Rear IRS Suspension Question

[evilC]

Originally Posted by fastbacker

My 911 track car's rear tires are 2.5" wider than the fronts making the rear track about 5" wider. The bug starts out with a 1" wider front track so with the proposed 6" added to the rear both cars would have the same stance. This is a great set up for the 911 so I can't see why it wouldn't be for the bug. But hey, I don't know.

Agreed. The 911 is in very simplistic terms a more powerful bug. The racing 911s all had IIRC wider rear than front tracks that stablised the straight line running.
If Steve C read my reply fully he will have noticed that I commented on the front suspension that was in addition to the subject of the thread. The WHOLE suspension design is important not just one end and I would have expected the front track to be increased in additon to the rear.

evilC

[fastbacker]

OK. So I think I'm going to look for some wide track aluminum 944 rear arms and brakes (along with t-bars, spring plates and axles). The information out there is a little confusing as it seems there are different versions of the same width arms (?). I did come up with this info on aluminum arms via some searching:

U.S. Models:
==========
86-89 944 S
==========
86-89 944 Turbo
89-91 944 S2
==========
89 944 Turbo S
90-91 944 Turbo
==========

Will all these options work to widen the track by 3" per side. Are all the brakes used the same? All things being equal (if so), are some more easily obtainable?
Any pros and cons in comparisons?

Thanks-
Craig

[wrenchnride247]

ALL 87 and later arms are the same. Four pot brembo's fit.

[evilC]

And besides the rear bearings are so beefy that Porsche racers can regularly use up to 50mm spacers to further increase the track. don't worry get some alloy arms and then fine tune the track with the available spacers.

evilC

[fastbacker]

I just sourced a complete 86 narrow track, aluminum arm, 4 piston caliper rear suspension for $400 usd. It comes with brand new bearings and, as luck has it, the pivot bushings removed. Everything's included - even the torsion bar housing and bare axles.

This seams to be a good deal. Right?

[evilC]

Sounds like it contains everything you are going to need including the inner pivot brackets that you will need to weld onto the original torsion bar housing. Make sure you have the handbrake cables as well as the outer cables fit the alloy arms and the VW ones don't. With the inner cables you use the VW ones but have two options - a) use the VW end and buy new converter swan necks or b) Cut the VW end off and braze the Porsche end on (I did as it was for me a no cost conversion). BTW if you need new handbrake shoes buy the BMW ones - they are 1/2 price of Porsche ones and cut a notch in the end to match the Porsche unit. Use the Porsche dust shields for the discs as they also keep the dust away from the handbrake side of things. The dust shield tabs are usually in poor condition so just pop rivet some new tabs on.
If you've got 4 pot calipers then you wil normally need to run 16" wheels but 15" ones can be used with some 40-50mm Porsche spacers.
Use the Porsche torsion bars they will be either 23.5mm or 25.5mm (if you're lucky) they add some welcome stiffness to the rear. Use also the Porsche spring plates that will give full adjustability together with the alloy torsion bar end cap suitably cut down. The alloy end cap will require the Porsche bush that is wider than the VW one but this will cause problems with the heads of the eccentric adjusters on the spring plate fouling the forged damper arm. I over came this by adding a 5mm PVC thick 'washer' to either side of a standard VW poly bush. The diameters of the washer and the bush should be the same. This spaces the spring plate away from the torsion bar tube to allow the eccentric adjuster to clear (by ~1mm!). The eccentric adjusters are worth having as they control camber and toe-in. You can use the VW spring plate but it will need redrilling to connect to the alloy arm - that IMO weakens the spring plate so on balance the Porsche one with mods work best.
Does the axle come with AR bar if so, it will be a very welcome addition. It should be 16mm and you will have to fabricate new brackets for the VW torsion bar tube or cut off the old brackets and weld them on.
Did the rear axle come off an auto gearbox car? If so, then the driveshafts will be different lengths. Get equal length driveshafts. Keep the CVs as Porsche supplied and change the IRS gearbox flange for a 100mm one from a Trekker/181 - they are available new = £80.00/pr. Hopefully, the CVs will still have the bolts intact with them. If not you will require the retainer plates and new 12.9 grade socket head bolts.

All of that and more is the learning curve that I went through. My axle cost me complete £67.00 then added 4 pot calipers £110, equal length driveshafts (original was a 924S autobox) £60/pr and new bearings/seals £54/pr so all up it was £291 or $436 at todays rate so your $400 is about right. On top of that cost was new discs/pads (never use the old ones), handbrake shoes, driveshaft output flanges and all new bushes.

evilC

[fastbacker]

Wow. That's some great info. Thanks EvilC. I am curious, though, on the part where you talk about welding the 944 arm's pivot bracket onto the vw torsion tube. I thought that if you replaced the the 944 arms bushing with one from a beetle it would bolt right up to the stock beetle mounts.