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Rear suspension subframe alignment?

Immortality

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Does anybody know how to check and adjust the rear subframe alignment? Fitted a new diff mount today and I'm sure the subframe is out of alignment.
file.php

As you can see the mount is as far back as it will go and the diff is still pushing the mount backwards and it's also not straight. The wheel gaps also suggest the passenger side is further back than the drivers side wheel.
 

EYY

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If you flip the part that bolts directly to the rear diff cover does that give you the clearance you need?

If it’s actually out of alignment something may be bent? Do you have the adjustable arms?
 

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Nahh. The angle of the pic is deceiving but it's even on both sides.

edit: I think the subframe front mounting bushes are probably a bit stuffed, they way the rear suspension springs sit/load up it would effectively push everything rearward.
 
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MYVESSV8

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off the shelf part or aftermarket, any better than whats out there, next why? (i like this sort of mods/improvements)
 

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We've had it on for a week now, I'm amazed at how much more stable the rear end is. Unfortunately I also replaced the rear shocks at the same time so I can't say with 100% confindence how much is just down to the rear mount. What I can say is it's the best this car has ever handled, the rear end is a lot more firm. The old shocks were still working but in my opinion well past their best. I also changes from Munroe GT gas to KYB Excell shocks.

Aftermarket part? Sure is, Harrop was probably the first to come out with something to firm up the rear end which was their Harrop Sports Cover and replaces the whole rear cover on the diff and incorporates a new diff mount with urethane type bushes. I didn't think I needed the sports mount as it's not a real high performance build. The Harrop was designed to reduce axle tramp I believe and these mounts seem to be known as "anti-tramp" mounts.

We all know that for suspension to work properly the mounting points need to be stable and rigid (note it's common to fit a front strut brace on a Commodore or any other car for that matter to improve steering). So with the Commodore IRS the rear control arms are mounted to the rear subframe with the springs and shocks located against the chassis. When you hit a bump the rear control arm absorbs that load via the spring/shock but because the rear subframe mount (the diff mount) has a fair amount of movement in it so the subframe moves up and down as well. The old rubber mount that came off had witness marks at both the top and bottom of the housing so under load the diff was moving up and down about 16mm (it doesn't sound like much).

It was getting so bad that combined with the extra power/throttle response and the poor handling in the rear the missus didn't like driving it when wet. I'm quiet happy steering with my right foot but apparently the missus isn't.
 

afstruct

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Don't know if this helps
Photos from harrop's instructions/ install booklet that came with my sports diff cover
20180909_094800.jpg

20180909_094553.jpg


And yes the harrop diff cover has pretty much got rid of my axle tramp.
I haven't got the alignment checked.
I did mention it to pedders but they picked a heap of other stuff needed fixing.
I went away and have since done rear CVs front struts and most bushes in the front.
I went to O'Neils to get wheel alignment, he seemed to know nothing about the subframe alignment and just did a normal wheel alignment.
Might try pedders again or have to try Holden.

From this link https://www.google.com.au/url?sa=t&source=web&rct=j&url=https://www.ls1gto.com/forums/showthread.php?t=179799&ved=2ahUKEwiA1q7i0azdAhWSd94KHSVoAJ4QFjAWegQIABAB&usg=AOvVaw3Oso0OjrStgWkoWuK5asN9

I've been doing rear suspension upgrades and believe this IS possible as a DIY. The manual has illustrations of the alignment tool and how it fits into holes in the body near the subframe bushings, and into smaller holes in the subframe itself, further aft & maybe a little inboard. The body holes are 19mm and are easy to find, they're between two big elongated holes in a pseudo "frame rail". My subframe has two sets of holes in the angled arms, I'm not sure which set the alignment tool uses, but I don't think it matters...I'll come back to that. I threaded a tape measure from the body hole, above the exhaust pipes, below the driveshaft (doesn't touch), and over to the subframe holes on the other side. Then switch to the opposite set of body holes and subframe holes and re-measure. It's not a perfect measurement because the tape has to go slightly up & over the exhaust, but it does the same amount of up & over both ways, and the measurement is mostly lateral - just compare measurements to see if the subframe is centered. Here's what I got after putting in new subframe bushings and diff insert:

Forward set of subframe holes: 36-15/16 (to near edge of subframe hole), L>R and R>L, 37-1/2 (to far edge of subframe hole), L-R & R-L

Aft set of subframe holes: 36-even (to near edge of subframe hole), L>R andR>L, 36-9/16 (to far edge of subframe holes), L-R & R-L

I had the tape hooked into the 19mm body holes, and used one hand to make sure it was seated all the way in (not slipping down any). The attachment is a rough diagram of what I was measuring, except I have a 2005 that doesn't have mufflers in the way. I don't think this would work on a 2004, sorry first-year guys!

I'm thinking I've got my subframe on center, within no more than a sixteenth, based on a total of eight measurements. What do you think? I've torqued my TTY bolts, but haven't done the "yield" step yet. If someone finds the fatal flaw in this approach, I will take it in to the dealer, but I think I've already got it centered.

I might add the handling of mine seems good
 

Immortality

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Cheers for posting :)

That first page looks like it came direct from the Holden Dealership service manual.

What they've done is what I was planning on doing, just measuring between the various mounting positions on the frame the factory jig uses.

If I knew it was right then it would be easy enough to make a jig (hmmm, I know someone who's had theirs checked by Holden, wonder if he'll let me borrow his car for a few hours to make a jig?)
 

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Cheers for posting :)



If I knew it was right then it would be easy enough to make a jig

Same. I might get mine checked and then make a jig as guessing I'm keeping it long enough that I'll one day remove subframe and strip and repaint it and do my diff.
 
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Immortality

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I got this one from TradeMe here in NZ, I've actually had it for about 2 years, was intended for my Senator (which is still in the garage in a 1000 bits...) so I decided to throw it under the Calais instead.

Tuff Mounts sell one too Tuff Mounts Billet IRS Mount
 
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