Busted Gearbox

Engines, Transmissions & Final Drive questions and answers

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Sheck
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Postby Sheck » Mon Aug 28, 2006 11:03 pm

thanks pete,
yea what he said, its all mid corner poping, unless i'm goin for the big entries and then in that case its a 3rd or 4th gear pop to get the thing going.
Scando flicks are alright but in some situations dont work, or dont work well enough or just look shite.

I've been researching all arvo and have come to the conclusion that i'm stuffed! heheh but also TII is a major operation including some things i didnt think of like moving the slave over to the other side which brings it closer to the exhaust plus theres heaps of \"releiving\" to be done to the box to clear bolts, exhaust and starter motor.
There's one mention of using a 88-89 929 box as it is more similar to the b series engine blocks which could make bolting it up easier, andanother sort mention of using, from what i can gather, an auto mx bell housing a TII (gen 2) middle and a TT (gen 3) rear. This would make it bolt onto the engine, have tought internals and have a workable rear (ie the ppf mount is on the opposite side but this might make it easier to make a custom mount).

Also i've been trying to find pics of an SR20 box as the place in WA that make the conversions has the custom ppf mounts already which would make that part easier.
But in my search i found that the MX5 6 speed is the same as the sr20 6 speed but just with different gearing ratio and different bell housing. So with any luck this would have th esame strength as the srbox but fit in with out as much of the trouble (wiring is different :cry: ). Then i'd have trouble with the ratios as i currently have a 4.3 gearing in my 1.8L rear - so i wonder if i could put the sr gearst into the mx box?
Also from what i have read the sr 6 speed weakness is due to a dodgy circlip between 3rd and 4th but if its welded in or recessed for better seating it fixes the problem.

The first box is at the mechanics so i'll find out exactly what happened, might just be a better that stock option to get a new stock gear set shot peened and heat treated.

Damn weak mx5 parts! Cant handle my abuse! :evil: :mrgreen:

Sheck
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Location: South East Brisbane

Postby Sheck » Tue Aug 29, 2006 7:56 pm

Ok so the verdict is a rebuild would cost around the $1700 mark. This is why noone bother to rebuild these boxes!!
He said the the gears are super small and just couldnt handle it, but he was suprised that they broke while using Redline shock proof. Basically the top layers of the gears were breaking off in small shards.

Now the search is on for a 6speed.
Question, does anyone know if they have the same size gears as the S15 gearboxes?? I know they are the same modle of gearbox made by Aisi (or something like that) and have heard that they are basically the same box, but i need confirmation!!

Any helpwould be appreciated!
Dave

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Sean
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Re:

Postby Sean » Wed Aug 30, 2006 6:48 pm

Sheck wrote:Ok so the verdict is a rebuild would cost around the $1700 mark. This is why noone bother to rebuild these boxes!!
He said the the gears are super small and just couldnt handle it, but he was suprised that they broke while using Redline shock proof. Basically the top layers of the gears were breaking off in small shards.

Now the search is on for a 6speed.
Question, does anyone know if they have the same size gears as the S15 gearboxes?? I know they are the same modle of gearbox made by Aisi (or something like that) and have heard that they are basically the same box, but i need confirmation!!

Any helpwould be appreciated!
Dave


The 6 speed and SR20 6 speed are very similar internally (different ratios), but the extena casings of teh boxes are quite different.

External case can have a pretty large influence on gearbox strength, the torsional stresses on teh box can actually flex the case, resulting in broken gearbox internals.
When results speak for themselves - don't interrupt.

Sheck
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Postby Sheck » Wed Aug 30, 2006 8:10 pm

Yea i've read about that, and it plays a tiny role in the weakness of the 5 speed. I've also read that you can brace the box with stainless steel straps to almost completely eliminate all the flex.
Heard about some guy doing that to a rotary gearbox on his 9 sec drag monster, he used a strapped out stock gearbox!! Apparently it held pretty well.

Dave

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Postby The Pupat » Thu Aug 31, 2006 11:03 am

Flex is actually one of the primary reasons the TX3 gearbox sh!t themselves so easily.
'92, Red, Hardtop, Noisy CAI, Even more Noisy Exhaust, AVO Shocks with TJR Springs (Not so Fuli drifto speco).

Sheck
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Postby Sheck » Thu Aug 31, 2006 3:17 pm

Wow now theres some good info for the TX3/Familia drivers, strap the hell out of your box!!
I wonder if welding \"straps\" of aluminium to the case would work?...

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Sean
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Re:

Postby Sean » Mon Sep 04, 2006 7:24 pm

Sheck wrote:Yea i've read about that, and it plays a tiny role in the weakness of the 5 speed. I've also read that you can brace the box with stainless steel straps to almost completely eliminate all the flex.
Heard about some guy doing that to a rotary gearbox on his 9 sec drag monster, he used a strapped out stock gearbox!! Apparently it held pretty well.

Dave


You're probably thinking of Pat Long's car CRITTA...

