The $10,000 driveshaft
 

So, we had a driveshaft made for the FC 'vert EProd car. We found a good company in the Tampa Bay area and had a new shaft made with servicable u-joints and told them, "make sure its balanced, we spin it over 10,000rpm". They say, "No Prob". Cost about $270
Daytona, yesterday: Qualifying, driver says there is a little vibration once as he pulled through 8000rpm in 5th gear. I think well lets take a look under there. I pull the drive shaft and the seal check things out, doesn't look to bad. I put it back together with a new seal and tell him to see if it is consistantly at that rpm and gear and no other combo.

I didn't mention the car was on the pole with a nice 2.3 sec/lap cushion over second. We were happy.

The race is a blow out, driver is loafing it after 3 laps, only driving as fast as he needs to to keep a nice spread back to second in the race group (different class). Second in class is waaaaaaayyyyy back.
Lap 4 after having a problem shifting he spins at the kink in the infield. Nice long slide, and just kisses the armco getting a little smudge on the nose. As he pulls back on the track I notice a little FIRE UNDER THE CAR!
The missed shift was because of the tranny lube leaving the car through the seal as the driveshaft wobbled at about 135mph. Enough came out to make the tranny shift notchy and then it was flung by the driveshaft onto the exhaust. When he spun, no more airflow to cool things a little. The synthetic oil reached it flash point and woosh a fire.
He pulled off the track, hit the fire bottle, crawled out and watched the car-b-que. The fire crew did a great job when they reached the car so it isn't a total write off. Cockpit and rear of car will need total going through but its nothing too bad.

So the next driveshaft will be from ACPT or Dynotech because $800 sounds like a deal now!

Any other companies I should look for guys? And, I hope everybody can learn from the little tale, if you are going to replace your driveshaft get a good one from a good company that knows how fast our driveshafts spin. Hopefully its a company that has many of them in service on our cars, that company might be named MAZDA for most peoples' applications who knows!

Is the driveshaft in that car between the engine and gearbox? I don't see how the motor spinning at 10k rpm really affects the driveshaft. It should be pretty much the same speed as any other engine after the gearbox. Sounds like you just bought a shitty driveshaft.

I was saying to driveshaft spins over 10k rpm. The driveshaft spins over 12,000 rpm when the engine is at 9500rpm because its overdriven. Most cars don't spin the driveshafts this fast because they don't run 5.12 gears in the rear. For the same speed, most cars run something in the 4-4.50 to 1 range gear. So at 135 mph their driveshaft is turning about 9500rpm compared to our 12000.
I didn't pull out a gear chart for these figures but you get the idea. Our peak HP is found higher in the rpm range than most piston engines so we have to let the engine get up there with a shorter rear gear.

dennysdriveshaft.com

I have never had a problem with the OEM driveshaft. But if you need the servicable ujoints I would use as small a diameter as possible and use a shop that specialises in race cars. They tend to understand what is needed. I have used the OEM driveshaft with no problem. I have not checked the prices lately but I thought they were much less than $800. with an e-prod you should be able to use the oem setup. Might want to convert the tailshaft bushing to a roller bearing if this has not been done. I have seen the bushing spin and push the seal completely out of the trans. Too bad the car was damaged it sounds like it is running great otherwise. glad no one was injured.

Thanks Tim, we had tried a couple stock shafts with similar vibe problems thats why we went to a different set-up. Its really only a problem on long courses like Daytona. The shop we used had a good rep with the roundy-round guys in our area but I guess what we are doing is out of their league(rpm wise). We will probably try stock again but we're always looking for an advantage any place we can get one within the rules.

I have heard about the roller bearing trick but could not find anything when I searched. Any help with finding that?

Talk to Mazdaspeed about the tailshaft bearing. They sell the bearing and can tell you what you need to do to install it.

bearing??? woah... got pics? i'm interested in that setup.

I wonder how much machining is required. And whether or not the 4352-25-130 will fit a stock driveshaft.

Won't work with the stock shaft. You need the hardened yoke which is part of the 1st gen comp driveshaft. I'm guessing you'll need a custom shaft to work with any 2nd or 3rd gen app.

Ah the joys of racing, custom this, custom that... I had the same thing happen to me... the driveshaft started to wobble and tranny fluid would start coming out. I noticed gold fluid on my garage floor when I got home 230 kms from the track. Too everything apart. Noticed oil was coming out of the rear seal. I thought it was the rear main engine oil seal at first, but my motor oil is always black, not gold.

I race solo1 and I'm only doing 3 hot laps at a time. so the exhaust doesn't really get hot enough to flash oil. It is still a concern though. The driveshaft I had was at 208,000 kms. I replaced one with another used one which is curing the problem, but that used one isn't in the greatest shape either...

