I’m looking to do some research into possible ways to strengthen the 20VT gearbox. I have phoned up a few gearbox specialists but they suggest that I need to know where they are breaking first. Can I ask all members who have blown gearboxes to post:

1) Torque they were running
2) What part blew
3) Any pictures

I can pass this information on and hopefully come up with a possible solution/prototype that I would be willing to test.

Ooohh, you beat me to it!

Also, if anyone has any experinces of having fitted other gearboxes to the 20VT such as the Integrale etc.

oooo more money

Not yet its purley research first.

Off the top of my head, 6 spds die from lack of lubrication at prolonged speeds high speeds.

5spds, well you'll have to ask the likes of nyssa7 as he's probably broken a few.

Barbz also used to add a strengthening plate to his coupe. I don't know where is was fitted though.

I remember a picture of this being posted on the TI website, but wasn't it a 6 speed box, with a plate welded on to the end of the gearbox? (That is, Euro spec drivers side/UK passanger side)

The plate was for the early 5 spd as they were able to split. But i want to look it to other methods aswell as a plate alone can't be enough.

It would be worth trying to contact MWT from the forum. He is in Brazil and has the Fiat Marea with 547 f/lb of torque

His pictures are here, http://s2.photobucket.com/albums/y39/TETEUS/
and his contact information is here
http://www.online-presence.co.uk/_coupe/details.php?record=126

Engines yes - gearboxes, surprisingly not so! Not run a 5 speed other than the one which came with my original 20vt donor car, it broke on the rolling road but anyone's guess what condition it was in, so doesn't count

Have punched the diff through the bell housing with a 6 speed, but other than that, I think strengthening gearboxes to be a low priority unless you plan to drag race and side step clutches

So how is it your racing and only killed one box and other roads users have been through a few. I'm still on my OE box but if it blows I’m planning on something a little bit beefier.

because on a circuit there is far less load on a clutch than when doing 1/4's or launching on the road - as long as you shift smoothly.

maybe because Leighton has no mechanical sympathy

Oh look at that, another zero appeared on your bill

Seriously though, I don't drive my car too hard except on the track or the strip. Ironically the first box let go on the dyno (crown wheel & pinion) and the last two on the road when accelerating in 2nd (blown diff) and 3rd (blown 3rd).

The cost of strengthening a box is considerable, a lot more than you are thinking Jason. My last box cost me £220 fitted.

you mean its going to be £200 now instead of £20

I think I'm going to keep a look out for another 6 speed and keep it in my garage

i have blown two boxes in a year,first one i blew was in 4th and it was messy oil everywhere and there was a hole in the casing and the second one let go flooring it in second but that was the diff that time that went

Blew the diff in one box but mangaged to get away with fitting a second had diff and and diff case.

Seems like the diffs are very strong.

I question how often if ever the average coupe enthusiast changes his gear box oil.

With a helicial gear the thrust forces are a lot greater then a straight cut gear (hence greater power loss)this can force the drives sideways reducing contact or rather leading to an uneven wear. High torque simply forces the shafts apart. In Bowen's book on gearbox building he mentions the addition of extra webs to OE castings as a method to keep the shafts in mesh, would need a very good welder and machined sections.

If you want to know then ask someone who had to go all out-http://www.jmcpower.com/ , Mike is the owner.

rich

maybe I change gear smoother? Not being clever or derogatory - certainly I don't bother with heel and toe crap when driving a road car, but have a good bash at matching revs on downchanges far more diligently on track. Puts it under less strain and less likely to lock the fronts changing down

we also do rolling starts in the LMA Euro Saloons so no giving the box grief from a standing start. Have done a couple of standing start races in the DMN series but I'm going to get so much wheelspin anyway, just get the thing rolling gently and then boot it. Any one who saw me pulling away at Santa Pod two or three years back - I got it rolling like I was towing a caravan, then hoofed up the strip with the wheels still spinning in 5th. Strangely, it wasn't long after that the diff went through the bell housing smashing all the casing. But still using the same gear set in a new case

Besides, I've made up in engines what I've saved in gearboxes ;-(

could you strengthen the 5 speed n/a box so it could take the torque of the turbo

You have to start with the basics!

There are 3 different 20VT gearboxes, so which one are you asking for?

