Rear end jerking right - Mustang Evolution

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Old 04-30-2016, 01:20 PM   #1
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Rear end jerking right

Ok so this is gonna be a long post lol

So I recently installed BC coilovers, BMR lower controls arms, relocation brackets and an adjustable panhard bar on my '13 track pack. There is about a half inch gap all around so the car is pretty low. I have the control arms in the middle hole of the brackets and I've had the car aligned at steeda.
So now the problem:
When under hard acceleration the car kind of kicks or jerks right almost like its losing traction. Feels like the axle is just sliding out. It happens usually in the middle of a 3rd gear pull or if I downshift and floor it. After it happens the steering wheel is offcenter for a second and then it goes back straight. Not sure why it's happening and it's not enjoyable to drive it hard knowing it's gonna happen. Anyone have any advice?
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Old 04-30-2016, 03:45 PM   #2
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Did you adjust the panhand bar to recenter the axle? It tends to shift when you lower these cars.
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Old 04-30-2016, 06:09 PM   #3
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Quote:
Originally Posted by Joaquin_ii View Post
Did you adjust the panhand bar to recenter the axle? It tends to shift when you lower these cars.

Yeah I adjusted it


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Old 04-30-2016, 08:03 PM   #4
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Sounds like you have this problem:
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Old 04-30-2016, 08:18 PM   #5
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I wish I could drive like that lol


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Old 04-30-2016, 09:55 PM   #6
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If you are veering in a certain direction under hard acceleration, I would think it's your trac-LOK friction plates in your differential. I had a similar issue as you described, where I had one wheel spinning faster than the other. This made hard shifting through 2nd-3rd gear squirrelly as a mofo - very hard to keep the car straight. I rebuilt my rear end with 4.10s and replaced the trac-LOK friction plates which solved my issue.

Now I am not sure if this is your problem, as it would appear this is the result of your heavy suspension mods... But I thought I'd just throw in my two cents.
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Old 05-01-2016, 11:20 AM   #7
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Quote:
Originally Posted by TRMN8ER View Post
If you are veering in a certain direction under hard acceleration, I would think it's your trac-LOK friction plates in your differential. I had a similar issue as you described, where I had one wheel spinning faster than the other. This made hard shifting through 2nd-3rd gear squirrelly as a mofo - very hard to keep the car straight. I rebuilt my rear end with 4.10s and replaced the trac-LOK friction plates which solved my issue.

Now I am not sure if this is your problem, as it would appear this is the result of your heavy suspension mods... But I thought I'd just throw in my two cents.
Just as information, the late model Mustangs have a Torsen carrier which does not have clutches/friction plates.
Read up on the differences;

Locking and Torsen - How Differentials Work | HowStuffWorks
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Old 05-01-2016, 11:26 AM   #8
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Quote:
Originally Posted by Floridasixer View Post
Ok so this is gonna be a long post lol

So I recently installed BC coilovers, BMR lower controls arms, relocation brackets and an adjustable panhard bar on my '13 track pack. There is about a half inch gap all around so the car is pretty low. I have the control arms in the middle hole of the brackets and I've had the car aligned at steeda.
So now the problem:
When under hard acceleration the car kind of kicks or jerks right almost like its losing traction. Feels like the axle is just sliding out. It happens usually in the middle of a 3rd gear pull or if I downshift and floor it. After it happens the steering wheel is offcenter for a second and then it goes back straight. Not sure why it's happening and it's not enjoyable to drive it hard knowing it's gonna happen. Anyone have any advice?
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First, I'd give BMR/Steeda a call and talk with them about your issue. My guess is that you've preloaded the rearend either with the coilovers or the angle you've got your LCA's at. With you car static what is the pinion angle?
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Old 05-01-2016, 11:30 AM   #9
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Not all of 'em...lots of friction plate diffs out there. You have to select he Torsen option, via TP. Anyway, this is a TP car so, the Torsen is in there.

Still potentially a diff problem but, lets start with something easy. If your tires aren't directional, switch 'em side to side in the back and see if it changes the behaviour. If they are, go front to rear, same side.

A little of this isn't unusual, as the pinion gear is off direct centre to make room for the ring gear in the housing, which will introduce a little bias.

Of course, check the obvious like torque on your suspension components and I hope you tightened everything with the suspension loaded normally.
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Old 05-01-2016, 11:40 AM   #10
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Quote:
Originally Posted by TRMN8ER View Post
If you are veering in a certain direction under hard acceleration, I would think it's your trac-LOK friction plates in your differential. I had a similar issue as you described, where I had one wheel spinning faster than the other. This made hard shifting through 2nd-3rd gear squirrelly as a mofo - very hard to keep the car straight. I rebuilt my rear end with 4.10s and replaced the trac-LOK friction plates which solved my issue.

