197 replies to this topic

[fuzzypumper]

Yes ^^^  that is simpler because to swap the rack over your gonna have to decouple the steering shaft anyway and to swap the upper control

arms your gonna have to unbolt and semi detach the K-frame as well to get the arms over to tower.

Plus with UC K frame you will also get the advantage of the heat shield cover for the steering flexi coupling.

Swap the whole lot.

Edited by fuzzypumper, 20 April 2013 - 11:14 AM.

[A9X]

Do nothing
If you are confident it's unmolested.
Bolt the complete 1980 k frame in
Add new coils and shocks
Get a quality wheel alignment
Enjoy

[A9X]

All the talk is changing LH and non A9X LX UCA positions to replicate A9X or LX RTS positions

As yours is an 80's UC , we can safely presume you have the latest in RTS geometry.

So bolt in and enjoy

[76lxhatch]

You could still re-drill them if you wanted, it does provide a little improvement in camber gain during suspension bump. Based on my own measurements it doesn't have any significant ill effects on bump steer so safe enough to do. However its not probably not something you'll really notice driving it down the street so you could just as easily leave it as-is.

[76lxhatch]

Probably not quite that much, closer to 25mm; you can't really get it wrong if you use the upper arm pivot to mark it. It should sit at the lowest point while still remaining flat against the cross member and allowing space for the shims to sit flat in between them. Make sure you don't change the angle between front and rear holes, i.e. they should be an equal distance lower than the originals.

[Ando]

Without going through the whole thread again.. I have all the parts to either build an A9X front end suspension design or I could restore a UC RTS front end.. The two sets of wheel combo's I can run will have 285 40 15 Yoko's on 81/2 Simmons & 91/2 Hotwire front rims.. They will work on either front end set-up.. I'm building the car for mainly street & some circle track fun so still a little undecided which front end geometry design is best for my application.. Any thoughts welcomed..

[Bigfella237]

As I recall, the only differences between the A9X and UC front suspension are:

 

1. the location of the UCA pivot point

2. the stub axles

3. the steering arms

4. the bump stops

 

No 1 can be changed by re-drilling the holes in the K-member, earlier in this thread it was stated that lowering the mounting point will slightly improve the camber curve and bump steer on suspension dive, but the biggest affect it will have is to dramatically lower the front roll centre, which is not necessarily a good thing unless you're also able to lower the car's centre of gravity (which drop spindles will help with) or mass, or preferably both. The farther the distance between the RS and CG, the greater 'leverage' the mass will have as the CG changes, in layman's terms, the more body roll you will have.

 

Stub axles are another compromise because of the lower included angle designed into A9X/Hx stubs (the included angle accounts for most of your KPI together with static camber), the lower the KPI the greater the scrub radius, which is most likely terrible already if your rims have a negative (outward) offset. The best option here would be a hybrid stub axle which retains the Torana stub's included angle but raises the spindles like an A9X and suits the A9X/Hx brakes (bigger wheel bearings would be a bonus too).

 

The steering arms need to match the UCA / stub axle combo, if using A9X/UC UCAs then you would either use the UC steering arms with the UC Torana stub axle, or the A9X (Harrop) steering arms if using the Hx stub axle.

 

The compression bump stops I believe were extended on the A9X because of the bigger diameter wheels and drop spindles.

 

So basically everything is a compromise, the brake setup you want to use may dictate the stub axle you have to use, which will also dictate which steering arms you use, but if it was a question of paying Harrop the big bucks to run the A9X stubs, or having the lower scrub radius of the Torana stubs, I know which one I choose, then I'd put the money you saved on the Harrop arms toward a Hoppers brake kit (which suits the Torana stubs).

 

But that's just me...

[Ando]

Thanks Andrew.. Great read.. I think what confused me in the past was the lx rts which I'm dismissing altogether..

 

I have mocked up my steering & front brake options..

 

The first 2 pics are the a9x/hx 1 ton stubs, harrop steering arms, 4 piston wilwood calipers 11" rotor & uc upper control arms..

 

2nd pics are the torana stubs, uc steering arms, same wilwood brakes, & uc upper control arms..

 

So it really come down to which is more suitable for my application & regarding roll centre, scrub radius, wheel offset, tyre width etc..

 

I will be running 285 40 15 tyres on the front on both sets of wheels.. 91/2 hotwires - 125mm backspace & 81/2" simmons - 120mm backspace..

 

I will be installing power steering so no problems turning these tyres lol but I need to decide which will be better without really knowing at this point..