The early 20VT box IS the grale box but with a different housing (maybe only bell housing)

The late 5 and 6 speeders are very similar with the obvious difference.
The whole linkage is different so in changing box between new and old style you also need to change the linkage


My opinion is that the number one problem is the OE gearbox oil is a pile of cr*p. In fact in response to 6 speed failures you will find that Fiat changed the recommended oil. Likewise what Rich said about changing the oil. I have had my gearbox oil changed regularly

I have never used the OE oil and in general my boxes have lasted better than expected. At 400BHP & 400lbs/ft I did about 25,000 miles and at 350BHP & 360lbs/ft for 20,000 miles+ all on one 6 speed gearbox. That box died about 3 days after I got 560BHP and the subsequent late 5 speed I had lasted only a short time. That might be because I was trying a very high viscocity oil. My current box has done about 2000 miles I think and is another late 6 speed.


I have 3 6 speeders and 1x 5 speeder in my garage all broken. On the 6 speeders one lost 3rd, one has the whole lay shaft moved, one had the rear bearing burn out. I think only one of the casings remain intact
The 5 speeder I'm not sure what happened to it

It will get increasingly difficult to find low mileage boxes that themselves aren't already worn.

Like flea I have a local mechanic who can swap them quickly and charged me only a couple of hours labour, and my box was also cheap.

Didn't you crack a gearbox on a pothole once John?

Some good info their John. I have always used proper gearbox oil. Do you have any pics of your broken boxes?

Yes, thanks for that John. I have always been very carefull to change the gearbox oil regularly. I use the fully synthetic oil that was recommended by Oilman.

In fact Jason, you should have a spare bottle of that oil that Roger at Powerfiat gave you....

yes good memory!

My car bottomed out on a major dip and rise in the road and broke 4th gear I think. That was another box again - a late 5 speeder.

Good point on the oil John, needless to say I'm not using stock gearbox oil either. As best as I recall, we're using Joe Gibbs synthetic that AAOil supply - its where I buy the fuel from so comes on the same delivery truck

wow...a dip and rise did that?!!?

fccuk me running...

yup, don't underestimate the oil, I'm oddly enuf using a 75/110 or likewise Joe Gibbs oil ( with a good bit of guidance from JohnS ).

It's very pricey, however seems to be keeping it all tip top at present : I must admit, with the gearbox cooler up & running, you can actually hear it humming away in trafic when coming off the motorway, so it does get hot.

Oddly enuf I checked it a while ago & there is NO hint of discolouration, where as with the new box I had fitted, after 1k, the oil was quite silvery :o, so it just isn't protecting

1) 74kgfm @ 6000rpm

2) 5x Diff and 3x 3rd gear (5 speed gearbox)

3) Pics:
http://i2.photobucket.com/albums/y39/TETEUS/Variados/11-08-08_2201.jpg
http://i2.photobucket.com/albums/y39/TETEUS/Variados/11-08-08_2203.jpg
http://i2.photobucket.com/albums/y39/TETEUS/Variados/11-08-08_2141.jpg
http://i2.photobucket.com/albums/y39/TETEUS/Variados/11-08-08_2105.jpg
http://i2.photobucket.com/albums/y39/TETEUS/Variados/11-08-08_2101.jpg
http://i2.photobucket.com/albums/y39/TETEUS/Variados/11-08-08_2100.jpg
http://i2.photobucket.com/albums/y39/TETEUS/Variados/11-08-08_1526.jpg
http://i2.photobucket.com/albums/y39/TETEUS/Variados/quebranitro.jpg
http://i2.photobucket.com/albums/y39/TETEUS/Variados/quebranitro1.jpg
http://i2.photobucket.com/albums/y39/TETEUS/Variados/quebra31.jpg

The original Gearbox supports up to + or - 60kgfm torque, above that I had problems with 3rd gear and diff, the diff broke 5x and 3x the 3rd gear, then i decided to make a straight cut Gearbox and LSD diff, never more broken.

I use Motul 300V.

http://i2.photobucket.com/albums/y39/TETEUS/MWT%20STAGE%203/28-08-08_1607.jpg
http://i2.photobucket.com/albums/y39/TETEUS/MWT%20STAGE%203/28-08-08_1657.jpg
http://i2.photobucket.com/albums/y39/TETEUS/MWT%20STAGE%203/30-08-08_1632.jpg
http://i2.photobucket.com/albums/y39/TETEUS/MWT%20STAGE%203/30-08-08_1605.jpg
http://i2.photobucket.com/albums/y39/TETEUS/MWT%20STAGE%203/30-08-08_1606.jpg

Cheers,
Mathew

Matt you have spent some serious money on that car. What was the origin of the straight cut gear kit, was is a Brazilian product or one of the Euro gear sets. I assume it to be dog engagement.

Rich

Excellent post exactly what i was loooking for.
I'm intrested in that gearkit. How much did it cost?