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Cortina Axle - Diff Change
Andy North - 12/12/04 at 07:14 AM

I have a Cortina axle where the diff loads in from the rear and it has brake drums approx 10" Dia.

1) How do I identify exactly what I have?

2) Anyone out there got a 4.1:1 ratio diff I can put in it?

britishtrident - 12/12/04 at 09:52 AM

Changing the ratio with this type of axle isn't easy ---- in fact personally I wouldn't attempt it if the ratio is wrong look for a more suitable axle. The ratio is most likely to be 3.55 or 3.77 or it just might be a 3.89.
Only 2 ways to tell once any id marks have been removed, either count the teeth or count the turns.
The latter is easier with this design.

Lock one brake drum so it can't turn, mark the other drum and diff input flange so you can tell when they return to ***exactly*** the same position .

Turn the input shaft one turn at a time keeping a record of the numbr of turns of the input shaft and each time the brake drum completes a full turn. Eventually both will line up exactly .
Then devide the number of turns of input by 2 and devide the result y the number of turns of the brake drum.
For example
Brake drum turns = 9
Input shaft turns = 70

70/(2*9) = 3.89

In this case the crown wheel has 35 teeth and the pinnion 9

Andy North - 12/12/04 at 06:17 PM

Fitting a new axle would also have problems for me (welding and fabricating the brackets), which is why I thought of the diff.

I now believe the present ratio to be 3.75:1

[Edited on 12/12/04 by Andy North]

FOSSIE - 16/12/04 at 07:31 PM

Hi mate, if you still need help with the diff change - send me an email or u2u - i build these day in day out, would be happy to help any way i can...

cheers
Tom

Andy North - 15/1/05 at 06:54 AM

While away at work, my wife sent me a picture of the diff, and it had a tag! When I returned home I noted the details:

3,75 0B06

P79BG-4004 ADA

Does this make any sense to anyone as to where I can get a replacement diff?

Jeffers_S13 - 18/1/05 at 09:54 AM

quote:
Originally posted by Andy North
I have a Cortina axle where the diff loads in from the rear and it has brake drums approx 10" Dia.

1) How do I identify exactly what I have?

2) Anyone out there got a 4.1:1 ratio diff I can put in it?


This sounds identical to mine which is a Mk5 Cortina. I had endless problems (and still continuing in a legal sense...) sorting brake parts out for it. I assume you have measured the outside of the drums, they are more likely 9" if you look carefully there will be a maximum dimension cast into it somewhere so you know when they are too worn and need replacing. I worked my ratio out and I think its 3.44, got a spreadsheet here with lots of ratios on to work out a speed vs rpm graph and havent labelled which on is in my car, doh ! but I *think* its 3.44.

Be careful when ordering brake parts and MAKE SURE you specify Mk5 9" drums not Mk4 as there IS a difference although some certain Ford parts suppliers disagree

Jeffers_S13 - 18/1/05 at 09:57 AM

quote:
Originally posted by FOSSIE
Hi mate, if you still need help with the diff change - send me an email or u2u - i build these day in day out, would be happy to help any way i can...

cheers
Tom


Hello

Im interested to know what sort of power/torque the Mk5 Cortina diffs/axles will take ?

Im putting a Nissan engine in my 7 and its standard output is 170BHP with a similar torque, Im hoping, nay praying it will be OK as I dont want the faff of putting another axle in...

Thanks

James

*sorry for the hijack*

britishtrident - 18/1/05 at 10:45 AM

Not all Cortina 3+ axles are the same 2 litre, 2.3 litre and a lot of 1600 cc cars have an axle with heavy duty half shafts. The axle with the smaller shafts was found in the 1300 and many 1600 models but is less common on later 1600 cars.

The heavy duty version wil take a lot of power it will handle a V6, small V8 or even a ful house Cosworth BDG without problem. The only time I ever saw a halfshaft break in one in tarmac competition use was beacuse some plonker had welded the shrunk on wheel bearing retaining collar.