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#Post#: 92714--------------------------------------------------
Overdrive:- Should I bother?
DIR By: juzza77
Date: September 11, 2014, 8:30 am
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I've got a Series IIa/III hybred with a 2.5 N/A Diesel from a 95
Defender. My top speed is only 40 mph which is quite fast
enough considering the brakes but the engine is working hard to
get me there. Is it, in the opinion of some of you more
knowledgable types, worthwhile finding an overdrive that works
and fitting it? What sort of benefit am I really going to get?
Any thoughts are much appriciated.
#Post#: 92719--------------------------------------------------
Re: Overdrive:- Should I bother?
DIR By: antiphase
Date: September 11, 2014, 9:29 am
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40mph? Have you tried lifting the clutch pedal all the way up?
:smilewide:
#Post#: 92720--------------------------------------------------
Re: Overdrive:- Should I bother?
DIR By: Doug_T
Date: September 11, 2014, 9:59 am
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If your top speed really is only 40 then I'd be looking into why
that is the case before shelling out on an overdrive. It should
do 55 and have more to go (but then your ears may start to
bleed). Realistically the overdrive will not make it much (if at
all) faster, but it will reduce the engine revs by about 30% for
any given road speed. They can be useful as a splitter gearbox
behind the naturally aspirated diesels (3rd + OD is a very handy
gear).
Problem is, if you are fitting it to primarily cut down noise /
lower revs then most of the S/H ones are expensive and worn
(i.e. Noisy) and new... Well the price of a new one buys an
awful lot of diesel with plenty of change left over for
soundproofing and ear plugs.
I've got one, but if I didn't then I probably wouldn't go out of
my way to find one, instead I'd probably look to a 5 speed
conversion.
#Post#: 92723--------------------------------------------------
Re: Overdrive:- Should I bother?
DIR By: ferretjuggler
Date: September 11, 2014, 12:19 pm
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My old series two bitsa had an early S3 diesel lump and 750x16
tyres.
It could actually hit the governors rev limit of 4,250rpm on the
motorway with some absolutely determined thrashing.
That's 70mph with no overdrive and prepare to go deaf.
Injector pump was of unknown parentage, revved well but lacked
bottom end grunt.
I dunno what a 2.5 N/A should rev to but even with SWB size
tyres and 4.7 diffs that's only 2,700rpm tops
Something definately wrong there.
Get a good diesel fitter to take a look at it.
#Post#: 92725--------------------------------------------------
Re: Overdrive:- Should I bother?
DIR By: juzza77
Date: September 11, 2014, 12:55 pm
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Thanks for the input so far. I say 40mph but that's just working
out from speed sensor signs in the villages around here, The
speedo has been disconnected for some years now as I've never
got round to refitting the cable. It's possible I can get to
50ish but it seems to be pushing it.
I've thought about changing up the box for a 5 speed but what's
the deal on Rangerover diffs? I've also been told that this may
help me out. Of course I've got no idea what I have as it's
made out of bits and where these bits came from they've most
likely been changed about too.
Lots of bodging goes on in Norfolk.
#Post#: 92728--------------------------------------------------
Re: Overdrive:- Should I bother?
DIR By: NoelC
Date: September 11, 2014, 1:20 pm
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I've moved this to technical as it's more relevant here than in
the welcome section. :thumbs:
I run a 2a ex-MoD ambulance in the US, and a series doesn't come
much heavier and less aerodynamic than that. Granted it's a
petrol, but it pulls a Fairey overdrive fine and is happy at
60mph on the flat. A 2.5 N/A shouldn't be out of puff a 40 or
even 50mph I wouldn't think unless something isn't right. Do you
have a sat nav or navigation app on your phone? These usually
show the speed worked out from GPS.
5 speed boxes are possible in a series, have a look through the
technical archive on here but they're not an easy fit. An
overdrive is very worthwhile and arguably the best way to go as
it doesn't affect anything else. 3.54 diffs are brilliant on a
Tdi, whether a 2.5 N/A would be happy all the time with that
increase in gearing I don't know. Perhaps someone will be along
who is/has run that setup.
#Post#: 92732--------------------------------------------------
Re: Overdrive:- Should I bother?
DIR By: Doug_T
Date: September 11, 2014, 1:40 pm
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RR diffs? In a 109 that's not necessarily an easy thing to do if
your rear axle is of late IIA or III vintage. Performance wise,
in flat Norfolk it may not be too much of a struggle for an
engine in best of health.
Just a thought, you say it's a bitsa, it doesn't have a
heavy-duty transfer box does it? They are lower geared.
#Post#: 92736--------------------------------------------------
Re: Overdrive:- Should I bother?
DIR By: juzza77
Date: September 11, 2014, 2:12 pm
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Hmm, I don't know Doug. It could, how would I tell? I shall
have to get onto my friendly LR tech and find out if I can find
him under the scrapyard he calls a garage. Have you any idea of
the best ratio for my needs?
Noel I've just got a new phone with such technology, I shall
give it a go but not for a couple of weeks as the caravan is
attached at the mo and will remain so for at least another week.
#Post#: 92737--------------------------------------------------
Re: Overdrive:- Should I bother?
DIR By: NoelC
Date: September 11, 2014, 2:19 pm
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To identify the transfer box, this is standard (look at the
cover plate, black, top left - it's dished inwards):
HTML http://www.lrseries.com/resources/user/b/d/1/c/bd1cf46393b2025f0e4fe159b8129ad9a33440ae/RTC2705-SERIES-3-GEARBOX-ASSY-COMPLETE.jpg
This is a one ton or heavy duty transfer box, the cover is flat.
HTML http://homepage.ntlworld.com/noel.clark/1tontransfer.jpg
#Post#: 92738--------------------------------------------------
Re: Overdrive:- Should I bother?
DIR By: NoelC
Date: September 11, 2014, 2:27 pm
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I'm guessing from the photo you posted of your motor it's a
series 3 109 so will have, most likely, a Salisbury back axle as
pictured:
HTML http://www.lrseries.com/resources/user/1/4/e/c/14ec762465a3df04202bb3203aa85a8d673853d6/FRC4408-STAGE-1-V8-REAR-SALISBURY-AXLE-ASSEMBLY.jpg
Salisbury axles have a bolt on diff pan:
HTML http://www.lrseries.com/resources/user/0/4/b/6/04b642d9a3c498b9abd97b06d2d8c7d4b7fdccc4/RTC844-SALISBURY-AXLE-DIFF-PAN-COVER.jpg
If that's the case a Range Rover or Discovery diff won't fit.
You'll need a diff or axle off a series 3 stage 1 V8 109 if you
want 3.54:1.
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