Jacking up car from subframe arms

[sujitroy]

Before Covid we has a tune and tech session where we take our car to a garage, lift it up on a 4-poster lift and take a look underneath. The mechanic placed proceeded to place a jacking point on each subframe arm. I told his this is not good and asked him to place an arm under the mounts bolt which he refused. I didn't let him jack my car up. I don't lift the car up from the bottom of the diff or the nose. is putting a jack on the arms occasionally OK? If the mounts are new, I don't see much of an issue, but as they age, lifting the car on two points can be an issue. When the car is on the ground the weigh is distributed on 4 points, but on a jack only 2.
Sujit

[Lingen]

Sujit. I think you were right to stop him. If you raise the car by the arms, the weight will be taken partly by the front of the diff, which is unwise, and partly by the bonding between the rubber and the metal tube in the centre of the outer mounting bush.. Not a good idea. I prefer to raise the rear of the car by placing the jack under the rear of the differential casing so that the body weight is carried by the rear mounting plate and the reinforced part of the body above it. Two strong areas. In addition, as this is nearer the rear of the car, there will be less weight to lift.
Mike.

[sujitroy]

Hello Mike,
I stopped jacking up the car from the bottom of the diff years back. As it seems raising the car from the bottom of the diff was a non-no too. Again the chances of breaking the flange attaching the diff to the front support. Is that not the case?
Regards, Sujit

[stag8manod]

Yes you probably right on an unstrengthen diff nose but I don't see a problem with one that has had webs welded in.
Cheers Ian A

[NeilR]

I do jack mine up under the suspension arms, where the spring seat is.
After all, that is where the weight of the corner is carried anyway, so what's the problem with that ???.

Neil.

edit: obviously, I meant the trailing arms.

[dasadrew]

I must admit to being more or less totally lost on this recurring subject of jacking points. OK, so the official jacking points are the sills where those little internal brackets sit. Now I don't know about others, but about the first thing I learned 40 years ago when jacking up old cars was never to put the jack under the sill! Even if it was designed that way for the Stag, I can't bring myself to do it.

When I jack up the car, it's nearly always on the scissor lift, so I need to have points LH & RH simultaneously. If I'm planning some longer work underneath, I've made up a cross beam with long padded blocks which sit on the weld flange between the rear floorpan and the heel board.

If I'm lifting the car just to quickly check some rattle or leak, I put pads with a cutout hole for the nut under the outer subframe arm polybush mounts (2 in pic). Now it seems that this is a no-go. Recently at a Stag meet in Germany one of the guys brought in a subframe arm which had broken in two at position 4 in pic. The general opinion is that the car had probably been jacked up under the outer mounting (2) so often that a fatigue crack had occurred.

To be honest, I seem to be missing something since I can't see why jacking there would put such a bending load on the outer flange. The diff is pretty well fixed by the rear mounts (1 in pic) and, when I jack up the car I can't see the diff nose (3 in pic) hanging down 6" and putting such a bending moment on the subframe arm.

Can someone gently point out where my logic has gone wrong?

Stag Rear Lifting Points.jpg

[richardthestag]

I have been jacking my own stag from the tail end of the diff just forward of the diff back plate for decades with no issue. I support the stands under the ends of the bolts that go through the subframe mounts.

If I am doing a diff nose bearing replacement.... again .... I put the stands under the edge of the sill near the jacking point. makes me very nervous though. Maybe the trailing edge of the floor under the heelboard would be a better place?!?

[mole42]

I use the rear sill jacking points quite often. That's what they are for. When I'm working under the rear of the car, I place the top of the axle stand tubes under the jacking point, using the locating pin to make sure they can't slip.
Since the rear of the sill is the point where the rear suspension loads are carried into the chassis (bearing in mind that the Stag isn't a monocoque, but has a chassis integral to the body), if it isn't strong enough to jack the car, then it isn't safe enough....

Richard

[JeffW]

I followed richardthestag's advice about putting the stands under the sub frame mounts, but then screwed myself as I had to remove them too, leaving me with no where to jack up the car post-diff removal. I ended up buying a 7' length of scaffolding board to sit across the stands under the rear floor. Makes me nervous though...

When my Mk II was at Faversham and I was 'helping' out (grunt cleaning work to lower my bill) Trev asked me to put a car on wheel dollies so he could move it. As I did not want to face his angry glare (anyone who knows Trev knows he considers every Stag in the world to be one of his and to treat them accordingly...) I asked where to jack it up. He said under the diff was the only place and to never use the jacking points under the sill. I did what I was told.

However, if removing the diff like I have done, I am really not sure if my scaffolding board is really all that safe.

Jeff

[Goldstar]

To break a subframe arm through jacking sounds completely improbable so as to be unbelievable. As richardthestag does, mine is always jacked up by the diff casing and if putting onto axle stands I support with boards under the rearmost floor pan.

As Lingen points out doing it this way puts a vertical load through a part of the car that always has a vertical load on it (albeit in the opposite sense) and so must logically be safe to do so. In a pinch I would use the subframe arms - as a one off sign NO alternative, I doubt it’s a problem unless your diff nose extension is already weak but I would always prefer not to do that.

Sujit where did you get the idea that it’s unwise to jack on the diff. case, sounds like an armchair expert making stuff up to me?

[stagwingnut]

I always jack up at rear of diff , placing axle stands with wood on top, underneath the rear of floor pans and heelboard welded joints

[dasadrew]

I made up two of these beasties which sit on that weld flange at the bottom of the heel board. These then sit in a "U" channel which traverses the width of the car.

DSC01717.JPG

[staggering]

ooh ****e - for 25 yrs I have been raising and putting mine on axle stands from the suspension arms (admittedly I think the PO had replaced them as they are still shiny black...). The only time I had to do some major beam supports / axle stand arrangement was when the whole lot came off to replace my diff nose extension because it collapsed at speed (very lucky not to have caused more damage). At the time I posted the incident, yes youve guessed it, I was outcast because people thought I had been jacking off the diff (ooer missus) and that had weakened the diff nose...... For this reason I never advise people on such structural matters. I am just about replace the rear springs - so now I dont know what to do - perhaps I'll get the good lady wife to hold the car up off the rear bumper while I replace them

Cheers
Ian

[wilf]

I have a strengthened diff extension, so will continue to jack from under the diff as usual.

[DJT]

For maintenance on the rear brakes/drive shafts/exhaust, etc. I have been lifting the car as described in para 3 of Drew's post above. My aluminium quick-lift jack has a rubber pad with a hole that the outer subframe bush bolt fits in just right. Once at the desired height, I put the axle stand under the trailing arm at the base of the rear spring. Been doing that for the past 30 years.

I also don't see a problem putting the pad of the jack under the rear flange of the diff, although it is not something I find a need to do very often. The lifting force runs straight up the rear mounting into the chassis crossmember as shown in Drew's picture.