DYNT

Grp 'N' - No straight cut is allowed.

U can shotpeend the gear to make oil pocket and improve the strength.
U can call Possum Bourne Motorsport and order stronger gear kit... which will break too .. even the Prodrive unit.

I personally think straight cut is the way to go ... that is after having to rebuild 9 gearbox for the past 3 month. Noise .... well U just have to make do wit it.

The Drive pinion shaft, Main shaft and selector is good and strong. Only the gearing is weak.

Prodrive will blueprint the gearbox. As for the gear set ... they will shotpeened it.
They will change the Main Shaft Rear Plate and Washer too.

Other then that ... is all the same. The hardest part is to BLUEPRINT it..... long hour.

Firefox - My connection is very fast ... *_*




[This message has been edited by DYNT (edited 09-11-1999).]

firefox

DYNT... do you sit on here all the time ? lol

Or you have a faster connection..

Prodrive internals are just uprated standard parts... as has been said... for Grp N.. the design has to remain the same for the gearbox and tranmission.

The PossumBourne kit is very good... on par with the prodrive kit and cheaper... I know someone who has run both.. and reckonmends the Possum gear kit.

In my opinion, the noise from a straight cut box would be too much for most people, unless you only use the car for fun and not as an everyday car. - forget having the radio on... lol

If you are running uprated internals.... like straight cut and with no synchros.. I would strongly suggest a mocal cooler....and a diff/gear box filter/seperator gauze.

J.

Lee

FYI - MY99 22,500 miles no problems.

Have to double clutch for reverse though.

oh and my old stage III Mini had a straight cut box..a lovely whining noise and when combined with big exhaust Wow..WRC moments !

stv555

More developments...

Took technician out in mine MY99, agreed with me about release bearing noise and synchro problems with 5th and 3rd.

Dealer is submitting 2 claims, one for gear bits...synchros, matching gears and hub assys. The other for new gearbox which is my preference, since if there is a batch fault what will stop another part going after reassembly...also if will be far quicker to swap boxes than strip and rebuild.

1st is starting to feel a little strange..anyone else with reasonable dealers ? I am sending a letter to the dealer and IM for clarification.

AlexM

Stv555,

I think IM will authorise replacement of the box, rather than a strip down.

This would cost them more in labour and parts than the cost of a new box (£2700), and as you say, wouldn't prevent the problem reoccurring with the other gears.

Those nice ACE Kensington people changed my box (with a little persuassion of IM required) as a result of 1st gear problems. The new box shifts much better, even though it isn't 'broken in'.

Cheers,

Alex

johnfelstead

just thought i would clarify a few points on the dog box, straight cut gears config.

Straight cut gears provide less power loss than a helical cut gear as there is no side thrust on the gear to provide aditional friction.

Dog boxes can use either helical or straight cut gears, but most will be straight cut.

what is a dog box?

with a standard gearbox a syncromesh is used to engage the required gear, it is a slipping device which as you engage the gear it syncronises the spinning gear to the spinning shaft before it engages fully. that is what the synco cone is used for and that is why it is cone shaped.

A dog engaged gearbox has no syncros. on the side of the gear are milled between 4 and 8 large square shaped blocks, usually about 5 mm in depth, these are the dogs. The shaft has a sliding dog ring which has another 4 to 8 square protusions on it.

when you select a gear the two sets of dogs engage and provide drive to the shaft.

there is no mechanism to syncronise the dog ring to the gear and that is why it is essential to match the speed of the shaft mounted dog ring to the speed of the gear you are selecting.

That is why you hear race car drivers blipping the throtle on the downshift into corners, modern F1 cars have the engine/gearbox electronics do the blip automatically, that is why it is very rare a modern F1 car misses a gear and yet lower level formula drivers still regularily do so.

It takes a great deal of practice to do this syncronisation automatically.

This is why you hear of people learning to heal and toe. This method is badly named as you actually brake and roll the side of your foot onto the throttle pedal, it has bugger all to do with the heal of your foot.

The above will probably illustrate to you why dog boxes are a nightmare for road use, and would be totally unusable by the average driver.

It also shows you a way of spotting a skilled race driver to a crap one as you often hear bad drivers crunching the gears on the downshift as they havn't learned to heal and toe properly.

hope the above is informative.

Mark Coleman

Has anybody thought about the extreme temperatures and power transmitted to the gearbox ??

Try touching it after normal driving

One theory I have is that normal grade gearbox oil cannot take the heat or power produced which then breaks the oil down until its no longer effective.

See the topic 'Gear Oil' for my experience of this and the complete cure I found. It may work for you