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Common Sierra diffs and drive shafts

bumpy - 15/9/15 at 02:37 PM

I've decided to change my diff from 3.38 to 3.92 and despite a seemingly fair bit of info out there its a bit of a mine field, so I have decided to capture what I have read and I hope you guys can correct anything that's wrong.

I will restrict the discussion to the push in shafts which in turn means only drum brake cars (unless some clever person has carried out a non standard mod)

Diffs

The two most common diffs are the 7" and 7.5". This is actually the size of the crown wheel, but fortunately is mirrored by the length of the top bolt fixing. In addition the 7" unit has an open bolt fixing and the 7.5" has a closed bolt fixing.

There is only one type of oil seal kit quoted, and I am assured the seals fit both the 7" and the 7.5". this is good in that one size fits all.

Given that the seals are the same it looks like the flat bearing surfaces at the top of the half shaft and just ahead of the splined area are also the same diameter. This is good as one size fits all - but, splines are different

The two most common upper splines are 26 and 28 splines. They are not interchangeable, and must marry up with the shafts.

Drive shafts

The right hand drive shaft is longer than the left and dimensions are shown here. http://www.super7thheaven.co.uk/components/sierra_rear_drive_shafts/

Bear in mind it is almost impossible to make measurements on the car as the half shafts float about to accommodate suspension movement.

Even though the left and right shafts are different lengths, all left and all right shafts are the same lengths. In this respect this makes them interchangeable.

Some shafts are 'skinny' at 24mm, and some are 'fat' 27mm. The thickness of the shafts does not denote anything about spline numbers etc and the two types are intechangable

[Edited on 15/9/15 by bumpy]

[Edited on 15/9/15 by bumpy]

DRM Black7 - 15/9/15 at 03:02 PM

I've entered into the issue this week, going from 3.62 diff to a 3.38 and sods laws states my 3.62 driveshafts are 23 spline and my new 3.38 diff is 26 spline lol typical.
Think that's the outer hub side are all 28 spline.
Tried to buy some new ones from J and R what a crap company, no help what's so ever. So got some second hands ones of Flebay.
Anyway hope she's back together for the weekend, fingers crossed

bumpy - 15/9/15 at 03:13 PM

quote:
Originally posted by DRM Black7
I've entered into the issue this week, going from 3.62 diff to a 3.38 and sods laws states my 3.62 driveshafts are 23 spline and my new 3.38 diff is 26 spline lol typical.
Think that's the outer hub side are all 28 spline.
Tried to buy some new ones from J and R what a crap company, no help what's so ever. So got some second hands ones of Flebay.
Anyway hope she's back together for the weekend, fingers crossed

Yes I think I read that all outer splines are 28.

You were unlucky to have 23 spline shafts and diff, apparently they weren't used much

I too phoned J & R and asked to talk to an expert - about as much use as a chocolate teapot.

Good luck with the changeover and don't forget to adjust the speedo

Paul Turner - 15/9/15 at 04:02 PM

quote:
Originally posted by bumpy
The two most common diffs are the 7" and 7.5".

Disagree with you there.

The 2 most common diffs were 6.5" and 7". The 6.5"'s were fitted to most Sierras sold with the 7" ones only being fitted to the less common 2 litres, 2.3 litres and 2.8 litres variants.

The 7.5" diffs were only fitted to the Cosworth models which relative to the all models were a very small percentage sold.

Don't forget that Granada's also used the same diffs but no idea what sizes were used.

CosKev3 - 15/9/15 at 04:38 PM

quote:
Originally posted by Paul Turner

quote:
Originally posted by bumpy
The two most common diffs are the 7" and 7.5".

Disagree with you there.

The 2 most common diffs were 6.5" and 7". The 6.5"'s were fitted to most Sierras sold with the 7" ones only being fitted to the less common 2 litres, 2.3 litres and 2.8 litres variants.

The 7.5" diffs were only fitted to the Cosworth models which relative to the all models were a very small percentage sold.

Don't forget that Granada's also used the same diffs but no idea what sizes were used.

I've never seen a Sierra 6.5 inch diff!!!

To correct your above statement two wheel drive Sierra cosworths used the 7.5 inch diff.
4x4 Sierra and escort cosworths used a 7 inch rear diff.

