Non-sliding left-right axle on one side causing damage? (911SC)

octanemaestro · 08:35 PM

If an inwardly bent trailing arm is pushing inwardly on an axle such there is there is no lateral slide movement room on the axle that would normally be had toward and away from the wheel by grasping the axle with your hand when the car is on a lift, and the lack of movability left to right is not caused by lack of lube, then what would the effect be on the the transmission of the axle pressure against the transmission as the suspension flexes while driving in such a scenario?

Plays with cars · Plays with cars's Garage

Not certain what is causing your axle not to move, but I'm pretty certain that if your trailing arm was bent that far that you would have some serious alignment/drivability issues. I did a quick check on my car and I have ~3/4" inboard/outboard movement of the axle.

Have you pulled your axles and checked your CV joints? Could be that you have a SERIOUSLY dry joint, or a worn cage that is binding it up. Think it would be worth checking before you have an inconvenient, or worse yet catastrophic, failure.

octanemaestro · 02-23-2017, 09:13 PM

Quote:

Originally Posted by Plays with cars

Not certain what is causing your axle not to move, but I'm pretty certain that if your trailing arm was bent that far that you would have some serious alignment/drivability issues. I did a quick check on my car and I have ~3/4" inboard/outboard movement of the axle.

Have you pulled your axles and checked your CV joints? Could be that you have a SERIOUSLY dry joint, or a worn cage that is binding it up. Think it would be worth checking before you have an inconvenient, or worse yet catastrophic, failure.

There is no question what is causing it not to move, and that's not what I was asking. It is not moving because some aspect of the suspension or unibody or banana arm mount is bent inward and therefore has decreased the available axle travel slide in/out capability that would otherwise allow it to move ~3/4" inboard/outboard just like your axle does. It is not dry nor does it have a worn cage. Yes, all CV joints have been checked.

The question is not why. Rather the question is what damage can be caused to the transmission by having an axle that can't move in and out?

DanielDudley · 02:57 AM

At some point in the arc of suspension travel you should have mobility. If your suspension is so far out that you are either pulling on the joint or pushing it together, that would be a no drive situation. Is there any way you could have reversed the cages or other parts during assembly ? I did that on a Subaru once, and it bound up. Taking it apart and correcting the orientation solved the problem. It always helps if you have a good one to compare the problem unit to.

If I had to guess, I would assume that your problem lies somewhere along those lines.

Flat6pac · 02-24-2017, 03:09 AM

If someone in the past took the balls out of the CV joint, put them back together, easily, than the CV is a problem and reason the full unit doesn't move in and out.
Just a thought,
Bruce

djpateman · 02-24-2017, 04:20 AM

Rear wheel position mystery on 911SC
WTB/Wanted: Left Trailing Arm 911SC IMMEDIATE NEED, please PM me
Axle slide side to side proper one side but other side tight due to bent Trailing Arm
Can an aluminum Trailing Arm get bent? Yes/No.
Can someone take exact same photo of undercarriage 911SC?
Aluminum Trailing Arm Casting Numbers, 74-77, 78-83, etc. Cross-fit of 911.331.513.OR

To summarize, you purchased this car recently, and the previous owner both knew about the problem, and tried to correct it. I presume you knew about it before purchasing. The car drives well, does not crab, and the primary evidence of the problem is the left wheel is inset much more thant the right side. The secondary evidence is that the left axle free play is absent. Other hints include the left lower shock mount, and the kink in the hard brake line. You also say that the left suspension droops more than the right when on a lift.

