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3.7 Differential conversion 

 

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 Post subject: 3.7 Differential conversion
Posted: Wed Apr 29, 2009 11:14 am 
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Hi people. I have a few questions on a mod that is on my wishlist in the coming months. I currently have a 3.27 diff in my ED 5.0L wagon and its the 4 pinion slippery type. LSD doesn't interest me. All I'm after is better acceleration off the line and through 1st and 2nd gears on the auto.

Could anyone tell me where I can find a place that sells the crown wheel and matching pinion? Is there a particular car that these came out of? I've read that the most likely car is the R31 Skyline/Pintaras but surely there would be an aftermarket mob somewhere that make these.

Also on the topic, as Ford never offered such a ratio, where and how would I adjust my speedo to suit?

Since the launch of the current Fordmods, the search doesn't function hence the many probably well covered questions in this post.

BTW, I'll be doing this conversion in my shed to keep costs down plus I'm a fitter-machinist by trade, so this will be a good way to go back to my humble roots :)

 

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 Post subject: Re: 3.7 Differential conversion
Posted: Wed Apr 29, 2009 11:30 am 
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i bought my 3.73 gears from Mal Wood, for $550, but i dare say prices might have gone up a little since then

http://www.malwoodauto.com.au/

To get the speedo reading correctly you use a Jaycar kit, or an already built kit from shiftkits.com.au

To wire it up to get the speedo reading correctly, and keep the shift points correct theres a trick, but its very easy. The info below is how i did my EF cyl, im not sure exactly how different an ED V8 is?

Quote:
basically gearbox sends a signal to the speedo cluster via the "speedo input wire". Intercept and alter this signal with a Speedo Corrector to show correct speed on the cluster.

Problem is, the modified signal then comes out of the cluster to the ECU via the "speedo output" wire, and mucks up shift points.

So you fix this by cutting the "speedo output" wire coming from the speedo cluster, and run the loom side of the cut "speedo output" wire and tap it into the "speedo input" wire before the speedo corrector has intercepted the signal. This is so the ECU sees the original "unaltered" signal that comes from the gearbox and shift points remain the same.

Hope this helps, as i know it can be confusing, especially since ive labelled the speedo input & output wires on the speedo corrector and didnt do the same for the cluster wires


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 Post subject: Re: 3.7 Differential conversion
Posted: Wed Apr 29, 2009 2:32 pm 
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Thank you FF. Yes the V8 stuff is a little different. It has the separate tranny control module(TCM) which needs a signal from the speedo (999 white wire).

Mine (EF 6cyl-EL V8 hybrid loom) has the 999 wire coming from the sender on the box, then to the instrument cluster. Then there is the speedo output(999 again) that goes to the ECU and the TCM.

Tell me what happens if I were to put the speedo convertor between the sender and the instrument cluster? You say that it stuffs up the shift points? From how I see it, both my ECU and TCM need an updated, accurate speedo reading so it can therefore provide the correct shift points.

My factory Ford workshop manual states this:
"The 93LE model (6 cylinder) is controlled by the EEC V module whereas the 97LE model (8 cylinder) Is controlled by a dedicated Transmission Control Module (TCM). These Powertraln Control Modules (PCM) utilize throttle position, engine speed, transmission output speed, transmission sump temperature, normal/economy selector and communication to the engine controller Inputs, to control all shift feel and shift schedule aspects."

I'm just trying to clarify real world experience here from forum members with what I'm reading in my manual. Thanks again FordFairmont :)

 

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 Post subject: Re: 3.7 Differential conversion
Posted: Wed Apr 29, 2009 2:58 pm 
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banarcus wrote:
Tell me what happens if I were to put the speedo convertor between the sender and the instrument cluster? You say that it stuffs up the shift points? From how I see it, both my ECU and TCM need an updated, accurate speedo reading so it can therefore provide the correct shift points.



like i mentioned, im not too familiar with the V8 setup, however i reckon it would be a similar outcome with regards to the wiring

basically when you fit short diff gears, and leave everything else 'as is' the speedo will be reading wrong obviously, but the shift points will remain correct (wont change too early or bounce off rev limiter)

when you go to intercept and correct the speedo signal, you will have a correct speedo signal, but then you have inadverntantly mucked up the shift points at the same time

the basic trick is you intercept the signal going to the speedo cluster with a speedo corrector to fix the reading, then cut the wire that receives info for shift points (possibly cluster to TCM wire), and tap it into the original speedo signal wire BEFORE it gets 'tampered' with by the speedo corrector
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 Post subject: Re: 3.7 Differential conversion
Posted: Wed Apr 29, 2009 3:12 pm 
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FordFairmont wrote:
banarcus wrote:
Tell me what happens if I were to put the speedo convertor between the sender and the instrument cluster? You say that it stuffs up the shift points? From how I see it, both my ECU and TCM need an updated, accurate speedo reading so it can therefore provide the correct shift points.



like i mentioned, im not too familiar with the V8 setup, however i reckon it would be a similar outcome with regards to the wiring

basically when you fit short diff gears, and leave everything else 'as is' the speedo will be reading wrong obviously, but the shift points will remain correct (wont change too early or bounce off rev limiter)

when you go to intercept and correct the speedo signal, you will have a correct speedo signal, but then you have inadverntantly mucked up the shift points at the same time

the basic trick is you intercept the signal going to the speedo cluster with a speedo corrector to fix the reading, then cut the wire that receives info for shift points (possibly cluster to TCM wire), and tap it into the original speedo signal wire BEFORE it gets 'tampered' with by the speedo corrector


Well that would make sense. Perhaps the instrument cluster converts the frequency signal into something else and this then goes to the ECU and TCM. Thanks again.

