1970 GTO Version 2.0

[subtlez28]

I wont guess on both forums, but I'm glad to see I wasn't the only one to notice the ceiling fan!

[Ron S]

I was given the inside scoop, it is interesting to see the difference Andrew. I never knew factory made it that way. Good talking to you. Ron

[7TSS]

Is it that the tube isn't welded on the center of rear bracket?

[andrewb70]

Is it that the tube isn't welded on the center of rear bracket?

Very good! That is correct, the bracket that slips over the rear end bushing is offset to the driver's side. Before you all demand the name of the vendor, I would like to point out that this control arm is the only one on the market that is built CORRECTLY. You see, the stock control arms are built with exactly the same offset as these control arms. Every other manufacturer, that I have seen, makes upper rear control arms so that the front and rear bushings are inline. This is INCORRECT! This also explains why the rear end in my car is offset to the passenger side by a good 1/2-3/4" as measured from the wheel to the frame. I have seen posts on various forums where people have complained about a similar problem. I also believe that this improper positioning of the rear end has been contributing the ever present vibration problem that I have been having.

I would like to thank Bret Voelkel and ridetech for making a fine product and paying attention to the little details that can have a big impact on the performance of our cars.

Andrew

[TomT]

That's an interesting tidbit Andrew. I just had to go look at my car to see if the factory controll arms were offset. It looks like G-Bodies were centered.

[andrewb70]

That's an interesting tidbit Andrew. I just had to go look at my car to see if the factory controll arms were offset. It looks like G-Bodies were centered.

Tom, I am not really sure why GM built the A-body arms the way they did. I was discussing this in detail with Ron S ($5000 mustang build) and he mentioned a few curious things. He does a lot of custom work and he has fixtures made to narrow a variety of rear ends. He was recalling a having to narrow a A-body 12 bolt rear end to be installed into a G-body. He mentioned how the position of the lower brackets on the 12 bolt were not exactly centered. I think it all has to do with having the pinion being in the proper position in the chassis and GM's desire to have equal length axles on the left and right sides. I don't know all this for a fact, it is just a theory.

In any case, the fact that my car has had a vibration since day one is very interesting. I have gone through 2 engines, 2 sets of tires, 2 different front spindles and brake packages, 2 rear ends and 3 different driveshafts. Everything seems to point to some sort of driveline misalignment issue. It is not a simple matter of pinion angles, because I have beat that issue to death. I think there is a lateral problem. The rear is offset to the side due to the control arms, that for sure. The other issue may be that my transmission output shaft and the pinion shaft may be out of parallel when viewed from the top (or bottom). This is an issue that few people think about. Once I am done with my classes I am going to install the transmission and really double check the position of everything.

Andrew

[Tony_SS]

Is it that the tube isn't welded on the center of rear bracket?

I noticed that too... but thought it was by design as I didn't think a manufacturer would mistakenly offset it like that. I'm glad a vendor out there pays attention to detail!

It's a little unsettling to think other vendors out there assume specs when it comes to these things though.

Andrew I hope that cures your problem.

[twosaturns]

interesting. lots of GM cars seem to have the rear off centered; I've seen lots of Novas that didn't drive straight down the road (my '70 was like that) and many early 2nd gen camaros are offset too (I haven't researched it deeply, but someone said this was done on purpose!). my brother's '70 camaro axle is a good 3/4" or more offset to the right IIRC.
btw, I really love this build, been following it for years.

[93Polo]

Good info on the LCAs Andrew

Have you decided on which trans is going in yet?

[TomT]

Andrew, You're right in that it seems the discussion always centers around pinion angle rather than lateral alignment. I'm assuming that you're rear end is mounted 90 degrees to the chassis center line even if it is offset a little (otherwise it would "crab"). If I'm thinking about this right then you would want the center line of your engine/transmission to also be parrallel with the centerline of your chassis in that same plane. I expect that's a little harder to measure than pinion angle at least with the body on. I guess you could use plumb bobs on the center of the balancer and tailshaft and mark it out on the garage floor. It will be interesting to see how you solve this one.
Tom

[andrewb70]

Andrew, You're right in that it seems the discussion always centers around pinion angle rather than lateral alignment. I'm assuming that you're rear end is mounted 90 degrees to the chassis center line even if it is offset a little (otherwise it would "crab"). If I'm thinking about this right then you would want the center line of your engine/transmission to also be parrallel with the centerline of your chassis in that same plane. I expect that's a little harder to measure than pinion angle at least with the body on. I guess you could use plumb bobs on the center of the balancer and tailshaft and mark it out on the garage floor. It will be interesting to see how you solve this one.
Tom

Tom,

You are right in stating that the vast majority of pinion related questions discuss alignment as viewed from the side. The lateral alignment is rarely addressed. There are two issues when dealing with lateral alignment. One is simply the position of the pinion in relation to the transmission output shaft. The transmission output shaft and the pinion should be inline. The other aspect is parallelism. This is the same concept that is addressed by the adjustment of pinion angle from the side. The transmission output shaft and the pinion need to be parallel not only when viewed from the side, but also as viewed from the top (or bottom). The position of the engine and transmission cross member becomes critical. If the engine and trans are angled to one side that can cause the output shaft of the transmission to be out of parallel with the pinion. Also, if the rear end housing is cocked to one side, that can cause similar issues.

