Experience of 3.4 diff in 998 Cooper??

General Chat with an emphasis on BMC Minis & Other iconic cars of the 1960's. Includes information on MK1 Action days.
Alex
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Joined: Wed Sep 09, 2015 11:22 pm

Re: Experience of 3.4 diff in 998 Cooper??

Post by Alex »

It's a 2.76 with the overdrive primary and first motion input gears fitted.

I've got a NOS Rover boxed od primary somewhere.

CooperTune
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Joined: Sun Sep 22, 2013 1:47 pm
Location: Coastal VA USA

Re: Experience of 3.4 diff in 998 Cooper??

Post by CooperTune »

Yes I run a 2.76 with two (O/D) drop gears. I find the (O/D) first motion shaft input gear in core trannys. The Primary gear does not stay with the tranny till I get them. I have three in service now and a fourth about ready to return to the road. Using the really wide ratio tranny allows good acceleration in all gears. Fourth gear is fairly useless under 50 mph. Third gear carries the same ratio as a 3.44 FD. The 1000 rpm drop between gears requires a engine with some torque.

I'm about to pull the 1360 Cooper S with this gear box and replace with a 998 with 3.1 CWP. Son Alex (age 17) and his sister Lizzy (age 16) are becoming drivers. Alex got his drivers and Lizzy got her learners the same day last week. I bought my first mini roughly 50 years ago. Son Alex is 50 years younger than I am, while not as excited about minis as I was it has been his and my only transportation since he was born.

Getting back on topic, I'm beginning to think of the 3.44 as the new 4.1. I drove a 4.1 for two years of college. My autocross car had a 4.35 and looking at my chart there is a 30 mph difference at 3000 rpm between the 2.56 and the 4.35 CWP. With (O/D) drops and so many CWPs there should be a ratio that works for most. Steve (CTR)

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snoopy64
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Joined: Sat Mar 07, 2015 8:40 pm

Re: Experience of 3.4 diff in 998 Cooper??

Post by snoopy64 »

Update...

Been on the rollers at SMMC (thanks guys) and it’s official my car is a screamer!!

All the readings pointing to a 4.1 diff... no wonder my ears were bleeding on the A34 going up!!!

Now it’s a case of how looow to go :D
Cheers

Kevin

Supersonic
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Joined: Fri Mar 20, 2015 5:25 pm

Re: Experience of 3.4 diff in 998 Cooper??

Post by Supersonic »

I've two 1293cc Cooper S cars both with these final drives. The 3.44 is nice and smooth for a road car. The 3.65 is nice for town work even with an upgraded camshaft :D :D

Alan

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snoopy64
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Joined: Sat Mar 07, 2015 8:40 pm

Re: Experience of 3.4 diff in 998 Cooper??

Post by snoopy64 »

Update.... going for 3.4 will let you know what it’s like next week ;)
Cheers

Kevin

liam-ds
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Joined: Tue Nov 20, 2012 10:39 pm

Re: Experience of 3.4 diff in 998 Cooper??

Post by liam-ds »

ive got a 3.44 in my mk1 mg 1100 engine and its perfect much prefer the drive over my 1293 mg metro engine that i had ive got in my first mini, keeps up with traffic well and get some looks off afew audi/bmw drivers while flying down outside lane on m1

Liam

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snoopy64
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Re: Experience of 3.4 diff in 998 Cooper??

Post by snoopy64 »

Ok. So all done. Fitted the 3.4 and I'm really pleased... takes the edge off the noise at 60mph but doesn't seem to have affected the performance at all.

Also overhauled some other parts and what I did learn was most baulk rings are pants! Blued a few sets up and it's amazing how poor the contact area is... Fitted Guessworks ones in the end and it's transformed the down shifts... the mini spares evo ones also came up really good.

All ready for a busy year now :)
Cheers

Kevin

CooperTune
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Joined: Sun Sep 22, 2013 1:47 pm
Location: Coastal VA USA

Re: Experience of 3.4 diff in 998 Cooper??

Post by CooperTune »

Nick, we run a 2.76 CWP with both OD drops primary and first motion input drop gear. I also use te French / 998 Metro wide ratio tranny gear set. With a 4 to 1 first gear I had to go from 145s to 165s to avoid wheel spin in first two gears. The only issue is the 1000 RPM drop with each gear change. Large engine built for torque helps. 70 mph is at 3000 RPM, 4000 is about 96 MPH. I see 70 every day going to the shop. I have seen 96 on my GPS even with windows closed the wind noise is too much for comfort. And there is the chance of getting a big ticket. I have three of these running for several years. Steve (CTR)

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