 

So which way?? Yes I know I'm spoilt for choice lol

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[Toranamat69]

Go the Tonner stubs, copy the A9X setup with top control arms lowered and Harrop steering arms.  Use the UC top control arms.  Especially if you already have these bits.

 

As you can see, far more top balljoint room to the rim.

 

It gives slightly better geometry going the A9X setup as it raises the front roll centre when you lower the top arm mounts (you want this in a torana) and improves the camber curve and helps with front tire wear on the outside edges.

 

Watch your static camber if you are lowering the car in the front, you may run into trouble getting back under -1 degree.

 

The scrub radius will be what ever it will be with each setup, but if you have the wheels legal offset and under a set of A9X flares, it will be fine.

 

Check with your engineer, they may let you go wider offset on the front with the H series stubs.

[Bigfella237]

~ 91/2 hotwires - 125mm backspace ~

 

Great photos Ando, that really illustrates some of the clearance issues.

 

So it looks like a 125mm backspace is just about the maximum possible for a front wheel regardless of the overall width, with 15" rims at least, you might be able to squeeze a few extra millimetres with a larger diameter rim as it would give a little more wiggle room around that top ball joint?

 

I don't suppose anyone you know has a 17" or 18" rim you could try on with roughly the same backspace, I'd love to see photos of how much difference a larger diameter rim would actually make?

 

~ it raises the front roll centre when you lower the top arm mounts ~

 

You had me thinking M@ as I'd previously stated the exact opposite, but you are correct...

 

 Roll-Center-with-Lines.jpg   75.03K   6 downloads

 

So lowering the UCA pivots raises the RC; and

extended upper ball joints would also raise the RC; and

extended lower ball joints would raise the roll centre as well as raising the spindle height (lowering the car)?

 

 Roll-Center-in-Dive-with-Li.jpg   79.9K   6 downloads

[axistr]

I agree with all of the above. But the higher the KPI the better the return to centre is and better the scrub radius especially with wider rims with negative offset. Higher KPI and more positive caster is the go, combined with the top control arms in the lower position to give a better camber angles through hard cornering. For every day driving either the UC or A9X set up is ok so long as its set up correctly

 

But going back to basics you can have the perfect set up and the wheel alignment can let you down every time. And remember the back end alignment is just as important as the front. I can easy spend 4 hours wheel aligning bad handling cars and the outcome can be astonishing to say the least. As I have said before sometimes its as simple as tyre pressures and or bad choice of rims & tyres.

 

Torana's also respond well to good adjustable shocks and heavy duty springs without going to firm, the more they float around the more input you need to control them. If we were designing a new Torana front end steering geometry from scratch it would be an entirely different situation, so basically we have to make compromises.      

[Bigfella237]

Forgive me if this has been asked before, but seeing as we share the same upper and lower ball joints as a lot of early Chevy stuff (Camaros etc.), has anyone looked at getting a pair of custom stub axles out of the US?

 

A quick google shows a huge range available and the most expensive I've found so far was around US$300 for a pair, heaps of different drop height options too but nobody seems to mention the included angle?

[yel327]

Ando, have you looked at the SCW (Southern Chassis Works) complete crossmembers with brakes, power steering rack etc? I'm going to invest in one for one of my HK's.

[Bigfella237]

Southern Chassis Works has now been owned and operated by Curley’s Rods & Customs for the last year, In that time we believe our IFS front end units have become the best on the market.

~

Starting at just $4500 for complete IFS units with man rack, brakes and adjustable QA1 shocks

 

http://www.curleys.com.au/

 

http://www.curleys.c...uthern-chassis/

 

Also see this thread: http://www.gmh-toran...ifs-front-ends/

[Toranamat69]

I'm watching closely how you go with 285's under the front, What tire size are you going to use?

 

I am about to embark on getting 275's to fit mine so I hope to learn a trick or 2.

 

Matt

[Toranamat69]

I reckon you may need steering stops like the UC has on the lower control arms too, so either copy them or use UC ones. 

 

The Harrop steering arms don't have the lumps on the side so you may need to make the stop a little bigger.

[StephenSLR]

The only thing is I can't see these photos which I think would be of great help to me. Any idea why I can't?

 

As you said, it's an old thread. What happened was the original posters put up the pics on Photobucket and either deleted the pics to make room for more, no longer have a Photobucket account or perhaps the photos expired on Photobucket. I found this out once when I hadn't logged in to Photobucket for a long time and when I logged back in the photo links regenerated and appeared again.

 

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