Maybe you could pull out a dyno sheet and figure out the exact torque that it took to kill the NA unit. Since first and second gears can have wheel spin issues with that much power and third calms down, if you know about how fast you were going you can work backward through the gear ratios and have a pretty good idea of the number.

It would be fun to be able to say, "NA trannys break at 371 ftlbs of torque, give or take a couple"

 

Wow didn't think it would cost that much to rebuild the transmission. Then again, that amount is probably minuscule compared to the total amount already spent on your car.

 

it usually isn't, the T2 trannies are pretty stout, 5th gear syncro is a definite to replace and probably 2nd as well. the input and output bearings are pricey but only necessary to replace if they whine. most shops recommend replacing the bearings because they can be damaged if you aren't careful during disassembly. the rear output bearing can be a real BITCH to get off sometimes. i've broken many pullers working on that one... the larger sysncros (lower gears) and bearings run about $40-70 each and there's 4 main bearings and 5 syncros.

the most difficult thing about tearing apart T2 trannies is fabricating bearing pullers.

 

there is a lot of labor time in there too, the T2 trans just takes a long time to take apart.

 

Last time I had the car at the dyno was two years ago and on the low side of 13 PSI it put down 392 RWHP and 300 FT-lbs of torque. My first transmission broke at just a little more power as I cleaned up the tune a bit a few months after the dyno. However, it did last for 2 years until it blew up this spring. This transmission was killed with only a few tuning runs at 16 PSI, and I have not had the car on the dyno at this boost level.

A transmission rebuild can be considerably cheaper, but I opted to have all the wear items replaced. If just what is worn out is replaced, it's around $600. I had an NA transmission done like that years ago and it turned out fine (until I shredded the input and cluster shaft gears). With this transmission I opted to have all the syncros replaced, and that ads a considerable cost.

 

We grenaded a newly rebuilt N/A transmission this past weekend. It had about 200 track miles on it. 2 subsequent corners where you top out 3rd gear at 8k rpm and let off, the 2nd corner it blew up. Luckily i had another one but now i will have to figure out what to do about a long term solution. NASA rules basically say if i change any of the forward gear ratios we take points that we don't have to give.

170 RWHP road racing car. First weekend since the car was built.

 

my rebuilt T2 transmission (3500 miles, had all bearings and synchros replaced by a competent shop) is grinding/clunking under really hard shifts into 3rd. I could be imagining it, but it seems to have gotten a little worse over the past thousand miles or so. Usually it will go into 3rd under this type of driving but I have now chosen to double clutch 3rd for hard shifts. The double clutching eliminates the problem completely. It goes into gear just fine and doesn't make any noise.

I'm not about to get some built T5 or other crap. I'll just keep double clutching the thing. Even if it's a fixable problem, I've spent enough hassle and money on the car, I'll just accept the additional 250 milliseconds of shift time. I have a stock shifter with new shifter bushings. I've considered a Corksport short shifter (just in case a more precise shifter would eliminate the problem) but I am still concerned about rattles. Plus I think faster/harder shifts would only be more abusive on the transmission.

 

yeah if anything you want a longer shifter on there.

 

Cryo treat?

 

Yeah, so it happened again....again....uh, again.

Last night I went to the 1/4 mile as it would be the last opportunity to do so for the season and a few other local RX-7 people (Casual John and FC3Sdrift) would be there as well.

I didn't expect much since I long ago reached the limit of my tires, and my new clutch was being overpowered as well (another story). On the first run, I lined up and made my launch at about 6000 RPM. Expecting at least some tire spin, instead I was rewarded with instant wheel hop and before my brain had told my foot to "LET OFF!" there was a BANG! and the car stopped moving under it's own power.

As to not spread oil down the track (too late for that...) I pulled off to the side. It was clearly not a transmission issue as I could hear it whirring, but the car wouldn't go anywhere....Then I saw oil dripping from the differential. Crap. The driver side stub shaft broke. And there must be other damage internally as well because the car wouldn't move under it's own power. You'd think an LSD would at least send power to one wheel even with a broken shaft.

Nothing could be done, so I was towed home on FC3Sdrift's CAA card (Thank you again!!).

I'm going to look my spare diff today and see if I can just swap the stub shaft with the diff still in the car. If so, then yay. If not, then I think I'm out for the season as my shop is full since I just started restoring my '76 Cosmo (see link in signature). Maybe if I can clear some shop space I'll swap the spare diff in...

 

nah even with LSD if you have one wheel completely tractionless (or a broken shaft lol) the other one will do nothing. you need a locker for that.

 

you'd think so, we thought so, but we popped a stub axle out on accident, and found that the LSD actually won't move the car.

good luck, hope its just a broken stub shaft!