Lots of 9 seconds passes with a stock as a rock supra turbo 5 speed with H pattern....
It's been in there for years and lets face it, reeling off 9 second passes would put more than a little stress on it. I suspect the style and quality of the mounting of the box is what keeps it together, I don't know for sure, but last time I saw under the car it was not strapped...

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Boags
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Re:

Postby Boags » Tue Sep 05, 2006 10:16 am

butters wrote:boost would be ideal but expensive


You don't know this car obviuosly Butters! :shock: :mrgreen:

I think Sheck runs 14PSI???

Boost is the issue here for sure, but not becasue he doesn't have any! :lol:

And 6speeds are hard to find, MX5 Plus only has one and it's in a car...

Boags
Spartan Motor Sport : http://www.SpartanMS.com.au

Sheck
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Postby Sheck » Tue Sep 05, 2006 7:32 pm

Yea thanks mate,
i am running boost about 12-13ish (not particularly stable). I'd like more power as that would keep clutch poping down, and i am sourcing a 6 speed (should have it soon).
As for the skinny tyres, the only problem with that is that the slippier you go in the rear the harder it is to control and the slower the slides will be. As i consider myself to be about intermediate, the last thing i want to do is slow down my slides (i love high speed!!!!!!).

I'm going to be doing a few more things to my car before i head out again, hopefuly it will help a bit. The following will come later but is def on the cards;
Basically i need new suspension, bushes, a really good tune (should be about 5-25kW in a proper tune) and some under body bracing. I especially need to cut the axel tramp out of my car, dont want the diff blowing too!!!

Cheers for ideas!!!!
Dave

Sheck
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Postby Sheck » Tue Sep 05, 2006 10:15 pm

Hrrm, that would be good actually!
Might have to do that this weekend, got another drift day comming up in a couple of weeks, so i want it as drift ready as possible. Lets hope the gearbox holds up :? :lol: :evil: :mrgreen:

Dave

Sheck
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Postby Sheck » Sat Sep 09, 2006 8:42 am

Ok guys, just got the 6 spped in last nite, and now a few quick questions:
1: Why am i getting alot of vibration? (not cool, everything is done up tight and in the right spot etc. Could it be the balance weight on the diff??)
2: Whenever the car is in nutral the revers light comes on! If its in a gear - any gear it turns off.
3: Its a bit noisy, not noisy like a stuffed box (i know what they sound like :mrgreen: ) but you can just hear every operation thats happening.
4: wow theres no turret oil, the oil from the box must suffice.

And my first impressions are that its waaayyy better haveing a 6 speed!!!! The gears are soo close i cant wait to go racing and drifting!!!

Cheers
Dave

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sabretooth
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Postby sabretooth » Sat Sep 09, 2006 11:09 am

Sheck wrote:2: Whenever the car is in nutral the revers light comes on! If its in a gear - any gear it turns off.

The 4 wires going to the gearbox - two are for reverse, two are the neutral switch. Swap the pairs. :)

Are you sure the gearbox is good, seeing as it's so noisy?

Are the boots for the gearstick still okay? I'm wondering if they're letting lots of noise in.

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JBT
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Re:

Postby JBT » Sat Sep 09, 2006 12:45 pm

Sheck wrote:Why am i getting alot of vibration? (not cool, everything is done up tight and in the right spot etc. Could it be the balance weight on the diff??)

Could be. Try re-attaching the tailshaft through 90 degrees rotation and see if that changes anything.
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Sheck
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Postby Sheck » Sat Sep 09, 2006 8:14 pm

Hey guys, that was a quick post before work this morning. On th eway i figured out that the vibration was from the exhaust. I damaged one of the mounts when i took it off and when i reattached it (without fixing the mount) it caused either the cat or something else to contact the body.
So i'm pretty sure that's the vibration sorted.

As for the switches - dad told me the same thing when i got home today. I didnt think of that!! hahahaha

And the noise, it's kinda gone a bit now, i can still hear it but it is quieter. My gearstick boots are completely stuffed and i cant see myself getting new ones anytime soon as i've been driving like that since i got the car. (yes i am very lasy!!!)

Thanks for the responses guys!!!

Damn i'm loving the smooth shifting!! Caint wait to get out on the track!!!!!

Dave

Sheck
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Postby Sheck » Mon Sep 11, 2006 4:02 pm

Ok all is fixed, i fixed the exhaust mount and made another to take some of the stress off it.
Reverse light are all good, and i tuned the car (turns out it was still good, rich but good)
Hurray for fishys in 3rd!!
While checking the mixtures in the wet today i was able to easily lose traction in 1st-3rd and 4th was having trouble maintaining constant traction, oh and that not snapping gears just changing lightly.
Now i just need the car to do this in the dry!!!

Butters also helped me make up one of his rear suspension braces, it has noticibly helped! A little less under and a bit more over :twisted:
Thanks butters!!!!! (oh yea and i was thinking the front brace would be possible with a couple of spacers/washers under the brace so the bar clears the subframe, then counter sink the bolts a little to keep clearance)

Cheers!!!


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