Hi all, Long story, but the short version is - can anyone tell me how much torque will cause failure on the MT75 4x4 gearbox?

have around 290lb/ft at the moment, but planning some engine upgrades and wondering if it's going to break things if the torque goes up to 340lb/ft

 

They're pretty good/strong boxes mine took a bashing and was fine! They're pretty cheap if your that worried get it rebuilt with uprated parts!

 

There's no hard and fast rule really, but don't expect it to never break. Too many people complain about diffs and gearboxes in RWD & 4x4's when in reality its a +20 year old worn part that someone has chucked new seals and bearings in (if you're lucky) and expects it to be bulletproof with a 50% power hike thrown in as well.

I've broken about 5 or 6 of these boxes over the years, even a brand new one from Ford that lasted about 3k milesand that was only on stage 3 and greens. The last one I detroyed lasted less than 5 miles after I put a T4 on, as soon as I gave it big licks it shat itself. Power delivery, driving habits & maintenance are all a factor, try it and find out, that's the basic answer. Plenty people run standard boxes on modded 4x4 saphs so I wouldn't worry about it unless it breaks, you can always de-tune it if you blow the box up.

 

Anything more than 300 ft/lbs and you're on borrowed time especially if you drive like a loon, you have to watch the big boost spikes particularly with 3rd gear, as said people do run big power cars with standard mt75 boxes, I ran mine for a few years with 400ft/lbs and the box lived even to be sold on when I had finished with it so driving style has a lot to do with it

Luciano

 

Thanks guys, appreciate comments & experiences

have already replaced one gearbox but the 2nd one seems ok so far. Like you say they're not too pricy to replace if it goes sideways.

The long version of the story - is that i'm using the LDV/transit van version of the MT75, which has the same gear design & front shaft components as the 4x4 version.

But. people don't go big-hp in LDV vans so... i thought it might be more useful to ask here

bolted to the back of a BMW 740i V8





and fitted in an old ford capri




And all because i didn't want to fork out £££ for the BMW M5 manual gearbox

 

the v8 could be a bit nicer to the gearbox as its not got the turbo kicking it in the back so should be smoother

 

NICE......

 

Going to be running 450 in my 4x4 on standard box and diffs, they will get upgraded but i want the car built and on the road and drive like miss daisy till I save for a big tooth kit and quaife diffs...

 

that's got to make you want to cry a bit!

interesting, was looking on the thread here on dyno maps for tuned cosworths, & noticed some have a big boost & torque spike, jumping from 150- 400lb/ft in the space of 600-1000rpm. Like this monster -




MathewPickup - like you say the V8s a far more constant torque curve. + being a 2wd with an old live-axle, far less torque actually hits the tarmac than it does in a 4wd.

 

I had big torque from my TT v6 and it used to fuck the input shaft bearing so lits of torque isn't always nice
Had something like 350 lb/ft @ 1900 rpm and with 4wd the box would last the most a few months and the least was 23 miles
They also don't like to shift fast I round as I coujd beat the synchros with a quick shift out fitted

 

you would be better off getting a 2wd T5 box and a custom bellhousing.

 

i plan to run 380ish bhp no idea about torque throw the standard 4x4 cosworth system , but if it keeps killing gearboxes I will just change it to 2wd

 

This is a graph I had from a RR run last year before the car was properly fixed/setup by Turbosystems. Torque isn't mental high but it was enough at the time to destroy a standard box no problem. Also depends on your setup, my car is on a 2wd manifold so they usually make less torque.

 

I think my new borg warner is going to make mincemeat of my box, they tend to make lots more low down torque. I am looking at the Opplinger Long Boxes (short ratio) big tooth syncro vs doing the tunnel mods for a Skyline box, I haven't re-trimmed my carpets yet so now it the time although the Peugeot 205 floor pan is already an odd shape with the Cossie tunnel in it.

 

Another name to throw in to the equation is the Fix It Kit for short ratio box on semi helical gears...anyone know how noisey these are?

 

Don't know about the noise but have been told they are a nightmare to get spares/bits for

Luciano

 

Thanks for that...useful info.

I am very likely to follow Mr Sheads advice and go for the opplinger long box with close ratio but I understand the wait might be a while. Get expensive too, especially with flywheel and clutch

 

I pretty much follow his advice too I have the oppliger in my car normal ratio, best value for money uprated 4x4 mt75 box out there imo company just has to step up a gear with turn around time, but they are alright


Luciano

 

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Luciano

 

Lol

Thanks.