Despite the left arm is cleaner than the right I do not believe that it has been replaced; the lack of axle free play, the shock bolt and the brake line suggest that the left arm is bent.
The wheel bearing, the CV joints, the differential bearings and the pinion bearings are probably at risk of increased wear due to thrust forces that are not normal.

octanemaestro · 02-24-2017, 06:24 AM

Quote:

Originally Posted by djpateman

Rear wheel position mystery on 911SC
WTB/Wanted: Left Trailing Arm 911SC IMMEDIATE NEED, please PM me
Axle slide side to side proper one side but other side tight due to bent Trailing Arm
Can an aluminum Trailing Arm get bent? Yes/No.
Can someone take exact same photo of undercarriage 911SC?
Aluminum Trailing Arm Casting Numbers, 74-77, 78-83, etc. Cross-fit of 911.331.513.OR

To summarize, you purchased this car recently, and the previous owner both knew about the problem, and tried to correct it. I presume you knew about it before purchasing. The car drives well, does not crab, and the primary evidence of the problem is the left wheel is inset much more thant the right side. The secondary evidence is that the left axle free play is absent. Other hints include the left lower shock mount, and the kink in the hard brake line. You also say that the left suspension droops more than the right when on a lift.

Despite the left arm is cleaner than the right I do not believe that it has been replaced; the lack of axle free play, the shock bolt and the brake line suggest that the left arm is bent.
The wheel bearing, the CV joints, the differential bearings and the pinion bearings are probably at risk of increased wear due to thrust forces that are not normal.

This post is highly appreciated. It's erudite, well thought out, very sensible analysis and terrific detective work like Holmes piecing together clues and thoroughly answers all the OP's question some of which hadn't been tackled by anyone else thus far. For example, the real world question of hey folks it drives fine but what damage am I doing? I truly hope the scenario is just the trailing arm that's bent as the reply from DJPatemen suggests, and not the torsion tube. I'm troubled that the banana arm is such a different color than all the red clay residue on "everything else" but maybe it's because someone had the banana arm off the car thinking they'd get a replacement and significantly handled it with greasy hands and rags and couldn't find a replacement and then just reinstalled it.

dad911 · 02-24-2017, 06:50 AM

If it was my car I would start removing parts and carefully measuring. Could be bushings, CV, bent arm, moved pick up points....

SCadaddle · 08:12 AM

Hey, I got a novel idea:

Mark the axle shafts as "Left" and "Right" and the ends with "inner" and "outer" with a paint marker, piece of tape, whatever. Then remove both and swap sides. See if the limited movement in the axle goes with the axle assembly or stays with the chassis. If I remember correctly, on the SC at least and perhaps others, there is a foam sticky back gasket that gets applied to the CV joints (or the mating flanges....been a long time) where they mate up to the transmission flange and the wheel hub flange to help keep the grease from flying out. Can't be too much loss in motion due to one axle having them and the other not, but that's supposed to be there nonetheless.

Disclaimer: I didn't sleep at a Holiday Inn Express last night.

octanemaestro · 02-24-2017, 08:23 AM

Quote:

Originally Posted by SCadaddle

Hey, I got a novel idea:

Mark the axle shafts as "Left" and "Right" and the ends with "inner" and "outer" with a paint marker, piece of tape, whatever. Then remove both and swap sides. See if the limited movement in the axle goes with the axle assembly or stays with the chassis. If I remember correctly, on the SC at least and perhaps others, there is a foam sticky back gasket that gets applied to the CV joints (or the mating flanges....been a long time) where they mate up to the transmission flange and the wheel hub flange to help keep the grease from flying out. Can't be too much loss in motion due to one axle having them and the other not, but that's supposed to be there nonetheless.

Disclaimer: I didn't sleep at a Holiday Inn Express last night.

I don't think anyone has suggested thus far that the axles themselves might be the culprit. Did I miss that on someone's post?

octanemaestro · 02-24-2017, 08:40 AM

Quote:

Originally Posted by DanielDudley

At some point in the arc of suspension travel you should have mobility. If your suspension is so far out that you are either pulling on the joint or pushing it together, that would be a no drive situation. Is there any way you could have reversed the cages or other parts during assembly ? I did that on a Subaru once, and it bound up. Taking it apart and correcting the orientation solved the problem. It always helps if you have a good one to compare the problem unit to.

