Type Three Tuning Page -- Rear suspension system
Please select the area of interest:
Check your lower shock mounts for cracks.
I had the same crack on both shock mounts. Luckily, they are easily fixed by
welding over the crack. Anyone with a MIG welder, like a muffler shop, can do
> I have a Swingarm rear subframe that has IRS trailing arm mounts welded on, IRS trailing arms,
>late model brakes, with IRS spring plates (the double type), IRS torsion bar cap etc. Do I use the
>irs torsion spring with this setup?
>Seems to me the swingarm torsion spring is the wrong length for the double springplate and IRS cap. I don't have the
>swingarm springplate and torsion bar cap to compare them with the IRS parts. Any ideas appreciated.
You are correct, they are different lengths. The length for the IRS ones are 676mm. The later single plate spring plate and
matching trailing arms are interchangable with the early IRS double plate sets. The torsion bars are also interchangeable
between T1s, T3s, 924s and 944s. There is 3 lengths of torsion bars and maybe 2 or 3 diameters (I only have the specs for a
swing axle car and the factory lists 3 diameters for them) of the longest bars which are used in the IRS. Remember that they
are left and right and you need to get them back on their respective sides.
Now the real fun Dark Side stuff begins!! Did you catch the Porsche model numbers thrown at you in the last paragraph? Yes,
you are getting an inkling, maybe? Yes the brakes off the back of a 944 will fit on a T3!!!!!!! It does widen the rear
track a bit so it really is difficult to get any kind of wider rim/tire combo under the fender with out rubbing. Just thought
I would get ya revved up and then dash your hopes of Joe Average doing this swap. Not for the faint of heart or mechanically
challenged. I have started down this path (and may the force be with me!) and have narrowed trailing arms on my Notch.
The following is an edited compilation of replys by Shad Laws of LN Engineering - Aircooled Precision Performance, http://www.lnengineering.com:
> The rear end of my car is not as pert as I would like- its all a bit saggy
> and the wheels kind of splay out a bit too much for my liking. Where the
> torsion bar housings poke through the oblong shaped bolt on plate on the
> side of the spring plates, they are not central in the hole but nearly touch
> it at the top.
You suffer a common problem: Your trailing arms are worn out.
The camber of your rear suspension is ~80% determined by the trailing arms.
The bushings on the inner end of the trailing arms don't go bad very easily,
although sometimes the pivot bolt falls out (make sure it's still there :-).
What usually happens is that with age, the weak little VW trailing arms bend.
The spring-plate bushings go bad with age very often. However, the thing
they're most responsible for is toe. It is a good idea to replace them, as
the ability for your car to maintain a constant toe will GREATLY help
handling, but it likely won't help very much with the excessive camber problem.
If you want, you can get early (83-85.5) 944 trailing arms. They are the
identical package size, track width, stub axle configuration, bearings, etc.
as VW, only they have extra interal reinforcement and are 10-15 years younger.
> So how do I measure/tell if they are really bad? Or should I just assume
> that they are because of the sagging?
First check the pivot bolts and make sure that they still exist. If they
still do (and I'm assuming they do :-), then just get new arms. When you
take off the old ones, take one old and one new over to a table. Place a
bolt/rod/etc through the pivot ends, then put the outer-most face of the
trailing arms (the part where the wheel would go) flat on the table.
Compare old to new... the difference in the angle of the bolt (that is up in
the air) should be SOOO notable that your naked eye will see it and you'll
exclaim "Holy crap! No wonder my camber sucked!" :-).
When you disassemble the rear suspension, it is DEFINATELY critical to get
it realigned. Camber and caster are next to impossible to adjust, but toe
is not. That's what the slotted bolt holes in the spring plates are for.
And, if major adjustments for more toe-in are required, you can change the
positions of the shim washers (this is very rarely required). If you want
to change the ride-height of your car, change it BEFORE toe adjustment.
If the rear toe is set incorrectly, expect horrible handling during turning,
especially at high speed. It won't be so bad that you can't drive it down
to the alignment shop, but it will be so bad that you will notice the
difference when it's fixed.
I set mine to zero toe, and would recommend the same for anyone else. Even
1/16" of rear toe out is noticeable...
> So would you recommend changing just the outers or doesn't that make sense
> without the inners as well? I think I'll try these first and see what
Do both. Taking the trailing arms out is 80% of the work, anyway.
The only problem you may hit with the 944 arms is the bolt pattern. IIRC,
it is identical to a '71-up T1 pattern. To make it work for the T3, IIRC,
you just have to drill one new hole in the spring plates, or alternatively
drill and tap one new hole in the trailing arm (IIRC it's that one bolt
closest to the front that IS threaded...). Or, if you're like me, you use
the other three bolts and leave out the fourth, increase the torque spec,
and consider the loss of the fourth bolt an excuse for more clearance
against your way-too-wide tires :-). Remember that all '71-up T1's, 924's,
and 944's only had three bolts... just 68-70 T1's and T3's seem to have four.
> Shad, can you tell us where the arms tend to bend?
I haven't tried to accurately measure anything, but there is no obvious
single point of bending. The main length of it just seems to fatigue and
bend little bits over time.
If you want a really rigid trailing arm, you can get 85.5-86 (~0.5-1" wider
track per side) or 87-up (~2"-3" wider track per side) 944 arms. They are
solid cast aluminum :-). But, if you do, you have to convert all the 944
stuff over. The stub axles are shorter (i.e. outer CV joints are further
outboard in the car) and use a totally different spline pattern to the
drum/hub/disc/whatever. The 83-85.5 ones have no track width change and
have the identical spline pattern for the drum/hub/disc/whatever.
> Is it safe to assume that such bending would be more common in squares where
> they might have been subjected to more load, or in other cars that were driven
> roughly, as in off-road, or from Sandy Eggo to Tijuana?
Yah, and excessive anti-sway bars, heavy shocks, and the like probably don't
help either. Especially not if you force the car to handle like a Porsche
on a daily basis. I'm screwed :-).
The only weak point of my suspension right now is the front. Unfortunately,
to get much better, it all has to go into the trash...the twin trailing arm
thing isn't so hot.
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The 944 is a Porsche. The engine is based on the 928 engine (and the 928 is
a true Porsche by any definition...nice piece of machinery). Many parts of
the car were changed and updated, and the 944 went from an over-hyped VW to
a true Porsche. But, some parts kept their VW heritage...the rear vented
disc brakes (and internal drum e-brake) are a DIRECT bolt-on to any T1/T3
IRS VW. Yes, direct...all you need to do is get 944 cable ends to put on
your stock e-brake cables. Very odd :-).
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