what kind of bhp/torque will the 4x4 mt75 box take before it explodes

 

Thats depends a great deal on the confition of the box itself, and how long its subejected to the loads for and how its driven.

There isnt a specific value at which it will suddenly break but at 1 lbft less it wont do that applies to all boxes.

Most people seem to consider them on their realistic limit at around 350-400bhp though.

 

an esc cos box IF used well.. wont last beyond 300 - 350

 

as above 300-350 after that it's pot luck or a matter of when rather than IF

 

they have been stated to be on limits at 375bhp max

 

Agree with Dave and Alvyn.... I have about 370bhp on my Esc Cos and have had 2 rebuilds. The last one was after totally destroying the box.

 

Seems to be a bit of a lottery, Si B has similar power, trackdays his car at every opportunity and absolutely hammers up and down the box reguarly on the road, and hasnt had a failure at all yet.

 

But aren't his internals shot-peened?

On the last rebuild I had, I had it all shot-peened.

 

The standard mt75 is only rated at 250lbft I belive or there abouts

 

I've driven an Escos on standard gearbox with 400+bhp and very agressive antilag and after 2 hours of trashing around the track sideways and kicking the clutch it was still there. It broke it once or twice but only whenracing from lights.

Depends very much how much mechanical sympathy you have during shifts and a bit on luck. AFAIK MT-75 usually fails due to flex of one of the shafts on 3rd gear bearing. It used to be big problem on grp.N rallycars, so 3rd gear wheel and bearing was rebuild after each rally, but in a road car it can last a while or nothing depending on your style.


I wonder if someone found a limit at which mere aplication of full throttle will brake the box?


Bythe way - it's not the power but torque thatbrakes the box so you can have quite a lot of power but further up the rev range and still get away with that.

 

Not that im aware of, but hopefully he can comment later

 

The only guarantee that can be offered with an mt75 is that it will break

 

Mt-75 on Escos is relatively good compared to other homologation specials of the time. Compare:

-Mazda 323 GT-R (brakes gearbox every time you depress throtle pedal)
-Subaru Impreza Turbo 94 spec
-Nissan Sunny/Pulsar GTi-R (niearly same as Mazda)
-Lancia Delta HF Integrale (same as others, lots of transmission failures)


You cannot compare it to very modern gearboxes like Evo gearbox or 6MT Subaru one. Escos one can be run at 400Nm range and last for many many miles - that is something!

 

Azrael

Let's be honest.... the MT75 boxes are utter crap.

 

Compared to what?

Skyline? yeah
Evo? yeah
RWD cars? yeah

Most other 4wd cars? no
(see those listed by azreal for examples)

 

I'm quite pleased with it compared to other cars of the kind of similar construction year. All my mates who drive jap cars are shocked that I can just easily swich into 1st gear before hairpin at 50km/h. No 5 speed Subaru can do that without double clutching or massive force used on the gearstick.

Gearshift quality is incredibly tractor-like but ou can live with that.

As I say - in early 90's homologation specials (remember they weren't designed like proper road cars are!!!) I'm quite fond of MT-75. Compared to Evo or STI gearbox it's utter crap.

 

I think thats the point people miss Azreal, they dont compare it fairly to equivalent boxes.

 

That's what I think. Every 4WD box will be shit compared to Getrag from Supra or M3, or in shift quality to S2000 box...

 

I think they break beyond there time because the driver cant drive properly

 

You won't change my mind on thinking they're crap, after all I've had to live with mine for 6 years and if I had enough money to get an uprated box.... I'd bin it tomorrow! They are sloppy long reach boxes with a huge weakness for stripping 3rd gear.

Hope no-one has the trouble I did a few years ago in trying to get a new 3rd gear, there wasn't one available in this country anywhere. My car was off the road for 2 months until I eventually sourced some in Germany and got a mate who lives there to get 2 for me.

