5MT rebuild options?

[BAC5.2]

I used to have a 2004 wrx ( stage 2 and full suspension) and those RA gearsets were options for that 5 mt as well. I remember guys discussing them on www.ClubWRX.net a little. Maybe poke around there for info.

 

FWIW most of the guys on that forum would go PPG 1-3 and stock 4-5. Seemed like common idea was that the RA gearsets were barely an upgrade over the STI. The stock WRX 5Mt was a timebomb at anything over 280 - 300 whp.

 

I think you mean PPG 1-4, and a stock 5th. You can't replace 3rd without replacing 4th too.

 

That's the typical arrangement. OEM 5th, PPG 1-4. It's the business if you want a strong trans without the hassle of a 6MT swap.

[05pearl]

That's the typical arrangement. OEM 5th, PPG 1-4. It's the business if you want a strong trans without the hassle of a 6MT swap.

 

Yes, but the PPG 1-4 set up will still cost well over $6K (w/ labor)when all is said and done. I won't consider spending that kind of money unless I blow my trans, and even then I may just look for a used trans. Right now, I just have a syncro going bad from 3-4 where I already double clutch instinctually. I would consider spending $1500-$2000 for gear upgrades but nearly 5K+ for just the internals is too much for me if my car is just a DD and not used on the track or strip.

 

I was hoping to find a lower cost option to make the 5MT stronger, but it sounds like there are not really any good options if the RA and Sti sets are no better than stock.

.

[rubberman]

No it doesn't.

 

Care to elaborate as to why it doesn't help?

[BAC5.2]

Care to elaborate as to why it doesn't help?

 

Typically, metals (and many materials) under minor compression exhibit a slightly higher yield strength. Shotpeening is a process that, through impact, places the surface of a part under minor compression.

 

That's great for fatigue. By introducing a minor compressive load, you can increase fatigue life. That'd be fine if gears failed from fatigue. They don't. What happens though, is that the compressive load built into the part adds to the load applied during operation, and you reduce fracture toughness... which is what prevents crack formation.

 

Of course, this is EXTREMELY dependent on the material choice, AND peening process. Material choice you have no control over, but peening process you do. And if you do it wrong, or don't optimize the process for the material, you do little more than hit it with thousands of small hammers without actually doing anything.

 

As for cryo-treating... The benefits are, in my opinion, marginal. Once a steel has been heat treated, the only way to change the microstructure is to re-heat-treat it. Typically, you'd reheat the steel to "quite hot" (~1500C), then rapidly quench it according to a specific diagram for that particular material. The heat-treating process is a BIG involvement. Do it right, and you can optimize your material. Do it wrong, and you bugger everything up. Since I assure you no one knows with 100% confidence what the OEM gear material is (not without X-ray diffraction... a machine costing a little more than 600k... and even then it's difficult to identify materials post-heat-treatment), correctly heat-treating is unlikely.

 

Cryo-treating was designed to be integrated into the heat treatment process by changing the microstructure from whatever the base composition is, into an almost entirely martinsitic state. That's why it's beneficial for tooling bits. Hardness is extremely important. But, the trade off is brittleness. Since tools see relatively little loading and almost no impulse when properly used (so long as the bit is harder than the material being milled), this is no big deal. A gearset, which is subject to SIGNIFICANT impulse, does not have those same requirements.

 

Sticking a gearset in a freezer and calling it cryo-treating is going to have a minimal effect on the microstructure (if any at all).

 

Combine the two, and I doubt you'd see more than a few percent increase in strength (if any).

 

To back that up, I once surveyed several companies and found failure rates of cryo-treated RA gearsets were almost identical to non-treated sets.

 

I wouldn't waste the time or money for whatever extremely marginal increase in performance that might be had.

[05pearl]

In my experience (using x-ray diffraction to measure residual stresses), shot peening could add up to 100,000 psi in compressive surface stress to a gear surface. While toughness is reduced some, imho the compressive stresses are a huge benefit in preventing failure.

 

I never saw any great benefits from testing before and after cryo. I saw big benefits from shot peening. The only problem is that all gears are shot peened anyway from the OEM suppliers - ie. our stock gears are already peened. So, any after market gears claiming the benefits of shot peening are not really any better than standard gears anyway.

