Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Changing the diff ratio of my 4/4 to 4.1

Ari Vatenan, 1976 Scottish Rally, His diff broke...Solution, flag down a passing motorist driving a three litre Capri and ask him, politely, if you can borrow his diff. Park the two cars side by side, change the parts over, tell the shocked motorist to get another diff from his local Ford dealer on Fords expense!

Footage on Youtube!

Arwyn

The previous post: http://www.talkmorgan.com/ubbthreads.php/topics/343096/Changing_final_ratio_of_the_re#Post343096

More than €2000 for changing two crogwheels?

Yes changing the ratio makes the car much more drivable. The extra 300 or so rpm enables 5th to be used a lot more so mpg has not changed for me. BUT be aware that in my case the diff "whines/rings" a little. I was warned that this might be the case.
As has been said it is not a cheap mod mainly due labour. Axle out & in & diff set up etc. Mine was over 2grand.
Was it worth it yes just a shame about the noise.
Those interested the noise is not loud you can't hear it with the hood down. It only occurres at certain narrow speed bands & only when cruising. I.e noise stops on acceleration or up hill & stops when taking foot off accelerator.
IMHO I do not understand why this ratio is not the standard set up. At 70mph the revs are around 3100 compared to 2800 so engine noise is about the same.

I agree. I made an estimate on the basis of a PLUS 4 2005.

Have a look of one of my post on the French forum, 17 feb 2016 6h53,

http://mog.vosforums.com/viewtopic.php?f...issance#p136928

comparison of different ratios and power configuration with use of the 5th gear.

For the noise of the axle, perhaps a problem of play adjustement and/or preload of the bearing?

Sorry for the French used for the charts.

Heinz, my mechanic, who is over 20 years specialized in british cars (Triumph, MG, Austin Healey ) told me, it takes 8 hours to change the diff.

Dealer price.....£100 per hour. .. ouch.

As the 4/4 has almost the largest wheel diameter of all Trad Mogs, has anyone experiences using a 4.3 rear axle ratio with this car? Or would it be too short for some reason? It would mean 62 mph at 3000 rpm in fifth gear instead of 66 mph using a 4.1 diff ratio. And 103.5 mph at 5000 rpm with the 4,3 instead of 110 mph using a 4.1 diff.

Benefit of using 4.3 could be an even better behave of second, third and fourth gear on winding roads. Drawback could be an almost unusable first gear and the fifth gear a little too short on the motorway? Using 4.3 with the 4/4 would be equal to the numbers of my 1973 911T. But I would like to use the 4/4 on longer distance trips as I do now, and the Porsche is just driven on day trips. So I have answered the question half by myself...nevertheless, what are your thoughts.

I always thought that it was the best mod I ever did to my 4/4. I had Mike Duncan do it. He sourced a used set of cogs that were in great condition and used a rally transmission company in my local town to swap the diff. All in, my cost was £1100 and was money well spent. The back axle was quieter with the new diff!

I've driven a few of the later Mazda gearbox 4/4s and the gearing feels different so I don't know if the 4:1 is a worthwhile mod for those cars.

Thanks for recommending Mike Duncan, John.
Does anyone has the ratio numbers of the older Ford gearbox speeds which was used in the 4/4 Sport? Then we could compare the gears and speeds because we have the ratios of the Mazda box (which was posted here last spring).

But anyway I guess that regardless of the possibly different internal 5 speed ratios, also the Mazda box based cars should profit from an overall shorter diff ratio. With the 3.73 diff my 4/4 should drive 150 mph at 6000 rpm and even rediculous 160 mph at 6500 rpm. I also don't feel the need to reach 112 mph in fourth gear, which is the case with the 3.7 final ratio. That' is nonsense in my view and waste of the given moderate power of the engine, which is so nicely rev willing and wanting shorter gears.