 

Says Phil the big pussy who has never had the courage to track a car

 

They are crap compared to the engine they are mated to, thats the problem i think!

 

The failure of third gear main and layshaft is a fundamental design floor.
The box is nothing more than a old ford granada gearbox and is cheap for ford and not up to the job.

 

The pulsar one is based on a 1.4 fwd pulsar box i believe?

So again, its not really anyworse than the other homologation specials.

Just ford forgot to install chocolate pistons to protect it

 

Tony...it is more than adequate for the standard engine!!...In theory an engine/transmission part should have a certain over engineered aspect and that 4x4 box diffs etc are just that around 50% over engineered..i think people forget the 2wd was rediculously engineered but then it was built around a touring car.

So to say the box is crap is rediculous!

 

what kind of floor Tony?

Laminate?

Real wood?

Carpet?


you old c*nt!

 

Still much better matched then BP6 superb Mazda engine with it's clay gearbox that was shot-peen, polished and handbuild and still fails even on heavily detuned road cars. (~180bhp instead of 300)



One can dare without problems to to full throttle launch in Escos, tune engine, use antilag and still get away with it. You won't get away with it on other similar cars of the era.

Because it's Granada/Transit gearbox it's simple and quite reliable if you know it's limits. Also you don' brake centre differentials, transfer gears, they don't split casings. Shifting is terrible quality but that's the price.

 

Mazda one is nearly the same as 1.8 N/A Mazda 4x4 family kickaround. Scoob one is N/A Legacy one with altered ratios and slight reinforcements - still cannot take even 300bhp realiably.

And intake exhaust restrictors like Mazda....

They only set this funny boost preassure and mapping...to protect it

 

The original poster asked "what kind of bhp/torque will the 4x4 mt75 box take before it explodes" I think by the comments made so far that 350bhp is realistically the max, so Phil I don't think anyone is questioning that it's not suitable for a standard 220/227bhp car.

Anything over 350bhp is just a lottery really.

 

And the more tickets (bhp) you buy, the greater your chance of winning a broken box!

 

Exactly!

 

It's like that with any box, any part actually on any car. Shame you cannot buy tickets and win reliable car at the same time :-(

 

thanks for all your help
the car has 400+ bhp and around 440 lbs of torque so ill be getting another box for a spare
still i cant belive the price for an up-rated gear kit thats just stupid, what makes them so expensive?

 

Small production volume and the fact that they are hand-made not mass produced. Material and machining prices are a factor too.


You can keep buying standard boxes, but at this power if you want to have any fun fromt he car I don't think it's good idea. You will be wondering with each change from 1st to 2nd if THIS is the last time or not yet...

 

I replaced my box in my car because third gear started to crunch, i got a replacement mt75 box from ford and had it fitted, it lasted just over 5k and just over a year so i was fooked with the warranty, third gear completely shreaded, i have put another mt75 in the car from ford and i,m scared to boot the car now incase it eats the box, big horsie power in 4x4 cosworths=drive train headaches, quaife box is the long term solution its just costs a lot money



C L

 

you ever tried to design and make a gearset?

 

also is there anyway to make 1st longer without messing with g/box ratios?
can you change the step off gear or diffs to do this?
as its a big turbo first just seems sh@t
maybe i just need to launch it

 

the cost of an uprated box is not alot of money really if people only think about it, its such a shame people see the engine as the heart of the car, then all the hard earned goes on the motor, the people whinge because the gearbox shits it self

for the region of £2500 buys you a decent used quaife big tooth box, some people will spend that on a fookin turbo ffs, as for the shift being bad, thats just a design to aid drivability i,e reduce noise and nvh

if you want decent shift quality you need one of these



as for the box ability to handle power , i would say it takes a midges over 330 ft/lb in a quick boost time to shred 3rd gear, which is not surprising when you see its profile

 

yes but will involve a fair bit of work, and will directly affect the rest of the gears

 

well my car with 230 of torque stared crunshing number 3