trailing arm question

[Drago]

Originally posted by gestalt1
Drago, you could buy axle assemblies for an SC and replacement inner CV joints for your 69. replace the inner CV on the new axles with the 69 type CVs.

After a little research here on Pelican I've found that CV joints for the '65-'71 models years are NLA...I have to purchase the entire axle assembly.

CV joints are available for the SC control arms though. Does simply changing the '69 axle assemblies outer joint to an SC unit solve the problem though? From the diagram:



It looks like the part that the bolts thread into would also need to be replaced (just to the left of the CV joint in red), which of course I can't find in the Pelican catalog.

[Drago]

Pump the bump.

Anybody been there/done that with regard to the above problem?

[911pcars]

Originally posted by Drago
OK, I read Sherwood's article and I have one question:

I'll be installing later style SC control arms on my '69T w/ the CV joint 10mm bolt attachements to the inner and outer drive flanges. Since the control arms are SC units they have the 8mm attach bolt provisions.

What, if any, solution do I have? Does anybody make CV joints with 10mm bolts on the inner flange and 8mm on the outer?

The author of the article states that he did this conversion on his '69 but he doesn't state what his solution is to this problem (short of transaxle replacement or using '74 (only) control arms).

Thanks in advance for any and all responses.

Drago,
One thing I regret not covering in that article was information on adapting the various CV joint. I realized later on this would have covered all the issues in converting to alloy control arms. However, there are several iterations of adaptation depending on the MY control arm, CV joint type and gearbox, probably worth another article.

I suppose I took the easy way out with the simultaneous installation of a 915 gearbox. This resulted in a harmonious match with an SC axle assembly.

Yes, individual 901 CV joints are NLA from the usual sources, but it appears Foreign Intrigue carries them:
http://www.foreignintrigue.com/search.asp?radiobutton=2&search=CV+joint

However, it looks like one axle assembly (w/2 CV joints) is cheaper than a single CV joint. If you need 2 CV joints, this is probably the way to go.

These links contain some solutions:
77 to 73.5 aluminum trailing arms swap
Do 87 trailing arms work on a 72???? and other ?????

Sherwood

[jluetjen]

What I did on mine was get couple of item 12 from a '76, and then had the diameter of the area just outside (to the right) of the splines in the attached picture reduced by 1 mm.



I think that I've heard that the later 915 gear boxes have a different splined pattern on these flanges which will then cause mating problems with the diff. In which case you may do better to replace the entire axle (including the outer stub axles that go through the trailing arm) with a set from a car which uses the earlier style 915 box, like a '76. Be sure to do a trial fitting because I found that my some of the stub axles will interfere on the trailing arm.

[Jeff Higgins]

Originally posted by 911pcars
However, it looks like one axle assembly (w/2 CV joints) is cheaper than a single CV joint. If you need 2 CV joints, this is probably the way to go.

Sherwood

Agreed. The CV joints on any given axle assembly are the same on the inboard and outboard ends. So with one donor SC axle assembly, with both ends in tact, it seems to me it should be quite easy to swap out the outboard CV's on your existing axles and wind up with a bit of a hybrid. 901 pattern on the inboard end, newer SC pattern on the outboard. These things are very easy to take apart; it's just one hell of a greasy mess is all.

The real question is whether or not the old and new axles have the same splines. There is a c-clip that holds the inner CV joint over the splined axle end. Pop that c-clip off, and it would be a snap to swap them. Or, if the splines are in fact different, are the inner CV joint pieces otherwise the same? In other words, would an early inner CV joint work with the later outer, with the same ball size and such? Hopefully the splines are the same and that is the easy answer; it would make me nervous to mix and match internal CV parts.

[jluetjen]

Jeff;
I tried taking that approach when I upgraded my trailing arms and found that the design (spline count and diameter?) of the axles are different, so you can't put a 901 stub-axle onto a '76 axle. I suspect that the same will be true for SC axles.

- John

[Jeff Higgins]

I was afraid of that, John. So much for the easy answer.

Drago, if you are doing this to get bigger brakes, the "M" calipers that are on there now should be fine for just about any purpose. If you are looking for mounting points for drop links to put a sway bar on it, the Weltmeister that it sounds like you have lined up doesn't use the mounts on the banana arms. It goes to the eccentric bolt on the spring plate / banana arm interface that is used to set camber. So maybe 5-10 pounds a side just isn't worth the level of hassle to change all of this out. Especially when you consider the shock tower clearance problem as well.

[randywebb]

That reminds me of a question I've had for a while...

Do all years of the Al arms have the same calipers on them?

- that's the 911 arms, not the 930 arms.

- I know the Carrera pads are a different thickness, but isn't only for the fronts?

[911pcars]

Randy,
The rear calipers on al. arms are either narrow A-type (20mm rotor) or wide A-type (24mm rotor) installed on post '84 911s. Both use the same brake pad as the front brakes. The exception are 911s/early 930 turbos with S al. front calipers that use a thicker pad, but the same sillouette.

