My six speed brand new UK gearbox has 23000 miles and 17 months use. The engine is a standard internals EJ257 and in this time has run est 395-450 lbft and 434-500 BHP on three turbos from 20G, Ion P450 and GT30R-12 rotated, lower figures on Optimax/smaller turbos, highest on the GT30R-12 with octane booster and 24 PSI peak. The gearbox has a Subaru quickshift. Oil was Redline lightweight shockproof 75W90 with some 75W90 NS in as well.

It seemed to be running OK until on Sunday at Crail having done high 11s on the 1/4 it popped out of 5th gear. My gearchanges have been getting quicker so that I've been nearly flat shifting on occasion, as it is obvious that doing this at track or strip results in much better times.

The box has been stripped and the primary failure is the bush that is part of the selector fork that engages in the hub (?) is very worn so it doesn't stay in gear. They are also worn on all the other selector forks, and all the synchros show signs of wear. It has been recommended to replace all the forks, all the synchros, and also replace 5th gear and its hub to do the job right which I want to do, although only the 5th gear selector fork is causing a problem. 5th gear was said to be borderline, and I don't know if the wear on it is due to the worn selector fork causing misalignment or not? Total bill with labour and VAT will be about £1500.

What I am trying to work out is:

1. Are these failures due to hashy gearchanges?
2. Do I need to drop my torque?
3. Would Syntrax have prevented these failures rather than Redline Shockproof which has been thought to be too slippy for 6MT synchros?
4. Should I stop using this as a daily driver?

Opinions/thoughts welcome. I don't have a detailed parts list or photos at this stage.

 

can you remember how many drag runs the aus? tuner did , before stripping and finding nothing wrong when the 5speed had failed in single figures?

no doubt fast , course changes will cause issues but in your case the high torque in daily use must also be a factor.

keeping the car as a weekend warrior could also speed up similar failures happening , so perhaps pavlo could supply something for your casing?

 

Think it was 100.

T-uk and I have discussed this, but how "experimental" are these kits that go in 5 speed casings and are any of them tough and streetable? Straight cut is out on a daily driver IMHO having lived with it already.

 

The effect of torque would be seen on the gear teeth themselves (rotational speed would also come into it, but I doubt you've been using excessively high revs anyway with the amount of torque you have available?) so that probably accounts for the 5th gear wear. Synchro and selector wear would be the result of your fast, high rev. gear changes as you have removed the torque from the equation by dipping the clutch. The quickshift obviously multiplies the force you are applying during gear changes, aggravating the situation further!
As for oil, yes there is a question on the suitability of full-syn oil to allow the synchro to function efficiently, so changing to semi-syn may slow your gearchanges a little but maybe synchro teeth may break instead of just wearing???? What you need is a straight-cut racing dog-box
JohnD

 

Thanks for the input John. Rev limiter is at 7500 RPM.

5th gear being relatively long can be used for quite a long time under a heavy torque load. Generally it has not been an overboost gear though due to using an AVC-R to control the boost per gear as necessary and out of sympathy to the headgaskets.

 

http://forums.nasioc.com/forums/show...ht=6mt+synchro

http://forums.nasioc.com/forums/show...ht=6mt+synchro

 

Is a helical dog-box suitable for daily use?

 

I think your expectations are too high John. I would not expect a highly tuned car using stock components (gearbox) to last as long as when its in stock configuration, especially when the car is tracked or on the strip. It seems obvious to me and I'm not trying to be patronising.

I don't know anyone else that's trashed a 6 speeder but I could have put money on a few names

Lets face it, dedicated sequential boxes, which cost £0000's go bang, so a standard road box is lucky to have lasted so well considering the conditions its used under. Perhaps you've found the limit of these boxes? Maybe a PPG gear kit in a 5 speed (fitted correctly) is the way to go? You could look at all your questions and come up with a formula to make it last a bit longer but thrashing a car car down the strip is bound to lead to failures sooner or later IMO.

I'm sorta unhappy that you've done this as I rather hoped you'd found a really nice package that I could aspire to. Damn your continual meddling, you just can't help yourself, its like a disease with you I remember when you vowed that you would never go FMIC (don't make me find that thread).

F

 

Mine was doing exactly this, i found that if put slightly in 6th it would glide into 5th no problems at all, after some harsh driving one night i went for 5th and found id lost all gears other than 2nd, when the box was stripped down it turned out i had "snapped" the selector rods which i can only assume were bent before finallly snaping which was leading to the crunch in 5th....

 

Disease LOL.

Had a good chat with the gearbox builder. 5th gear itself is to be replaced because the dogs are worn on it, not the gear itself. The synchros are being done just because the box is out and it would be wrong not to given that they do show wear. The selector forks with nylon end pieces are a poor design.

So they have said I do not need to reduce my torque, but if I want the selector forks and synchros to last longer I should moderate gearchange style.

 

Few. Operator mis op! Hurrah

F
PS seem to remember Tim doing the same fork snapping trick with his 5MT then deciding to pack it all in...

 

Maybe get rid of the quickshift? Wear rate is probably exponential to the change speed?

JohnD

 

Wonder what is the best way to get a shifter mechanism?

 

I haven't had real problems with my 5 speed box, bearing in mind the synchros, forks and rods were all well used when the gearset was fitted. I have done at least 70 drag runs on the box, and 3rd and 4th synchro are just beginning to wear a little, as I get a slight crunch if I try to downshift too fast at high revs. I thought the 6MT had triple cone synchros on all gears, the 5MT has it on 2nd gear.

When did your car have a straight cut gearbox John?

Paul

 

iirc, 1st and 2nd are straight cut on the PAR kit?

good to hear that the wear on 5th gear is not torque related. so a proper built engine with decent boost would not need to be **** shifted

bit worried about my 6speed since "that hashy doctor ****" has borrowed my car while his is off the road

bet the m3 does not have these sort of issues but then I can give you 15002 reasons not to buy one.

