951 Scotty

FYI: I have an 86 951 with 50,000 miles on the clock.
I posted awhile back concerning the klunking noise coming from the left rear wheel area and received lots of great advice about CV vs wheel bearings. I couldn't diagnose the problem properly so I took the old shot gun approach. I have now had the wheel bearing pressed in by the dealer and I replaced the axle/cv joints while I was in there.

Now I'm trying to figure out how to torque the axle/hub retaining nut. My manual says 300+ ft/lbs of torque !!!!! for my aluminum swing axle, but my wrench only goes to 150 lbs. I already tried about 75 lbs and the wheel would barely roll when I took it out for a test drive, under power. I tried 35 ft lbs and man all I hearing is a horrible grinding sound. Could the wheel hub be deflecting into the surrounding metal due to low torque. Could I have destroyed my new bearing by driving it about 500 ft??

I am really bummed out since I want to go to the SCCA regionals at Wendover Utah today.

Any help would be appreciated.

Ahmet

You're talking about the self locking nut that goes on the axle shaft in the back (center of the hub) right?

If so, tightenning torque is indeed 500 Nm. You can perhaps try a breaker bar, instead of your torque wrench, and try to get it as tight as humanly possible (with a pipe, over the breaker bar perhaps).

I'm not sure if you've damanged your bearings, are you sure the noise is coming from this area?
Ahmet

951 Scotty

Yes, Ahmet,thanks for your quick reply!
I am refering to the self locking nut!
Question to you or any physics majors listening.
If I extend my breaker bar by one foot, to two feet long, then I would only need to apply a force of 250 Nm (180 ft-lbs) to the end of said bar to acheive approx. 500 Nm???

Ahmet

Yes

MadMax

Scotty,
Torque = F(force) x d(distance)
150 fl-lbs divided by the length of your torque wrench is the amount of force you will have to put on a shaft twice the length to equal 300ft-lbs.

Example: 150ftlbs/2ft(pivot arm length)= 75lbs.

75lbs x 4ft(pivot arm)= 300ft-lbs

However you will still not be able to use your torque wrench for the measurement. All you can use it for is to gage how much effort has to be applied to the cheater bar with a 4ft pivot arm to achieve 150ft-lbs, since that is the maximum break of your torque wrench. I hope I have made sense to you. Even with a 4ft cheater bar you will still only be able to measure torque up to the maximum of your torque wrench. It can help you estimate but that is it.

I would just go rent a 400-450ft-lb torque wrench. You should always use a torque wrench with at least 25% greater maximum torque measurement than the torque you are trying to achieve. They are not that accurate near the max and min of the scale.

Good luck, I hope this has helped some.

Regards,

IceShark

Max, you are missing the idea they have in mind. I've done it myself. It is commonly known as a crowsfoot extension and is an extension off the driver, not an extension of the wrench handle as I suspect you are thinking. Maybe Scotty is thinking this too, now that I reread his post.

The right way to do this is to either buy a crowsfoot or make one up yourself. You set up a lever with the nut socket on one end and a fitting on the other to accept the torque wrench driver. Snap the torque wrench on the end and they apply force to the specified value taking into condiseration the leverage effects and angle of the torque wrench's force application.

Easiest way is to do a straight line extension if you have the clearance. Here is a link for a homemade job and the calculations required. You don't have to worry about angles which would reduce the leverage effect since the wrench and extension are in a straight line. Pay attention to measure the existing torque wrench length to the center of where you place your hand when applying force.
http://website.lineone.net/~mike_how...ue/torque.html

Works fairly well, I've actually seen it done in Nuc power plants, if you can believe that. Much better than a SWAG.

[ 06-30-2001: Message edited by: IceShark ]

[ 06-30-2001: Message edited by: IceShark ]

951 Scotty

Thanks Ice Shark for that link. Got it saved and will review calculations later.
Went to Sears and bought a 3/4" drive bar and 1&1/4 socket. Using a pipe extension and all 200 lbs of my weight at about 20-24" lever arm I think Im close enough to 300lbs on the nut and will go ahead and risk taking another test drive.

****** I found the cause of the grinding****
When I pulled the aluminum swing arm to try and drive out the bearing I managed to bend the caliper mounting flange while it was clamped in my vise by about 1/16th". The grinding was the inside edge of the caliper trying to destroy the rotor. Yes it did some damage, about 1/2" wide nasty ring that I will need to take care of. I was able to move the caliper inboard about one washer width and it now clears the disk. I need to take the car out for a test drive realizing I am trashing the inside brake pad. Fortunately I have some Pagid Orange Pads waiting to be mounted.

Do you think I need to replace the swing arm?

Thanks for your help.

Julian Allen

If the trailing arm mounting ear for the caliper is bent, I would suggest replacing the trailing arm. You really can't bend the ear back without risking fracture, and your caliper isn't really in the right plane unless the ears are in the right place. Sheet metal places, yes, they can be bent back. 3/8" mounting ears on the trailing arms should't be bent back, not when they are essential to the brakes. IMHO.