WTB: Sierra 7" Diff 3.9 or 4.1 or just CW+P. Have spare 3.14 CW+P

[PH1]

Hi All,

I'm looking for either:

A 3.9 or 4.1 CW+P for a 7" sierra diff.

A 3.9 or 4.1 7" sierra lsd diff with the lobro bolt fixings.

A 3.9 or 4.1 7" sierra diff.

I have a sierra 7" diff with a 3.14 ratio and a quaife atb.

I'm looking to change ratio from 3.14 to 3.9 or 4.1 in the most economical way.

Piers

[KevB]

Hi

    Sorry I can't help you directly get one but i am interested in doing a deal on your 3.14 diff once you are sorted out and if you are selling it.

 

3.92 diffs come up regular but be careful you dont end up with a 7.5"

 

There is a 7" on ebay now for 100 quid deliverd.

 

http://www.ebay.co.uk/itm/6883-Ford-Sierra-7-Differential-3-92-Ratio-Push-Driveshaft-/350906859951?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item51b3adc1af

 

Kevin

[Stu Faulkner]

Are the CWP's interchangable between 7 and 7 1/2 diffs?

And what about CWP's in  push in shafts and bolt on shaft diffs?

[Dave Eastwood (Gadgetman) - Club Chairman]

No. It's a common misunderstanding with Ford diffs; the sizes don't refer to the width of the case betewwn mounts, though those do often match - deliberately? The size is the diameter of the crown wheel, hence the bigger power/torque a diff can handle, the bigger the crown wheel and pinion usually are. AFAIK, over here, we only get/got 7 and 7 1/2" diffs, over in the States the (" was most popular for decades, and although long since dropped by Ford, is still available in the performance aftermarket.

 

So it's a physically bigger diff internally too.

[Dave Eastwood (Gadgetman) - Club Chairman]

Sorry, missed the second bit. Other than ratio, and overall size, the CW&P as far as I know, are identical regardless of shaft type.

[Stu Faulkner]

Cheers dave.

Even though i've built one before, I always thought the 7" just related to the case.

You learn something new every day........

[PH1]

Now I'm confused (its not hard). But if I've got a 7" case, Iv'e got a 7" diff and need a CWP for a 7" diff right?

[KevB]

Now I'm confused (its not hard). But if I've got a 7" case, Iv'e got a 7" diff and need a CWP for a 7" diff right?

 

Yes All you beed is a 7" 3.92 CWP if you want to keep your original diff and housing, add to that you will need a new set of bearings, seals and crush washer.

 

While you have it apart might aswel change them as you will have to reset the pre-load and back lash so you don't destroy your new CWP.

 

All you need to read up on Sierra diffs here:-

 

 

http://www.super7thheaven.co.uk/Sierra_Rear_Differential

[PH1]

Thanks Dave - sounds like im on the right track

[Dave Eastwood (Gadgetman) - Club Chairman]

Be very wary about stripping the crown wheel and pinion out of a diff yourself and doing a complete rebuild. It ain't easy! The specialists use a variety of special toolds to make it a little easier and quicker. It is possible to do yourself, but it's not a job I'd really recommend unless your pretty confident and experienced.

 

There is a half way house that's not too bad to do, but even then diff stripping can be a pain of a job!

 

The tricky part of a full strip is realigning the pinion and crownwheel when both have been removed from the casing, as you no longer have any references.

 

However, if you leave the pinion in place, then you can use that as a reference and adjust the position of the crownwheel to match it.

 

So for instance you find a 4.1 open diff, but want to make it into an LSD, you open up the 4.1, take out the diff cage with the 4.1 CW attached and remove the CW. You then do the same thing to the diff with the LSD fitted. Take the diff cage including LSD and half shafts from the old diff, bolt on the 4.1 CW and re-fit into the 4.1 diff casing.

 

You can now adjust the CW to realign with it's matching pinion. (Normally with a combination of a dial gauge and some engineers blue).

 

The only thing I would say, is it's one of those jobs that you can get slightly wrong and not know about immediately. It's only later on when you've suddenly got lots of noise or some other symptom that you find there was a problem!

 

That said, I've rebuilt loads now, and done quite a few LSD swaps, touch wood, I've never had an issue, so as long as you take your time and methodically follow the Ford manual you should be OK.

[PH1]

Nope, not for me thanks. I'm just gathering the pieces then taking them to the professionals.. Thanks for the info anyway. Im sure another member with a bucketload more confidence and experience than me will find it useful.