I know this have been written about before, but I have some questions.

I remember reading an article in a magazine of the press-launch of the works rally GpA Sierra Cosworth 4x4 way back in the beginning of the 90's.

It was written the they could set the center diff torque split according to the drivers preferences, one prefered 45/55 and another 40/60 etc.

How was this done?
Was there just other ratios in the planetary gear and could it be set to 50/50?

Must underline this was the early 5 speed rally MT75 transmission,
not the later 7 speed MS90 transmission.

I also read in a mag about a rally Escort Cosworth with a R&D transmission, which I belive is based on the MT75(correct me if I am wrong), and I belive it was written that the torque split was 50/50 with visco center diff.

Anybody know anything about this transmission?
Are they available?

Hope someone has the time to answer!

ESV

 

bttt

 

Are you sure it isn't like the DCCD?

 

there was never an adjustable mt 75 centre vc split, but there are some 50/50 centre planetaries around if you can find one.

there is an r + d based on the mt 75, but i dont know what they used for the centres.

 

the split is dictated by the gears inside the transfer box
if you get different sized gears you can get whatever split you want, but it's going to be a bit pricey me thinks

you can also get the viscous coupling rating higher so you get more grunt to the front, i think the normal ones are only rated at something like 80 or 90 ft/lbs, i know the escos ones are higher but i can't get to the book just yet (its in the loft and we've lost the loft ladder pole thingy )

 

a bit off the mark there pal , teh torque split is done around the vc with the planetary gears pal, has nothing to do with the drop gears, as for the vc, the road going models were no where near that high, less than 50nm mate,

 

In the old days, grp'n' esc with the standard box used a 50nm centre diff as Mark says.

There were lots of variations on the Saph's, the Quaife was the most popular after the old 'sport' box, both were based around the MT75 transfer box so had similar options with regard to split. Generally tarmac cars ran the viscous arrangement with the 50/50 being used on the gravel cars.

It's similar with the front and back diffs, different drivers use different ramp angles in the diffs, all depends how they like to drive.

If you've ever driven a car with a 50/50 split you'd certainly want to understand transmission better, they have to be driven with extreme commitment as they push on in corners tremendously.

The later modern rally cars are a compromise between traction and drivability, as they vary torque split and ramp angle at different times during acceleration and deacceleration to maximise the two...

R & D boxes were again based around the MT transfer box AFAIK, never actually owned one but they have ventured slightly into electro mechanical centre diffs as well.

HTH

Ian

 

 

but isn't it the epicylic (sp?) stuff inside the transfer casing that dictates this?
you get one spinning at twice the speed of the other, so you get the 1/3 and 2/3 split?

 

yes epicyclic unit is inside the transfer, but its a complete unit, with planet and sun gears, so not as easy as just a gear change to make 50/50, this then splines onto the vc

 

thats what i'm saying mate can be done but i couldn't afford to get it made on my wages

 

I'd like to resurrect this old thread, as it is of interest to me atm, I just want to run my theorys past some of you guys......

I'm currently bulding a 4X4 24V V6 Puma for stage rallying and will be doing a variety of loose and grippy surface events. The car has 4X4 Sierra transmission.

I have 4 or 5 MT75 4x4 units, mostly all with good transfer guts, so plenty of bits available to "play with"

I have one apart on the bench ATM.

What I want to do is have 3 different set of transfer guts, which can be fitted prior to the events, depending on surfaces to be driven on.

The first option is easy, stock guts for tarmac use with standard F&R torque split.

The second option looks very easy to me, a 2wd opion, basically a blanking plug for the front prop seal, remove front prop.

Remove centre visous diff unit, and all other parts not needed, chain etc, then weld the rest of the relevant bits together, so I'm directly driving the rear propshaft flange only, thus giving me RWD to enter RWD only events.

I'm struggling with a fried brain, to get my head round the 3rd and final option, which is to retain centre viscous diff action, but turn the front and rear propshafts at the same speed, thus getting a 50 / 50 split (??) to use on gravel / loose surfaces.

It looks to me at this stage that if the sun gear, planet carrier and outer annulus ring is all locked together (welded, bolted, pinned), then I'll get the desired 50 / 50 split, but still have centre viscous diff action.............

Anyone have any thoughts or tried this out ????

Cheers Dave