einTier

OK, here's a weird situation. I replaced the 5 speed in my 928 racecar.

Everything went great, until I went to put the last bolt in the transmission -- the one that secures the lock collar around the input shaft to the torque tube.

My problem? The holes don't line up.

Basically, the hole/cutout in the collar doesn't line up with the space on the splines of the torque tube driveshaft. I can see spines where I should see a space. In addition, this cutout is about 5-6mm too far forward in the access hole of the transmission. I can get a socket on it, but if I could tighten it down, it won't clear the access hole to come back out. That doesn't mean I can't get the socket out, it just won't be easy.

Looking at the old transmission, it looks like the collar is too far forward. I'm wondering if the junkyard guys that pulled it didn't yank it off the input shaft just a little bit. What do you guys think? Should I try pounding it back on the input shaft? Did I get a different collar? Since it's a race car and I don't expect it to last another 10,000 miles, should I just re-notch the driveshaft to clear the bolt, bolt it up and hope for the best (knowing that I might be replacing a torque tube in the future)?


My racecar is 1979 Euro model, the car this transmission came from is a 1983 US model -- if that matters at all. The transmission shifts fine, other than the fact that it wants to "rest" on the 4/5 rod rather than the 2/3 rod.

I can submit pictures if it helps.

BC

The 78 TT is different, IIRC.

einTier

Looking through the Porsche PDFs, it would appear this is true. Different part numbers for the 79 torque tube than the 83. Wikipedia says "torque tube changed to accomodate longer gearbox.

Wonderful. I thought they were all interchangeable.

Now what?

Lizard928

The transmission has a different 5th gear which is the input shaft.

You can use everything you have but will need to take a drill and drill the hole that the bolt goes in.
Do not drill through the threads, but just up to them. This creates a notch for the bolt to pass through the splines allowing you to clamp it down.
I would not recommend driving without it clamped.

If you do not wish to do this, you need a manual transmission rear crossmember, and a later manual transmission torque tube.

Disclaimer added:
The proper way to do this is to use the later TT, and crossmember. If you do drill it out, there is a possibility of adding a stress riser, or the TT shaft could fail. Though this would simply leave the vehicle immobile.

BC

Its all coming back to me.

einTier

So, shaving off that little bit on the driveshaft won't cause a balance problem?

It would seem that the drive shaft is made of hardened metal, do I need special drill bits?

GregBBRD

You need the proper torque tube and proper rear suspension carrier.

If what Colin is suggesting really was the solution....why wouldn't have Porsche just done the same thing, instead of making new pieces? Way cheaper than making new pieces with different dimensions, right?

einTier

You would be correct. Unfortunately, reality says that I don't have the budget to make it correct. In the application I will be using this in, it just needs to be "good enough", not "perfect".

Rob Edwards

Racing? Lemons endurance racing? Seems to me 'good enough' in this instance would have to be 'pretty good' to not fail on you.

GregBBRD

I'm guessing you already own an axe and enjoy using it?

Dennis Aase (Aase Bros dismantling fame....great race car driver....great race team manager....great human being) tells many funny stories about people coming into his Porsche junk yard, looking for parts for their race cars.

"Well, it doesn't have to be perfect....it's only for my race car."

Where he would just kindly smile and tell them that he couldn't help them.

Dennis perhaps gave me the best advice I ever heard....back when I was just a youngster working on race cars:

"You better do the best work possible, with the best parts you can find....because when you are sitting on the witness stand facing the relatives of the person who just died in something you worked on or sold parts for....you can be 100% sure that he didn't tell him that it was his sole decision to use something inferior...or if he did tell them, they have conveniently forgotten being told."

You need a shorter torque tube and a different rear cross member....not an axe.

Lizard928

Greg,

While I agree getting all the correct bits to make it all a bolt in application is 100% best without a doubt.
But drilling that slot is not going to cause a catastrophic blow out. Is it optimal, absolutely not. But it is better than driving it without the pinch bolt at all.

einTier

Noted. I hear the forum consensus -- use the correct parts or buy a new transmission.

Looks like I won't be using this transmission.

danglerb

Early cars get scraped all the time, how hard is to get the right pieces?

Mrmerlin

it might take a few weeks or a few days to find the right parts.

Since your a member simply put a WTB post and see what floats to the top.

might be the next town over with all the parts you need,
Goodluck on your project

GregBBRD

I have not done this....so I will defer to you.

If the torque tube shaft doesn't bottom in 5th gear and thus put preload on the input shaft bearing inside the transmission....cutting an additional "notch" in the torque tube shaft should work fine.

Also not sure what happens with the "dimension change" from the transmission cross member not being changed....does this change the geometry of the axles?

One of the reasons given, for the "exceptional" life of 928 C/V joints is that they do not have angularity problems in two plains, like the 911 series vehicles, which "eat" C/V joints and axles at an amazing rate.