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BMR upper control arm installation problems

Old 3/3/19, 05:04 AM
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BMR upper control arm installation problems

Hi there,

yesterday, I have installed not adjustable BMR upper and lower control arms with PU mounts on my MY 2012 Boss 302.

I was using a car lift in a workshop.
Everything went pretty smooth since BMRs instructions are rather helpfull.

I noticed though that to rear end of the upper control arm seemed a tad bit wider than the metal sleeve in the original rubber bushing in the rear axle.
I assumed that the UCA ends would pull 'emself together when the screw was being torqued down at the end of the installation. At the end, I torqued it, but forgot to check whether after that, the control arm was tight on the sleeve in the axle's upper rubber bushing or not.

When driving the car after having left the workshop, I noticed that when either applying throttle / torque to the differential when accelerating or when decelerating by taking my foot of the throttle, I had quite a bit of lateral movement from the backend.
This movement was not there before with original parts and I doubt it's intended.

I'd assume that is because the reax axle's upper rubber bushing has some play in the newly installed control arm.
And I am gonna check that tomorrow when I am in the workshop again.

In this installation video, at 7:22, I can see the mechanic even has to pry the UCA ends apart a little to make then fit over the bushing's inner sleeve:


In my case, the ends had about 4 mm of space to the sleeve I believe.

Just in case I find that the UCA rear ends have been pressed together tight by the screw on the axles rubber bushing sleeve, I want to make sure I know what else to look for.

My questions now are these:
  • Are these top reax axle rubber bushings and sleeves different in different mustang types from 2010 to 2014?
  • Does the 2012 Boss have a special bushing and needs a special UCA?
  • Can I just put steel washers between the bushing's sleeve and the UCA to make it a tight fit?

Neither the packaging of the UCA nor the UCA itself was labelled.

I assumed it was this UTCA30 because that is what I ordered, and it looked the same:

https://www.bmrsuspension.com/?page=...943&superpro=0

On thing I found out is that in the instructions I downloaded, the torque spec for the control arm mounting bolt that is accessible from the inside under the rear seats was 125 ft lbs or something.
I know found out that in the 2010 to 2014 Mustang, the bolt is bigger and needs to be torqued to 240 ft lbs.
Could the lack of torque for the center bolt have caused that much movement of the rear axle?

Any help or hints are appreciated!

I will update once I am back from the workshop tomorrow afternoon.

cu

Oliver aka Tomcat0815
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Old 3/3/19, 11:17 AM
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The uca prevents the rear differential housing from rotating and maintains pinion angle, it really doesn't do anything for lateral stability. The bushings and uca were the same on the GT and Boss. The Shelby GT 500 used a different bushing/uca. If the problem isn't readily determinable I would contact BMR to make sure you have the correct pieces for your car.
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Old 3/3/19, 12:44 PM
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@EF1 thank you for the feedback. I will check tomorrow if I did the install right first. I suspect the insufficiently torqued UCA mount is the problem here. Like I said, I only toruqe dit to about 125 ft lbs ore whatever the BMR Instrucitons for 2005 - 2009 need instead of 240 ft lbs the 2011 . 2014 needs. I read some threads that this creates what I am experiencing.

If that does not help, I am gonna uninstall the UCA and check with BMR.
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Old 3/4/19, 06:08 AM
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Back from the workshop. Problem of lateral movement of rear axle still persists.

Everything around the UCA was torqued properly, no play or space between the sleeve that goes into the rear end of the UCA and the UCA itself.

What I realized is that the replaced panhard rod bolts were a bit too lose. Also, the panhard rod bushings are rather soft rubber bushings.
If the panhard bar bushings were too soft, could it be that this causes lateral movement of the rear axle when accelerating / decelerating?

I will be in the workshop again next saturday. I will then first replace the panhard rod with the original one and do a test drive, see if the problem is gone. If not, I will replace the BMR UCA against the original one.

Last edited by Tomcat0815; 3/5/19 at 01:20 AM.
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Old 3/4/19, 06:04 PM
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Ok, a little info on these here parts...

