> Because it is not uncommon (especially on the PI models) for the
> front right bracket to shear under the torque effect on the
> differential.
>
OH, you noticed that??????? This is a design flaw that is the result
of the stresses of DRIVING... not jacking!!!!!! (Or does jacking a car
somehow put stresses on only the right bracket, as you suggest?)
Like I said before... if those mounting studs break while jacking...
it's a good thing... because you will learn of a metal fatigue fracture
and/or rust damage while you're jacking the car... rather than while
you're on the road... cuz if jacking car is the straw that broke the
camels back... it was going to break anyways....
> > Think about the sort of strains those bushings encounter when you throw
> > down that gas pedal! And with your outer axles thumping up and down and
> > your drive down a rough road... No, it's not a live axle... but if the
> > differential weren't encountering strains... they would have mounted
> > them in garden-hose washers....
> >
>
> They dont mount them with garden-hose washers and they still shear,
> it is the torque effect that causes problems.
So what does the "torque effect" have to do with JACKING??????? Those
bushings are big and sold because of that torque effect... and they were
certainly "designed" to handle pressures greater than jacking up your
car!!!
>
> > When you're jacking a car... it's a gentle slow process... Those
> > bushings can handle it... the load is spread amongst 8 thick solid
> > bushings!!!! the structure can handle it... it's the same piece of
> > steel that handles your springs and suspension!!! And once the car is
> > in the air, it's put on jack stands... so it's not even being kept on
> > that weight for very long.
>
> It does'nt matter how long it is jacked for, it still weighs the same.
>
Let's talk about weight... From my quick calculations... I cum up with
about 60 lbs per square inch on the 4 bushings that would support the
car while jacked by the differential.... (conserative numbers: 1/2
weight of car/area of bushings in contact with support frame) (And I'm
sure more than 1/2 the weight of the car is on the front!)
You think that is excessive?????
> >
> > Honestly, I would just let this ride... but when I think of some
> > percentage of the newsgroup falling for some misplaced theory about the
> > dangers of jacking a car by the differential... I feel a need to say
> > something...
> >
>
> It may be misplaced, but the chassis rails are stronger, and that's
> why I recommended that method.
>
Why leave people believing that jacking up the differential is going to
cause damage to their cars? It's an acceptable way of lifting a car.
A good chunk of inexperienced users are going to walk away, teaching
their sons... of the evils of jacking up the car by the differential...
hog-wash!
Go ahead and suggest that there are other ways... but don't do it in a
way that leads to disinformation that will only confuse those who are
learning automotive mechanics for the first time here.
> > If you have two jacks... and no floor jack... by all means... jack up
> > the outside rails... as you suggested... but if you have a floor jack...
> > (every shop should have one)... and you'd rather spend time working on
> > your car, than jacking it... just jack the diff and lower the car down
> > on a pair of jackstands... and be done with it.
> >
> > --Justin
> >
> > Steve Chandler wrote:
> > >
> > > I have to disagree with your theory here. When you lift a TR6 on the
> > > differential you are compressing the bushings which were not designed
> > > to carry this sort of weight. I dont know if the mounting are strong
> > > enough or not, but the bushings will certainly be abused by this.
> > >
> > > Also I do not know how you can say this is less stress than driving
> > > the car. This is not a live axle, there is very little stress on the
> > > diff itself when driving.
> > >
> > > I would still recommend jacking up on the chassis rails with a piece
> > > of wood between the jack and the frame, and if you have 2 jacks do
> > > both sides at the same time, to minimize frame twisting.
> > >
> > > Not a flame, just my $0.02.
> > >
> > > cheers
> > >
> > > steve
> > >
> > > Justin Wagner wrote:
> > > >
> > > > jonmac wrote:
> > > > >
> > > > > John
> > > > > Many people use the diff for lifting as it is central. That does not
>mean
> > > > > it is a wise thing to do. There's a risk you might pop the diff
>mounting
> > > > > bolts through the top of the chassis....(snip)...
> > > >
> > > > I would differ with you on this...
> > > >
> > > > When you jack up the differential... you are NOT jacking up the mounting
> > > > studs... you are jacking up the BUSHED differential... which spreads the
> > > > weight across the structure very nicely... with little stress on the
> > > > studs themselves... In edition, there is not much SHEER strain on them
> > > > when lifting.
> > > >
> > > > The stresses encountered by the differential and it's mountings, while
> > > > jacking, are far less than anything they encounter on any given drive
> > > > around town, with speed bumps and potholes... If jacking your car by the
> > > > differential causes a mounting stud to "pop" through the chassis...I
> > > > would say, "BETTER TO FIND OUT NOW, THAN WHILE DRIVING AT SPEED, ANd
> > > > HITTING A BUMP"...
> > > >
> > > > Jacking "side to side"... takes time... and I would argue, the more
> > > > messing around one does while jacking a car exposes you to more
> > > > danger... and it is human nature that people will tend to try to speed
> > > > things up, by going up in higher intervals... leaving one side of the
> > > > car jacked up inches higher than the other...
> > > > Which again... exposes you to yet even more danger... AND... for those
> > > > concerned with damaging there car... this does put a lot of strain on
> > > > the car when flexed like that.
> > > >
> > > > I've jacked up TR 4A's, in the rear, with floor jacks under the
> > > > differential since 1977. I never experienced a broken stud... (on my
> > > > IRS) about 8 years... nor do I have any problems with my solid axle
> > > > 4A... (When IRS studs snap... it's because they're rusty and/or already
> > > > have a stress fracture, etc.) And my brother and I, the mechanics in
> > > > the family, have jacked up the family cars over the years... 280zx,
> > > > Jensen Heally, Jaguar XJ 6, Corvette Stingray, Mustang Mach I, 280 zx
> > > > Turbo, TR 7, Camaro, Ford LTD. Station WAgon with 429, and more... all
> > > > by the rear differential.
> > > >
> > > > Jacking by the differential is safe. Safe for the car, safe for the guy
> > > > under the car. My humble opinion... others are welcome to comment.
> > > >
> > > > --Justin
> > >
> > > --
> > > Steve Chandler - Chandler-O'Bagy Associates stevec@rtd.com
>
> --
> Steve Chandler - Chandler-O'Bagy Associates stevec@rtd.com
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