If I had to guess, I would assume that your problem lies somewhere along those lines.

What are "cages" in this context?

SCadaddle · 02-24-2017, 08:49 AM

Quote:

Originally Posted by octanemaestro

I don't think anyone has suggested thus far that the axles themselves might be the culprit. Did I miss that on someone's post?

Well, since posting that I've read through a couple of the other linked threads you've started. Might be a larger issue than the axles as I suggested, but it's a pretty easy thing to do to swap them and rule them out.

Others have given you tips on where to look for accident damage in the chassis. I know of one SC locally that was hit in the right rear corner to the point where the chassis under the oil filter area adjacent to the engine tin has a definite kink, the rear decklid fits poorly with regards to the gaps in the rear fenders and the rear overhang at the top corner of the fenders, the lower rear of the right hand door rattles against the rocker panel......yet the car is aligned perfectly and drives fine.

Wheel offset differences: Somebody already mentioned the obvious of swapping the wheels/tires left and right to eliminate that.

Plumb bobs and measuring from resulting marked reference points on a flat level surface would be reasonable. For that matter with the car on the ground and bounced a few times you could use a carpenters level and a few shims against the wheel/tire to roughly measure the camber of the rear suspension and compare side to side with the same air pressure in each tire.....

SCadaddle · 02-24-2017, 08:56 AM

Quote:

Originally Posted by octanemaestro

What are "cages" in this context?

The "cages" are what holds the balls in the CV joint. There are 4 components to the joint itself: The inner race, the balls, the cage and the outer race. Like someone has already mentioned, if it was disassembled, cleaned and put back together "easily" then it was put back together incorrectly. It takes some contortion of the inner race in the joint to put it back together correctly. You could use google to search for images of what it is supposed to look like i.e. the position of the inner race relative to the outer race and see how yours are oriented once you remove the axles and wipe away the grease on the surface.

SCadaddle · 02-24-2017, 09:49 AM

Cv joint cage orientation

KTL · 02-24-2017, 11:15 AM

The axle shaft itself effectively changes length as it travels upward and downward. The ball bearings ride along the race grooves to allow the axle to move in and out of each CV joint and thus changing its length.

With the trailing arm bent inward and the axle "frozen" in place, the axle has been pushed beyond its typical shortest length and probably wants to go even further beyond. Therefore the axle is pushed to its physical length limit and that means within the CV joint, parts are trying to go further than they allow themselves. Basically the inner part of the CV joints are trying to go beyond what the outer part of the joint will allow and something has to give and break. I also suspect the inner part of the CV joint could be contacting the cupped interior of the transmission output flange, which it's not supposed to do.

As far as the influence on the transmission, it would seem the axle is pushing the transmission to the side and that is putting a load on the rubber mounts. Internally, it would seem the axle is putting excessive lateral force on the output flange, which is directly bolted to the differential. So the differential has lateral force placed on it, which is pushing one support bearing slightly out of its race and the other further into its race. One bearing is being slightly unloaded and the other excessively loaded.

Plus, given that the problem axle is on the passenger side, the lateral force on the differential is trying to push the differential side cover away from the transmission. So the side cover is being flexed outward. When the side cover flexes outward, the differential ring gear would then be moving away from the pinion gear. None of this is good for the transmission.

djpateman · 02-24-2017, 03:45 PM

The drive shaft can be removed, but I suspect with a lot of difficulty. If it is bound up, or pinched in position, then there will be no free play to separate the CV from the flanges. I suspect that the whole arm assembly will need to be removed even to get the axle out of there. Once removed, the axle free play will be evident. However I think there will be damage done to the CV`s and the axle should be replaced. A replacement arm with sway bar connection should also be obtained.
It would be very useful to know what incident caused the damage; was a wheel replaced already? Normally the arm is designed to bend in an accident to prevent damage to the body whenever possible.
Dave

Walt Fricke · 02-25-2017, 12:24 PM

One of SCaddle's suggestions is not part of whatever is causing the issue here: the separate grease seal in the CVs. The presence or absence of this seal (I don't use them)has no effect on the overall length of the axle assembly. There is a machined cut-out recess for this seal in the output flange, but even with the seal in place there is metal to metal contact between the CV outer (the big part) and the rim of the flange. The seal itself is slightly compressed within this relief.

