gearbox disaster! what caused this
Turbo Mini Forums

running 10psi boost top gear around 60mph BANG!

thought the diff pin had gone, not so! all the drop gears were all ok the clutch housing cover idler gear thrust to case,
no wear?
on strip down found this??
has anyone had or seen this before & found the cause!
the rest of the box is in excellent condition, iam slightley miffed.


all the other components are fine although there is a shade of movement, not excessive in the first motion shaft bearing
the engine came from a 85 turbo model

thought the diff pin or the drops would have gone first!

wrestling wether to buy outright built dog box and have done with it

it can always go on my next project

Edited by BENROSS on 9th Sep, 2005.

cracks in the roots of the teeth...?

Alex

AlexF

could well be alex one weak one & then the domino affect with the rest

Cracks in the root of the teeth is barely an acceptable answer for the overall failure - but this is a strange place to see a failure, after all the Headset ratio is only seeing what, 1.2, maybe 1.3 times engine torque... If it was to go anywhere, it would normally be on 1st, 2nd or 3rd.

Be interested to see the failure surfaces themselves. Any sign of 'beechmarks' or other markings at the failure surfaces?
Once again, if the bearings are indeed in good order, is very strange!

The high speed of the gears would quickly clear the other teeth - I suspect you'll see one that might be more obvious as the failure propogation.

I'd junk the rest of the gears personally. Keep the synchro parts for future use, but lose all the gears. It could just be a manufaturing issue being an early box...

cheers dave i will pull the gears, clean inspect & try further to find the route cause

will heed your advice

fitting minispares crosspin diff & SC drops with timkin idler, close the tolerences up

i have a few boxes to go at

i thought it strange! just my luck i got a Chocolate gearset!.......lol

Get sc mate if you can take the noise.

Its only a bit of metal. If it blows it blows!

http://www.putfile.com/mini300bhp

I got one that looks like that

If you were in top at the time why the layshaft and input gear ??

4th still worked on mine but the rest never

Metro turbo weekend driver,Mini turbo in the making again!

ive seen it quiet a few times on helicals on a powerfull motor or when you do a lot of quick starts.

basicaly this gera transfers the power to the layshaft and then into 1 2or 3 gear.

if one was going to fail then its this one.

if you are running anything over standard car the i would swap to sc drops, sc gear set 4 pin diff problem sorted.

i personly think the timkin sc idler is expensive for what it does.

always looking for them bigger bunches of bannanas

Depends on how much power you want mate.

Its only a bit of metal. If it blows it blows!

http://www.putfile.com/mini300bhp

miniwilliams hasnt got one aND NEVER HAD A PROBLEM WITH THE IDLER YET AFTER EN YEARS OF TRYING.

NOT SAYING THE AINT WORTH IT BUT I CAN FIND ANOTHER USE FOR THE SPARE CASH

always looking for them bigger bunches of bannanas

O dear Ben very sorry. theres always some thing for more expense!

very true Hogster i don't.
but then again i don't have the power your hoping for mini300bhp so how know you might.

Edited by Miniwilliams on 10th Sep, 2005.

Best 1/4 mile 13.2 seconds @116 mph
First 5 port miniturbo to make over 200 bhp on a carb?
First 5 port miniturbo to make over 200 bhp on Injection?

http://www.mattwoodsphotography.com

I was told that the A+ with its larger bearing is fine, its more of a problem with the smaller A series bearing?

Ive not had experience of both so i wouldnt know.

Basically long and short i got told not to bother by a very reputable engine builder.

The straight cut drops are fine!
No worries.............

i thought i would go to the timkin SC just for a touch more insurance

alas this is not my problem at the moment.

as my workshop,etc is in the stage of planning.
& my working conditions are hideous to say he least, with just moving house.

iam i touch miffed that it failed and no signs of the standard helical drops or the diff pin going POP!!!!

do i try another gearbox standard!??

with SC drops, cross pin diff

or go the way to a SC gear set ???

the SC gearset is the way to go! i know

but we have talked about these helical gears not been a problem.

this is my mess about motor for now!

i am miffed that the input drive gear to lay shaft failed

i would have taken these items as one of the last to fail!

Your opinions please.

Heres mine

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=5073

Metro turbo weekend driver,Mini turbo in the making again!

Dangerous that says it all buddy

that input gear takes all the grunt and they will brake as sure eggs will.

the idea for nsc drops is to stop side loading on the transfer case for the idler, the primary gear and side loadings on the first motion shaft.

and basicaly the gear set does the same for the whole box plus they are stronger as i have never yet seen a brokern sc gear yet through normal failer only when another component has failed.

the torque is the biggest killer of the gears.

always looking for them bigger bunches of bannanas

this happened to me too. check the box where the first motion bearing sits mine was cracked through to the top of the box

i know which direction iam going to go

in essence i was asking too much out of a worn standard box even at 8 to 10 psi boost with the modulator ditched

too much torque killed it.

thanks for the input guys

Ben, if there's anything I can help with give me a shout, have got plenty of shims etc at the moment from when I built my 'box........

You have my mobile number........

ive got a spare a+ 998 box as well for free its still attached to the block mind!

Look at it this way, if you get the cheaper drops and they break then you'll want to get the roller one anyway and you'll end up buying twice. Might be cheaper in the long run to get the rollers?

turbo hogster, I can see where your coming from with the torque killing the gears, but when a wheel starts spinning, surly torque is relieved, minimising gear damage risk. On that note, will your drops hold up if you fitted an LSD and maybe some gripier tiers miniwilliams?

Its only a bit of metal. If it blows it blows!

http://www.putfile.com/mini300bhp

you are quiet right 300 when the tyres spin the relieve the whole box but its when you are in the higher gears you still have all that tourque still loading through the box especially when you are travelling at speed you also have to counteract the airodynamics of a brick eg the mini and the engine is pushing all the torque and hp through it trying to push it foward.

the transmission does take a hell of a pasting.

but the drops dont seem to take as much as we think in capartive terms to the actual box it self.

ive never seen yet ( the will bve the first) a helical drop to fail in normal running only the damage they cause, but have seen loads of stripped gears and smashed diffs to over indulging driving and powerfull engines.

a standard helical set up is stressed enough at a normal turbo set up thats why they modulated the boost at max torque to starve the engine of peek tourqe knowing it wouldnt last and i didnt.

always looking for them bigger bunches of bannanas

On 10/09/2005 00:45:04 Dangerous said:

I got one that looks like that

If you were in top at the time why the layshaft and input gear ??

4th still worked on mine but the rest never

Edited by stevieturbo on 11th Sep, 2005.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

"On that note, will your drops hold up if you fitted an LSD and maybe some gripier tiers miniwilliams?
"

How Knows that answer!, but i would also think the some thing, in that the box would break first before the drop gears!

Best 1/4 mile 13.2 seconds @116 mph
First 5 port miniturbo to make over 200 bhp on a carb?
First 5 port miniturbo to make over 200 bhp on Injection?

http://www.mattwoodsphotography.com

thanks tom and iain for the offers

ian i have many gearboxes to go at
i may be going the way of SC drops
the clubman type off minispares

the ratios are as follows
1st.....2.58

2nd...1.711

3rd... 1.250

4th...1.1

fitting a 2.95 F/D

oppinions please!