Very good company http://www.iedls.com/

jgrewe,
Give Dave over at Mazdatrix or Jim a Mariah Motorpsorts a call. Both have quite a bit of experience with drive-shafts in E-Prod. On the Mariah cars, we use OEM driveshafts without any issues. But you have to make sure your drive-shaft geometry is set-up correctly though, to avoid vibration problems.

Also, I'm sure E-PROD on this forum can offer some input.

-Bern

To run the roller bearings in place of the brass bushing, you have to first weld up the OD of the tail shaft housing to make it thicker, then you must have it bored out to accept the roller bearings. Yes, you must run the hardened yoke with the roller bearings, because the yoke becomes the inner race that the rollers ride on.

In my IMSA GTU car, when I ran a Mazda Comp factory racing tranny (which comes with roller tailshaft) and I ran the hardened yoke, and I ran stock engine mounting location, and if I had the Tri-Link adjusted properly to make driveshaft U-joint angles perfectly even, then everything was fine. With my PP motor turning 9200 rpm in 5th gear 0.88 overdrive the driveshaft turned 10,450 rpm.

About 3 years ago I switched to a G-Force tranny, and I had to get a custom driveshaft built by a local shop, and then I had all kinds of vibration problems. It turns out that all of these driveshaft shops cannot balance driveshafts at high rpm; they do not have the balancing machine capable of hi-rpms. Almost all driveshaft shops machines can only turn about 1800 rpm.

I then went to a NASCAR driveline specialist, Tex Racing http://www.texracing.com/ These guys are used to building Hi-rpm driveshafts, and they said that there is only one hi-rpm driveshaft balancing machine in the USA (can turn 7000 rpm,) and it is in Michingan. Tex also knows how to calculate natural frequency of vibration, and can change shaft diameters to get away from resonant frequencies. Tex built me a new drive shaft, then Tex sent it to Michigan and had it balanced at 7000 rpm, and then it was returned to Tex for final assembly. It cost me about $450, but it cured my vibration problems.

Are you sure you have your U-joint angles exactly equal at normal ride height?

I just purchased and installed a ACPT carbon fiber driveshaft for my '05 STi. I could not be more pleased with the results, the driveshaft has exceeded all my expectations. No extra noise or vibrations and the car accelerates faster.

Mike

Speedturn, I'm pretty sure that balancing was done for you at Dynotech. They also built driveshafts and say they can balance them to 8000 rpm. We don't have the variable phase issue with the IRS rear(FC), but since you mentioned it that will be one thing I go over with a fine tooth comb. I'm going to double check the geometry with the solid mounts we made for the diff., it might turn something up.
About the hardened yoke, do you use it when you make a custom driveshaft or replace the stock one? Do you think that one of the aftermarket co's would be able to get them from anybody besides Mazda? I don't know if that part is that special in the driveshaft construction business.
Great leads guys, thanks
And Mike, I'm a big Scooby fan also. One of my other cars is an '88 323 GTX, love the rally cars!!
I'll post pix of the car when my wife gets back in town with the camera.

^^^^

Very cool! :bigthumb:

Mike

I have used a standard driveshaft with the roller bearing in the tailshaft. You need to check the wear from time to time, but I have used it for many racing miles without failure. I don't remember the welding and boring issue. I believe I sourced the bearing that directly replaced the bushing. The tex shaft sounds like a good alternative and the cost is okay for a high end racing driveshaft. Tex does great work on transmissions, so it would seem likely they know a thing or two about driveshafts. I had one of their Jericho's in a stock car and it was great. I wish the owner of the car hadn't sold it.

Where is this bushing?

Is this so called brass bushing the rear oil seal, aka part number M502-17-335A?

Cheers, it would be in the tail just ahead of the seal. I didn't find it in the drawing but I didn't look very long. The output shaft goes through it but the ID fits the OD of the sliding yoke on the driveshaft.

I'm looking a the FSM, but unfortunately it does not talk about replacing this bushing during disassembly or re-assembly of the tranny. But am I correct in assuming that in order to change this bushing You would have to remove the tail section of the tranny and either knock it out press it out?

you are correct about the repair and service of the bushing. this is the "bearing" the driveshaft turns on. On your pic it looks like the bottom right hand part(no number) looks like a small tube with a couple holes in it.

jgrewe,
So that's what happened. Dammit man, I hated seeing that. I hope Ed can get her fixed and back out quickly. I'm just glad he is ok. The speeds we run there combined with the hard walls make every small problem a potential big one.

For those that don't know this car, Ed's RX7 is almost too pretty to race.

Jim

We have started the rebuild already. Its all apart and we are updating the cage since we have to redo the entire cockpit area. Pretty much from the shifter back needs to be repainted inside and out. Did you know burned paint comes off pretty easy with a wire wheel!
Ed has a small burn on his elbo but he's OK. He said its his first fire in 40+ years of racing.

I sent my front yoke and rear flange to Tex, and they provided everything in between.