Did RnD do a 3.9 ration 7" front diff
 

Does anybody know if RnD done a 3.9 ratio 7" cossie front diff

Thanks
Marc

Have one in mine and there gear box not sure on ratio mind

Don't think so Marc

The 3.9 front diffs originally came out of the 2 litre 4x4 sierra if that helps at all

He's on about the RnD diffs Paul not the standard 6.5" 3.9 diffs, which again im sure were only 3.6

Yeah as you say it seems I can only get a standard 6.5" front diff so I'm going to look into an Oppliger thick wall casing and a gripper plated front diff and use my standard shot peened and super finished 3.9 cwp

I think Bara gave me an r n d option when I went 3.9 front quaife but maybe it was different ratio and using drop gears?

He is right about the ratio 2.0 XR4x4 diffs

Yes that's correct but not on RnD, also the XR4x4 3.9's are supposedly like chocolate, best off stepping gearbox down and sticking with 3.6 up front

Problem is the skyline r32/33 Gtr gearbox I use doesn't have step down gears

Don't forget that your car is probably lighter than a normal sierra. Bara built me a Quaife LSD in 3.9, it has two diff supports and a strength plate, I think it is thick walled. He explained that the weak link was the CWP but with pretty much 500 ft lb of torque I have not broken it yet, he explained that if I do break it I could either replace with another OR try an Rnd. I ran that with my skyline box and now with the bara build oppliger.


I know my 205 is very light but the front tends to spin less than the rears so I guess there is a lot of power going through there. Bara uprated the VC in the box when he built it.


Hope this helps but maybe speak to bara to see what he would suggest? 07970 197 377


ALSO: I don't think you are so much in to Donuts and drag strip launches so with a bit of mechanical sympathy it may not be quite as chocolate as others have experienced? Track driving doesn't rely on racing starts so I expect you will not be as hard on the car, especially if not using slicks.

Hi Toby

I have emailed Bara and he gave me a price on a new thick wall cased gripper front diff costing about £2300 inc vat

I am starting to prep the car for sprinting and hill climb regs and they are all standing starts so will be a lot harder on the front diff hence me wanting to update it but as you said and Bara mentioned to me in the email it's the CWP that breaks normally but as I really don't want to change back to 3.6 diffs I don't have much choice it seems

Yeah, thats a bugger.

I asked bara if the CWP breaking is likely to damage anything else such as the diff and he said it unlikely but you don't want to ruin a race meeting with that going pop.

Have you got a standard open diff in the car now?

If you are going with the Sequential box surely you could then get drop gears to suit a different diff ratio or are you sticking with Skyline now?


If you are going racing with the Skyline box I think the shift speed will annoy you and you are going to end up dinking the syncros sooner or later and once you get the racing bug it is only a matter of time before a sequential goes in there.

Yes mate the skyline straight cut sequential will be going in so no option of drop gears in that box

Currently I have a standard 3.9 front diff with strengthening plate and stud conversion

Nothing wrong with the shift ln the Skyline std box, its the animal behind the stick. I've rallied mine and had no synchro issues.

The sequential is just a bonus.