Increasing Gear Durability 2

[spedtoe169]

Hi, I'm a Mechanical Engineer by education and a Racecar Engineer by trade and I have a question I've not been able to answer anywhere else.

I'm building a transaxle for my street car and need it to last with the added power I'll be putting through it. The car is a '94 Toyota Celica ST with the C52 Manual Transaxle. When all is said and done I'll be making about 300hp at the crank and it will be a daily driven car. Aftermarket gears are not available, they would have to be custom and would likely be very costly.

I have a spare tranny that I started disassembling today and there was visible wear on the pinion (not so much on the ring gear). I haven't had much time to look at the other gears but they looked ok on first inspection.

My question is this: What treatments are available to increase the strength and durability of transmission gears and which of them work? I've read everything I can find about Cryogenic treatments and they seem to work although nobody knows why. I've had our racecar transmission REM treated. This seems to lower gearbox temps and reduce friction but I doubt it really does much for durability (other than the obvious stuff less heat does for you). I've also heard of shot-peening gears.

What does everybody think?

Thanks!

John Dolecek
Team Engineer
Wheels America BMW

 

[Metalguy]

Find someone who can make you a new gear from Nitralloy 135 modified and have it nitrided. That works in helicopter trans.

 

[drwebb]

Some production transmission gears have a phosphating treatment applied to reduce wear.

 

[Tmoose]

To reduce chances of suffering a gear failure, first swear a sincere teary-eyed oath not to make abusive starts or shift above 3500 rpm. To help honor your commitment it might make sense to put on slippery tires and skip installing the limited slip diff. There are electronic devices to limit power in the lower gears.

Oh, and magnaflux ANY new or used gears you plan to use to see if they are pre-cracked or have surface defects that may be polished out.

It sounds like you feel wear may be your immediate concern. First I'd determine if what you saw is indeed wear, or simply a polished well broken in surface. Even if the surfce condition "wear" is normal, you may need something more at higher outputs. Then high viscosity lube is full time solution. Beefing up anti-wear and EP and surface treatments are useful short term, or to help things survive being "worn in."

To make gears less likely to crack under heavy or especially impact loads, deburr and polish the roots and edges, then shot peen with propely graded steel shot to the appropriate Almen spec.

 

[toytech]

You could also swap in an e-51 transmission from an mr2 turbo if you are running a s series motor, or an mr2 sc or corolla gtz if you are running an a series. These transmissions are heavier but have been proven to live in 5oowhp mr2 drag cars.
Or just don't drag race your celica, shift it smooth and don't drop the clutch at 7k and it will likely out live your engine.

 

[Jeepwidow]

I work for a off road race team, and we cryo treat almost all axle parts due to extreme breakage. Parts that would last one weekend maybe two now last 4 plus i beleive. These were already used parts and new materials are on the way, but it has worked for us in the mean time.

 

[spedtoe169]

Thanks guys.

Perhaps the condition I saw could better be described as 'deformation of the tooth surface'. Its hard for me to explain. Its not like the teeth were dramatically bent, but it seemed like the driven side of the teeth had been compressed slightly. There seemed to be some localized expansion along the axis of the gear.

 

[Tmoose]

"Perhaps the condition I saw could better be described as 'deformation of the tooth surface'. Its hard for me to explain. Its not like the teeth were dramatically bent, but it seemed like the driven side of the teeth had been compressed slightly. There seemed to be some localized expansion along the axis of the gear."

None of that sounds like normal failure modes in a transmission gear. I would (and did) get ahold of the Dudley or Drago books and compare their pictures to my gears.

Its probably too late to ask the transaxle "sweetie, where have you been?'

 

[Xtrema]

You may want to consider high performance lubricants to increase film thickness, decrease temperature, and enhance shock loading of the gear teeth.

 

[enginesrus]

Planetarys will take more stress than the gear sets in a manual transmission.The load is more distributed. Unless you plan on adding another counter shaft. Go with a nice automatic transmission.

 

[HarrisDE]

Two questions that go together - how fast do you want to go? and how much money you got?

It is possible to increase the life of gears but most options are not realistic:
*Use a super-clean steel - CEVM or low oxygen content
*Super finish - surface fatigue is directly related to contacting surface quality
*(Carbo)Nitride - you could find a local heat-treat house to anneal back and then reheattreat your gears in an carbon+amonia atmosphere. The functional surfaces need to be redressed following heat treatment.
*Synth oil - really only useful if you are in a marginal lubrication situation (it won't hurt but may not help enough)
*Cryo treat - probably the easiest and a proven fatigue aid but be sure to start with good (used not worn) parts

On your gears, it can be hard to tell what is a physical or merely optical feature. If you have gears where material has been removed in the contact zone - that is wear. Most likely it is advancing surface fatigue that gets polished by continued operation. New oil will help but nothing will undo the damage.

 

[76GMC1500]

Get yourself one of them Corvette transaxles. It's based on the Tremec T56, and it is currently surviving behind a 405hp v8 in a 3100lb car. GM currently has plans to build 500hp and 675hp versions of the Corvette, but I don't know if they'll be putting the T56 transaxle behind them.

 

[bigtomwcp]

seems to me gears are available in japan. REM will only help if you have them design a special process to polish in the root of the gear but it helps a lot. we have tried everything from cryo to having everone on the crew urinate on the gears(didnt help but thought it might have mojo).

 

[EfiOz]

Try micro finishing (or isotropically finishing) and deburring the gears. Then use a good synthetic like Mobil SHC7590 or Fuchs HLS7590.

 

[mikeymike123]

For all your unanswered gear questions, you might try the "ask a technical question" at

http://www.bostongears.com

Good luck

 

[gretta007]

I have not answered this question before. Spedtor 169 you asked about shot peening gears, con-rods and Crank shafts? I threw the others in since some one in their response mentioned the MR2. Everything in that motor has been shot peened from the manufacturer and is required to or should I say should be shot peened again during overhaul. When you remove weight off the part But, want to maintain the same characteristic of the original heavier part, then shot peen the item. I could take a damaged crankshaft shot peen the shaft and this crankshaft will out last any new or unused crankshaft. Cryrogenics ahd Heat Treat stress relief parts. However once these parts are placed back into a stress or cyclical load enviroment, the stress's will return back to the part. Shot peening applies a compressive residure layer of compression on to the surface, which now will resist stress corrosion cracking, Fatigue failures, galling and fretting. Plus the dimples made in the surface acts like little oil wells, which will prevent dry start-ups and noise. Shot peening will also increse product life from 100% - 1000%.