When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Using heavy duty clamps can hasten the split TTs demise. This is due to approximately one quarter inch of material having been removed from the split area. So when you try clamping it, you will move the tube's ID the opposite direction from the split which will cause a misalignment of the drive shaft. Too much and it goes bad quicker, not enough and you haven't done anything. Its that "just right" place which is very difficult to achieve unless you have the tube out of the car and do a lot of measuring as you tighten the clamps. And the clamps can loosen when the car is being used since they will be sitting right above the heat from the exhaust.
John has documented a viable solution and I believe he would be interested in replicating it for others as needed.
Attached is a picture of a fix we engineered to take care of this problem in the early days. However the risk/reward equation was weighted too far to the risk side so we decided to not go forward with it. This picture shows the split tightened too much actually from what is optimum.
Yikes - I've been running with clamps tightened "by feel", with no care taken whatsoever as to the tightening torque, for five years, and many, many brutally hard track miles. Have I just been lucky all these years? Or maybe they've worked their way loose to the point where they aren't doing any good, but not doing any harm, either. I'll check them next time I'm under the car.
I'm sure John would have many customers if he decides to go "into production" with his solution.
Could be you hit the "just right" tightness with the clamps. If they are still tight and all seems okay so far, would advise to leave them alone.
Most important is that you are aware of the problem with split torque tubes and of your options in the future if you want to keep your 968 when it's time to change out the TT.
Hopefully that's the case. And yes, I've been aware of the problem with the spit torque tubes for many years (which is why I applied the clamps five years ago), but this thread really brought it into focus. The options are extremely limited, though - I even toyed with the idea of eventually turning my car into a mid-engine car! But the tube normally containing the torsion bars (mine are removed in favor of coilovers) to which the inner trailing arm attachment points are welded is right in the way. So, it appears that John's fix, should he decide to build them for "customers", is the only game in town, at least for a track car.
Very informative and overall great thread. Thank you. Had a question about the affect, relating to vibration issues, of putting a solid TT in a split TT car. Any ideas of the affect of this additional vibration on these cars without changing over to a heavier crank?
Looking at your image of the split TT:
Originally Posted by Isaacsracing
Porsche 968 Torque Tube Repair
Notice the two "half butterfly" braces in the image. One just before each end of the split. Would guess these are made of tubing that has an ID that is the same dimension as the OD of the TT.
I would love to hear thoughts about taking a non failed split TT and welding a full butterfly brace in the middle of the split and replacing the bearings with Black sea bearings.
This is probably way too simple, because if it worked, somebody would have already done it, but why not insert a thin, rectangular piece of metal the same width as the width of the split in the torque tube, inside the split, tack welding it into place, and securing everything with a series of clamps (maybe five total) along the length of the split?
Hi Spark1,
Thanks for your questions and comments.
Quote: "about the affect, relating to vibration issues, of putting a solid TT in a split TT car." I really won't know if any noticeable vibrations are presented by putting a non-split tube into a car that had a split tube. In fact, being a race car with solid mounts, monoballs, and a loud exhaust, I can't imagine ever noticing any increase in vibration over all the other vibrations occurring (but the car isn't assembled yet!). Personally, I don't think that anyone would notice in a stock 968 either though. Remember that Porsche stopped splitting the tubes mid-1994 for the final year and a half - I think because they determined that a split was a detriment and not an advantage.
Quote: "without changing over to a heavier crank" I'm not sure what you are referring to. A heavier flywheel? Can you clarify the question?
Quote: " I would love to hear thoughts about taking a non failed split TT and welding a full butterfly brace in the middle of the split." That wasn't an option for me, because my tube had already enlarged. My thoughts on welding are that the metal moves and deforms anytime you weld something. If you start with a good split tube and try to weld on a brace of some type or try to weld up the seem, you need to be able to control the expansion and contraction of the metal. The act of welding burns through the metal, warps and reshapes the metal constantly. This is why someone who is talented and thoughtful in their craft needs to be working the project. I think you'll see that Constantine tried various ideas, but the fact that the heat of welding causes deformation is the route of all evil on what otherwise is a logical solution on your part. Notice that the welding done for my project occurs 2 inches from the front flange, well away from the secure location of the first bearing.