Ron S, please chime in. I talked to Ron and he told me how when he builds a chassis or backhalfs a car he has plumb bobs hanging everywhere. He told me how critical it is to make sure that the engine and rear end need to be plumb and square to avoid vibration problems. We drive old cars that have been through God knows what, and we often assume that frame stands, engine adapters, crossmembers, control arms, etc...locate the driveline components in their proper place. I think this is far from the case in many instances and people should pay special care to double check everything to assume a smooth running car.

Andrew

[Ron S]

That was explained very well Andrew, you should be a teacher. LOL

Andrew and I were talking on the phone about chasing driveline vibrations. I was telling him about a few cars I backhalved through the years. I am a bit anal about things being level and square, so I use plumb bobs hanging off the pinch welds, then run two strings along the length of the car,and two 90 degrees to them.I use all that to reference axle, and driveline center lines. I remember one car that the rear was 4" offset in the car. I was putting rear rails in it, and to square the rails and rear in the car, the tires were flush with the quarter panel on one side, and 4" in on the other. The car looked normal, but the body was so out of square,the driveline couldn't help but vibrate. The owner of the car was clueless of the problem, the correction was expensive.

I only mentioned this to emphasize that we really don't know where these cars have been, and the life they have lived. Andrews car is a little different, because the car must be squared off the chassis instead of the body like you would do on a unibody car. If the chassis has easy places to measure off of, the plumb bobs aren't always required. Unfortunatly this really is the only way you can be sure that the axle is straight in the car, and the engine and trans are 90 degrees to it.

[andrewb70]

Last Thursday I finished my last final, so I am officially done with the spring semester. I am ready to relax and get back to my GTO. It's hard to imagine, but it was three years ago that I completed the L92 engine swap. My, how time flies. In the summer of 2008 I put about 6,000 miles on the car. The plans for this summer are more modest, but I would like to attend a couple of events and maybe visit some friends out west. After much deliberation and for a lack of simple options, I have decided to get the Richmond 6 speed rebuilt. Richmond Gear has been working with me and we came to an agreement. They are currently in possession of my transmission and will give it a thorough inspection. All the gears will be magnufluxed and all parts that are damaged will be replaced. I never had any fundamental objections to the Richmond. I always felt that it shifted fine and offered an awesome, close-ratio gear spread for gears 1-5 and a comfortable .62 overdrive. Keeping the same transmissions will also allow me to keep my current crossmember and not worry about an alternate shifter location.

With road trips planned for the summer, I once again turned to a problem that has plagued my car since day one. Despite numerous efforts I have been unable to completely eliminate the high speed vibration that my car exhibits at speeds about 75 mph. It's really frustrating on long highway trips, because the car feels amazing cruising at speeds between 75 and 80 mph.

I have already posted what my thoughts are regarding the rear end position. I will be swapping out the current rear upper control arms for ones made by ridetech. I firmly believe that while the rear end position may not be entirely responsible for my vibration, it is certainly a factor. I will also be doing other driveline upgrades at the same time. What I have planned may be a little overboard, but I believe that it will completely eliminate any driveline alignment and vibration issues in the future. Here is the plan....

The first step is to get a rear pinion yoke that is machined with the kind of tolerances that are required to achieve smooth operation at sustained high speeds. I chose a 1350 billet yoke from Mark Williams:



With the rear taken care of, the next item to tackle is the driveshaft. There are many fine companies that make driveshafts, but given my alignment issues, I wanted to pick a vendor that was able to offer something unique. I have worked with Frank at The DriveShaft Shop (DSS) in the past when I needed custom axles for my RX7. Frank has always been attentive to my needs and has provided a quality product that has met and exceeded my expectations. The DSS is widely known in the sport compact world for making bullet proof CV axles, and recently they have also been doing some innovative work on the many modern muscle cars that use independent rear suspensions. Cars like the new Camaro, Dodge Charger, GTOs, and Cadillac CTS-V are rear drive, high HP, and heavy. That combination is the perfect storm for breaking driveline components, and DSS has stepped up to the plate with upgraded CV shafts, driveshafts, and complete 9" IRS swap packages.

