Had the car aligned and the Thrust angle was 0.18.
The specified range is -0.15 to +0.15

How can this be adjusted to fall within the prescribed parameters?

Note: I have adjustable LCA's on the car. They were put on the car because for some reason the passengers side distance between the LCA mounting points on the vehicle was approx. 1/8" shorter than it should have been, resulting in mismatching alignment problems with the standard aftermarket LCA mounting hole spread dimension. The reason this condition wasn't noticed with the OEM LCA was because the bushing in the LCA is so large and is so flexable, it would still align and mount with no problems.

Since my LCA's are adjustable, I thought perhaps I could adjust them slightly while on the alignment rack and bring this specification back where it needs to be.

TIA

 

Not sure what type of alignment equipment is being used but in all the years I did alignments I have found that not only can alignment equipment be off by small increments (degrees or inches measurements) from shop to shop but, re-installing the alignment heads and verifying that run-out compensation from alignment head to wheel mounting are consistent. You may find that the reading shows up a little different.

Either way, I have seen thrust angles out more severe than this on solid rear axles and since the front is aligned to match the T-angle of the rear, this "out-of-spec" rear is completely unoticeable to the driver in regards to handling. My suggestion....before you get to serious about making any adjustments, just be sure to verify that run-out compensation is accurate and tires are properly inflated.

BTW-You asked how can this be adjusted? Thrust angle is a total of individual toe-in both left rear and right rear.....The only way to change the Thrust angle on any vehicle is to change the Total Toe within the given parameters you have listed above.

 

Adjustable lower control arms can be used to correct thrust angle. I've done this on a number of F-bodies. Lengthen one arm while shortening the other arm and you can set the thrust angle easily.

 

It sounds like to me you messed up the thrust angle with the ajustable LCA's. I would take those off, and put them back-to-back with a long bolt through one end, then adjust them to the same length so the second bolt will pass through the other two ends. Just move the axle around until they both reinstall.

 

I originally bought BMR non-adjustable LCA's with the rubber/poly bushings. On the passenger's side I made that LCA fit even tho the axle wanted to be 1/8" further out (wider)on the LCA attachment hole spread dimension than the corresponding hole spread dimension in the LCA. Both fixed LCA's were identical on the hole spread dimension. Driver's side LCA fit perfectly with no issues. This extra width on the passenger's side would make the bushings deform (because on that side that axle really wanted to be where it was). When I would hit the brakes hard the axle would shift and I'd have to steer quicky or I'd run off the road. Then when I'd get on it the axle would flex the opposit direction also requiring a quick adjustment in the steering. This was scary as hell as well as dangerous.
BMR let me trade these in on a set of adjustable LCA's. I took the "fixed" LCA off the drivers side (there was no binding on the drivers side, the holes all aligned) and adjusted the new LCA to fit the exact spread (same spread as the fixed LCA).
I repeated the process with the passengers side. The bolt came out just like it went in, I had to unscrew it all 3.5 inches-all the way because of the binding from the axle pulling rearward on that side. (Note: when I removed the LCA there was so much binding force you could see the imprint of the threads from each LCA bolt in each end of the center steel bushings (facing outboard) on the LCA)

I adjusted the second new LCA to fit where the axle wanted to be. I can probably adjust it a little but I'm afraid if I move it back to the original spread (same dimension as the fixed LCA) I will get the same problem back again that I had with the handling.

If I could figure a way to push the passenger's side of the axle fwd just enough to match the original hole spread (same as the drivers side) and then mount and torque down the LCA into place without the axle deforming the bushings it may just solve that problem. The trick is to do it without doing any damage to the car/body as I'd have to put force on both ends of the car to move that axle where it doesn't want to be.
I guess it would be easier if I remove both LCA's at the same time but I'm afraid the axle may shift and roll out of position.

If you have any ideas how best to do this I'm open to suggestions.

It would be so easy If I could adjust the LCA on the car to the correct position, the problem is how do I measure it to determine the exact location where I would need to stop.

I suppose I could contact BMR to get the exact hole spread of the fixed LCA's (or perhaps a member here has this information-I forgot to write this down prior to returning mine to BMR) and use a tape measure (not very accurate but could get it close). With the correct torque on the bolts to begin with (seems like the spec. is 87 ft lbs-if I recall correctly)surely the bushings wouldn't deform as they did before.

This wasn't a problem with the OEM's because the bushings are so large and the durometer spec (hardness) is pretty soft that it would conform to the axle position (my belief).

