SpoolinShark

So over the years I've heard that the Beta transmissions like to grenade under boost in 5th gear but was curious to what was actually failing. I'm now in the boosted club and obviously don't want that to happen. I also have swapped to the Beta II trans which is known to be stronger so that makes me feel a bit better.



So when they do fail, are teething breaking off the gear or does the gear itself explode? I'm curious to what the stock tranny will actually handle outside of 5th and in boost.

Visionz

5th gear syncros are the most common problem with these cars. You should be ok under normal street driven HP, but if it's a high boost / high power drag car, then you'll have some issues with the tranny and even the axles if you have sticky tires on.

SpoolinShark

I'm about 95% sure I'm in the 300s and that will be going up once I get my built block off a member on here. Realistically I'd like to shoot for 500hp and was mostly curious to what the highest hp number has been on a stock tranny.



I know aftermarket axles exist which is fine but I'm not interested in getting a custom set of gears made because that's in the 2k+ range. I suppose shot peening the trans internals is always an option.

MaverickLC

My friend had RD with 320HP and 5’th gear went out on highway. Teeth’s come off the gear. But what he did was that he push it WOT from 100km/h in 5’th gear and around 180km/h gearbox failed.



After that he had RD with 400HP and didn’t have any problems with gearbox. He newer torture his car again by WOTing it on 100km/h in 5’th gear and he rather shift it to 3th or 4th gear and then WOT it.



I am driving with 286HP for few years now and don’t have any problems with gearbox and I did Drag races, Track days etc.



I really don’t know where did you get that Beta II transmission is stronger? On stock power GK have fails on 1-2-3th gear especially if you make aggressive gearing but I never hear that someone had 5th gear fail.



Maybe it is just me but I would always go with RD gearbox rather than GK gearbox…

tdonnell

I've probably got more experience than anyone else on this topic. I've broken gears due to torque overload easily over a dozen times and gone through at least 8-10 transmissions. 60-70% of the failures were 5th gear due to the higher pitch of the gear teeth (more teeth, not as thick at the base of each tooth), but I've also sheared the teeth off 3rd and 4th gears as well. When 5th gear goes at least you can nurse the car home (most of the time) because the majority of the gear teeth will remain in the outer portion of the case (plus you can replace 5th gear without pulling the trans). When 3rd or 4th gear fails you better be close to home or you're getting a tow truck. I made up to 425 hp / 399 ft/lb of torque at the wheels on the stock bottom end without having frequent transmission failures (sure they broke, but on a much lower frequency than after I built the bottom end and turned the boost up to 2 bar). Now if I run at 2 bar boost (unknown power/torque as I haven't dyno'ed the car with this setup) I'm pretty much guaranteed to break 5th after approximately 10 pulls in that gear (sometimes more, sometimes less). I did a track day at Pocono Raceway in PA and turned the boost down to 12 PSI to try and combat the 5th gear issue. I broke 5th about 5 minutes into my 2nd 20 minute session. I will point out though that there were extended WOT pulls in 5th gear that day due to the track layout - I was getting up to 140-145 MPH on the straight away's with only 12 PSI boost. When the gears fail, the teeth just shear off. The center of the gear and internal spline remain intact, but the teeth on both of the meshed gears (one on the input shaft and one on the output) will get ripped off. Basically what I experience during a gear failure is going from a loaded pull in a particular gear - straight to redline after the gear teeth let go.



I'm currently waiting for my custom straight cut gearset to be completed by PAR Engineering in AUS (been waiting 18 months). This set should be able to handle 650+ hp/tq, but is big $$$, $2k is a very low estimate for a one-off gearset. One advantage though is being able to choose custom gear ratios, this new set will give me gearing to reach 150 MPH in 4th (for drag racing) and 185 in 5th (for road-race courses).



Also remember the single disc clutch is about done at 400 ft/lb of torque. I had the push conversion with a custom ACT pressure plate to increase clamping and load holding ability and it still started slipping on rare occasion in the higher gears where I still had traction. I've since gone with a custom Clutchmasters Twin Disc rated for 750 ft/lb.



You are correct that shot-peening / cryo treating should increase the load holding ability of the factory gears, but it's unknown how much of an improvement you will get. If you go that route I'd definitely be interested in knowing how well it holds up!

03tibe85

I know this is an OLD thread but I'd love to hear how this all turned out, especially from TDonnel. The racer I'm building a motor for is looking to possibly get a stronger 5th gear and I'm not sure that's technically feesible without replacing all the other gears as well?

tibbytib

Have you considered shot peening? Cryo? Just read this article and apparently their is a new treatment like shot peening but is suppose to be better. Gives better surface strength with the added benefit of a more viscous surface.



Shot Peening and WPC

03tibe85

yeah problem is what seems to happen with over 500hp is the teeth tend to shred off the higher gears. Doubt anything other than a fully forged set of gears can cure that..



Shot peening and/or cryo may help with a gear that only needs to survive 1320 ft but when your going balls to the wall in every gear up a Pikes Peak rally...well....

03tibe85

Where is TDonnel!! lol I wanna hear how his tranny adventures are going!!

187sks

Way better than hearing about Faith's tranny adventures.