Now I am not sure if this is your problem, as it would appear this is the result of your heavy suspension mods... But I thought I'd just throw in my two cents.
Sorry, since most of the late model Mustangs I've worked on had Torsen units I assumed....my mistake.

Quote:
Originally Posted by 5LHO View Post
Not all of 'em...lots of friction plate diffs out there. You have to select he Torsen option, via TP. Anyway, this is a TP car so, the Torsen is in there.

Still potentially a diff problem but, lets start with something easy. If your tires aren't directional, switch 'em side to side in the back and see if it changes the behaviour. If they are, go front to rear, same side.

A little of this isn't unusual, as the pinion gear is off direct centre to make room for the ring gear in the housing, which will introduce a little bias.

Of course, check the obvious like torque on your suspension components and I hope you tightened everything with the suspension loaded normally.
All TrakPak Mustangs came with Torsen carriers...the OP's is a TrakPak car....I didn't realize they were still using clutch carriers after 2011.
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Old 05-01-2016, 11:57 AM   #11
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ONLY the TP and Boss cars get a Torsen, as I said. Everyone else gets the Trak Lok, even BBP. Nothing wrong with the good old Trak Lok in general service. It's been a decent LSD since the the 1970s.
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Old 05-01-2016, 10:04 PM   #12
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I also have this issue, i thought it was normal. The only suspension mods are hotchkis panhard bar, springs and lower controls arms.
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Old 05-01-2016, 10:51 PM   #13
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It is normal if you haven't set up the rear suspension to compensate for torque.
I am sometimes amazed at people just lowering their car or adding coilovers, or springs and aftermarket LCA/UCA and not checking to see where the pinion angle is........guys this is suspension 101........without knowing where the pinion angle is you are not going to be able to setup the car to go straight when you foot is on the floor.
When I got my 14 TrakPak it would do the same thing you are describing...going sideways. After changing the OE to adjustable LCA's, UCA, and pan hard, lowering springs and changing the carrier bushing to a BMR....and with the proper pinion angle and 1 piece driveline the car was 100% better than when I got it....although it would still spin the tires it went straight as a dime.....and would actually squat under very hard acceleration.....like a suspension should.
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Old 05-02-2016, 11:28 AM   #14
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The problem didn't happen until all the aftermarket stuff was installed. I did suspect pinion angle but I'm not sure. Since I did the install with hand tools I had steeda tighten everything up. I had considered that maybe the shocks where set too stiff not allowing the rear to squat properly. I've noticed now that when I downshift and punch it it wiggles too


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Old 05-02-2016, 11:30 AM   #15
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Quote:
Originally Posted by olerodder View Post
It is normal if you haven't set up the rear suspension to compensate for torque.

I am sometimes amazed at people just lowering their car or adding coilovers, or springs and aftermarket LCA/UCA and not checking to see where the pinion angle is........guys this is suspension 101........without knowing where the pinion angle is you are not going to be able to setup the car to go straight when you foot is on the floor.

When I got my 14 TrakPak it would do the same thing you are describing...going sideways. After changing the OE to adjustable LCA's, UCA, and pan hard, lowering springs and changing the carrier bushing to a BMR....and with the proper pinion angle and 1 piece driveline the car was 100% better than when I got it....although it would still spin the tires it went straight as a dime.....and would actually squat under very hard acceleration.....like a suspension should.

The problem didn't happen until all the aftermarket stuff was installed. I did suspect pinion angle but I'm not sure. Since I did the install with hand tools I had steeda tighten everything up. I had considered that maybe the shocks where set too stiff not allowing the rear to squat properly. I've noticed now that when I downshift and punch it it wiggles too


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Old 05-02-2016, 01:43 PM   #16
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For what it's worth, I have the following suspension components installed on a GT with the Brembo package: (3:73 gears)

One piece aluminum driveshaft
J&M Extreme Joint Lower Control Arms (rear)
Steeda Frame Rail & Torque Box Braces (welded in)

...and I don't have any slipping/jerking to either side under hard launches/acceleration .

Midas installed all 3 components so I'm assuming the pinion angle is correct or within spec. (haven't had any problems that I've noticed)
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Old 05-02-2016, 04:10 PM   #17
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I would be willing to bet Midas never checked the pinion angle...their a muffler shop not a suspension shop
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Old 05-02-2016, 04:13 PM   #18
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Quote:
Originally Posted by Floridasixer View Post
The problem didn't happen until all the aftermarket stuff was installed. I did suspect pinion angle but I'm not sure. Since I did the install with hand tools I had steeda tighten everything up. I had considered that maybe the shocks where set too stiff not allowing the rear to squat properly. I've noticed now that when I downshift and punch it it wiggles too


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Kind of suspension 101-A is not to change every suspension part you have all at once...when you run into a problem it can take 2 to 3 times longer to isolate it.
First thing to do is check the pinion angle...since you probably still have a two piece driveshaft check that as well.
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