Unless there is something else happening that I've not yet considered.

I posted on this condition before I bought the adjustable LCAs, but at the time no one seemed to have a real answer to this condition/problem.

 

The axle doesn't have any particular place it where it "wants" to be. You have to put it where needs to be by making sure both of your LCA's are the same length and your panhard rod is the correct length. If you are doing this work with the axle at full droop, you won't know if the panhard is the right length, and it may very well seem that the axle "wants" to be somewhere else. There is a different correct panhard bar length for every ride height. So if you have changed the ride height, you need an adjustable panhard rod. You should set all this stuff up with weight on the rear wheels or with the axle supported by jackstands, so you are not fighting with the axle on where it "wants" to be.

 

Well mine does.

Like I said, I started with the non adjustable LCAs. They were the same length. The passengers side would not fit. Did you even read through my posts? The Panhard bar is stock, the ride height is stock, NOTHING has been changed except the addition of the shock tower brace and SLP bolt in SFC, and a Mac differential cover.

I had the weight on the rear wheels, every time I've removed or installed the LCA's the weight has always been on the rear wheels.

 

I think Cal is trying to help....I agree with what he's saying. The answer to your question is yes, the adj. control arm will correct your thrust angle problem. I did it with mine. When my car was bone stock, the thrust angle was about .15-.18 deg off. Thats probably only 1/16" or 1/32" of adjustment on your control arm length.

 

I did read all of your posts, but you also have to think about what I'm saying here. Yes use your adjustable LCA's to correct the missalignment, if there really is one. Normally you would not have a problem like this with equal length LCA's. If you are, that means the car is bent or not built straight, which are unlikely unless it has been in a major wreck.

My sugestion is to make them equal and actually check this thrust angle again to make sure you are fixing the problem, not a symptom. The thing that made me think this was your comment about the axle "wanting" to go in a certain way. I have had my rear axle off many times, and it never just "wants" to go in straight. You have to use a pinch bar, jack or what ever tools you have to get it in right.

 

Im supprised anybody even posted in this thread after you gave attitude to someone who was trying to help you. My advice is take your car to a shop thats willing to adjust thoes parts while its on the rack. I did so today. Going into it I had around .2X for mine, we played around with the different parts and got it down to .0, we took the sensors off the wheels and put them back on and it came to .01. Took them off again and it came to -.0. Also you should get a panhard bar for the car reguardless if its lowered or not.

 

Well I didn't mean to give Cal attitude, and for that I apologize.
This problem just has me fustrated.


Cal:
I'm going to adjust the passenger's side and bring it as close as possible to the driver's side, then take it for realignment.
You probably are correct in your assesment.
The car hasn't been wrecked that I know of, it only had 15 miles on it when I bought it.
I'll let you know how it works out.

 

Weezer, your description of the problem confuses me ...

Is the distance between the front and rear LCA mounting points different from side to side or is the physical mount where the bushing goes squeezed together, not allowing the LCAs to fit into the mount?

If it's the first, like Cal said, with the diff hanging free, you can move the diff around to get equal length LCAs to align. If this is you issue, I'm wondering if you are supporting the car on the axle instead of from the frame ...

If it's the latter, the sandwich mounts will squeeze together, especially when over-torqued and soft stock rubber bushings are used. Just spread the mounts apart, get the new bushing in and retorque. The mount will conform ...

HTH

 

Its a variation in the hole spread distance between the frame and axle. I installed the arms with the full vehicle weight on the axle (did not remove the tires, did this while the car was on rino rams). I went this route because the installation instructions stated not to torque the bolts to spec without the weight of the car on the axle.

 

That's the part that is confusing me. The LCA's are what sets this distance.

OK this may be the problem:

You need to support the car with jackstands under the frame, but have the axle supported by a shop jack on wheels so you can move it around to get the holes lined up. The tires should not be touching the ground. The purpose of the jack is to push the axle up close to ride height, yet not have the weight of the car on it. This will keep the panhard rod from shoving the axle too far to the side like it would if the axle were at full droop, yet still allow you to move the axle around.

The LCA's locate the axle for and aft, not the other way around.

Weezzer, sorry if I'm frustrating you more, but this should not be a difficult problem.

 

Yes, that's the issue ....

Install the LCAs with the rear diff hanging. You can move the diff around in order to get the bolts to align.

Then, support the weight of the vehicle on the diff, like with rhino ramps, an then do your torque.

No wonder you couldn't get the holes to align ....