[Edited on 15/9/15 by CosKev3]

Doctor Derek Doctors - 16/9/15 at 10:00 AM

quote:
Originally posted by DRM Black7
I've entered into the issue this week, going from 3.62 diff to a 3.38 and sods laws states my 3.62 driveshafts are 23 spline and my new 3.38 diff is 26 spline lol typical.
Think that's the outer hub side are all 28 spline.
Tried to buy some new ones from J and R what a crap company, no help what's so ever. So got some second hands ones of Flebay.
Anyway hope she's back together for the weekend, fingers crossed

I've ended up with 23 spline shafts as well....! How much do you want for your 23 spline 3.62 diff? (if you want to sell it?)

tims31 - 16/9/15 at 11:25 AM

quote:
Originally posted by CosKev3

quote:
Originally posted by Paul Turner

quote:
Originally posted by bumpy
The two most common diffs are the 7" and 7.5".

Disagree with you there.

The 2 most common diffs were 6.5" and 7". The 6.5"'s were fitted to most Sierras sold with the 7" ones only being fitted to the less common 2 litres, 2.3 litres and 2.8 litres variants.

The 7.5" diffs were only fitted to the Cosworth models which relative to the all models were a very small percentage sold.

Don't forget that Granada's also used the same diffs but no idea what sizes were used.

I've never seen a Sierra 6.5 inch diff!!!

To correct your above statement two wheel drive Sierra cosworths used the 7.5 inch diff.
4x4 Sierra and escort cosworths used a 7 inch rear diff.

[Edited on 15/9/15 by CosKev3]

Agree with this, my diff came from a 1.8 Sierra Saphire and that is a 7.5" diff.

bumpy - 16/9/15 at 11:55 AM

What function do those large castellated rings serve where the drive shafts enter, they don't seem to hold the oil seals in place.

Also my spare diff has been stored without drive shafts and hence the innards exposed for some time (before I bought it). What should I use to flush/clean it out - I am thinking paraffin or petrol.

Paul Turner - 16/9/15 at 12:16 PM

quote:
Originally posted by tims31

Agree with this, my diff came from a 1.8 Sierra Saphire and that is a 7.5" diff.

Sorry but you are very wrong.

1.8 hatch and saloons came with either a 6.5" or a 7" diff. Estates were fitted with a 7".

7.5" only came on the Cosworths and according to legend some 2WD V6 models.

Think you need to recheck your facts.

Johneturbo - 16/9/15 at 04:35 PM

quote:
Originally posted by bumpy
What function do those large castellated rings serve where the drive shafts enter, they don't seem to hold the oil seals in place.

Also my spare diff has been stored without drive shafts and hence the innards exposed for some time (before I bought it). What should I use to flush/clean it out - I am thinking paraffin or petrol.

Them castellated rings do a very important job to hold the side bearings in place and to set the backlash!

bumpy - 16/9/15 at 05:39 PM

quote:
Originally posted by Johneturbo

quote:
Originally posted by bumpy
What function do those large castellated rings serve where the drive shafts enter, they don't seem to hold the oil seals in place.

Also my spare diff has been stored without drive shafts and hence the innards exposed for some time (before I bought it). What should I use to flush/clean it out - I am thinking paraffin or petrol.

Them castellated rings do a very important job to hold the side bearings in place and to set the backlash!

Thanks. So not to be played with then

CosKev3 - 16/9/15 at 07:55 PM

quote:
Originally posted by Paul Turner

quote:
Originally posted by tims31

Agree with this, my diff came from a 1.8 Sierra Saphire and that is a 7.5" diff.

Sorry but you are very wrong.

1.8 hatch and saloons came with either a 6.5" or a 7" diff. Estates were fitted with a 7".

7.5" only came on the Cosworths and according to legend some 2WD V6 models.

Think you need to recheck your facts.

Somebody could well have fitted a 7.5 inch rear beam on the saph he bought though!

Rob Allison - 16/9/15 at 11:40 PM

quote:
Originally posted by Paul Turner

quote:
Originally posted by tims31

Agree with this, my diff came from a 1.8 Sierra Saphire and that is a 7.5" diff.

Sorry but you are very wrong.

1.8 hatch and saloons came with either a 6.5" or a 7" diff. Estates were fitted with a 7".

7.5" only came on the Cosworths and according to legend some 2WD V6 models.

Think you need to recheck your facts.

Not true.

Ford used any diff they had in the last years of the sierra and saphirre. so a 1.8 sierra could have had a 7" or 7 1/2" diff.

