TF box change - ratios & speeds confusion

[mudgreaseandfrustration]

Hi, apologies my first post for ages is so long, I'd be very grateful for any comments from anyone that can bear with me all the way!

I am trying to decide whether to embark on changing my transfer box or not and would be grateful for some words of wisdom and experience. I'll explain my dilemma but currently having read other posts and done the maths using ashcrofts website I think i will change it, and at least see if i prefer it or not!

So, I have a 1986 90, originally TD with 205 tyres. Now has a 200TDi lump, original gear & TF boxes and 7.50 tyres. The 200Tdi replaced the original TD a few years ago and as i was advised to expect, the top speed is less even though it is far more powerful. I gather this is due to simply how fast the 200TDi can run and the ratio in the main gearbox (50A) is less than that in the 200TDi (56A) ones. I have changed the tyres to 7.50s which clearly increased my speed somewhat (by GPS speed not the speedo!). However, even if i push it to the engine limiter (which i have only ever done twice to test the max speed briefly!) i get just over 70 by GPS (62ish speedo) and certainly it sounds far happier around 60GPS (54ish speedo) which becomes tedious on long trips!

I have been advised and research confirms that a D1 TF box with a 1:1.222 ratio instead of my current 1:1.4 will do the business to "speed it up" to a more acceptable speed/revs ratio and i have acquired one that i am ready to fit.

However, some people have commented to me that they are surprised that with the bigger tyres i still need to do this and that it seems odd that my current speeds are as they are.

The only thing i can spot from the calculator on ashcroft's site that might be odd and causing this anomaly if correct is if either

a) my current TF box has been re-cogged before i had it, or

b) the axle ratios have been changed.

So is there any way of checking these and/or anything else i should explore before changing the TF box?

Also i understand i can get the speedo correct by changing a cog in the TF box but have no idea which one i want - any suggestions on type of cog and where to get them please?!

Thanks again in advance for any thoughts.

[western]

for 7.50 tyres you ned the blue 20 tooth FRC3310 gear as fitted to most 110's.

doubt the diffs have been replaced, unless it has series diffs fitted which IIRC are something like 4.7:1, your originals should be 3.54:1

[mudgreaseandfrustration]

for 7.50 tyres you ned the blue 20 tooth FRC3310 gear as fitted to most 110's.

doubt the diffs have been replaced, unless it has series diffs fitted which IIRC are something like 4.7:1, your originals should be 3.54:1

Thanks very much. I'll have a look at what gear is currently in the D1 box i've got lined up tomorrow - fingers crossed its the blue one!

I'm pretty sure the diffs are original as i've taken the axles apart to change all the wheel and kingpin bearings so would've thought i'd've had trouble with the new parts if they were different and like you say it seems unlikely that would've been done - to put it in perspective, when i got the 90 it was in pretty much standard condition with no mods or extras to be seen so that makes it seem even less likely that something as odd as the axle gears being changed for a different ratio would've been done.

Thanks again

[kiwi_110]

On your 1.222 T/case, check that it's mainshaft is cross-drilled before you fit it. This will extend the life of the splines on your g/box output shaft. Worth doing since you are increasing the load on this area with the higher gearing. If it isn't x-drilled, you can do it yourself with a 10mm masonry bit and a half-decent drill press. Also this t/case will be quieter, as it probably has the 33mm gears rather than 27mm.

Ray.

[mudgreaseandfrustration]

Hi guys,

I will certainly check the main shaft and hope that it will be obviously what i should be drilling when i see it - thanks for the tip - that is looking like saturday's job!

On the subject of the speedo gear, from manuals i think it should just prise out - is this right and are there any tricks to this? (i failed earlier this evening!)

Last thing - the manual talks about making a bracket to support the box whilst removing it. Obviously i know how heavy it will be from the replacement one - am i risking disaster if i just ratchet strap it to a trolley jack to lower it?!

Thanks again!

[kiwi_110]

When I drop mine, I do it through the hatch in between the seats with an engine lifting boom poked through the drivers door. I'll post a pic here soon of a mainshaft cross-drilling, just nipping downstairs to get one.

Here you go, so you drill 4 x 10mm (or thereabouts) holes through to the approximate mid-point of the splines, at 90 degrees to one-another. This allows oil to be flung into the spline area by the hi-ratio gear, which is in-line with this area of the mainshaft. the drilling is hard to start and then easy, then hard as it approaches the splines, because the surfaces are hardened. Take it slow, use a bit of cutting fluid, or beef dripping on the masonry bit. You guys all have dripping smeared on your bread yeah?

[CwazyWabbit]

The replacement cross drilled gears have longer splines in them which is handy if your gearbox output shaft is shafted as it means you can get a few more miles out of the gearbox before having it rebuilt as it will run on the virgin bit of the shaft as seen in the pic here.... just thought I'd point it out in case yours look like this

[mudgreaseandfrustration]

Thanks for all the advice. All done, swap complete along with nice new disc handbrake. Didn't have quite enough oil annoyingly so will have to wait til this evening to take it for a spin and see what the new ratio feels like so hope to repost with some news later!

[kiwi_110]

Didn't have quite enough oil

But you've got plenty of beef dripping, yeah? Just imagine the delightful scent wafting up from under the seats as you admire your 450 rpm reduction...