Hi All,
I have just got a 1972 Series 3 SWB Safari that had a reconditioned 19j 2.5 TD dropped in 20yrs ago. I am upgrading the front hub brakes to 11 inch but also have been advised to upgrade the Diffs as its reving too high at 45mph - it has plenty of low end pulling power so would Range rover difs help ? 3.54 or 4.7 or something else ? thanks for any advice, BR Phil
Ultimately there is no single answer here. It will come down to what you want to achieve, what you want to spend and where you are willing to compromise.
A brake upgrade is fine, although good order standard brakes should be fine too. A servo upgrade is probably worth considering if going for bigger drums and just a general check up that the entire braking system is working as it should be.
Gearing..... (making the assumption you still have the standard Series 4 speed gearbox and standard transfer box).
Firstly it is not revving too high. It is revving at exactly the same rpm that an original factory 2.25 petrol or diesel would be. Changing an engine doesn't alter this.
The difference is, you now have more power and torque and more easily attain higher speeds than a stock engine.
Overall the gearing is low on a Series, but this was on purpose given the power plants and intended use.
On the flip side, the 19J doesn't really like to be thrashed, that is when they tend to crack pistons and do head gaskets. Treat them gentle and they will generally run rather well. A factory 90 with the 19j in designed to run at mega high speed either and a fairly short 5th gear.
There are lots of options.
Tyre size is certainly one to think about. What size tyres are you running? Bigger tyres can certainly help reduce cruising rpm for a given speed. If you are on small 205's now, you might want to consider going up to a 7.50 or a 235/85. You could potentially even run all the way up to a 9.00 x 16 or something of similar height.
Changing the diff gears is an easy option. Although 10 spline 3.54 diffs are rarer these days, most are the latter 24 spline. So you'll have to hunt about. Also most Series diffs have the diff filler on the diff casing, not the axle like latter vehicles. So most 3.54 10 spline diffs will mean you'll need to fill the axle with oil by jacking up one wheel slightly and pouring it in through the axle tube, or modifying your axle to include a filling port.
The trouble with 3.54 diffs is. It makes 1st gear a bit tall, even more so if you are on taller 7.50s already. So you need to slip the clutch a bit more when pulling away. Not a major issue, but it will be noticeable and feel like a down grade in peppiness off the line. It is more of an issue if you ever tow or haul heavier loads and will be far more evident in these situations.
For me the bigger issue is it creates a large gap between 3rd and 4th due to the internal gearbox ratios. You'll find that 4th feels a tad too low for 30mph (esp if there are any inclines or hills), but 3rd will feel like you are revving it a bit hard at this speed.
Another issue with 3.54 diffs, it'll ruin your low range crawl speed. If you do off road you'll notice this, as you won't be able to go as slow as it does currently.
That said, a diff swap is the cheapest and easiest way to majorly address gearing and will give you the ability to sit and cruise at higher speeds.
There are two other main options:
-Fit an over drive. Not sure if the Roamerdrive is suitable for a Series or only Defenders, you'd need to check. Fairy used to make an over drive and a few others. This will be something that bolts to the transfer box and will essentially give you to sets of gears for each regular gear, both in high and low range. It'll give you another lever to control too. Many will just use it like a 5th gear and only select when cruising, but you could have it engaged all the time or use a combination of the over drive and transmission gears. Giving you in theory 8 forward and 2 reverse in high range and the same again in low range.
Downside is, OD units are a bit pricey and sometimes not the most reliable or at least prone to a bit of an oil leak.
-Higher range gear set for the transfer box. Ashcroft do (or at least did) offer a higher range gear set for high range. Thus retaining the 4 gears and spacing, but dropping rpm in each gear for a given speed. Typically I think it means 4th would be about equal gearing to having an OD fitted, so same rpm per 20mph in top.
It is possible to mix and match several options, although don't get carried away and end up massively over gearing the vehicle. I don't think an OD and higher high range are compatible though. So it would be one or the other.
I had a 200Tdi Series III 88, I fitted the 3.54 gears which was good in some ways, but it drove better with the 4.75 original diffs. One of my plans was to revert to 4.75 diffs and fit an overdrive.
There are other more extreme options, such as a complete transmission and transfer box upgrade to something like a 5 speed (or even an auto!!!
) and a latter transfer box. But this is quite a custom thing to do with a lot of other potential changes.
Or even look to fitting a more rev happy petrol engine. It won't change the rpms you see now, but the right petrol engine may be more happy about maintaining such rpms.