 

This is an n/a diff? Back I blew my n/a LSD in a very similar fashion. I was at a dragstrip (with a couple thousand people there btw), launched at 6500, and heard a "BANG!" sound. The whole crowed jeered as metal chunks went flying out from under me. I let the clutch out but the car was going nowhere.

Btw, changing from Mobil 1 to Redline MT-90 in my tranny fixed my third gear grinding.

 

I have not looked at the diff yet because I wanted to spend the day in the shop starting to fill the extra holes (antenna, door handle, etc.) in my Cosmo. It will also be at least a week before there is enough space to bring the RX-7 in, so I'm thinking of just storing it for the winter and fixing it next season.

Yes, that's an NA diff. Actually, a FULLY REBUILT NA diff which was NOT cheap (those clutch packs are super expensive). The plan now is to get a TII diff, have my driveshaft modded to connect to the TII diff, and make hybrid TII-NA half-shafts so I can keep my 4 lug wheels.

 

Bro I could've told you that this diff was going to blow. An n/a diff can't stand up to a drag racing with a nonturbo engine, speaking from personal experience

 

That's too bad, Aaron. But there is no sense scrambling to fix it, this late in the season. Parking it for now, and focusing on the Cosmo makes sense. That gives you time to think things through. And if you decide to swap out your tranny, I'll be first in line to take it...I killed the 3rd gear syncho in my car that night. She grinds from 2nd to 3rd all the time now. I'm gonna have to practice double-clutching for now.

 

Heyy Aaron, I see where you are coming from with the True N/A turbo. But you have already done it, and well, far surpassed the limitations of the components. IMO you have done extremely well but I would def. upgrade to T2 components. You essentially still have a true N/A turbo, just with upgraded parts to handle the torque. This "should" avoid any headaches in the future and will cost you far less. I would not discredit you the N/A turbo status, and i take my hat off to you. Happy thanksgiving btw. take care and drive "fun".

 

kinda surprised it held up as long as it did... good luck with the rebuild

cant wait to see the carnage pictures.

 

The previous diff in the car was the stock open diff installed in '86. Likely on the order of 500 or so NA drag launches, 100 or so stock turbo launches, and 50 or so GT40 launches. Now, obviously, it held together because it was open and the tires were a safety fuse. But, it certainly stood up to the abuse.

Going to LSD and increasing traction put a lot more stress on the diff. And the glue they laid down (which they almost never do) was the nail in the coffin of wheel hop.

Exactly. I think it will wait until the spring. Note that I have a freshly rebuilt TII transmission in the car which was installed last winter. I won't be swapping it out. At this point I'll just start shopping for a TII diff then deal with prepping it over the winter. I think I'll try my hand at a diff rebuild...doesn't look that hard.

That sucks about your syncro, but it actually would not be too bad to replace. I bet it would be about $600 to replace the bearings and the bad syncro if you remove and reinstall the unit yourself. Winter project?

Probably no pictures until next spring.

 

Am I missing something here? You have a Turbo2 Transmission... You're going to get a Turbo2 differential...

Why modify the driveshaft? Wouldn't it be more cost effective to sell the shaft you have now and find a Turbo2 driveshaft? (Maybe from the donor that you get the differential from, if you haven't already sourced a diff yet?)

 

i agree, i broke a GSL-SE ring gear with the wheel hop... stock engine and 400+ treadwear tires too

 

HE's got an NA trans.

Don't forget about your shed.

 

He had a turbo trans going to an n/a LSD connected to 4 lug hubs. Now he wants to have a turbo trans connected to a turbo LSD connected to 4 lug hubs.

 

grats on figuring out that the n/a drivetrain is too weak to sustain those power levels! i'm actually surprised it did this well but i don't know why anyone would beat their head against the wall trailering their car when upgrade parts are readily available for reasonable prices.

i'm guessing you like whips and chains?!

 

I had a brain fart. What I meant to say was to have a TII driveshaft made. I could use a stock shaft, but they have weak and non-replaceable u-joints. The local driveline shop can make me a brand new TII sized shaft that has massive u-joints (they come from some kind of huge Dodge truck) that are easily replaceable. So that's the direction I will go. My TII trans to NA diff shaft (with big u-joints) will be up for sale at some point ($200 is the price).

Basically, yes. And the only reason I am concerned with staying 4 lug is because I just did the all the bearings, and I really like my wheels. In fact, I think they are about the only aftermarket wheels that suit the car and actually look good. For that reason, I will go to the length of custom shafts so that I can keep them. So I'll just have custom shafts made to connect a TII diff to the 4 lug hubs. Should be an easy job for the driveline shop.

Considering how "weak" most people think the NA stuff is, it lasted quite a long time at high power levels. Not until the 500HP mark was the car reliably breaking transmissions, and not until a drag launch with both wheel hop and glue did it break and NA diff. I think that's still pretty impressive for driveline stuff that a lot of people like to call "weak" and "junk".

You're damn right!