Issacsracing. this is where I got the heavier crank as a transition to the solid TT
Originally Posted by Constantine
Hi John,
Great to see you finally post all the work you've done making a solid 968 torque tube (TT) from a solid 944 TT. Thanks for the kind words on our behalf and it was our pleasure to work with you in an advisory capacity with this venture. Many have discussed doing this, but to my knowledge, you are the first to have actually done it. It will be great to hear about your driving impressions once your racer is all back together.
For those following along, Porsche used a split TT design initially in the 1989 944S2 to quell the extra driveline vibrations from the new and larger 3.0 liter 4 cylinder engine used in them. This TT design was then carried into the 968 since the same engine was used. Porsche stopped using the split TT design sometime in 1994 through 1995 when the 968 model was retired. They stopped using the split TT since they added more weight to the crank assembly which quelled the vibrations without the need of the split TT.
To answer the observation by H.F.B. above, a loose pinch bolt on the short shaft would not result with the damage seen in the pictures above. Loose pinch bolts would result in deformed splines of both the coupler and drive shaft. We have seen this same failure before in 944S2s and 968s with split TTs when the front bearing unit fails.
To answer the question from Yogii, we have done one 944 TT with 5 Super Bearings due to the owners insistence. All 944 and 968 TTs came with four bearing units from the factory. The 968 is a bit shorter and 4 bearing units is more than enough to hold and support the drive shaft in the correct position needed for trouble free operation.
I understand you had no choice doing what you did. I commend you for the idea and the ultimate result.
I am only suggesting a possible pre-failure idea/fix that makes sense to me. I am very familiar with the affect of heat on steel. Especially with high heat (such as steam) and tubular steel.
Trying to fix the split TTs in the 944S2 and 968 as I stated previously, is a dead issue for us. Very hard to get the needed ID to secure the bearing unit and guarantee it will not move afterwards. As shown above, the method we came up with was the best solution since it could be adjusted, but we still felt we were taking on way too much risk. Due to the problems with split TTs, we do not sell our products for use in any split TT.
However we understand that statements like these is like waving a red flag in front of a bull. Especially to a group whose members include engineers, machinists and technicians who have had to find ways to keep their beloved machines on the road or track due to parts being unavailable, expensive, or fixing problems that have been found with their chosen Porsche platform. That's how we started in our business so we get it.
IMHO, John's method is the best since it guarantees the needed ID to hold the bearing unit in place and the careful attention during the fabrication and welding should make it trouble free. Since he will be using it for racing will certainly test the modification, so time will tell. In conversation with John, I believe it is his goal to be able to offer this service to others.
As far as increased NVH issues in the drive line, our products have been engineered to a much higher performance standard than the Porsche OE bearing unit. Due to this, happily we have had no reports of increased NVH problems from our customers in both the 944S2 and 968 platforms, which are mostly street driven where increased NVH issues would be readily felt.
Thanks Isaacsracing. That is my son on the bike about 15 years ago.
Thank you Constantine for your information.
I know you both have invested a lot of time developing your solution. I applaud you!
I have one more question that may have been answered but I can't seem to find it:
For those who have an undamaged shaft and came to you for a solid TT and bearings. Would it make sense for you to source tubing and flat stock and make a new TT vs. sourcing a 944 TT?
I have one more question that may have been answered but I can't seem to find it:
For those who have an undamaged shaft and came to you for a solid TT and bearings. Would it make sense for you to source tubing and flat stock and make a new TT vs. sourcing a 944 TT?
That's a great question, and it begs a follow-on: There are a few intrepid Porsche transaxle owners who have fabricated their own torque tubes from scratch, including a few who have made them out of aluminum. So at least there's existence proof that it has been done before.
This evening my friend Iain and I installed the new flywheel (old one was damaged by the bad TT) the Stage 4 Spec 6 puck clutch, Sachs pressure plate, short shaft and the newly produced Torque Tube with Super Bearings. That took about 2-3 hours. We aren't fast, but we were careful. Everything going in is so clean!
Here's a closeup of the front of the TT going in. Its placement is very particular and the 6-foot tube must line up perfectly to go in. We put the short shaft into the clutch first, but I suppose the short shaft really should be on the torque tube first.
Here's the TT in its final position and fully bolted in. You can see the weld seem just aft of the access hole if you look carefully. Hopefully, this never gets removed from the car again - fingers crossed.
There are many more hours left to put the rest back together. Next up to go in is the transmission.
12-27-2018, 03:37 PM
