Hi all, first post. I see there is plenty of knowledge on here of Sierra diffs but i couldn't find an answer to my exact problem so hopefully someone can help.

I'm changing from a 3.9 LSD 7.5" Sierra diff with Lobro joints to a 3.3 non LSD 7" diff with push in joints. (or at least i hope i am if it's possible)
The question is what needs to be done in order to get these components to fit?

Why not put the 3.3 crown wheel and pinion in the LSD diff

It's possible, but the 7.5" and7" diffs have different case sizes, so it may not slot straight in.

that would be an ideal solution but i dont think that is possible. I was led to believe that crown wheel and pinion are different on the 7" and the 7.5" and not interchangeable. or was it that the LSD is not interchangeable between the 705" and the 7". I cant remember. Can anyone confirm or deny?

Might be worth digging deep and buying a Quaife or Tran-x kit for your 3.3 diff, sell the existing viscous LSD to go towards it.
Personally i don't think the viscous diffs are much use in a lightweight car, especially when most have a rake of miles on them.

Can't fault the Quaife unit, but have heard the Tran-x is even better.

Al.

quote:

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Originally posted by rob_king
Hi all, first post. I see there is plenty of knowledge on here of Sierra diffs but i couldn't find an answer to my exact problem so hopefully someone can help.

I'm changing from a 3.9 LSD 7.5" Sierra diff with Lobro joints to a 3.3 non LSD 7" diff with push in joints. (or at least i hope i am if it's possible)
The question is what needs to be done in order to get these components to fit?

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the Quaife option just isn't a runner for me based on cost i'm afraid

The 7" diff is called that because the crown wheel is 7" diameter
The 7 1/2" diff is guess what 7 1/2 " diameter swap not possible.
Lobro to push fit needs some shaft modification as the push fit shafts are smaller than lobro.
You can fit lobro ends to push fit shafts but need the Desiel push fit shafts, I've been looking for years.
There are rumours you can fit lobro stubs to push fit diffs, we have for a Super Stock oval but it needed some adjustment as the stubs locked the planet wheels
The option for you is do without the LSD or put the crown wheel and pinion from the 3.3 into a 3.6 7" LSD flog on your 7 1/2"
Nothing is simple with a kit car.

ok that's most helpful. I had accepted that i was going to have to loose the LSD. Assuming i cant get Diesel push in shafts it sounds like putting the lobro stubs into the 7" push in diff is the only option left. You mentioned some adjustment was necessary, could you elaborate a little?

Dont fancy the cost of a Quaife ATB..then take a look at the EATON Truetrac
http://www.mc2racing.com/products/xr4ti/driveline/differentials/index.html

3.36 7.5" diff

Then swap over the LSD.

[Edited on 8/3/12 by Liam]

oo that looks perfect...if it is a 3.3. seller contacted. Thanks for the heads up.

bought it.

Deffo a 3.3 - cool!

So now all you need to do is stick the LSD mech into the 3.3 case and have yourself a 3.3 LSD.

Anybody know the weight of the 7.5" diff? i'm guessing 35-40kgs. Getting some crazy prices to get it shipped to Ireland

A 7" is around 26kg, so add a lilttle more for a 7.5" and packaging and that's probably about right.

Parcel monkey?

wow they want over £100! there seems to be some good deals on ebay but most have a 30kg weight limit

Yikes!

Hmmm if you ask the seller to ditch the rear rubber mount, drain it and maybe even take the flanges out into a seperate small package, the diff itself could come under 30kg if that's some sort of silly price threshold?

Wonder if the Locostbuilders delivery service extends to the Emerald Isles - maybe someone is planning a holiday by ferry?

Got it sorted through PPL logistics via ebay. £26. 00 which is a bit more like it!

Good to hear