Some careful measurement and observation should show whether or not the torsion tube is bent or twisted. If it is, the relationship of the transmission mounts (which are welded to the torsion tube) would no longer be the same side to side or diagonal distances from other fixed measuring points on the chassis, or might be at different heights, or both. The centers of the two large transmission carrier bolts would be where you'd measure from. There are factory distance specs for measuring, but the key is variation from side to side.

octanemaestro · 02-25-2017, 02:21 PM

Quote:

Originally Posted by KTL

The axle shaft itself effectively changes length as it travels upward and downward. The ball bearings ride along the race grooves to allow the axle to move in and out of each CV joint and thus changing its length.

With the trailing arm bent inward and the axle "frozen" in place, the axle has been pushed beyond its typical shortest length and probably wants to go even further beyond. Therefore the axle is pushed to its physical length limit and that means within the CV joint, parts are trying to go further than they allow themselves. Basically the inner part of the CV joints are trying to go beyond what the outer part of the joint will allow and something has to give and break. I also suspect the inner part of the CV joint could be contacting the cupped interior of the transmission output flange, which it's not supposed to do.

As far as the influence on the transmission, it would seem the axle is pushing the transmission to the side and that is putting a load on the rubber mounts. Internally, it would seem the axle is putting excessive lateral force on the output flange, which is directly bolted to the differential. So the differential has lateral force placed on it, which is pushing one support bearing slightly out of its race and the other further into its race. One bearing is being slightly unloaded and the other excessively loaded.

Plus, given that the problem axle is on the passenger side, the lateral force on the differential is trying to push the differential side cover away from the transmission. So the side cover is being flexed outward. When the side cover flexes outward, the differential ring gear would then be moving away from the pinion gear. None of this is good for the transmission.

>"Plus, given that the problem axle is on the passenger side, the lateral force on the differential.... "

In my case the problem axle is on the driver's side. Does that make a difference to your explanation?

djpateman · 02-26-2017, 07:09 AM

KTL's explanation is a little off due to the wrong side analysis. However, as I said in a previous post, there likely are thrust forces acting on the differential bearings and the ring & pinion that are not normal. This could lead to accelerated wear on these components. If the inboard CV can be removed from the transaxle flange then you might have a good idea if the left suspension is pushed in towards the transmission; and if the free play in the drive shaft is restored.
I honestly have no clue as to how the left rear suspension could be shifted 5cm without making the car do odd things. I once hit a curb due to a large quantity of gravel across the asphalt on a ramp at an intersection; it was like driving on marbles. The left arm bent upon impact, but the car was still drivable even though it crabbed noticeably.
The first thing I would do is to measure the distance between the lower shock bolts to the centerline of the transmission on both sides; they should be equal.
The second thing I would do is to remove the CV from the transaxle flange, and check out the axle free play.
Then redo the shock bolt distances again. If you can do these things and report the results, then perhaps we can do a bit more than speculate.

DanielDudley · 02-26-2017, 07:11 AM

I still contend that the axle would be a lot shorter when the suspension is fully loaded, simply because the angle of the driveshaft between the two points is greater when the suspension is at full droop. It just doesn't seem likely that the axle is fully compressed at both normal ride height and full droop unless the axle is pushing the swing arm in and out, and it is always under compression. That may be the case, but it takes a lot longer to try to theorize this problem than it would to take out the axle and examine it.

However, you could jack up the car and see if the length of each axle is the same at full droop, by measuring each axle from the same points. You wouldn't be looking for super accuracy as much as you would be looking for a major discrepancy.