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The Driveshaft Shop is absolutely bad ass!!! by andrewb70 on 17 May, 2011 14:38
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Many of you are familiar with the Driveshaft Shop, because they sell axles for all kinds of CV shafts that are used on the RX7s. They make everything from upgraded bars, all the way to complete kits that include everything from the inner stubs, CVs, bars, and outer CVs. Frank and his crew do some amazing work.
In addition to doing CV axles and replacement driveshafts, the DSS can also do custom work. Most of you probably don't know this, but before I was playing with FC RX7s, I was (and still am) into muscle cars. I have a 1970 GTO, that I've owned since I was 15, which is fully restored and have been featured on the cover of Popular Hotrodding magazine and in Car Craft.
Ever since I've owned my GTO is has had a high speed driveline vibration. The vibration has persisted through 3 different engines, 3 rear ends, three sets of tires, four driveshafts, two different brake configurations, and more headaches that I can count. After running down every possible driveline component the issue seems to come down to driveline angles. As you all know, the proper set-up for the transmission output shaft and the pinion shaft is for them to be parallel. The GTO uses a 4 link rear suspension design with a solid axle and I have adjustable upper control arms, which makes changing the pinion angle relatively simple. The problem is that my car is lowered, a lot. It's hard to say how much lower it is than stock, but I would say 3" in the front and 4" in the rear. What happens when this type of car is lowered that much, especially in the rear, is that the rear starts to ride higher in the chassis than the output shaft of the transmission. So while I can make the front and rear working angles the same, the angles end up more (greater than 3 degrees) than desirable for smooth, high speed operation.
The solution is to raise the back of the transmission so the front working angle becomes less, and adjust the rear to match. The problem is that there is only so much room in the transmission tunnel. My transmission is already so high that the front slip yoke is only 1/8" from the top of the driveshaft tunnel, and the working angle is still too high.
I discussed my problem with Frank and he came up with a very elegant solution to address the problem. Instead of using a regular u-joint in the front, Frank suggested to use one of his 108mm CVs. A CV joint doesn't care about matching angles. They can operate at very high angles without issues. The upgraded 108mm CVs used by the DSS are rated at 8000lb/ft of torque, so durability is not an issue.
As of now there are no vendors that make a slip yoke with a CV cup already machined into it. The DSS took a Spicer 32 spline slip yoke and machined it down and TIG welded one of their CV heads to it. 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. The CF tube is probably overkill, but I wanted it to further dampen any driveline harmonics that might be present.
The reason that I am posting here is that I have read several people posting about high speed vibrations. This can easily be the result of improper driveline angles. Both the FD and the FC have non-adjustable rear diffs, so changing the rear working angles are almost impossible to adjust. Many of you are running T56 transmissions that use a 27 spline slip yoke. The DSS can easily perform the same modification on that style yoke and use a CV joint at the front of the driveshaft. A CF tube won't be needed because RX7 driveshafts are much shorter than the 54" driveshaft in my 1970 GTO. A 3" aluminum tube should be more than enough to handle any reasonable power levels.
Andrew -
#1 by digitalsolo on 17 May, 2011 14:42
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That's a pretty slick setup, hopefully it solves the issue.
I feel your pain, I've been chasing some vibrations in my BMW for years. No fun at all. -
#2 by zbrown on 17 May, 2011 14:53
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Wow that is a BA piece!
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#3 by Covert5150 on 17 May, 2011 15:13
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That was one pretty penny.
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#4 by mefarri on 17 May, 2011 15:25
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Very Nice.
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#5 by andrewb70 on 17 May, 2011 16:01
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That was one pretty penny.
It wasn't cheap, but at this point I am out of options. Like I said before, the CF tube is not needed for RX7s, but its a nice option. Adding a CV adds about $450 to the cost of a the driveshaft. That amount includes the necessary modifications of whatever slip yoke may be needed for your particular transmission.
Andrew -
#6 by cool on 18 May, 2011 13:07
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Nice piece.
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#7 by southside427 on 18 May, 2011 22:46
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holy sheet!! you said the CV was rated at 8000 ft lbs didnt you mean 800??
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#8 by andrewb70 on 18 May, 2011 23:10
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holy sheet!! you said the CV was rated at 8000 ft lbs didnt you mean 800??
Nope, I meant 8000. Think about an engine that makes 500lb/ft of torque at the crank. Then it goes through the transmission and in first gear it gets multiplied, lets say 2.66 in first gear for a T56. So the driveshaft sees 1,330 lb/ft of torque. Then the power goes through the rear end, lets say 4.10 gears. So now we are looking at a little less than 5,500 lb/ft of torque at the rear axles, but we have to divide that by two, since we have two sides of the diff. The point is that the CV that is used on this driveshaft has plenty of capacity to deal with any power that I will throw at it.
As a side note, the DSS has done destructive testing on their carbon fiber driveshafts, and the Neapco 1350 u-joints failed at about 3,000 lb/ft of torque. They were only rated at 2,000. The CF tube or the end yokes, never failed.
This driveshaft is bad ass!!!
Andrew -
#9 by 346fc3s on 19 May, 2011 17:47
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That's awesome! Good to know there are other options out there than just messing with angles until your head hurts and still having a vibration. Good work and thanks for sharing the info.
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#10 by Jordan Innovations on 19 May, 2011 18:58
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Excellent solution to a persistent problem.
We broke a 4" carbon fiber driveshaft last year in Conrad Grunewald's 2010 Camaro (approx 600whp, 315/30/19 Hankook R-S3's) at the final round of Formula Drift (Irwindale), the carbon delaminated after a season of abuse from the 'inner' part of the yoke. We've since switched back to aluminum (like most competition vehicles).
Prior to that debacle, I've never heard of anyone breaking one. Plus they're supposed to be much easier on transmissions/rear ends. -
#11 by andrewb70 on 19 May, 2011 19:50
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Excellent solution to a persistent problem.
We broke a 4" carbon fiber driveshaft last year in Conrad Grunewald's 2010 Camaro (approx 600whp, 315/30/19 Hankook R-S3's) at the final round of Formula Drift (Irwindale), the carbon delaminated after a season of abuse from the 'inner' part of the yoke. We've since switched back to aluminum (like most competition vehicles).
Prior to that debacle, I've never heard of anyone breaking one. Plus they're supposed to be much easier on transmissions/rear ends.
Check out the DSS's website. On the blog section there is a detailed write up about the various components that go into making their CF shafts. They have their own unique pattern machined on the aluminum end yokes and are using the latest 3M adhesives and bonding techniques. I'm very excited about this because it's going to transform my GTO.
Andrew -
#12 by NOROTOR on 23 May, 2011 18:32
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Very nice, Andrew!
Please keep us updated when the car is back on the streets.
Jesse -
#13 by andrewb70 on 30 Jun, 2011 19:20
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I thought I would post an update for everyone. I measured for the length of the driveshaft and Frank worked with me to get the shaft out to me in the time frame that I needed. I was trying to make an event in Michigan for Father's Day with my son, and Frank delivered.
Here is a picture of the back of the shaft installed on the new Mark Williams billet yoke on my 12 bolt rear end.
This is what the front looks like with the modified slip yoke and CV.
Just another shot.
In short, the driveshaft cured my vibration problem. I road raced the car at Gingerman raceway and also took it on a 4300 mile road trip. It's smooth as glass.
Thanks Frank!
Andrew -
#14 by Andrew R on 30 Jun, 2011 21:18
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Love it.