 

Only the 1st gear is straight cut on the PAR, and I didn't think the 2nd and 3rd were that noisey at all, except on overun perhaps.

I think John's expectations are too high for the money spent, which when compared to say a racing gearbox designed to take only 500hp, is peanuts.

Paul

 

John:
Does all this cost mean you are actually returning the box to stock spec?
If the selectors are a weak design, surely by now someone in Aus/Japan will have something to offer?

The Modena 5 speed racing gearset I think is mainly all steel (and is bullit proof?) could they by now have the ;right; parts to uprate the box?

Off subject a bit, but I had a Porsche works quick shift on my hill climb 911 for a year and smashed the box quickshifting (£1300 bill in 1996!), stock shifter is slower but 'cheaper'

Floyd:
What do you mean 'fitted correctly' in respect of the 5 speeder?

Given all this, would it be fair to say it is the driver technique and not the bhp/lbft that killed the box (absolutly no offence meant John, you should see me doing my best to get a good start...)

Graham.

 

I too hope some uprated forks can be sourced without the nylon bushes.

paul , do you still use the cdtech addy?

 

all email comes to me! I am getting some PPG billet forks for 5 speed in, they should be available for the 6 speed too.

Paul

 

John,
Having trashed many Mini gearboxes with a quickshift, i'd be seriously tempted to remove it, and be a tad more gentl when changing, that probably means driving slower.... but at least the box might last a bit longer!!!

Ron..

 

IIRC David at API said recently that he knew of two different styles of OEM 6MT selector forks....alloy and steel. He didn't discuss the nylon bushes but he will possibly know if he has handled both.

 

Thanks all. I am not expecting too much since I didn't know ultimately how long it would last. Now I know there is an issue I can work around it. I'm not too upset considering the abuse.

 

Okay, I got the impression you were pretty narked. I wonder if the failure of the nylon pads cas caused further problems.

Paul

 

I am actually very surprised how jb has taken it. he even went as far as saying that "£1500 every 23000miles is cheap considering the abuse"

I am probably more shocked as I know jb is not that course and know the exact history of his box.

 

Got to agree really, its fairly cheap all things considered.

 

STi Version 7 6 speed forks are steel whereas Vers 8 and VERY PROBABLY Uk ones are alloy. Alloy forks are bulls*it forks but are done that way for cost and weight reasons. Prodrive Gp N and recce cars still run alloy forks - I asked last week. BUT they do get regular attention

I would buy Version 7 steel forks and replace the nylon selector pads with bronze hand made ones.

As for a ' failure' like this, of a stock component, after 23000 miles and a fair amount of abuse, my comment would be I'm surprised it didn't happen sooner.
The 'failure' is entirely user generated and by strengthening the forks as I suggest I expect to have synchro cone and dog teeth damage as a consequence.

The only way around that JB, is regular rebuild programme.

Otherwise l'd have to say that the 6 speed is pretty bullet proof for its price.

David APi
www.apiengines.com

 

david,

do you have steel forks and bronze bushes in stock?

could jb's daily 400+lb/ft torque , be an issue even with gentle shifts with these alloy forks, especially with the ratio jump from 4th to 5th?. I would assume that even with the clutch down there will be increase load shock with everything spinning faster and harder even shifting slower.

that is worrying as although the failure was at a drag day , I do not consider jb in any way hashy. he has sped up his shifts in the last 2000miles or so but still no quicker/hashy , than most of the scoob drivers , I have been in cars with. iirc, his 6speed has done one track day and under 20 drag runs up the strip so if this failure is not torque related , I am a bit surprised at how quick it has come to light. I run a MY02 sti UK box so hopefully steel/nylon forks unless it is all UK's , early and late thay have the alloys?. I do not have anywhere near jb's torque but do shift gear faster when going for it. with me , it has done the same track day as jb's but only 8 drag runs with under 5000 road miles. it had 12000 or 15000 miles on it when I bought it but has always felt slicker than jb's despite his being brand new. perhaps john is just a bit unlucky to have found this issue before me unless I do have steel forks.

could jb running redline shock proof also be a factor? , I know some do not rate the stuff in the 6speed.

would this help to keep any future repairs cheaper with possibly/hopefully a quicker turn around , given jb saying that all synchros and 5th , due to dog damage are getting replaced anyway.

thanks

 

T-UK,

I don't keep the steel forks as we have never needed any before. Even Prodrive don't have any. Obviously Subaru have decided that the alloy ones do the job hence the change.

If I recall the Vers 7 ones were just under £600 including air freight and customs and so on. The bronze pads would need to be hand made in the Uk by a Clever B*stard [ IE not me ] There is a chance I guess, to get a batch made if demand suggests it necessary. They will transmit noise - no question, because that's why the pads are 'nylon' or whatever. Maybe an idea would be to get a set made and see, If the noise level is unacceptable then there would be no point having 20 sets available........

Gear oil is gear oil Simon Opie [ Oilman] may correct me. In all my years in competition transmissions I worked on the theory that oil is oil in a transmission and as long as it has the right amount it'll do. Works for me !! AND FORD AND GM AND a number of private factory teams.

In my opinion it is unreasonable to expect a standard part to cope with power way above its standard design limit and not service it from time to time.

David APi

www.apiengines.com

 

Thanks David.

 

I only snapped the end off the 3rd/4th Selector rod Floyd The slector fork was replaced as well because it had cracked the nylon pads when it jammed in third gear on the changed up to fourth when the end fell off the rod...there was no damage to the rest of the 'box, and it only cost me two hours labour plus about 20 quid in used parts to have the 'box put back together by Phill Venn