After deliberating with Frank about my GTO and the issues that I am having we came up with a very elegant solution. Frank will make me a custom driveshaft with a CV joint in the front. People in the 4x4 world have used double cardon CV joint driveshafts for a long time to deal with extreme driveline angles. But double cardon joints are bulky and heavy, and just didn't seem appropriate for a car. What will be used in the front is a 6 ball, Porsche 930 style CV. Like this:




CV joints are designed to operate at high speeds and at extreme operating angles. Furthermore, there is no need to match the front and rear angles, as you need with a shaft that uses u-joints on both ends. With the CV joint in the front I will adjust my pinion angle so that the pinion and the driveshaft have almost a zero working angle. A slight angle is required only to make sure that the needles in the u-joint caps get lubricated. The rear working angle will be less than .5 degrees.

Since a new shaft will need to be fabricated, I have also decided to go a little overboard and opt for a carbon fiber tube. This may be a little over kill, but I am not taking any chances. In fact, Frank felt that my problems can be solved by using a driveshaft made from aluminum. However, a CF driveshaft is lighter than aluminum and offers plenty of torque capacity. Using a carbon fiber driveshaft also tends to significantly lessen the noise generated by the driveline. In some ways its like Dynomat for the driveline. I had the opportunity to drive a friends RX7 with a carbon driveshaft and it felt amazing. When cycling the driveline from load to coast the sensation was like there was a piece of plastic between the rear and and the transmission. It was a firm feeling, yet it lacked the sharpness that is felt with metal components. It was quite amazing.

With my current combination of gears and tire size the driveshaft will be spinning 3675 RPM at 80mph. While this doesn't seem like a lot, when you consider that my old driveshaft was made from mild steel and was 3.5" in diameter, the forces that were generated by such a heavy shaft were significant, even with a properly balanced driveshaft. The DSS has recently installed a new balancing machine that has the ability to spin a shaft to 9500RPM. They have been working with some NASCAR teams to solve some of the driveline issues that they face. Keep in mind that NASCAR race cars operate with the driveline spinning anywhere from 7500-9600RPM. Balancing driveshafts at that speed is a whole different ballgame than your typical 1000 RPM balance job at your local driveline shop.

The resulting driveshaft will be very similar to the shaft that they sell for 2010+ Camaros.



Instead of the billet adapters that are seen in the picture, my shaft will be connected to a modified slip yoke. The rest should be very similar. The finished shaft should be about 17 pounds with the slip yoke. Here are pictures of the components that are used in making the driveshaft. The parts on the left are used for carbon shafts, and the parts on the right are for aluminum shafts:



The bars that mate with the CV are 30 spline and are made out of a high tech 4130 alloy. The dimensions are similar to a Viper T56 output shaft. DSS has gone to great lengths to validate all the components that are used in making the CF driveshafts. This includes destructive testing, which few manufacturers ever do:



As you can see, the 1350 u-joint failed before the tube or the aluminum yoke. I feel very confident that this shaft will outlast every other component in my driveline. I can't wait....

Andrew

[andrewb70]

The first part of the driveline project arrived yesterday. The Mark Williams billet pinion yoke is a work of art. There are numerous machined surfaces taht can be used to measure runout.





Andrew

[TomT]

It will be very interesting to see how this all works out. It sounds like DSS could help me when I get ready to put the Ecotec and 5MT into the Vega (that trans doesn't have a slip yoke).

[andrewb70]

Tom, I am quite sure that Frank will be able to do whatever it is you need done.

I am once again impressed by Frank at The Driveshaft Shop. He had the yoke done by last Friday and today he was able to have it black oxide coating applied to it and have pictures taken.

Here is the modified Spicer yoke:








The gold colored part is a cap that keeps the grease from leaking out the back of the CV:




This is a detailed shot of the modified yoke with the CV and front of the driveshaft:



Finally, a shot of the complete assembly. Interestingly, Frank was building a shaft just like mine for another project that had similar driveline alignment issues. It's a custom 1961 Corvette that will get a monster twin turbo engine.



Frank will send me the slip yoke so that I can give him the final measurement for the driveshaft.

Andrew

[gearbanger]

Man, that is some exotic lookin sheeet!!!!!

[parsonsj]

Andrew, I'm digging this technology! U-joints are (and always have been) a poor method of allowing misalignment between drivetrain components. CV joints are way better, and the carbon driveshaft will put the critical speed of the driveshaft well over any top speeds you'll be running. Very nice.

I'll be calling to get some contact information for Frank. That shaft seems like the best solution for 200 mph. Any chance this stuff can hang on to 1300 hp?

[andrewb70]

I just got word from Richmond Gear and they said that with some luck my transmission might be ready to ship by the end of the week. Looks like things are coming together and I might be able to get the car ready to attend the MotorState event in June.

Andrew

[David Sloan]

Very nice Andrew
hope we can hang out at some of the events this year.
Any idea as to a price range for a shaft like that? maybe some contact info for DSS
Thanks for sharing!!