not on one with independent suspension.

[Frank D.]

Re: Jacking up rear

Only run the car in gear with the wheels suspended if they are NOT at full drop. This was a bad idea when the cars were new and particularly bad now when many repro shocks allow the wheels to hang farther down than factory shocks.

You can run the car with the wheels suspended but its best if you put some blocks under the trailing arms where they enter the frame cavity near the front bushing to get the wheels up to an acceptable height.

I'd be somewhat concerned your engine builder doesn't understand this aspect of the C2 3-link rear suspension.<br />
<br />
If you want to see the issue, with the car jacked with the real wheels off the ground, carefully turn one of the wheels by hand (parking brake off) and you will see and feel the U-joints clacking in an unnatural fashion.<br />
<br />
I don't even let the U-joints get stressed when installing parts (call me paranoid)

[Jack J.]

Re: Jacking up rear

No, it does not make sense.

As already noted it puts a lot of stress on the u-joints and half shafts.
OK on a solid axle car, not on one with independent suspension.

Just read the replys and I went out and lowered the car back down onto the tires. Plan B?? Jack J.

[Frank D.]

[Mark E.]

Re: Jacking up rear

Frank, that was the point of my question. My engine builder wants me to raise tires off ground, start engine, shift into 4th gear and run engine for 10-15 minutes to bring the engine temp up to a normal driving temperature in order to wear/seat rings under load. Also checking for leaks, unusual noises,vibration and brakes. After that, then drive the car close by. All this is done AFTER I replace the engine brake-in oil using a pressurized container. Make sense?? Jack J.

Hopefully the engine experts on the forum will chime in, but this is an odd method. First 20 minutes or so is usually no load above 2500 rpm to break in the cam. During this time, diligently check for leaks, noises, oil pressure, coolant temperature.

Then for the next few hundred miles, drive gingerly at different loads while avoiding constant rpm to break in the rings. This process may vary based on the type of rings used.

No need to jack up the rear of the car for this. And do not run the drivetrain when distended.

[Frank D.]

Re: Jacking up rear

The whole thread has changed from the safeness of jacking the rear of the car from a single point to proper rebuilt engine break-in procedures. I think the OP needs to revisit his mechanic's process. I'm just sayin'