 

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 Post subject: Re: 3.7 Differential conversion
Posted: Wed Apr 29, 2009 3:22 pm 
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Nah the signal is still the same, it's because the TCM calculates shifts off the VSS (I assume how it figures out shiftpoints is basically a load vs speed table, thats how I picture it in my head anyway :) ), and if you feed it a modified signal, it will still be trying to shift at the speed it's programmed to shift it.
It doesn't realise that, due to your ratio change, this speed now occurs at approx. 8000rpm, so it will decide to bounce of the limiter a few times before it realises WTF is going on.
So the trick is to keep feeding it the OLD signal, where the speedo is wrong. But the speed vs RPM still matches.

Hope that makes sense, I (FordFairmont too? :lol:) explain this differently every time and confuse myself LOL
It should probably be a sticky or something.

edit: which is all a brainfade on my part anyway, cause I'm pretty sure EA-ED split the signal from VSS to cluster and ECU/TCM (double check workshop manual on this), so you don't have to worry about what FordFairmont has mentioned.
Just a bung a corrector in the VSS line at the dash and voila.

 

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 Post subject: Re: 3.7 Differential conversion
Posted: Wed Apr 29, 2009 3:52 pm 
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Steady ED wrote:
edit: which is all a brainfade on my part anyway, cause I'm pretty sure EA-ED split the signal from VSS to cluster and ECU/TCM (double check workshop manual on this), so you don't have to worry about what FordFairmont has mentioned.
Just a bung a corrector in the VSS line at the dash and voila.


Understand everything now, just got my simple brain around this and it all makes sense now. Thanks

 

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 Post subject: Re: 3.7 Differential conversion
Posted: Wed Apr 29, 2009 11:25 pm 
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were the R31 Skyline/Pintaras with 3.7/3.9 gears a 25 spline or 28 spline center?
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 Post subject: Re: 3.7 Differential conversion
Posted: Thu Apr 30, 2009 1:37 am 
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well it wouldnt really matter, because the crownwheel gear can be swapped to many different centres.

with adjusting the speedo gear dan, keeping a manual its simple right?, just install the jaycar kit?

if i go into Jaycar, what should i tell the person to ask for. because im sure they would have no idea if i tried to explain it :P

 

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 Post subject: Re: 3.7 Differential conversion
Posted: Thu Apr 30, 2009 8:33 am 
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just ask for their MKII speedo corrector kit. But it comes in pieces, so might have to pay extra to ge them to put it together, or you can pay a bit more and get a ready made one from shiftkits.com.au

to install, find a pinout diagram for your cluster, and use the speedo input wire to intercept with the correcter
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 Post subject: Re: 3.7 Differential conversion
Posted: Sat May 02, 2009 1:55 pm 
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[quote="markwright"]well it wouldnt really matter, because the crownwheel gear can be swapped to many different centres.

Yes it would matter. 25 spline axles centres will interchange crown wheel & pinion of the nissan gears with no problems. correct me if im wrong, falcon sedans and wagons are 25 spline so no probs there. 28 spline found in commercials will have a different housing, therefore the pinion bearing will need to be shimmed up using 70thou shim +/- to use the nissan gears.

Pretty sure that the Pintara normally carry 4.11s so that should narrow down the search and you may need a half decent exhaust to mask the whine commonly found with nissan gears. Not all but most of them and hard to tell when you pick up from a wrecker. Depending what you are after it may be worth paying $$ to buy new and you know you will be happy in the end. Ive fiited the 4.11s to 28 spline centre and extremely happy with them, has a slight whine but I only hear it when my baffles are in pipes and thats not often. :)
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 Post subject: Re: 3.7 Differential conversion
Posted: Sat May 02, 2009 2:00 pm 
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Why wouldnt you want an LSD with that ratio?
You need to get traction to get acceleration .

 

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 Post subject: Re: 3.7 Differential conversion
Posted: Sun May 03, 2009 11:50 pm 
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so does a crown wheel and pinion from a 25 spline center, fit a 28 spline center and vice versa?
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 Post subject: Re: 3.7 Differential conversion
Posted: Mon May 04, 2009 12:08 am 
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itd have to. theyr basically all interchangeable. a borgwarner gear set, can fit 25/28/31 spline open centres/LSD/minispool and 4wd lokkas.

 

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 Post subject: Re: 3.7 Differential conversion
Posted: Mon May 04, 2009 12:14 am 
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only thing i can add is Borg Warner '75 series & '78 series 3.73 gears fit into eseries housing that had 3.23 or 3.45 gears originally.
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