 

I think the PPG gears are strong due to thicker teeth where as the Sti and RA gear teeth thickness do not sound much better than stock. But I am not going to pay nearly $5K for a gear set, sorry.

[BAC5.2]

That's entirely dependent on method and media used for shot-peening, right? You could fire lead or copper BB's at a part using a pellet gun, and call it shot-peening. Not all peening methods would give you that amount of compressive load.

 

Shot peening definitely improves fatigue life of a component, that can't be argued. But how would 100ksi of compressive surface stress prevent failure in an impact-induced, mode-1 failure scenario? I haven't done any instrumented testing regarding that, but I cant think of how that would be an advantage.

 

Are you sure the OEM gears are shot-peened to induce compressive surface stress? They don't have any tell tale signs of being shot peened... unless they shot peened the billets before final machine work... which doesn't make sense.

 

I think PPG gears are strong due to far more than thicker teeth. Material choice is the overarching factor when it comes to strength.

 

I look at transmission options three ways.

 

1) Make less than 300whp and 300 ft-lbs, and don't launch the car or shift fast.

 

2) Spend the money to do a 6-speed swap the right way (Working DCCD, Brembos, 5x114, R180, etc). If you can't sit around and wait for deals to come along, expect to spend a little over $6k for used, and more for new (including everything).

 

3) Spend a lot less than a 6-speed and get PPG's (the price follows the exchange rate, and there are occasionally group-buys for almost 50% off). Spend a bit more, and get PPG's with a front LSD. You'll have a brand new transmission, with brand new gears, and brand new synchros. Plus, you'll have a tried and true proven setup.

 

You can't go wrong with a 6-speed or PPG's. Either will be more reliable than stock, and the deciding factor is what you'll end up doing with the car.

 

When it comes to rebuilding the 5MT, I'd say anything other than PPG's is a waste of money. You always run the risk of blowing the replacement set. What's worse than spending $4500 on PPG's? Spending $3200 on something else... twice.

 

If you don't want to spend that much on a gearset, spend a little more and do a 6-speed swap.

[05pearl]

There is no proprietary steel per se that is far better than others. No company uses a far superior high strength steel - hs steel is hs steel and while they may vary a little in tensile strength, they don't vary that much. It's not like PPG is using Inconel for their gears. High strength steel + shot peen is a long proven combination for fatigue life and resistance to tensile failure. Shot peening is used on every high cycle fatigue steel in auto and aero applications; gears, springs, valves, crank shaft... the list goes on forever. Proper shot peening is done by mil spec usually, and there is no magic to a "special" shot peen. Everyone knows the proper shot size, hardness, and intensity to use. It has been refined to a science. And, all auto companies have optimized the process. Here is a typical application: http://www.shotpeener.com/library/pdf/1953007.pdf

 

If you look under a microscope you can see the 100% dimpled surface on the gears.

 

BTW, if you see a group buy 50% off of PPG gears for the 5MT, I would consider jumping in. That is the best advice I have heard yet for rebuilding the 5MT.

[BAC5.2]

I think there was one in the GB section of Nasioc. PPG's for $3100, or $4050 built or something like that. I'd call Andrewtech.

 

On steel selection, I'm not so sure about that. There is a significant difference between one company running some 4000 series steel vs. another running a more exotic 8000 series. Heat treatments play a massive factor as well. There is a lot more that goes into material selection than tensile strength.

 

When I was doing micro-hardness tests of various materials, one of them was an OEM Subaru gearset. I was using section samples from the input shaft (which have clear machining marks on them), but I wasn't really concerned with surface treatments. I've wanted to do some more testing, so perhaps I'll snag a few 4th gears and have a looksee at the surface on a micro-scale.

 

On the shot-peening issue, I have no doubt it's a science. I have doubts about companies who tout the benefits of them, and their adherance to mil-spec proceedures. And, if the gears are in-fact shot peened (which I don't doubt, I just haven't seen it), then there is absolutely zero benefit of having it done AGAIN.

 

Now that I think about it, it does make sense to shot-peen a gearset. Not necessarily to prevent gear tooth failure, but simply to extend the service life of the component under normal usage. I imagine that shot-peening is typically a finishing process, performed after heat-treatments are complete?

