As above, I'm looking at a close ratio box but its got standard drop gears. Just wondering as I have all the 7.5 stuff if I could get a cwp to fit?

 

The 7.5 was the 3.62, the 7" was the 3.64.

What are you trying to do?

 

U sure? I'm building and escort rally car and I have a group n front diff standard ratio and wanted to use a 7.5 diff on the back so I'm using the 108 shafts. I'm pretty sure the 4wd is 3.62?

 

So you want to stay on 3.6 front and rear? iirc im am 99% sure I am right, the 2wd had a slightly higher top speed than the 4x4 hence 3.62 for 2wd.

But, you could run a 3.62 7.5" rear and a 3.64 6" front with std 31/31 step off at 1:1 without issues.

I ran a 4.27 rear and a 3.64 front with a step off I had made by DOME, worked fine. for difference between front and rear you have to work to the 2nd 10th of the ratio before it becomes a problem.

e'g. 3.62/3.64 = ok, 3.62/3.72=not ok.

I spent moths working out potential ratios, step off, front and rear ratio, chain lenths etc on my last car. ask away if you need to know anything

 

I'm still sure the 4wd is 3.62, but if what you say is true then it doesn't matter. I will run the 3.62 on the front and 3.64 on the rear and this will be ok. The reason being the bigger shafts for strength.......

 

dont forget the amout of drive to the rear on a 2wd is 100%, the 4x4 is proportional to the split of the centre diff, at worst 64% to the rear, the 100mm shafts dont give issues, but given the choice i too would take the 108's.

the diff mix at that wont be an issue.

the lack of performance out of chicane will though. been there done that.

Even with a 3.9:1 I had to clutch it to get a T3 spinning back up on 17" wheels with a quaife c/r box.

4.44 is the one to have, small tip for you, the late bug eye scorpio has a 7.5" 4.27:1, though you will need to match to the front.

there is only one step off gear in the country to match it though, I know I had it made, where it is now I do not know, I sold it with a rear diff setup when i went to wrc stuff.

 

Yeh I hear what you are saying. Funds are the problem. I'm hoping to have in the next week a straight cut 6 speed box so I'm hoping this helps. To be honest I'll only probably do a couple of events with this set up and then get the 4.4 diff and drop gears fitted. Ive already got the 108 shafts and stub axles, so i just need the diff just now.Just can't afford to do it all at once...

 

I know the feeling.

good luck

 

Mark quick question for you if I may, For my race car I have a 7" 3.9 rear diff and std 3.6 front diff, I have bought some alledgedly 3.9 drop gears and chain, they are a lot smaller cogs and chain length than thr original but can you tell me how many teeth each should have please?
I will count them tommorrow and post up how many mine have
I just want to confirm they are the right ones before putting them in the car!

cheers
steve

 

The two things you have to consider for the step off is the required ratio change and to keep the drop chain tight, not all gear combination will support the chain tension correctly.

Iirc 28/26 is the right gears for 3.9, count them and let me know, I will tell you if they are for 3.9 std is 31/31

 

32/26 = 4.44:1 iirc

 

Surely it will be easier and cheaper to get a 3.9 front diff, rather than splitting the transfer case and changing the drop gears and chain. 3.9 front diffs were used in the DOHC XR4x4, DOHC Sapph 4x4 and the DOHC 4x4 estates. They are popular with the sprint/hillclimb guys so I guess they're strong enough.

 

Hey MarkK you mention right tension. I have a couple of standar step off 4x4 boxes and the chain noise is pretty well chain noisy...One's in my rally car and one in a customer road car with sound proofing etc..

Those boxes always noisy?
Anything to do about the noise???

The rally car is going "Back to the Futre" as in back to 2wd but that leaves wif a noosy box or 2 on the shelf...


Ahhhh soon I can just drop in a nice Toyota Supra diff with a nice 4.3 (our rally roads are big, and wide, and blazingly fast so 4.3 is good for us, and Canadians. (even faster up there---BIG trees, BIG semi-trucks to haul out the trees longways so all the curves and junctions are made for 100 foot long trucks) (FAWWWWK is what I say when we have straight 2 miles long)

 

When the chains stretch yes they are noisy, a method I was going to use was a back roller on the slack side of the chain out of nylon with a bearing in the centre.

There is room in the case for it, just need to weld bosses into the case to accept the roller assy.