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Stock 5 Speed Transmission Power Limit Reached...

Cody@LoveFab

Cody@LoveFab

Experienced Member
Joined
21 October 2005
Messages
1,416
Location
Traverse City, MI
My second transmission in just under a year failed last Friday. Shifted into third gear, rolled into the throttle, boost built, then WHAM, the engine slammed right to the rev limiter.

With a series of gut-wrenching grinding metal noises and loose foreign material behind me, I quickly pulled over and called the wife to grab the truck and trailer.

This transmission had witnessed two days of HPDE use, twenty 750+WHP dyno pulls, one staggering 920WHP dyno pull, two weeks of daily driving at ~850WHP(tank of race gas!) and around 6,000 miles of abuse at power levels never lower than 600WHP. Not too shabby in my opinion! I will pull the transmission sometime next week to ascertain the damage.
__________________________________

A year ago, the same thing happened to me and I quickly swapped in a spare trans, tossing the breaker on the shelf. After this Friday's event, I decided that I need to learn to rebuild these things, so I devoted a morning to learning how. At this point, I have only gotten as far as diassembly, but once I order a few parts, I'd like to cover the rebuild.

Anyway, here is what I found!

NSX%20Trans%20017.jpg


NSX%20Trans%20018.jpg


NSX%20Trans%20020.jpg


NSX%20Trans%20021.jpg


NSX%20Trans%20022.jpg


Surprisingly, the rest of the transmission seems to be A-OK! I was able to clean everything very well and determine that besides a few small scratches in the case surrounding the Differential(easily cleaned up), there is no other damage. I plan on ordering a third gear set and probably new Syncro's all-around while I'm in there, and rebuilding the transmission for round two.

Thoughts?

Anybody else have any transmission carnage stories?
 
A few things I noticed:

Third gear is in the middle of the Primary and Secondary shafts which means more possible flex due to less support in the middle of the shafts. Basically, under power, the gears would tend to push away from each other.

Third gear at a glance is pretty thin. I'll Mic it the next time I'm in there, but thin gears can't help either.

The final thing I have noticed is that we need a bulletproof transmission so that I can really push things without counting on these results every time I push huge power levels.
 
Would it be feasible, or even help, to go to straight-cut gears? I would assume the partial thrusting nature of helicals makes any flexing of the shafts (and thus separating of teeth) worse.
 
Welcome to the world of high HP NSXs... and their problems :)

KazO said:
Would it be feasible, or even help, to go to straight-cut gears? I would assume the partial thrusting nature of helicals makes any flexing of the shafts (and thus separating of teeth) worse.
Click to expand...
If you have a source that can make stright-cut gears for a reasonably expensive price, we're in!

Dog-rings too would be a great addition. Problem is their are no current options that aren't out of this world expensive. Many sequential options out there cannot hold up to these power and torque levels.


Don't forget: Straight-cut = gear whine.
 
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I have a couple of sources I'm going to look into now that I have an idea of what to look for.

I would assume 2nd, and 3rd would be ideal candidates for replacement? 2nd, 3rd, and 4th? In my experience, this would be the case...

Just checking with others and their experiences so we can possibly solve this issue...
 
Tinker219 said:
Third gear is in the middle of the Primary and Secondary shafts which means more possible flex due to less support in the middle of the shafts. Basically, under power, the gears would tend to push away from each other.
Click to expand...

Also the gears are side cut so the load under power is pushing. You could get a set of cut gears?

Or cheaper why not dog bone the shafts together in place of reverse :confused:

For a track high HP car reverse is over rated :biggrin:
 
cody, have you cryo'ed these gears.....you should look into it...its cheap, and it is supposed to make them like 30% stronger.....
 
01blacks4 said:
cody, have you cryo'ed these gears.....you should look into it...its cheap, and it is supposed to make them like 30% stronger.....
Click to expand...

How is your trans holding up ? I am getting ready to raise the boost and I am not sure where I should stop. I am thinking of running 525 RWHP on low boost and 575 - 580 RWHP on my high boost setting.
 
01blacks4 said:
cody, have you cryo'ed these gears.....you should look into it...its cheap, and it is supposed to make them like 30% stronger.....
Click to expand...

That still won't be enough IMO, though it sure will help! Honestly I'd like to be able to run at 800-850WHP without worries. Those two weeks this past summer were freaking awesome! I can tell you that going from 110MPH to 150MPH in 2-3seconds was pure bliss :biggrin:

I'm going to do some research and update the thread as things progress. I basically have six months of winter starting in a few weeks so it's not like I'm in a hurry...

Brandon-

Devin's transmission has survived quite a few years of 500+WHP, and more than 2 years of 550+WHP.

Glenns transmission has gone through a few different motors and setups IIRC, ranging from 400WHP up to where he's at now. I know he's been at 500WHP for well over two years, but this spring we bumped that up to the high 500WHP range. So far so good I presume!

I think it's safe to say that things get nasty above 600WHP, considering I have duplicate failures at the same HP levels.
 
Welcome to our world… That’s why we have six extra transmissions on the shelf ready to go and an open order to purchase more of them as they come available. We busted our cherry about 3-4 years ago when we were putting down 750rwhp. At that time it was mostly ¼ mile stuff two-stepping out of the hole. Third gear and the R&P have been repeat offenders. On the dedicated road course car 700rwhp has been fairly reliable with only one failure to date and constant maintenance to the trans. Daily driving in the 550-620rwhp for a few years did not result in a trans failure but it probably didn’t help as they did go out on the track soon after.