Upper Control Arm (UCA) purposes: Align axle/pinion to driveshaft/transmission, and axle to body front-back. Prevent axle wrap/axle from trying to spin top-to-back. This would be very bad. Also support up and down motion for suspension travel in the center.

Lower Control Arms (LCAs) purposes: Align axle/pinion to driveshaft/transmission, and axle to body front-back. Prevent axle wrap/axle from trying to spin bottom-to-front. This would be very bad. Also support up and down motion for suspension travel at either side. And also to transmit power from the axle to the body and move the car.

Panhard Bar sole purpose: Axle left-right alignment to body (and therefore centerline of body, which aligns driveshaft.)

Worn bushings in any of these components can cause an unwanted/unexpected left-right motion. But most especially the Panhard. The others, not so much, but they will cause it to a degree.

It sounds greatly that you have some worn bushings or loose bolts in the system, most likely the Panhard, but all points of connections should be inspected and dealt with if not optimum.

The sway bar and shocks do not enter into side-to-side issues. Sway bar is for roll/body lean in a turn. Shocks stop motion (aka dampeners.) So they're not the issue, but they should also be inspected/dealt with if needed.

And all that is just about the suspension... it could be your sidewalls of the tires you choose to run. For example, the Cooper RS3-As are known to have a little 'lag' in a turn, aka, it feels like the car is sliding out just a little, then they catch in the turn and they're nice and solid. (It was a little odd at first when I ran them on my 17 inch wheels but I got used to them... then I swapped out the wheels and I can't get them in the right size I need, but dang, they were good grippy tires...)

So maybe a different tire is indicated, possibly. Don't run more air in them, that's not the answer.

Good luck, hope that helps!

Last edited by houtex; 3/4/19 at 06:20 PM.
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Old 3/4/19, 06:29 PM
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Originally Posted by Tomcat0815 View Post
Bck from the workshop. Problem of lateral movement of rear axle still persists.

Everything around the UCA was torqued properly, no play or space between the sleeve that goes into the rear end of the UCA and the UCA itself.

What I realized is that the replaced panhard rod bolts were a bit too lose. Also, the panhard rod bushings are rather soft rubber bushings.
If the panhard bar bushings were too soft, could it be that this causes lateral movement of the rear axle when accelerating / decelerating?

I will be in the workshop again next saturday. I will then first replace the panhard rod with the original one and do a test drive, see if the problem is gone. If not, I will replace the BMR UCA against the original one.

The loose pan hard bar is most likely the problem. It centers the rear axle and prevents lateral movement. You did not mention changing the pan hard bar in your initial post.
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Old 3/5/19, 01:27 AM
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EF1 Yes, it seems I forgot to mention that I changed the panhard bar. Turns out the Panhard bar is a rather old model of a German manufacturer (which is where I am located) and they had trouble with too soft bushings. They are rubber bushings, later models have PU bushings.

Though I am suprised that the rear end lateral motion is caused my applying positive or negative torque to the rear axle. If it was the panhard bar. I would expect it to cause movement when the rear end of the car cahnges height, eg. the springs are compressed.

Anyhow, I will put in the old, original panhard bar this saturday and see what happens.
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Old 3/5/19, 11:46 PM
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Well, the torque applied to the axle is trying to twist it in some way. Some is trying to make the axle ends flip left-right, but most is trying to make the axle twist opposite how the wheels are trying to turn. That makes the car hunker down as you move forward, or raise up when you go backward. Just the way the geometry and power transmission of the control arms work.

All this movement (and arresting/retransmitting thereto) causes some movement up and down as the control arms do their thing and keep the axle from doing what it really wants to do: spin around opposite the wheels. This movement up and down with a panhard bar involved requires the axle to move in an arc. If the axle moves up relative to center height, the axle gets pushed left (driver side). If the axle moves down, pushed right (passenger). (Assuming left hand drive here, of course, re: driver/passenger.) This is because the panhard is a fixed length and fixed at one end. The left side motion describes and arc, therefore the axle must as well.

