Transmission Ratio - calculating

Grumble is (probably) going Auto...

So, I have in mind - to place between the 4.6 V8 and the wheels, a standard 4 speed auto box, but cannot decide upon transfer box. My thinking is as follows: A Borg Warner box has fixed ratio and although quieter, has the disadvantage of chain stretch...

So, looking at an LT230 (as it also has the diff lock) as an alternative, but cannot get my head around the ratio to go for. Having standard 101 front and read diffs (which are fairly low ratio) but bigger wheels 28.5" - I want to try to avoid having too high a ratio (cruising at 70 doing 1,500rpm is not good for a V8 and makes for frustrations for the driver).

Anyone care to shed their light on this?

Reply to
Mother
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You sure about 70mph at 1500rpm? By my calculations, all else being as expected, you should be hitting 4000rpm at 70mph.

If the gearbox, transfer box & diffs are standard, and only the engine & wheels have changed....

Engine Speed (rpm) * 1/1 * 1/1.174 * 1/5.57 = Wheel Speed (rpm) | | | Top Gear ratio -------+ | | | | Transfer Box ---------------+ | | Diff Ratio ---------------------------+

So - 4,000rpm Engine speed = 611.69rpm Wheel speed

With 38" dia. wheels & tyres, 1 rpm = pi * 38 inch/min, or pi * 38 * 60 /

63360 miles/hr

so 611.69rpm = 69.15 miles/hr at the aforementioned 4,000rpm engine speed.

If you specify what engine rpm you want at 70mph (or 611.69 wheel rpm), you should be able to plug numbers into the above and work out what transfer ratio you want.

From what I've seen, the final drive on an auto box is probably 0.7:1 or thereabouts. Sticking 0.7/1 into the top gear ratio indicates that you'd need to swap to Range Rover diffs (at 3.54:1) in order to see 70mph at about 3700, otherwise you'll only get 48mph @

4000 rpm.

I hope all that's of some use - if anyone can see anything wrong with what I've done, feel free to chip in...

- Andrew

PS. Useful links :

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For 101 gearing ratios
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For General L.R. Gearinginfo

Reply to
Andrew

You have mail. A spreadsheet that calculates road speed for given RPM and gear ratios.

Reply to
Tim Hobbs

Sorry - it's 1/0.7 that you stick into the top gear ratio, and that means that you'll get 70mph at about 2800 rpm with the 101 diffs and all else remaining the same.

- Andrew

Reply to
Andrew

Tim Hi,

I would be extremely obliged if you could also send me this calculator.

Thanks in advance

Take care Pantelis

Reply to
Pantelis Giamarellos

Yup - this and Tims Spreadsheet have me sorted, TVM

BTW, the wheels are 38.5 (not 28.5 - that was my typo). I was using the 70mph @ 1,500 RPM as a demonstration - not what I'd get - as that'd be very scary! :-)

Reply to
Mother

Top notch - many thanks!

I've modded it for a 101 (with credit) and placed it here in case anyone wants to play:

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Reply to
Mother

OK, here's the plan - not too cunning and a bit of a soft option...

Standard ZF 4 speed box - ratios as per spreadsheet mentioned in reply to Tims post. Also standard Rangie transfer ratios - geared box so as to avoid chain stretch in Borg Warner. Essentially the unders of Grumble will be the same as when it was built, but upgraded Range Rover parts rather than older ones ;-)

Now... Cross drilled input gears anyone? I'll assume that later boxes will already have them - when were they added?

Also, what's the score with the hanging in 1st gear problem associated with these boxes? Again, would a later box have overcome this?

Initially - as this is an experiment and I want to limit my financial exposure, I'm going to go get a s/h box - if this works out alright, I'll put an Ashcroft box in next year. Otherwise it'll be back to the LT95... Hmm...

Finally, Charlotte and I both - at the same time - last night mentioned to each other that we'd never (ever) driven an Automatic!

Reply to
Mother

Do you remember that Rolls Royce engined special that RR cars insisted not be called a RR or have a flying lady, built by someone called Dodd?

Geared at 100mph per 1000rpm and rev limited at 2900rpm!

AJH

Reply to
sylva

On or around Fri, 30 Jul 2004 11:49:08 +0100, Mother enlightened us thusly:

never heard mention of it on the ZF... they date from about 96 on manual boxes. Maybe the ZF output shaft is better quality?

If you want to hunt an LT230-type setup, you're looking at an ex-disco one. I suspect the BW transfer box arrived at the same time as the ZF in the RRs, although I'm open to correction on that.

neither of the SH ones I had suffered that. I think it's more liekly to be down to crappy maintenance.

if buying a secondhander, I'd go the whole hog, buy a filter (about 25 notes) and lots of ATF and make some attempt to drain the TC as well as the box, which you can only do when it's out, so as to get a decent oil change etc done before installing it. Unless you know the history... sump off to change the filter, but it's got a big rubberoid seal which should be OK to refit.

auto in the 110 was great. You can make it play tunes, by applying more or less boot. You can also force it down into low gears with the shifter. generally, I really liked it, if the engine hadn't been s**te I'd still be running it. I wouldn't have gone back to a manual. almost tempted to hunt an auto for the current disco, rather than hunting a better manual box. Almost...