Hand lapping, cryo, and REM polished seemed to help a bit with the issue. The B-series cuffs may also work but would negate 5th and reverse??? In any case hopefully somebody will solve the problem so that platform can take the next step.
 
Tinker219 said:
I have a couple of sources I'm going to look into now that I have an idea of what to look for.

I would assume 2nd, and 3rd would be ideal candidates for replacement? 2nd, 3rd, and 4th? In my experience, this would be the case...

Just checking with others and their experiences so we can possibly solve this issue...
Click to expand...

If people are really serious about getting stronger gears, I can look into it. I have a source in Chicago, they use to make the gear sets for Trans Am circuit cars as well as some Indy cars.
 
jorligan said:
If people are really serious about getting stronger gears, I can look into it. I have a source in Chicago, they use to make the gear sets for Trans Am circuit cars as well as some Indy cars.
Click to expand...

That would be a YES :biggrin:
 
I replied similar to Tim/jorligan last night, but the site seemed to be down when I actually finished typing and tried to "submit reply". Here is a copy/paste of what I wrote then saved when it wasn't loading:

If the demand is there, I believe I can have entire tranny's or individual gears made of different materials which are significantly stronger. I know anyone could probably do this, but I met with a company overseas that can do it for a decent amount less then it would cost to buy a sequential from Hewland. They also noted that they could strengthen the gears by changing the designs and running everything through tests(of which were over my head.. engineering and metallurgy talk..)

The issue I see with making individual gears is the mating of the different metals/densities wouldn't work very well unless you make matched sets for anything they are mating to. At that point.. make everything? Anyways, up until now, I didn't hear enough interest, but if we can get enough interest, I'd be interested in getting it rolling. If anyone else is interested in helping with the process, I’m open.

If any of our local engineers have any suggestions, or comments, I'm sure we'd all love to hear what you have to say.

BTW, the company I met with does a lot of work with a few OEM’s and some F1 teams, so I'm sure they are up to the task.
 
Tinker219 said:
That still won't be enough IMO, though it sure will help! Honestly I'd like to be able to run at 800-850WHP without worries. Those two weeks this past summer were freaking awesome! I can tell you that going from 110MPH to 150MPH in 2-3seconds was pure bliss :biggrin:

I'm going to do some research and update the thread as things progress. I basically have six months of winter starting in a few weeks so it's not like I'm in a hurry...

Brandon-

Devin's transmission has survived quite a few years of 500+WHP, and more than 2 years of 550+WHP.

Glenns transmission has gone through a few different motors and setups IIRC, ranging from 400WHP up to where he's at now. I know he's been at 500WHP for well over two years, but this spring we bumped that up to the high 500WHP range. So far so good I presume!

I think it's safe to say that things get nasty above 600WHP, considering I have duplicate failures at the same HP levels.
Click to expand...



So far no problems with the 6 speed at ~590 rwhp. I do not do hole shots, but I am always on it 2nd to 4th gear and everything seems to be fine. I wonder if the fact that I crack the tires loose all the time prevents the torque from being too high on drive train components.
I agree that 600 whp seems to be the tranny limit for extended reliability, and probably for stock rods too.
 
I think the issue is TORQUE, not HP. HP is torque times RPM, so high HP can be made with relatively low(400'/lb.) if you turn it fast enough. The problem is big boost turbos have very high torque numbers(600'/lb.+) at relatively low RPM. I know this is obvious, just needed to say it since it has not come up yet in this thread...:rolleyes:

Interesting the way the teeth chipped off, low on one gear, high on the other. Makes me wonder if the snap ring is bending enough from the angle cuts on the gears to push the gear over, as well as flexing the shafts, or the case? How tight is the snap ring in it's groove? How much end play did you have in the secondary shaft?

Has anyone looked external reinforcement of the tranny case? I have seen older Porsche cars doing this in race applications for the same reason. It seems more likely the case is flexing, than the shafts or a combination of the 2 items.

Any thoughts on increasing pre-load on bearings to hold it all together longer? That might help if it is only the shafts, not sure it would buy you anything if the issue is the case.

A tie plate that replaces the reverse gears would not be too expensive to make, should be able to use off the shelf bearing parts and machine a steel floating plate for them to ride in. Loosing reverse is OK for a race car, seems like a non-starter for the road...
 
Lost of folks are running 4.44 OS Giken, I have one in my 6 speed. Most of the track cars Shad at Driving Ambition are using them. He was talking about a stock, 4.08 gear in the works. Should work well for turbo cars as far as ratios go. The lower final drive I run will reduce the load on the transmission gears and increase load on the final drive. It might be a way to help keep the transmission together.

I am at a low 450 RWHP, so I am not concerned with the gears shearing or blowing up my transmission at this point.
 
titaniumdave said:
Lost of folks are running 4.44 OS Giken, I have one in my 6 speed. Most of the track cars Shad at Driving Ambition are using them. He was talking about a stock, 4.08 gear in the works. Should work well for turbo cars as far as ratios go. The lower final drive I run will reduce the load on the transmission gears and increase load on the final drive. It might be a way to help keep the transmission together.

I am at a low 450 RWHP, so I am not concerned with the gears shearing or blowing up my transmission at this point.
Click to expand...


OS Giken just released the diffs that employ the stock 4.06:1 ratio
 
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