Gearboxes - how they break

[jamiep_jamiep]

Guys, I'm just trying to get an understanding of why/what it is in boxes that lets go when they do fail - is it material problems (teeth stripping, cases flexing) with the damage because of shock on the parts? How much of an effect on breakages does the way in way the trans & engine is mounted/braced have?

So, as a bit of a rundown, could anyone let me know what parts would be likely to go, what would cause it, what *may* prevent it and in what order (if any) you would expect them to each become a problem.

Thanks everyone!

[Fastbrit]

For starters...
First gear – shock loads it was never designed to take. Can be helped by pre-loading trans to take up the slack.
Diff casing – as above. Spider gears try to push the casing apart
Spider-gears – 'One-wheel' burnouts cause them to overheat
Case – Stresses it was never designed for! The gears try to move apart under load and can distort case, leading to cracks (especially across drain plug)
Ring & Pinion – Takes more power (usually) but will fail due to shock loads. One tooth cracks, they all eventually fail. 3.88:1 = strongest
Synchros – power-shifting/sped shifting can wreck synchro rings or cause them to spin on gears
Third gear – spins on shaft after speed-shifting etc...

There are lots more ways to wreck a VW transmission, but that's plenty for you to be practicing with for now.

First get a Super-Diff and a side casing to keep spider gears and ring & pinion together, respectively. But six words (or is it three compound words?) will help: pre-load, pre-load, pre-load

[BeetleBug]

Or to sum things up;

Our transmissions break because their (v)weak.. you can put all sort of heavy duty stuff in there and you still have a weak box. Luckily for us our boxes and their parts are cheap.

[Phil West]

First get a Super-Diff and a side casing to keep spider gears and ring & pinion together, respectively. But six words (or is it three compound words?) will help: pre-load, pre-load, pre-load
[/quote]

Wise words.  I always preload and this happens!  Haven't broken a box (ever) on launch so it's got to be a good idea.

[John Rayburn]

Perfect example of a car literally climbing the ring and pinion! If he didn't pre load, the teeth on the ring and pinion would slam together. You can't get away with that shock very long. So the pre load helps his wheelstanding parts live alot longer!! Nice shot, by the way.

[Felix/DFL]

nice pan 

[Bewitched666]

Case can give up to after internal damage

[deano]

When you look at how small the first gear (mainshaft side) is, compared to the others, you realize that it is on borrowed time when you add a bunch of power and larger tires. Back in the gasser days, when they used a stock mainshaft and 1-2 gears, the best most of the racers could hope for is about 18-22 passes before first gear would break. The engine torque applies so much pressure to the transaxle, that it wants to separate, or pull apart. The key is to keep the gears meshed together at all times, and eliminate any flexing, both in the mounts and internally.

[ESH]

...  I always preload and this happens!  Haven't broken a box (ever) on launch so it's got to be a good idea ...

Having less weight in the car helps too. 

[jamiep_jamiep]

Thanks very much guys - at the moment I run a Rancho pro street, but hope to be adding slicks next year and am wondering about what parts I'll need to upgrade to keep it together. Plus I'm very much still a beginner at the moment, so learning the best way to launch is a must - so I hope to get as much track time as possible this year on street treads while I'm learning. Anyone have a good rundown on a 'best practice launching', a kind of  101 for beginners? At the moment I seem to be spinning the wheels lots & lots on the line (launching at around 4000 rpm, street tyres at 20 psi).

I am still trying to work out the best way of pre-loading the box, getting a launch rpm correct and remembering to go when the light changes all at once! It looked so easy from the grandstands...

[banditina]

Case can give up to after internal damage

  .....

[nicolas]

that 101 on keeping the box together is more then welcome. who can teach me how to launch properly? i have to learn how to preload.

[jamiep_jamiep]

After searching I found the thread that I've now bumped back to the top... it would be great if we could get a bit more laucnh info on there for us newbies!

Thanks

oh, heres the link in case it disappears back down the page:
http://cal-look.no/lounge/index.php/topic,4713.0.html

[Tekken]

Use some time and money to find the correct clutch setup,that will save you a lot of trouble.

[BeetleBug]

Use some time and money to find the correct clutch setup,that will save you a lot of trouble.

x 2!

About pre loading your box.. put your car in first gear, no brakes, and try to rock it back and forth. Can you feel the slack? This slack is what you DO NOT want when you are standing in front of the lights. I started out using the park brake to pre load the box but this only pre loads the box and not the car. After a little practice I started using my line lock to pre load.

[Frank LUX]

Use some time and money to find the correct clutch setup,that will save you a lot of trouble.

x 2!

About pre loading your box.. put your car in first gear, no brakes, and try to rock it back and forth. Can you feel the slack? This slack is what you DO NOT want when you are standing in front of the lights. I started out using the park brake to pre load the box but this only pre loads the box and not the car. After a little practice I started using my line lock to pre load.

Hi BB,

I do know the Park Brake thing, but how you do it with the Line lock...

Frank

[BeetleBug]

Use some time and money to find the correct clutch setup,that will save you a lot of trouble.

x 2!

About pre loading your box.. put your car in first gear, no brakes, and try to rock it back and forth. Can you feel the slack? This slack is what you DO NOT want when you are standing in front of the lights. I started out using the park brake to pre load the box but this only pre loads the box and not the car. After a little practice I started using my line lock to pre load.

Hi BB,

I do know the Park Brake thing, but how you do it with the Line lock...

Frank

I do believe Tekken should answer your question since he is constantly managing 1.23 60ft times  I use the line lock and moderate brake pressure on the pedal to stage/pre load my car.

[Phil West]

Use some time and money to find the correct clutch setup,that will save you a lot of trouble.

x 2!

About pre loading your box.. put your car in first gear, no brakes, and try to rock it back and forth. Can you feel the slack? This slack is what you DO NOT want when you are standing in front of the lights. I started out using the park brake to pre load the box but this only pre loads the box and not the car. After a little practice I started using my line lock to pre load.

Hi BB,

I do know the Park Brake thing, but how you do it with the Line lock...

Frank

I do believe Tekken should answer your question since he is constantly managing 1.23 60ft times  I use the line lock and moderate brake pressure on the pedal to stage/pre load my car.

Yep i do the same - just get into staging light 1 then moderate braking and hold the lineloc.  Then just shunt the car into 2nd light and I'm set to go.  Really feel the back end dropping right down and the front end comes up as the car is straining to be unleashed.

Mine gives consistent 60foots in the 1.5-1.6 bracket, best of 1.52.  1.23 is bloody jawdropping!  I only have 180HP at the wheels so my guess would be there must be masses and masses of HP to achieve such amazing 60ft times.  I've never seen even a drag car over here pulling those sort of numbers!  Do what Tekken does!

Phil

[BeetleBug]

Shunt - That was the word I was looking for.

I`m not consistant at all and my best 60ft is 1,58. But my car was a full weight 65 (one seat but 6 point cage and I`m not a little guy.) My rear end set up is quite simple with original torsion springs/plates and bus snubbers, Red Konis adjusted as hard as possible. Rigid mounts all around and Berg look a like rear bar. Our local strip is known for being a gear box killer and there is never a race day without 2-3 broken boxes. Knowing this I use quite a lot of air (23-19 psi) in my DOT slicks and only a small burn out to get rid of the water. I adjust the launch RPM between 6500 - 7800 rpms and do not side step the clutch. Clutch is a black magic and a stage 1.

My KCR gear box with super diff is still holding...... knock knock!