Modified IRS K-frame for Lowered Cars

[[TUFFVQ]Participant Melbourne1991 VQ 304 View build HERE Member since: March 2, 2015 Posts: 171]

I’m looking to modify the inner attachment points for the trailing arms on my IRS k-frame. A later model one is shown below.

The idea being is that I’m trying to reduce the camber and toe on my VQ which runs SSSL’s and a spool. It chops the inside of the tyres out and I’m only able to use less than half of the available tread width (As evidenced by tyre marks).

I originally used a 4point point adjustable kit. The bushes fairly quickly disintegrated and the spool elongated the mounting holes. I pulled it back out again, put heavy duty fixed outer bushes and adjustable inners. I also put doubler plates on the mounting points. I haven’t looked in a while but it would seem this is holding up, however the alignment is pretty average.

So has anybody modified the inner bolt holes? I suspect I need to weld them up, then re-drill them forward and up (i.e. toward the front of the car and the floor pan.

Additional bracing will occur at the same time.

(Don’t want to change the springs or remove the spool, so please don’t suggest that. )

[VRSenator065Participant Adelaide SAVR Senator LSx454 1960 Kombi (project) 1921 Nash Hot Rod (future project) View build HERE Member since: February 17, 2015 Posts: 5 777]

Hi mate,  just trying to think that through, what about instead if you were able to raise the back of the whole K frame, it only attaches behind the diff, would that do the same thing?  Would it be possible to attach the mount on the back of the diff lower, or somehow modify the car where the mount fits to make it higher.  Not sure if any of that makes sense?  Just thinking out loud really.

[ImmortalityParticipant 97 HSV Senator 185i 02 VX L67 Calais View build HERE Member since: August 31, 2015 Posts: 534]

Somewhere towards the end of the production cycle Holden altered the mounting points as well as altering the angle of the bush mount in the swing arm to improve the geometry as the wheel moves through it’s range of motion.  No idea though at exactly what model these changes were introduced.

[[TUFFVQ]Participant Melbourne1991 VQ 304 View build HERE Member since: March 2, 2015 Posts: 171]

As the arms move through their range of motion in compression, the amount of camber and toe in increases;  Lowered cars have their typical operating range down at the position of greater camber/toe.

If you alter the position of the inner arm bushes you can ‘twist’ the arms back into a position with less camber and toe (trying to bring it back to the geometry of standard ride height or better). Ideally I’d like 0 deg camber and as close to 0 toe as possible; this is a straight-line car only.

Conversely this means that at ‘standard’ ride height you could have positive camber and toe out. Not stressed about that part.

[ImmortalityParticipant 97 HSV Senator 185i 02 VX L67 Calais View build HERE Member since: August 31, 2015 Posts: 534]

Is this a dedicated drag car or is engineering/road worthiness an issue?

How fast are you going?

[VRSenator065Participant Adelaide SAVR Senator LSx454 1960 Kombi (project) 1921 Nash Hot Rod (future project) View build HERE Member since: February 17, 2015 Posts: 5 777]

Sorry mate, now I get it.  Your essentially trying to get the nominal camber/toe to suit your (lower) “normal” ride height.  I was thinking it was the drive shaft angle that was the issue.  Still buzzing in my head a little though, if somehow we could move/mount the whole K frame higher up in the chassis, essentially your lowering the car but keeping the same suspensions geometry.  You also get a lower ride height but with a longer spring so better ride etc.

[[TUFFVQ]Participant Melbourne1991 VQ 304 View build HERE Member since: March 2, 2015 Posts: 171]

Immortality wrote:

Is this a dedicated drag car or is engineering/road worthiness an issue? How fast are you going?

Not that quick. Down the line (one day) i’d like to be able to nudge high 10’s but the next step is to get closer to an 11. I’m just sick of chopping out the inside of the tyres while having literally un-touched outer edges.

The car wouldn’t pass RWC now due to a number of reasons.

VRSenator065 wrote:

Sorry mate, now I get it. Your essentially trying to get the nominal camber/toe to suit your (lower) “normal” ride height. I was thinking it was the drive shaft angle that was the issue. Still buzzing in my head a little though, if somehow we could move/mount the whole K frame higher up in the chassis, essentially your lowering the car but keeping the same suspensions geometry. You also get a lower ride height but with a longer spring so better ride etc.

The biggest issue I would see with this is the forward mounts – there is no way to move these up easily without modifying the floor – something I don’t want to do.

