lsd question

Well there goes my dream...

I took a peak under the car today. Used a green scrubbing pad to remove the gunk from the diff where the stamping is (passenger side). I saw an "I" where the "S" would be for lsd so no lsd. also I believe it has 11 39, what ratio is this (3.54-3.55)?
 
While you calculated the number right, I don't think they made a 39:11 diff, only the 38:11 size, which is a 3.45. They did, however, make a 39:12, which was used on the CSi's, which translates to a 3.25 ratio.
 
While you calculated the number right, I don't think they made a 39:11 diff, only the 38:11 size, which is a 3.45. They did, however, make a 39:12, which was used on the CSi's, which translates to a 3.25 ratio.
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Maybe you are correct, I will look at the numbers again when I get back home. The 3.25 sounds like a pretty good rear to have, yes?

What does the "I" stamped above the ratio mean?
 
I am basing my results off the variations of diff on realoem.com. As for the I, I don't remember seeing that on my open diff.

3.25 is good for the original 4 speed trans, but the ratio is pretty low for an OD trans, as it would make 5th pretty low combined ratio. It would give very good mileage, but be pretty sluggish off the line. A lot of people prefer the 3.64 to go with the OD 5 speed, but for the stock 4 speed or the CR 5 speed, I'd say it isn't too bad.
 
Re: Well there goes my dream...

I took a peak under the car today. Used a green scrubbing pad to remove the gunk from the diff where the stamping is (passenger side). I saw an "I" where the "S" would be for lsd so no lsd. also I believe it has 11 39, what ratio is this (3.54-3.55)?
Click to expand...

The "S" stamp is often not on the flat where the ring/pinion numbers are stamped. Look all over the right side of the diff near the output flange. Don't expect it to be stamped upright, either. Sometimes Deiter had his (3 beer) lunch before he did his stamping...
 
How can I determine if my 1970 2800CS has a L.S. Diff?

How can I determine if my 1970 2800CS has a L.S. Diff? What are the external markings on the housing, and what other tests may I perform? I suspect that it does have an LSD because of the way the tires react under heavy acceleration.
 
Re: How can I determine if my 1970 2800CS has a L.S. Diff?

How can I determine if my 1970 2800CS has a L.S. Diff? What are the external markings on the housing, and what other tests may I perform? I suspect that it does have an LSD because of the way the tires react under heavy acceleration.
Click to expand...

Read above posts.
 
Both of the CSis I just sold failed the same direction wheel test, so I assumed them to be open diffs. They were both Italian delivery. The one with the highest VIN was registered as a '72 and the lower numbered one registered as a '73. I suppose the '73 sat on the showroom floor longer before it sold?
 
Differential Ratios, Weight and Instrument Calibration

I'm trying to decide which ratio to use in my 1970 2800CS restoration. I will use a 3.5l B35 Motronic engine, a Getrag 265 5 speed. A 3.64LS is ready to drop in. However, I also have a 3.25 open (from a 1973 CSi I parted last year) and a 3.07LS (from a 1979 Euro E24) as well. Jim at Mesa says Powertrain Industries in Gardena can make a 3.25LS by combining the 3.25 and 3.07 bits. There may also be a 3.45LS available.

My daily driver is a 91 E34 with a B35 Motronic, Getrag 265 and 3.64LS; I love the combination. The car pulls like a freight train in 2nd and 3rd, but still cruises nicely on the highway and averages 19-20mpg.

Two questions:

1. Although the comibination of 3.5, 265 and 3.64 works great for the E34, the E9 is about 500 lbs lighter. Would a lower ratio provide similar performance in the E9...or would the 3.64 be too much for the E9?

2. Does the speedo or any other instrument need to be recalibrated? I know the speedo drive reads off the transmission, but will changing the diff ratio from stock affect the speedo reading?
 
The 3.64:1 was only used for US market 3.0CSs, as the european coupes weren't strangled by emissions equipment. The US 2.8L e9 put out 192bhp, while the US 3.0L put out 170*. The 3.64 was neccessary to keep the upgraded motor from being a downer -- especially in the press. I know you didn't mention this, but I'm guessing the CSi got a 3.25 instead of overdrive.

That said, I suspect the 3.45LS would be a good choice for the street, especially if it's ready to go. If you want to connect yet more B35 torque to the pavement, you could always do it later. 3.64 is autox material.

19 to 20 mpg on the highway? That's awful :wink:

*see:
http://www.cscoupe.org/press/rt_feb_1970/page105.jpg
and
http://www.cscoupe.org/press/rt_july_aug_1973/page91.jpg
 
Chris,

My stock motor has a Getrag 265 OD with 3.45 rear. I thought only the automatics got the 3.64, which my car once was. Take-offs are probably a bit more leisurely with the 3.45 and the 3.64 would still be OK for cruising. The difference is only 5% between the two. I think the 3.25 with overdrive is too long legged. At 3,000 RPM I think I'm at 80MPH but my speedo is off 10% on the low side.
 
Both of the CSis I just sold failed the same direction wheel test, so I assumed them to be open diffs. They were both Italian delivery. The one with the highest VIN was registered as a '72 and the lower numbered one registered as a '73. I suppose the '73 sat on the showroom floor longer before it sold?
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My '70 2800CS fails the "wheel spinning on jackstands test" too, but it has an LSD and will leave the same twin stripes as in Mr. Petrus' picture. I've yet to find a sideloader LSD that passes the off the ground test, including the recently rebuilt 40% 3.64 in my e12. That car lights up both rear 235/45's with ease, and on track days leaves no doubt the LSD is working. I don't think that's a good test for these older diffs.

Another thing you guys should be looking for -- on the older diffs, the "S" is not always a painted stamp -- on my cars, it's stamped with a metal die stamp, just like the ratio numbers, and it's only about .5" tall.
 
RE: Chris in Laguna

1. I have a built 3.0 with a 265 and 3.45 L/S. I swapped the 3.45 to replace the original open 3.64. Personally, I think the 3.64 is better for US driving conditions. For me, going to the 3.45 essentially dropped my engine below the best part of the torque curve. I downshift more now. I now have a 3.64 L/S and will eventually swap to that.

2. The speedometer calibration is related to the differential ratio. I wound up putting a 2800CS speedo in my 72 3.0. The type font on the 2800 CS instrument face is slightly different from the 72.

Also, I agree with Tony (velocewest) on diff IDs being stamped. The stamped numbers are small and not heavily stamped, so hard to read. I don't think the painted "S" came until the late 70s.

Finally, you have to be careful about comparing SAE horsepower readings from that era. The US changed from "gross hp" to "net hp" in 1972, so the figures Michael quotes aren't comparable
 
Finally, you have to be careful about comparing SAE horsepower readings from that era. The US changed from "gross hp" to "net hp" in 1972, so the figures Michael quotes aren't comparable
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True enough Bill, but I'll blame it on R&T, as they express the figures in bhp. If SAE hp was the measure (at the flywheel), expressing the value as bhp (at the output shaft), as R&T does in both articles, is misleading.

I think the point about the 3.0 being down on power due to emissions and needing a taller ratio at the back end still stands, however. The 0-60 time for the '70 2.8 is 9.3 and the '73 3.0 is 10.0. The 3.64 box was an effort to keep the strangled 3.0 competitive.
 
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