Solid Mounting Rear Subframe Confusion & Diff Friction Plate Question

[OLLIE_NZ]

Hi fellas,

Bear with me as I'm not sure how much sense my post will make. (I've done a fair bit of searching and not found any solid answers)

I'm just in the process of fitting a set of Driftworks solid subframe bushes to my '94 R32 GTR.

The subframe came out last night with little hassle and I spent the morning chopping out the old bushes so I could fit the new aluminium ones.

Now I'm noticing a problem, with the new aluminium bushes installed the subframe is going to sit too high. The studs that hold the subframe run out of threads before the nut can support the subframe.

Now my question is do I need to re-use the metal collars that came off the old bushes. not the ones that are pressed into the subframe but the ones that go over the stud on either side of the subframe.

I have heard of people having to use a spacer, as even with the metal collars that came off the car it still sits 6-7mm too high (see pics attached).

Quick drawing of the subframe showing the heights of the old factory bushes

To get the car to sit at the same height I'd need to machine up some spacers that are ~15mm thick, making some spacers up is no problem as I have access to Cnc lathes etc.

My question to you guys is, do I try and match the exact height that the subframe used to sit at or will it be of advantage somehow to have it sit a bit higher?

Next question is to do with the diff, as we are replacing the factory diff bushes with Powerflex ones we wondered whilst the diff was out if there was anything we could do to it to help us on the circuit. I've heard about swapping some of the plates around (see below quote) and also read about shimming it to tighten things up (which I've read both good and bad things)

Apparently from factory only 4 of the 6 friction plates are oriented the correct way to grip.

Another way to tighten it up, is to swap the other two plates around so all 6 are doing the work.

Has anyone got any pro tips?

Cheers guys

[Marlin]

Wish I could help you Ollie, but I can't mate, I prefer to keep mine soft.

Surely a subframe guru will step in sooner or later!?

[fatz]

you can flat mount them to the chassis

you will need spacers on the underside so that you dont run out of thread

down side of the flat mount to the chassis is you cant get the wiring through for the attessa, you need to massage anout 4 mm of a little corner of the chassi, its very tight on the rear attessa lines, you need to dick around with the hand brake cable as the 2 inches makes a diffrence and it shall be noisy as fcuk

[fatz]

upside is you can run the car 2 inches lower withought f**kig the geometry

[Noddy]

It does mess with geometry. Be prepared to loose lateral grip as the roll center gets lowered. If the car is lowered as well..... it is even worse.

[BOZ22N]

I thought by solid mounting the sub frame to the chassis would give better traction? and the lower roll centre would assist with handling?

[-Jimmy-]

Yeah that is correct. Hope you come up with a solution.

[Risking]

In a skyline the COG ( center or gravity) is higher than the roll center. If you lower the roll center and leave the actual COG you will increase the roll couple and create body roll.

Go the other way you will shorten the roll couple and reduce the roll couple, sane goes for moving the actual center of gravity.

By raising the subframe you have lowered the roll center ( its a relative measurement to the ground) and also lowered the center of gravity by the same amount. Roll couple remains the same.

The reason they loose mid- exit corner grip is due to the floor pan of the car and the location of the pins. The angle of the subframe changes and you actually flatten out the lower control arm reducing anti squat.

Normally I'd space the subframe accordingly to try and maintain the original anti squat angle and then lower the

front with corrections to the front dive angles for the same reasons.

I've been contemplating running a small suspension day workshop to demonstrate on a few jigs I have what actually happens when we move things like subframes. Might be of interest to some people who contemplate doing this sort of thing, knowing the basics would help.

[Risking]

Go the other way you will shorten the roll couple and reduce the roll couple, sane goes for moving the actual center of gravity

That's meant to say reduce the body roll not roll couple

[fatz]

so the rar mounts nees a 2mm spacer to maintaing the cradle angle?

[Risking]

The subframe to top of bush height normally is

Front 14.5mm

Rear 16.5mm on an r32

If you wedge it straight up to the chassis you raise the rear up by 2mm and reduce the anti squat angle by 5degrees I think from memory.

From what I've seen r33 subframes are the other way around 17mm front 15mm rear so you increase anti squat angles.

Late model S chassis bushes are

Front 15.5

Rear 13.5

All those measurements are ladened with the vehicles weight sitting on the subframe

Pete put a 4mm spacer between the rear and the chassis. Little more anti squat than factory unless you fitted an r33 rear subframe?

Pick up points are different.

[savant]

Even after all that i'm not sure what we're supposed to be doing! Is it fair to say we should be doing a 4mm spacer at the rear, nothing at the front?

Given the 9mm lip on the solid bushes, this will mean the subframe is raised around 17.5mm at the back and around 19.5mm at the front? We can make up any spacers to suit so just trying to do "whats best" I guess.

Edited June 17, 2011 by savant

[hrd-hr30]

By raising the subframe you have lowered the roll center ( its a relative measurement to the ground) and also lowered the center of gravity by the same amount.

I think you've got it the wrong way around.

All other things being equal, if you raise the subframe you raise the roll center and Cg is also raised slightly by the higher cradle and diff.

Alternatively, if you raise the subframe AND lower the car by the the same amount, then the RC remains the same as before, and the Cg is lowered.

[Super_Dude]

I thought the r32 had to much antisquat anyway? Wouldnt this help?

[fatz]

ill give you a bell about it brad

[BOZ22N]

So confused arrr

I will have to do some measuring and reading I think. I first thought to solid mt the sub frame and lower the rear suspension by 5 mm. Don't you put the subrame spacers at the front when you want more traction?

[OLLIE_NZ]

Willie (savant) and I are hoping to put the subframe back in today but have read so many conflicting threads about it we still don't feel confident about how to space the subframe/ lower or higher at the front etc.

[Risking]

ill give you a bell about it brad

No prob pete.

I've spent a fair wack of time on duncan's car lately so there is probably a whole heap of things you'll want to do to yours in the front end geometry as well.

Your always going to read conflicting things on the net. Reading won't help you at all.

My advise would be find someone who builds/modifies chassis, has the right measuring equipment to take some guess work out of messing with geometry and work with them to improve the car, instead of trying to do it yourself and going backwards......

duncans basically standard engined GTR running tiny old tires lapping in the 6's at Wakefield.

It's got no power, but is sorted and almost ideal suspension wise. It still remains stock to look at as well. Garrantee his not read the Internet to get the information to make it so quick though........

[260DET]

I thought the r32 had to much antisquat anyway? Wouldnt this help?

Yes, generally speaking anti dive and anti squat are not good for a circuit car because they reduce the sensitivity of the suspension and its reaction to the track surface. Heavier springs than OE on a circuit car usually make both the antis unnecessary anyway.

Edited June 18, 2011 by 260DET

[OLLIE_NZ]

So fellas, currently in the workshop on the lathe machining 2 x 4mm aluminium spacers for the rear of the subframe.

From our readings we've concluded that we want the rear of the subframe to sit 2mm lower than the front (which is what the spacers should provide.

Any thoughts on this Brad?

Cheers, Ollie.