 

"Good practice" says, what, 10^6 cycles to failure for fully reversible loading? 10^6 cycles goes by PDQ at 3000RPM. That's just under 6 hours of operation! And that's just for the input shaft! The output shaft turns far more than that! Obviously, cycles to failure can be designed into the shaft in other ways besides the use of imposed compressive stresses, but that does add another factor of safety layer. I imagine it wouldn't be uncommon to see ~5x10^8 cycles on the input shaft during the service life of a transmission.

 

So, I do agree that there is a benefit to shot-peening for fatigue life. Gearsets are under fully reversible loading everytime a load is applied (either acceleration or deceleration). I stand corrected on that front, but stand behind the opinion that repeated shot-peening is pointless.

 

Whether or not shot-peening improves the strength of the gear teeth, I'm still not convinced.

[05pearl]

I absolutely agree that shot peening, again, is useless (except for the dual shot peen technique which I won't get into). I was just saying its funny that companies tout "were better because we shot peen" when everyone shot peens.

 

Proper shot peening can make a component have infinite fatigue life depending on the loads seen and the compressive stresses imparted.

 

I don't know what you mean by improve strength of gears. The word "strength" is a bit subjective by itself and can be interpreted different ways. Parts typically fail in tension, not compression (except for submarines ) and failures typically initiate at the surface. Adding -100 KSI compressive stresses to the surface of a part adds that much more loading capability and safety factor to the component.

 

Shot peening is a finishing process that is usually done after heat treat. But, sometimes a slight heat treat after peening can be performed as long as it is done in a way that does not stress relieve too much of the beneficial residual stresses from the peening.

 

As far as materials, I highly doubt that PPGs materials are significantly better alloys than OEM. There are many alloys of high strength steel, but none are 4 X as expensive as others. And, most of the basic properties of those used are within the ball park of each other.

 

You and I agree - it is PPG's thicker teeth that make their gears able to withstand higher loads. Are they worth 3-4 X as much as oem for a daily driver? To some, obviously it is. To me, I just have a bad syncro right now and wanted to upgrade my gears if I had to have the tranny pulled apart. Would I spend $4K on gears? - I doubt it. Would I spend $2K? I would definitely consider it.

[BAC5.2]

Strength might not be the best word, but I should say resistance to fracture.

 

Tooth failure most closely approximates a mode-1 failure. A crack forms at the surface, propogates, and failure shortly follows. Failure is almost always the result of impulse (producing brittle failures).

 

PPG prices are high for a few reasons, I'd imagine.

 

1) Low production. Subaru makes tens of thousands of gearsets, all in extremely large batches at extremely advanced manufacturing facilities. PPG makes, probably, 1/10th those numbers (and not only for Subaru). OEM gears are subject to the economies of scale, PPGs arent. A full OEM gearset costs ~35 to 40% of a PPG gearset, and are made in enormously larger quantities. The material may only be 10% or whatever more expensive, but manufacturing costs favor larger runs.

 

2) They are a business. No one is in the business of giving things away (we'll leave politics out of this). They charge what they charge to cover overhead, and make a profit. Subaru profits very little from parts sales (in fact, it's almost entirely dealership profit that you are paying for with OEM parts).

 

I do agree that the tooth profile, root thickness, and face width are all significantly larger than any stock Subaru offering, and that does contribute to their increase load capacity. Still, I doubt it can account for all of the increase. Not all steels are created equal. If they were, the field of material sciences would be pretty boring.

 

One thing I know for sure, the material is not even close to the same as any OEM gear.

 

For someone who doesn't make a ton of power? A 6-speed and PPG's are probably overkill. For me? If I blew my trans, I wouldn't spend $2k on something with a MUCH higher failure rate than the $4k option. What if you are one of those failures? You'll either have to bite the $4k bullet (costing you $6k total), or buy another $2k gearset that you already broke (which would have made PPG's or a 6-speed the better investment).

 

For you, with just a blown synchro... I'd replace the synchro and button it back up. Save your money for something that might come up later. I think it would be foolish to spend $2k to fix something that ain't broke yet.