Sherwood

[Walt Fricke]

I think Sherwood is in his cups. But all our fingers slip from time to time.

He knows as well as anyone that all the aluminum 911 banana arms have the same 3" bolt spacing for bolting on an M caliper (not an A, which is exclusively the province of the front strut). I'm pretty sure (but the convenient parts reference doesn't give a part # for the whole banana arm) that all the aluminum banana arms are the same (other than the previously mentioned change in sway bar mounting). And that the wider 3.2 rear rotors were accommodated by widening the M calipers.

My race car (a '68 tub) came to me with the LWB steel bananas. The shock towers had been modified to accept coilovers. The steel bananas had been modified by welding on a lug to the rear of the stock shock mount, and that was where the shocks/coilovers were mounted. I think that was done to clear the Spicer U joints that were used on it (I replaced with CVs pretty quickly - U joints are not good with the angularity involved). But when I switched to the aluminum bananas I don't recall having any problems with the shock mounts. I know (from reading) that there was a change in the top shock mount location at some point, but doubtless the work done to accept the coilovers gave me enough clearance). So I have been in blissful ignorance of any work needed on the banana for certain updates. Can one make up for the "wrong" upper shock mount by moving the lower one out some with some machining?

I really like the fact that the stock mount is unthreaded for a ways. Makes it easier to get the bolt started, as it slides in and holds things before you need to get a wrench on it.

Drago: the thing to the left of the red colored CV in the diagram is just part of the CV boot assembly. Some are two piece - steel flange and separate boot that goes over it. Some are one piece -
the rubber boot is permanently attached into the steel part, which is rolled closed around its bottom. Getting a boot is the least of your design concerns. Once you know what CV you will use, then you can just get the right boot.

Myself, I like the two piece kind of boot assembly. When the boot rips (as it eventually will), you just get another boot and keep reusing the flange. I use a one size fits all boot from JCWhitney. Inexpensive, works great. Just cut off a couple of the biggest accordion bellows parts and it is ready to go.

Walt Fricke

[911pcars]

Hi Walt,
Thanks for the mild-mannered correction. Would it suffice for me to say, "I meant M, not A"?

Sherwood

[randywebb]

OK, so my '77 Al arms (likely) have the narrow M-type (20mm rotor), assuming nobody futzed with 'em.

[Walt Fricke]

I'm missing something here: the arms don't have rotors.

The hubs do, but the rotors all interchange - fat, thin, all fit on the hub. Of course, the caliper has to fit the rotor. But the '77s had the 20mm thick rotor per Aichele's table, and whatever M caliper you have will bolt right up to it.

Having the proper piston diameter could be a different matter - over the years there were at least two rear caliper piston diameters. And then there were the front M calipers, which could be bolted onto the rear by mistake (pistons much larger).

You never know about references, though. Aichele would have one believe that the '81s were the first to get the thicker 24mm rotors. But the Porsche Parts Reference book says (in effect) that the change happened where we all thought it did - in '84.

Walt

[Drago]

Thanks for all the great information guys.

Alas, Jeff is right (again). Not worth the hassle for ~10 pounds. Easier to loose that weight and more off of the driver anyway.

Someday the car will see a 915 and maybe then I'll revisit the aluminum control arm upgrade.

In the mean time she's getting 22mm/29mm front and rear torsions, 22mm and 19mm adjustable front and rear sways with Koni Reds all the way around.

I plan on driving the hell out of it!

[Scooter]

Originally posted by Drago
In the mean time she's getting 22mm/29mm front and rear torsions, 22mm and 19mm adjustable front and rear sways with Koni Reds all the way around.

And......

you are going with SC front struts with the 3.5" spacing for your SC brakes, right?

[jluetjen]

Originally posted by Drago
Thanks for all the great information guys.

Alas, Jeff is right (again). Not worth the hassle for ~10 pounds. Easier to loose that weight and more off of the driver anyway.

Someday the car will see a 915 and maybe then I'll revisit the aluminum control arm upgrade.

In the mean time she's getting 22mm/29mm front and rear torsions, 22mm and 19mm adjustable front and rear sways with Koni Reds all the way around.

I plan on driving the hell out of it!

Keep in mind, taking 1 mm off of a pair of 915 transaxle output flanges is most likely less then $20 at your local machinest. Buying a pair of used 915 flanges is pretty cheap too. Just because it requires cutting a little metal should not stop you.

[Drago]

Originally posted by jluetjen
Keep in mind, taking 1 mm off of a pair of 915 transaxle output flanges is most likely less then $20 at your local machinest. Buying a pair of used 915 used is pretty cheap too. Just because it requires cutting a little metal should not stop you.

That is not what is stopping me. I don't mind cutting chips at all. It's just that I'm pretty much ready to tear into it minus some 'A' calipers and one small Pelican order for miscellaneous stuff like ball joints and tie rods.

The extra work involved in swapping the control arms, at least at this point, doesn't seem worth it to me.

Anyone have a set of 'A' calipers they'd like to sell?