Experimenting with a K-frame, on the other hand, is pretty much an exercise is using my own time.

[VRSenator065Participant Adelaide SAVR Senator LSx454 1960 Kombi (project) 1921 Nash Hot Rod (future project) View build HERE Member since: February 17, 2015 Posts: 5 777]

[TUFFVQ] wrote:

The biggest issue I would see with this is the forward mounts – there is no way to move these up easily without modifying the floor – something I don’t want to do. Experimenting with a K-frame, on the other hand, is pretty much an exercise is using my own time.

Agreed, but I was thinking you may be able to modify the end of the sub frame, so the mounts etc on the car stay the same?  Its not easy I don’t have my car home at the moment to look at, but basically cut the top off the end, and reweld it to the bottom keeping the overall height for the urethane the same, effectively moving the frame up.  Just kicking around an idea thats all, might be stupid.

 

[[TUFFVQ]Participant Melbourne1991 VQ 304 View build HERE Member since: March 2, 2015 Posts: 171]

If i’m going to the effort of re-welding the front mounts, i’ll need to mod the rear mount also.

Which brings me back to my arm mounting modification thoughts

[[TUFFVQ]Participant Melbourne1991 VQ 304 View build HERE Member since: March 2, 2015 Posts: 171]

Could even go something like this but on the inner arm. (These were used on a mini-tubbed IRS arrangement for more tyre clearance)

Would have great, solid adjustment on it. Haven’t thought about it enough to determine if the ‘cam’ style adjustment on the aftermarket bushes is required versus the heim length only adjustment.

[VRSenator065Participant Adelaide SAVR Senator LSx454 1960 Kombi (project) 1921 Nash Hot Rod (future project) View build HERE Member since: February 17, 2015 Posts: 5 777]

^nice bit of kit, I reckon I have seen them before, not sure where.

[ImmortalityParticipant 97 HSV Senator 185i 02 VX L67 Calais View build HERE Member since: August 31, 2015 Posts: 534]

I think it was Street Machine mag that did something similar for some ute they made that was running on 20 or 22 inch rims on the back, they basically ended up fabricating completely new tubular arms welded to the original cast hub assembly.  It was sitting really low and was tubbed as well I believe.

[[TUFFVQ]Participant Melbourne1991 VQ 304 View build HERE Member since: March 2, 2015 Posts: 171]

Building arms like that is actually quite easy. Build a jig for the mounting points, cut up a few bits of plate, bust out the TIG. Rock and Roll.

[VRSenator065Participant Adelaide SAVR Senator LSx454 1960 Kombi (project) 1921 Nash Hot Rod (future project) View build HERE Member since: February 17, 2015 Posts: 5 777]

^agreed you can make/do anything if you try hard enough.  Unfortunately the problem is at a fundamental level the Commie IRS design is crap.

• This reply was modified 8 years, 7 months ago by  VRSenator065.

[cava454Moderator 93 VR BT1 View build HERE Member since: February 20, 2015 Posts: 2 390]

Just re shell it. That’s what I did lol

[VRSenator065Participant Adelaide SAVR Senator LSx454 1960 Kombi (project) 1921 Nash Hot Rod (future project) View build HERE Member since: February 17, 2015 Posts: 5 777]

Hey mate, I just came across this, this is exactly what you had in mind isn’t it?

http://www.shop.gforce1320.com/product.sc?productId=367&categoryId=932

Has a full write up etc.

 

 

[sands vsParticipant vs commodore View build HERE Member since: March 1, 2015 Posts: 619]

cava454 wrote:

Just re shell it. That’s what I did lol

 

 

Rigid rear?

[cava454Moderator 93 VR BT1 View build HERE Member since: February 20, 2015 Posts: 2 390]

sands vs wrote:

cava454 wrote:

Just re shell it. That’s what I did lol

Rigid rear?

 

yep. Bye bye IRS

[dazedv3Participant VIC92 VP Calais View build HERE Member since: March 8, 2015 Posts: 31]

VRSenator065 wrote:

Hey mate, I just came across this, this is exactly what you had in mind isn’t it? http://www.shop.gforce1320.com/product.sc?productId=367&categoryId=932 Has a full write up etc.

 

Ive seen that before always wondered if it would work on VP-VS subframes.

[vnssnvParticipant victoriaWhite, red and grey vn ss View build HERE Member since: March 2, 2015 Posts: 26]

If your handy with the tig. Have you thought about removing the irs completely and fitting a solid vn diff? All problems solved then.

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