Hi all
Wondering if anyone has views on fitting 3.53 diffs to a 109 series that already has an Ashcroft high ratio transfer box fitted to a 3.5v8. I’m planning a super long road trip / expedition and want to be able to cruise at 65 easily for long periods of time. Although the Landy is great for short motorway trips it still gets pretty hard work for longer stints so am thinking of all options.
Thanks
Alex
Has to depend on many things. The V8 often sounds like it is revving hard when it isn't. You'd run a 4 pot at the same revs for instance.
It is very easy to over gear a vehicle. And how fast do you want to go?
I had a 200Tdi S3 88, I did put 3.54 diffs in, but had the standard transfer box. It did improve cruising. But it also sort of ruined the vehicle IMO. It made 1st gear quite tall to pull away, which you noticed if you were towing. It also impacted low 1st crawl speed off road. But for me, the biggest issue was the gap it produced between 3rd & 4th. As in, 3rd at 30mph felt like too many revs, but it no longer wanted to pull 4th really. Not unless it was flat level ground. However, the different Series boxes do have different 3rd gears, so might not be an issue for you. Mine was a Series 3 box.
Don't get me wrong, it wasn't terrible at all. But my plan, had I kept the vehicle was to return to 4.7 diffs and fit an overdrive to the gearbox.
The good thing is, swapping diffs isn't the most amount of work or money. So it is easy to try and out and reverse if you don't get on with it. Ultimately, I suspect the only real way to know is to give it a try and see.
Looking at the calculator your current setup should be approx 2600rpm @ 60mph, which doesn't sound too bad to me.
3.54 diffs would drop 60mph in 4th down to jut below 2000rpm. But I'd wonder how usable 4th gear might be below 50mph, at it would all be sub 1500rpm. And mot low CR 3.5's are not all that grunty really.
