Hi all
Im building a bit of a project car + will most likely using 4x4 mt75 box with cossie diffs

Just wondering how much power box + diffs will take?
Front diff will have the strengthening plate fitted

The car will only be weighing approx 1000kg + i want to running at least 400bhp
ive heard 350bhp being the limit for the box but wondering as the car is lighter than a sierra or escort it may well be ok with the power

thanks for any replies
James

 

It's the high torque that kills 3rd gear, you may be ok depending on your setup. MT75 boxes can be had quite cheaply these days so could be worth trying a good standard box & see how it goes. No point upgrading if its not needed.

 

as you say they are getting cheap + as the bellhousing is being modified i could always use the xr4x4 mt75 as they seem to be cheaper

any idea on diff strength?

cheers for your reply
James

 

you can buy diff strengthening plates fairly cheap, and about 380bhp is where id imagine they will start going wrong.

 

Heard of people running 400BHP with a standard front diff with a plate fitted. They only see 34% of the power but it depends on how hard a life its had. 2nd hand diffs can be had for £50 upwards so very cheap in comparison.

Best bet is get the box & diffs rebuilt so you know you have a good starting point.

 

its not a case of how much bhp an mt75 can handle,its the torque which is the important factor.anything over 350 ftlbs of torque is pushing the mt75.I have sheared of 3rd gear teeth with well over 400ftlbs of torque but my car has only 300 bhp.
personally i dont think its the front diff case that is a problem,it's the strength of crown and pinion teeth.how can fitting plate make the gears stronger!! the gears break off then wedge themselves between the crown and pinion, then it breaks the diffcase.

 

the front diff cases flex and cause the teeth to move out of place on each other that then causes what you have described.