The 6.5" diff was only an early sierra fitment and on some 1.3 and 1.6 sierra's. It is a very uncommon diff.
The 7" is the most common for sierra's. This was used in most of the range in various ratios. Including the 4x4 saphire cosworth and the escort cosworth. All 4x4 sierra's, saphires and estates were fitted with a 7" lsd diff.

The 7.5" is the next one. This was found in late Dohc's and some 1.8's. I know this as my 1990 DOHC had a 7.5" 3.92 pushin type diff. It is most likley to be a 2wd cosworth either 3 door or saphire. The 2000E saphire will have a 7.5" bolted 100mm flange diff.

But dont forget the granada and scorpio's also had the same diff. The scorpio post 1994 is slightly different in the case design and back plate.

You can swap all the internals from any 7" diff into another. i.e. if it an open push-in you can fit the centre and drive flanges from an lsd diff. The same applies to the 7.5" It does require the diff taking appart to do this.

One more is that you can fit a push in diff and have disk brakes or have a bolt on type diff with drum brakes if you find the right drive shafts. These shafts were fitted to late 1990 models some diesel's and others with ABS fitted. They are a thick shaft which will accept the lobro joint spline and the tripod joint spline.
I have not done this and dont have any further information. But if you go on the sierra owners forum and join, in their members area is a full write up.

Rob Allison - 16/9/15 at 11:51 PM

quote:
Originally posted by bumpy
I've decided to change my diff from 3.38 to 3.92 and despite a seemingly fair bit of info out there its a bit of a mine field, so I have decided to capture what I have read and I hope you guys can correct anything that's wrong.

I will restrict the discussion to the push in shafts which in turn means only drum brake cars (unless some clever person has carried out a non standard mod)

So to this.

You could get any 7" diff with a 3.92 ratio and fit the centre with the correct spline size for your shafts from your 3.38. I guessing this is a diesel diff.

Or you can make up some hybrid shafts if you can find the right tripod joints or shafts. This i can't help you much with.

bumpy - 17/9/15 at 07:36 AM

quote:
Originally posted by Rob Allison

quote:
Originally posted by bumpy
I've decided to change my diff from 3.38 to 3.92 and despite a seemingly fair bit of info out there its a bit of a mine field, so I have decided to capture what I have read and I hope you guys can correct anything that's wrong.

I will restrict the discussion to the push in shafts which in turn means only drum brake cars (unless some clever person has carried out a non standard mod)

So to this.

You could get any 7" diff with a 3.92 ratio and fit the centre with the correct spline size for your shafts from your 3.38. I guessing this is a diesel diff.

Or you can make up some hybrid shafts if you can find the right tripod joints or shafts. This i can't help you much with.

Thanks Rob

Yet more options

Today I will be looking for new rubber gaiters to fit my older shafts. Out of interest has anyone tried those very flexible gaiters that fit over the CVs using a cone so one doesn't have to dismantle them?

https://www.youtube.com/watch?v=WV9jyJu2Ku0

From measurements it looks like the inner and our CV gaiters are the same, but they seem to be listed as separate parts. What is the correct answer?

[Edited on 17/9/15 by bumpy]

Rob Allison - 18/9/15 at 01:39 AM

Yes use the stretch cv. They work, warm it first

bumpy - 18/9/15 at 07:52 AM

quote:
Originally posted by Rob Allison
Yes use the stretch cv. They work, warm it first

Thanks Rob

Did look at the Ford ones. Including clips they are now about �20 each from Ford dealer. This compares with the cost of 4 stretchy ones that includes the fitting cone

For future reference the inner and outer have the same part number so are identical. I was quoted part no 1017661, but have no idea if this number is the same for both the skinny (24mm) and the fat (27mm) shafts.

[Edited on 18/9/15 by bumpy]

bumpy - 18/9/15 at 10:12 AM

Bit more progress on the half shafts.

Have cleaned off all the rust and flaky paint for a respray and have peeled back one of the existing gaiters.

First thing I noticed was that the (cold) grease poured out like treacle - I guess it was well past its sell by date

Second thing I noticed was that both the shaft and CV casing are 'grooved' to accept the gaiter. The gaiter, in turn, had similar profile inside to fit these grooves. (Photos attached)

Is this common for all drive shaft gaiter fitments and would it making fitting the stretchy gaiters a problem as they are universal and almost certainly will not be sculptured to fit these grooves.

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