Reply to
Austin Shackles

Does the cross-drilled gear problem apply to the autos?

If it's OK I might buy it off you! Seems fair as I'm letting Warren practice on yours before doing mine!

Do you want to practice in my Volvo? Mandy hadn't either, but it's easy as pie. Tuck your left leg under for a few miles otherwise the emergency stops can get tedious as you try to bang the clutch in.

Hardest bit is driving a manual again afterwards. I keep driving the Merc 10 yards down the road on the starter motor....

Reply to
Tim Hobbs

A big improvement I'd say!

Reply to
Tim Hobbs

I'm not certain this is an issue with the ZF, I've never known anyone have a problem... certainly haven't done anything to any of mine.

This is a problem with all the ZF boxes and is usually caused by the O rings inside the governor housing. They are easy to replace/inspect with the transfer box removed. Sometimes the governor itself gets scored and cuts the O rings in which case a new governor will set you back about 30 quid. It takes about 10 minutes to fix once the xfer box is off.

Check the oil colour in the box - a nice clear pink and all is well ( probably), a brown colour could mean trouble. If there is no oil in it then pull the sump plug out and take a look. Brown sludge or lots of metal on the magnet (built in to the plug) could mean trouble.

While I remember, if you get the ZF and the xfer box seperately, make sure that you can get hold of a suitable output shaft. The ZF to BW output shaft splines stop about half way down the shaft. The LT230 needs full length splines.... Discos and early 4 speed classic RR were factory fitted with LT230s.

Watch out for (maybe avoid) the electronic ZF version from later models as you will need an ECU to control them. You can make your own controller for them but it can be a bit of a pain, particularly the speed control which uses a pulse width modulated input signal.

Go on, you know you want to :-)

cheers

Dave W.

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Reply to
Dave White

Yep, you're right, it does need correcting :-)

There were some classic RR fitted with the LT230. The BW Xfre box wasn't fitted until the 1989 model year. The ZF was fitted from 1986.

cheers

Dave W.

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Reply to
Dave White

Smashing answer - feel a bit better now :-)

So it's probably worth doing this anyway, whilst out of the vehicle?

Good idea. I'll mention this to Warren when he goes looking. I'll be flushing and refilling anyway but a neb before buying is a very good idea.

Ah, yes - came upon this somewhere else. I'm going to try and get a complete gear and transfer box out of a Disco or Rangie (did they both have the same transfer ratio?).

Just have - albeit not very far. I can see two things happening;

  1. My left foot will kick through the front of Grumble until I'm used to not having a clutch.
  2. My left leg will lose weight and wither away once I get used to not having a clutch.

:-)

Reply to
Mother

Oh, and another thing :-) I guess for the 101 you'll be creating your own transfer box lever (a lot easier with the Borg Warner BTW !). But if you are thinking of utilising an LT230 lever assembly make sure you get the mounting plate for the auto box.

On some manual boxes the xfer lever bolts onto the top of the gearbox directly. On a ZF you need a mounting plate and these cost around 60 quid new so best to get one with the ZF if you can.

cheers

Dave W.

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Reply to
Dave White

Definately worth a quick look. While you're in there, check the parking pawl as well (the governor is actually bolted to the disk the pawl locates into.

Yes, they both used 1.222, only the Defender used 1.4 and 1.6 AFAIK.

LT230's that came from the back of a 3 speed RR auto are almost 1:1 ratio BTW.

REAL auto drivers use left foot braking, essential when you need to get away from the lights fast or your engine tickover isn't what it ought to be. It can also be used for high speed cornering and to allow a quick exit from a slow corner. All this is going to be relative with Grumble though :-)

cheers

Dave W.

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Reply to
Dave White

I remember, from years and years ago, reading about a guy who had installed a Spitfire engine into his car (the V-12 aeroplane Spitfire, not the piffly little Triumph 1500cc Briggs & Stratton affair) - had to use a lorry clutch as I recall, but it was good for about mach 17 at 2200 rpm apparently. Possibly the car you're referring to? It might have been one of those drag-racers now I think about it.

Hmmm. I wonder if I could squeeze the engine from one of Her Majesty's warships into my S-IIa....... ;)

Steve

Reply to
Steve

Kin eck - a contender for the Darwin Awards no doubt!

Reply to
Mother

I remember this one. The engine, although originally designed for the Spitfire, was actually out of an Air Sea Rescue launch. The owner was an insurance broker. The whole issue came to light when a polite letter was received by Rolls Royce asking that they not road test their new models on the German autobahn as the high speeds were causing the traffic monitoring equipment (some sort of measure of density I think) to fail

Alan

Reply to
Alan Brown

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