A lower number means fewer engine revolutions to go a specified distance. Here are some real world examples. For a 126 chassis running 195 70R14 tires here are representative rpm with different ratios at 65mph

2.47 - 2180
2.88 - 2541
3.06 - 2700
4.11 - 3627

These are calculated values assuming a manual transmission without overdrive (1:1 ratio) In practice you'll see about 200 rpm higher due to torque convertor slippage. Rear end calculators are all over the web so it's easy to calculate the results of different ratios, transmissions, tire sizes, speeds, etc. With the 722.x transmissions without lockup torque converters you'll show something a bit different on your tach depending on whether you're going uphill, downhill, level, accelerating, decelerating or steady state cruise.

Hope this helps...

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Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

I could be wrong, but in think you can use the SD front driveshaft section and the 380 back section. I had bye 2.47 in my 85 diesel conversion, it was perfect. I miss that car.

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2004 F150 4.6L -My Daily
2007 Volvo XC70 -Wife's Daily
1998 Ford F150 -Rear ended
1989 J-spec 420SEL -passed onto its new keeper
1982 BMW 733i -fixed and traded for the 420SEL
2003 Volvo V70 5 Speed -scrapped
1997 E290 Turbo Diesel Wagon -traded for above
1992 BMW 525i -traded in
1990 Silver 300TE -hated the M103
1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one
1979 Silver 300D "The Silver Slug" -Sold

Here is the section in the FSM that talks about the flange and nut. The diagram on page 306 shows it very well.
https://www.startekinfo.com/StarTek/outside/12253/program/Chassis/35-530.pdf

Pretty straight-forward of using an in/lb torque beam wrench and 30 mm, double-hex, deep socket to turn the assembled rear differential, axles and wheels. Measure the force needed to move the assembly and note.

Then set the brake to remove the locking nut and flange. Install the new flange and new locking nut. Torque in incremental steps until the friction torque, previously noted, is met. Then use a punch to peen the top of the locking nut.

I made the special holding wrench, shown at the first of the section, by using bar-stock and 3 bolts. Took all of 20 min. and I found it came in handy for rear wheel bearing replacement as well.

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Sam

84 300SD 350K+ miles ( Blue Belle )

Clemson:

As you have noted, you do not feel comfortable changing either the transmission or rear axle yokes.
Given that, the simple solution is, per both mach4 and dude99, to use the front, internally splined piece of the driveline from the 617 engine/trans package, and the remainder of the driveline that is original to the SE chassis.

I would not mix driveshaft sections. If you have ever dealt with trying to iron out driveshaft vibration problems, you wouldn't advise this. I have and believe me it isn't fun.

That locknut and flange is about as simple as it gets. It's only a nut and measuring the turning friction beforehand.

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Sam

84 300SD 350K+ miles ( Blue Belle )

I do not want to have a drive shaft balanced. The tubes have radical difference in diameter. It might be due to a PO 'fixing,' something.

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84 300SD
85 380SE
83 528e
95 318ic

The 210mm differential (especially V8 engines vehicles) driveshafts have the largest diameter tubes compared to the other diffs. I wouldn't want to use different halves on them. The best bet is to swap the trans flange and use the 380 driveshaft.


.

__________________
1983 123.133 California
- GreaseCar Veg System

It should be a blast.

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84 300SD
85 380SE
83 528e
95 318ic

If vibration is a concern you could always mark both halves of the original driveshaft so you could return it to its stock orientation if necessary.... but swapping the flange would work just as well... If you do swap a flange I'd be tempted to swap the rear seal while your in there....

__________________
2004 F150 4.6L -My Daily
2007 Volvo XC70 -Wife's Daily
1998 Ford F150 -Rear ended
1989 J-spec 420SEL -passed onto its new keeper
1982 BMW 733i -fixed and traded for the 420SEL
2003 Volvo V70 5 Speed -scrapped
1997 E290 Turbo Diesel Wagon -traded for above
1992 BMW 525i -traded in
1990 Silver 300TE -hated the M103
1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one
1979 Silver 300D "The Silver Slug" -Sold

There is not a little irony in the sizing of the driveline and final drive of the 380SE vs. the 300SD; the 300SD engine produces more torque than the US-spec 380, yet the 380 chassis was fitted with the larger driveline and final drive!

Inasmuch as the individual pieces of all drivelines are balanced separately, and then checked as an assembly, the interchange of pieces between assemblies will, at most, result in a very small imbalance condition.

Thank you, I can handle this operation. For now I'm just going to change the differential yoke and get try to work on getting the car on the road. In the future perhaps I will replace the ring and pinion gears with the SD's originals.

The drive shaft on the SD appears much larger than that on the SE but the yokes on the SE are thicker and the flex disk are larger. The hole pattern are further apart on the SE flex disk.

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84 300SD
85 380SE
83 528e
95 318ic

does the driveshaft seperate in two? can you use the SD front,with the gasser rear half?

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

That will lead to an out of balance driveshaft, as others noted above.

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

If you piece the DS together from the two cars it should work. I would send the DS unit out for balancing. Here that costs about 50$. You have to have the DS in good shape though. All bushings,center bearing, U joint, and flex discs must be in good shape for the balancing to work. To cut my DS was only 200$. If all parts must be renewed for balancing your looking at around 400$. I would make sure everything is up to snuff before sending it in. If you send it out without renewing things, they will have you for some$$ if things are in need of replacement.
It went like this for me.
Brought my DS in for shortening. was quoted at 250$ for cut and balance. Of course my judgement on the shape of the DS was not correct. It was fine while driving before. Once it was out it needed a complete rebuild. He would not balance it without. Everything listed above was replaced. The cost was around $400 including flex discs. so Ended up Paying 675 or so for a completely rebuilt and shortened DS. OUch! Had no choice.

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Chris
84 280sl
82 300d euro

In the interest of covering all of the potential options, here's the solution used by Druk who installed a 606 engine in his 107. There are easier solutions, but this one is pretty elegant-

Not "another" diesel 107!!

__________________
Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica