24 replies to this topic

[Todd Lamb]

The 5th gear failures we saw were due to no-lift shifts. Throttle trace didn't lie

[Parity]

Virtually every used race trans I take apart has a twisted spline on the lower shaft. The shaft has reverse gear splined to it. Then a non-splined spacer, then 5th gear splined to it. The splines actually twist under the unsplined spacer. I have a splined spacer that I put in my race transmissions that helps save the shaft.

A splined spacer also having a larger outside diameter would definitely help.The stock spacer has a smaller OD that the gear flange face so it starts to dig in to the face which allows deflection.

[Mark McCallister]

We lost 5th gear before the last race in May.  Pulled up on the banking at Daytona for the first lap and there was like a wall where 5th gear used to be, no gear engagement at all.  Stu said it was a detent failure of some sort, I didn't follow up and just left it with him.  Transmission was rebuilt maybe a dozen weekends before, but I don't know by who.  Every other gear including R was fine.  Shifter bushing was broken when I opened it up which I thought at first was the problem (would have been a lot cheaper!), but no, I probably just broke it trying to jam it into 5th... 

[Steve Scheifler]

Back to the original topic. Why shouldn't Hoover's hubs be allowed? Has anyone examined a set? What dimensions if different would exclude them? I know for fact that the bearings in the hubs I run today are not identical to either those that came in the car or the ones I would buy as "stock" today. Do we know that the improved hubs offered by Mazda are dimensionally identical in every respect?

Let's talk more about what Hoover is offering here. If the only real difference is the bearings then I really don't see how they can be excluded.

[SaulSpeedwell]

We should probably set up a separate thread to talk about trans issues.  My goal in bringing up the topic with Frank was not to make it a driver or builder scorecard on failures, but to determine if there is a problem, and to pursue a solution if needed.  Slightly back on topic, simply hoping that 1990-2005 OEM parts quality will return to hubs and crate transmissions is not realistic, and not an actionable plan that any of US can do something about.

 

Without claiming I've never had a gearbox quality issue that was my fault and not the driver's, I'm not seeing the countershaft issue at near the rate Dave is seeing.  Not because I am casting a magic spell on the countershaft, but because Mid Ohio has a lot less 5th gear shifting and braking and slamdrafting than Road America. 
It is reasonable to believe that the countershaft and 5th gear issues definitely correlate differently depending on the tracks.

 

It is clear me there is no single causal factor, except in those cases where you have a driver that will blow up any and every gearbox in fairly short order.  At the other end of the spectrum, drivers known to get seasons out of a transmission will occasionally fail a trans in only a few laps or hours.

 

For any given transmission except a brand new one, the following factors apply regardless of the CURRENT driver or builder:

-How many miles were on it?  Was it from a wrecked car?  Was it from a turbo autocross car? (I have a customer with a 250 RWHP NA1.8 that does full clutch dumps all day long.  As best he figured, it had 40 autocross weekends on it and a bunch of street miles before he finally lost 3rd gear.  I didn't do anything special to that box, but that car has convinced me that SM is harder on a transmission than his usage and application)

-How many racing shifts were on it?

-What tracks, what gears?

-How many bumpdrafts/slamdrafts?

-How many wheel-to-wheels, wall-to-wheels, sandtrap excursions?

-Rebuilt from stock or rebuilt race trans?

-And Dave mentioned the damper wobble issue, which is also something I haven't seen - again, most likely a track-dependent thing.

 

 

The crate transmissions are around $1600 to your door last I checked, and they fail rapidly when abused - and the countershaft twists more readily than the 1990-2005 units - so that isn't a solution, in my mind.

 

Are competitors having more fun on 225/50-15.5 (see what I did there?) at 20mm effective offset than they would on a true 195/50-15 at 35mm effective offset?  Are unsprung puck clutches more fun than stock ones?  That's for the class to decide - but simply wishing 1990 OEM parts quality to come back and save us on bearings and transmissions is not going to happen.  I think I did the napkin math on the hubs and decided we were exceeding the original design by 4-12 times, depending on what "Gs" you pick for the shock loading of hammering over the Road America rumble strips versus hitting a pothole once a week.  Well, the transmission is experiencing a similar situation with WOT shifts with puck clutches and tires with more grip and stiffness than 185/70-14s.

 

Future trend/prediction:  So long as the crate transmission continues to be one of the most expensive and most fragile choices, transmission failures ARE going to climb.  Used transmissions will be harder to find and will be more expensive.  We already occasionally buy a crate transmission and "rebuild" it before it ever gets used, similar to the pro motor situation.  Other solutions are putting in new gear sets - the 5th pair is $275 to your door, 3rd is $100+, the countershafts are $375 .... or developing solutions for checking/testing/and re-processing the gears.

 

Former unlisted diagnosis videos .... unit reported to have 14 hours before failure.  Driver known to be "gentle" on gearboxes.  Best guess from driver reports is that he experienced a "slamdraft" under braking while in 5th.