Ergo: Body movement in relation to the axle when power is applied.

Panhard bar setups do this. The quad links didn't so much, but they don't handle as well, apparently, one of the reasons Ford moved to the three link. Only other way to make it stop is to put in a Watts suspension or get an independent suspension back there. All poly bushings may help, or spherical bearings, but you get more noise, harshness and vibrations. Also, polys need greasing because they don't like cold or their grease washes out eventually. But they won't wear out as much, so there's that.

Fun with live axles. Heh. Gotta love 'em!

Last edited by houtex; 3/5/19 at 11:48 PM.
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Old 3/6/19, 04:09 AM
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houtex The thing is that the rear axle did not do that, or at least far less noticable, before I swapped UCA, LCA and panhard bar. So no I am trying to figre out which of these parts I swapped is the cause for the lateral movement having become so much stronger than before.

But like I said I am gonna start with changing back to the original panhard bar because that it's easy to change and also because the panhard bar's bushings seemed far too soft to me in the first place.

I am gonna report what it was once I found out.

On rear axles: I switched from an BMW E46 M3 to the Boss 302. I had a pretty decent set up in the BMW and tracked it a lot. And I was REALLY suprised how well the Boss and the live axle handled in comparison.
I was very afraid that hitting kerbs on the track would cause havoc, but the original set up of the Boss' live axle is pretty forgiving.
On some tracks, I reached the same lap times as with the BMW instantly.
Which probably tells more about the driver (me) than both cars but so far I am pretty happy with the Boss.
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Old 3/9/19, 10:08 AM
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Hi folks,

quick update after returning from the workshop:

Part by part I reverted my mods until the problem disappeared.

Panhard bar

First, the panhard bar, a german product with a rather bad reputation and really soft inserted rubber bushings.
Also, the left metal sleeve running in that rubber bushing was way too short. Even when torquing the respective bolt to spec, the sleeve still had play.

BMR LCA

After the panhard bar was replaced with the original one, the problem persisted.
So I removed the BMR LCAs. And there, the rear left PU bushings now looked a little worn to me. I saw it when installing them but did not think it would have such a dramatic effect (bought them used from some forum guy here in Germany).
After removing the LCAs and replacing them with the original ones, the car performed as before.

BMR UCA

I then torqued the UCA center bolt from the inside to 240 lb fts as specified because I had no tool to do that the last time is was in the workshop.
I doubted that this was a problem but I just wanted to be sure.

Results

Now the car drives like before, everything is fine again!
What I actually experienced during acceleration / motor braking was not as I thought a lateral movement of the live axis but a steering movement of the axle because of the worn out bushings on one LCA I suppose.

Rear axle Outlook

I am gonna get me LCAs and an adjustable panhard bar when I need it once I lower the car. The original parts are gonna stay in place until then.

Other work done

For fun and in order to do more than just install old parts, we did the following things:
  • installed the whole whiteline sway bar kit
  • checked and set camber to -1,7 (more was not possible with just camber adjustment screws)
  • checked and set toe angle to neutral / 0
  • changed brake ducts to 3" from 2"
  • replaced transmission oil with something said to improve MT82 shifting (some Castrol stuff, most oils recommended here are not available in Germany)
  • slotted stop tech rotors and and pads for the front brake

Well, that was it.

Next trackday is on March, 16th. I am gonna see how everything turns out.
I put the sway bars to rear=soft/4th of 4 holes and front=less soft/3rd of for holes to reduce understeer) but I am planning on adjusting them during the track day.

Next parts waiting for install are braided clutch line and MGW shifter arm bushings but these will have to wait.

Thank you for your help and support, that helped me a lot!

Best regards

Oliver aka Tomcat0815
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Old 3/9/19, 04:30 PM
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Happy to hear that you figured it out. Good luck on the 16th.
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Old 3/12/19, 02:14 PM
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thanks for the informative update, glad you got it sorted out and have fun at the track!
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