Differential for 1973 CS Automatic swap to Getrag 5 speed box,

sfdon said:
Just threw away five 3.64 diffs. Nobody wants a car that you have to shift 1/2 through the intersection when the light turns green.
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Not necessarily. Amongst the E3 Club we have a gang who all converted their 3.0 Si D-Jet to the wide ratio Getrag and the 3.64 final drive. These people are predominantly Bavarians, that's why I call this the south German layout. For this particular engine it may make sense as the Si D-Jet has a steep torque curve, unlike the Zenith or L-Jet engines. It has an immense punch but only between 4000 and 5500 rpm. The 3.64 makes it livelier in low gears and at the same time reduces revs a bit in 5th on the motorway.

Usually the 3.45 seems the best choice for most E3 & E9, except the 2500/2.5 CS or the heavier 2.8 L. Interestingly, someone at BMW must have thought about a 3.27 (probably 11/36) final drive for both 3.0 S & Si. I have two identical E3 brochures from 1971, one German from July, one Dutch without month. The Dutch brochure says 3.27, the German 3.45. Legend has it that 3.0 CSi & CSL only got the 3.25 to make sure they had a higher top speed than any E3.
 
On paper, the 3:45 will give you a top speed of 165 before absolute redline using a 5spd OD box. I can’t guarantee that, as I’ve only had mine up to 135mph before the front end got too light (no aerodynamics). But the 3.5 liter still had plenty of go. That said, and never having taken it above 80 since, I like the 3:45 for it’s driveability around town and cruising, and there was no need to change the speedo on my car.
 
sfdon said:
We will talk in August
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Hi Don, have you ever got in LA, If you ever come don in LA stop by please and take a look at my 3.0csi with M3 engine, that I submit it to BAT waiting for an answer and I got a gift for you, I got this under fender aluminum cover but couldn't install and don't know what to do with it it is so big I can not mail it there is no that big of box to post it, if you ever come down and if you can use it for your car pick it up. I hope to see you down in LA.
 

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Christoph- our entire shop is coming to Bad Herrenalb in two weeks from today.
We will each pack a 3.64 diff as our Welcoming gift to your Bavarian gang.
 
OCCoupe said:
Focus on the 5-speed swap then drive the car to see if you are happy. The 5-speed is essentially the same gearing as a 4-speed with the advantage of overdrive. The factory sold these with the 4-speed and the 3:64 diff. You can always change the diff at a later time.
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That is the plan now. Thanks for the input, pardon the pun.
 
Stevehose said:
All this trash talk about 3.64's is giving me 3:45 envy, what is the going rate for an open 3:45 in ready to go condish? My engine rebuild is preventing me from even considering an LSD.
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PM, sent. I have what you are asking for and am open to a reasonable offer.
 
I have a 265/6 od box, with a 3.64.

As mentioned, first 4 gears roughly same as original. Totally depends on what personality you want the car to have. Do you want leggy cruiser 3.25 , do you want an all rounder daily feel 3.45, or are you torquey hair on fire type who loves the sound of his own engine (and voice) 3.64..... Read into that what you will :)
 
I believe that the 3.64 was installed on USA cars to compensate for low Hp engines and in 1973 the National speed law was enacted and BMW laughed at their good fortune. Those silly Americans and their stoplight to stoplight, 1/4 mile fascination and low speed limits got exactly what they needed.

Our shop produces engines with Euro spec performance. Torque moves our cars though intersections- not gearing.

For clients that drive locally- a 3.45 is excellent.
For clients that like the long haul trips- we like the 3.25

Just like BMW intended it 50 years ago when they first offered those diffs as factory European equipment.





“In 1973, Congress enacted a national speed limit of 55 mph (89 km/h). Some states, such as Washington, enacted lower speed limits.”
 
Now joking aside. Don is right, the use of the extreme ratio is probably best for automatic transmissions. On my E24 with 0.81 4th gear I wanted to be revving higher to exploit the power band at legal speeds. Don got me about 10% higher revs by replacing the differential and I suspect I could have gone all the way up.
 
August Arde? are you coming to Monterey?
We missed you last year.
 
sfdon said:
August Arde? are you coming to Monterey?
We missed you last year.
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Yes, last year I had commitments in NY and showed up pretty late... Saw some races but not much in terms of human interactions... This year I am free, and have been doing improvements in the Aptos house, so folks are welcome to swing by. The spa will be warm and the beers cold...
 
It’s all just sitting in rubbermaid tubs, but my hope is to run my 265/5 with the 3.25 LSD. The final drive will behave the same as a CSI/CSL, and hopefully the 3.25 will take the CR gearing a bit.

If all else fails I still have a very functional ZF 4spd and a 3.45. Sadly no LSD in the 3.45.
 
That set up of a CR transmission and a 3.25 third member was pretty common on the big coupes. Only about a 6% increase in rpm helped out with all that extra weight.
 
sfdon said:
I believe that the 3.64 was installed on USA cars to compensate for low Hp engines and in 1973 the National speed law was enacted and BMW laughed at their good fortune. Those silly Americans and their stoplight to stoplight, 1/4 mile fascination and low speed limits got exactly what they needed.

Our shop produces engines with Euro spec performance. Torque moves our cars though intersections- not gearing.

For clients that drive locally- a 3.45 is excellent.
For clients that like the long haul trips- we like the 3.25

Just like BMW intended it 50 years ago when they first offered those diffs as factory European equipment.





“In 1973, Congress enacted a national speed limit of 55 mph (89 km/h). Some states, such as Washington, enacted lower speed limits.”
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Thanks for the input!
 
Seems like a good thread here to ask some (maybe dumb) LSD questions. I have a 3.64 LSD I'm planning on putting in my e12 530i with 265/6 so I guess Im a torquey hair on fire type who loves the sound of his own engine (and voice) LOL... not sure about that. We'll see how it preforms. I have a long distance hwy cruiser 635 with a 3.25 diff, this car is more of a zippy around town hotrod :cool:
Anyhow, I just came into a 3.25 sideloader. It seems to be stuck or jammed. I tried to test break away torque and it wouldn't budge. I removed the LSD carrier and it looks OK. Cleaned with solvent and soaked in oil, no dice. Next I plan on taking it apart and checking possibly installing new clutchs etc. Who sells the clutches? I haven't had any luck online. Its a later 10 bolt ring gear.
 
Thx very much Don. I just looked at the link. The sideloader uses the same clutch kit as the later medium case 188mm diff? I kind of thought so but wasn't sure ,
 
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