Trailing arm loose?
Thread Starter
Instructor
Joined: Jan 2007
Posts: 191
Likes: 1
From: MONTREAL QUEBEC
Trailing arm loose?
My 71 has over 1/2 inch of play at the rear wheels when rocking them (jacked) at the 12 and 6 o'clock position. The play is at the trailing arm where it meets the frame. There are 3 alignment shims on each trailing arm.
Why is there so much play and can I fix it by just adding more shims?
Why is there so much play and can I fix it by just adding more shims?
Pro
Joined: Aug 2005
Posts: 627
Likes: 1
From: Naperville IL
Is there actually space between the shims and the trailing arm bushing? The pivot bolt won't have anything to do with the arm rocking at the 12 and 6 position. I'd look at your halfshafts and strut rods first. If your're missing shims, the trailing arm will slide back and forth giving you more play in the 3 and 9 direction...It's also possible the front bushing is worn which would would be like missing shims.
Pro
Joined: Aug 2005
Posts: 627
Likes: 1
From: Naperville IL
you have to look at what is actually moving when you get the play. It could be the strut rod bushings, but I think the differential yokes usually wear first which would cause the halfshafts to have some play. the halfshafts act as the upper link in your rear suspension
Thread Starter
Instructor
Joined: Jan 2007
Posts: 191
Likes: 1
From: MONTREAL QUEBEC
From what I can see only the trailing arm is moving at the front bushing when rocking the wheel from 12 o'clock to 6 o'clock. Is 1/2 an inch excessive play? What would be the normal amount of play? Car runs and drives excellent but unfortunately the inspection shop believes it's excessive play and I can't register the car until it's fixed.
Drifting
Joined: Dec 2002
Posts: 1,946
Likes: 28
From: Long Beach CA
Yes, 1/2 inch is excessive. There are bushings in the front of the trailing arms by those shims that could be worn out. Bad shims will let the front of the trailing arm move up and down and side to side. But adding shims and/or replacing the bushings won't take care of your excessive rocking of the tire. The 12 and 6 o'clock movement is controlled by the bushings at the ends of the lower strut rods, and by the yokes in the differential that the halfshafts connect to. When you're rocking the wheel/tire, look at how far in and out of the differential the halfshaft yokes are moving.
Race Director
Joined: Nov 1999
Posts: 10,643
Likes: 8
From: Foxfield CO 1970 Convertible
I agree with the others. There should be no humanly detectable play when rocking at 12 and 6. Also, if there is any play at the front of the trailing arm, your alignment is shot. You may not notice it, but your tires will be wearing out faster than normal. Also, there are numerous posts which show what happens when a rear wheel lets go - it's not pretty!! 
If you get rid of this play, your car will handle much better than it does!
If you get rid of this play, your car will handle much better than it does!
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Thread Starter
Instructor
Joined: Jan 2007
Posts: 191
Likes: 1
From: MONTREAL QUEBEC
You're right the yolk on the passenger side moves in and out 1/8 of an inch when rocked from 12 o'clock to 6 o'clock not the 1/2 inch that the inspectors claimed. The drivers side is tight and the strut rods show no play on either side. The trailing arm on the passenger side does twist when rocked. Is this 1/8 " of play excessive as well? What do I need to replace to fix it? Thanks.
Team Owner
Joined: Oct 2004
Posts: 23,831
Likes: 10
From: Springfield MO
St. Jude Donor '07
I agree with the others. There should be no humanly detectable play when rocking at 12 and 6. Also, if there is any play at the front of the trailing arm, your alignment is shot. You may not notice it, but your tires will be wearing out faster than normal. Also, there are numerous posts which show what happens when a rear wheel lets go - it's not pretty!!
If you get rid of this play, your car will handle much better than it does!
If you get rid of this play, your car will handle much better than it does!
Thread Starter
Instructor
Joined: Jan 2007
Posts: 191
Likes: 1
From: MONTREAL QUEBEC
I'm sure the front bushing is gone and most likely the bearings are on their last legs and while I'm at it the half shafts and the yolks in the diff. But summers up here are short and I just want to drive it all the time and work on her in the winter. So in the meantime if I get adjustable strut rods and extend them enough will they stop the 12 and 6 oclock motion. I think they might I need your opinions I'm just trying to pass the inspection for now. Thanks again.
Pro
Joined: Aug 2005
Posts: 627
Likes: 1
From: Naperville IL
if the halfshafts have play and the strut rods now are in good shape, then replacing them with longer ones won't help anything, it'll just change your camber. It sounds like you're gonna be replacing a differential yoke eventually.
Drifting
Joined: Dec 2002
Posts: 1,946
Likes: 28
From: Long Beach CA
Yep, if it has that much play and the inspector isn't going to sign off on it as safe, then you're stuck. You're going to have to get the rear diff torn apart and take care of the yokes to get rid of the play. Might as well get new bushings put in the front of the trailing arms while it's apart. Get a wheel alignment, and you'll be impressed with how well it handles.
