84 300D

I have a choice of getting a good 85 300D rear differential or a good 85 300SD differential and am wondering if anyone can give me numbers for the final drive.

I am not interested in gear ratios. I would like to know about highway speeds versus rpms. For example, my 84 runs at 3k rpm at 70 mph and 3.3k rpm at 75 mph. So comparisons to either pumpkins at these speeds would be apt.

I am not concerned about acceleration effects, just highway cruising speed rpms. Numbers?

I am also aware, correct me if I am wrong, that the 85 300SD differential will require me to either shorten or extend the drive shaft. Does anyone have the information I would require for this?

2.88/3.07=.938

You should get about 94% of the cruise rpm with an '85 rear end that you currently get with the stock '84 rear.

Not sure about a driveshaft change for the SD rear.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

I put an 85 SD rear end in my 83 300D. Plug and play, no drive shaft mods, although it will have an ABS provision probably on the passenger side near the pinion end. I removed the sensor, drilled, tapped, and plugged the hole, then had the whole thing powdercoated.

You could also just leave the sensor intact, but Im pretty sure it has a short pigtail that will need to be resolved or tucked out of the way

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This post brought to you by Carl's Jr.

My 85 300SD does 60 mph at a tick under 2700 rpms, so 70 at 3000 rpms is about right for my 2.88. I agree. The rear ends should be plug and play. I'd simply leave the ABS sensor in and drive it.

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Thanks,
Mark in NC

"Spark plugs?...We don't need no stinking spark plugs!"
1985 300SD "Der Silberne Schlitten" 420,000 mi


Wish these were diesel:
2003 Ford Club Wagon 130,000 mi

the 2.65 in my 87 turns about 2700 at 65 there's not a HUGE difference in RPM at 70 between 84/85
wait... I took pictures of my speedo when it went over 200000 a few days ago... lemme look at the photo evidence...
yeah. I know I have a bulb out...

and it's hard to believe my trip missed showing 124 by 10 miles!

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Vstech is showing what I want. So now that it doesn't matter if I get a 300D or SD differential, in terms of installation, I ask if there is a best year for differential gearing? Years that are a direct swap of course.

Further, I have a couple options on cars from the junk yard. I also can choose from a couple of w124s but have no compatibility knowledge. Are those differentials a direct swap and if so any better gearing?

I mentioned the 85 300D differential because I heard it was the best ratio for the 300Ds'. I am not set on it, it's just available. And if the gearing isn't that much of an improvement I am not interested.

the BEST gear ratio available in a bolt in diff would be from an 84 or so, SE/SEL/SL with a 2.24 diff. quite slow at take off, but not terrible. 2.47 is a tad better also available in those vehicles. no 124 diff will bolt in. different subframe assembly...

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

What tranny do you have in the car?

The '85 tranny had taller 1&2 gears to overcome the lower diff for takeoff. The 3&4 are the same as the '84, I believe. Anyhow, I have the 3.07 from my '84 in case you need it. I'd love to get it out of the garage.

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'85 300TD "Puff The Magic Wagon" - Rolling Resto
'19 Mazda CX-9 Signature - Wife's sled
'21 Morgan 3-Wheeler P101 Edition
'95 E300d - SOLD
'84 300TD "Brown Betty" - Miss this one
'81 240D "China Baby" - Farm grocery getter

85 rear end is considered the best rear end for the 617. 2.88 ratio lets the engine spin slower on the freeway, while having next to no noticeable torque loss when leaving a stop sign. I went from a 3.07 to a 2.88 in my car with the manual transmission and I can tell you the clutch feel when leaving a stop sign is pretty much the same, and on the highway its nice and smooth at 70mph.

I got my 2.88 from a 123 and put it in a 126. the only difference between 126 and 123 is the ABS sensor. since my car doesn't have ABS it was a direct swap.

124s have a totally different rear suspension and thus the rear end does not swap over.

w114, w115, w116, w123, w126 (maybe R107 cant remember off the top of my head) all have the same rear suspension thus the parts are interchangeable. there is a large pumpkin and a small pumpkin. The diesels come stock with the small pumpkin. depending on the chassis your putting the rear diff into you may have to look into the axle lengths if your going from small pumpkin to large pumpkin.

easiest thing to do, get the 2.88, its a direct swap, and it works well. and you said you already found one... sounds easy and you'll enjoy the results.

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I have an 85 tranny that I got when I swapped my engine out. I had a parts car from 85 and always wished I took the differential. Then I was at a pick and pull lest Friday and found that very same parts car. That's when I decided I wanted the change the gearing.

Fortunately the yard had an SE and SEL but I don't know the year. I'll do a write up if I go ahead with the swap, but am pretty sure I am about to put a hot rebuilt engine in my Ducati 916. If I do that I'll hold off on the differential. If I don't, I'll do the swap this or next weekend.

Thanks for all the information.

which pick n pull have you been to around town? I have this week and next off. I think I might call the one up north of Liberty Hill, almost to Lampasas.

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'85 300TD "Puff The Magic Wagon" - Rolling Resto
'19 Mazda CX-9 Signature - Wife's sled
'21 Morgan 3-Wheeler P101 Edition
'95 E300d - SOLD
'84 300TD "Brown Betty" - Miss this one
'81 240D "China Baby" - Farm grocery getter

I don't know that one. Let me know what they have in terms of cars. I'm looking for some tan sun visors from an 84 tan color and the cloth lining housing rubber that runs along the interior body between the door and the seat belt.

I've gone to Houston and Waco yards but the only one in Austin that I have been to is the one of 71 south a few miles past the airport toward Houston. I am aware of what they have if you need me to look for anything let me know.