[05pearl]

I called IPT. They claim to rework the 5MT as below for $2800. Note, no new gears. Just reworked gears with peening and cryo which as we discussed may be usless (but reworking the gear surface after 54K miles can't hurt). Guy on the phone claims 40% increase in strength over stock 5MT. Does anyone believe this? Anyone have experience with a 5MT rebuilt from IPT as follows:

 

Upgraded Lube System by machining

Gears are Shot Peened and Magnetic Particle Inspected (Magnafluxed)

Gears Chamfered and Hand Detailed

Extreme Duty Synchro Rings

Heat Treated Splines

Cryogenically Treated Gearsets and Shafts

Hardened Shift Rails

Heat Treated Forks and Premium Heavy Duty Bearings

[BAC5.2]

I don't believe a 40% increase in strength.

 

How are they upgrading the lube system? There is no lube system.

 

Why would you chamfer the gears? That won't provide any benefit (except possibily introducing surface imperfections, and removing the most hardened part of the gear i.e. the surface).

 

There are no such thing as extreme duty synchro rings, Subaru makes the only ones, and they are all the same.

 

The splines are already heat-treated. Are they re-heat-treating JUST the spline areas? That would provide no benefit other than to introduce a brittle transition at the boundary of the heat-treat.

 

How are they hardening the shift rails? Heat treating them? Why? There's very little risk of damaging a shift rail in a synchronized transmission.

 

How can they heat treat the forks? They are cast aluminum...

 

Premium HD Bearings? No one makes bearings other than Subaru... unless they are custom bearings, which would be a pointless investment.

 

I don't buy it.

 

I also don't think you need to worry about re-working the gear surface. Lubrication is provided by hydrostatic pressure. The wear on the teeth after break-in is marginal at best. I've seen the insides of transmissions with over 200k on them (my old Forester trans). The gear teeth looked no different than a set with 10k out of a WRX.

[Silverstar]

Subscribed as I'll be shopping for a new tranny after mine took a dump on me today.

 

Apparently HTA68 + E85 + infamous > 5MT

[j255c]

anything >375wtq is a ticking timebomb transmission.

[05pearl]

Someone needs to offer some decent options for upgrading the 5MT without spending a fortune.

[Silverstar]

^^+1

 

looks like I'll be dropping in a salvage unit, then will be saving up for a PPG gearset and rebuild on my grenaded unit.

[05pearl]

^^+1

 

looks like I'll be dropping in a salvage unit, then will be saving up for a PPG gearset and rebuild on my grenaded unit.

 

Let us know how much you end up spending on the salvage unit.

[Silverstar]

I'm finding prices ranging from $800-$1500. I'll post up what I end up paying after I end up paying it.

[BAC5.2]

You could always consider mFactory as a small upgrade if you really cant justify PPG. At least they'll be better than RA's or STi's. I had heard that Andrewtech was going to be working with them to come out with a new gearset. I'd call them for options about that.

[05pearl]

^ Yea, another option that I did not know about. I wonder what they cost.

[Bolksey85]

What we need is an option that is no more than about $2500-3000 for a 1-4 gearset that can handle upwards of 400AWHP. Something that can handle power without PPG pricing. There's a lot of people who would be interested in a nicely built middle of the road gearset without going over the top on price. Leave the PPG's for the 35R crowd, this should cater to the 20G crowd, IMO.

[05pearl]

^ +1, a $2000 1-4 gear set rated at 400whp should get some decent aftermarket LGT and WRX business. You are correct, there are no "middle" power gearsets available.

[Silverstar]

^ Yea, another option that I did not know about. I wonder what they cost.

 

~$3k

http://www.teammfactory.com/products.php?category=PRO Synchro Gear Sets

[theotherguy]

Legacy GTs have some strong gear sets as they are.

http://forums.nasioc.com/forums/showthread.php?t=1040104

Non RA STI gears

 

I have an OBXT set up for my '00 RS with a built 2.0.

[Silverstar]

Let us know how much you end up spending on the salvage unit.

 

The prices I listed above aren't quite right. Once they find you you need the turbo manual trans, then it gets a little more expensive.

 

Prices ranged based on mileage. On the low end I found a 110k mile unit for $1500. On the high end I was quoted $1995 for a 42k mile trans.

 

Prices included shipping.

 

Time to start reading up on transmission changes and buy a trans jack!