How bad would a 2.47 be in a 300D with a 4 speed? - PeachParts Mercedes-Benz Forum

Jarod · #1 03-27-2016, 09:58 PM

So with my grey car diff failing more and more, I've stopped driving it now that it leaves a puddle of gear oil anywhere I stop...

Anyway, I'm now more intently looking for a diff, I'd love a 2.88 but don't have $600 to drop on a diff.

I'm having a hard time convincing my wife that around 200 seems to be a going price for pretty much any ratio thats gonna be usable, higher than 3.07 is going to murder my engine around here, highway minimum of 80.

I've found a pretty good deal on a 2.47 from a early 80s 380 of some kind, which should fit according to what I've read.

I'd like a little lower cruise rpm, but do still use the car around town, which northeast tennessee is pretty hilly and the roads are windy, so I'm uncertain if a 2.47 will be drivable around here.

with the 4 speed, 1st gear seems useless, parking lot speeds is it, beyond that it has no purpose, if I'm rolling at all trying to start in 1st is silly, i go straight to 2nd.

which makes me think significantly lower diff would be A-OK, but I'm not convinced. now and then I do tow a jetski, but I'm still leaning towards the 2.47

I figure if I'm gonna drop a bunch of cash, I may as well attempt to improve drivability, I've looked for a 3.07 nearby but no junkyards seem to have any, and anyone who will ship wants about $250 including shipping.

If I can get my pontoon boat sold then I'll have a little more wiggle room, could go pick one up somewhere. Sorry for rambling, I'm just trying to determine what I should do to get my car usable again.

Mölyapina · #2 03-27-2016, 10:17 PM

A 2.88 should not cost anywhere near that much unless it's barely used. Shipping on most diffs actually shouldn't be too horrible -- I would think $100 at most? So that would bring you to $350 for a 2.88.

As for the 2.47, I know people with a 2.88 in a 300D have said that it holds back the car a little bit already... that said, if you can get at one cheaply, it might be best just to swap it in, and, if it doesn't work out, get a 2.88 or another 3.07.

t walgamuth · #3 03-27-2016, 10:55 PM

Taking off especially on a hill would involve a lot of clutch slipping with the 247...bout like taking off in second.

mach4 · #4 03-27-2016, 11:19 PM

I'm running the stock 2.47 rear end in my 380SL with the 617 turbo and I love it. Unlike Roncallo who put a V-12 in his 107 I'm more into quiet open road cruising and not performance. That having been said, the MB people that have driven it are surprised at the performance. So for an economical open road machine, it's perfect.

There are a couple factors that might be problematic for you and that is the manual transmission....might require a lot of slippage to get it going. I'm running the 722.3 automatic. Also the SL is a few hundred pounds lighter.

I think you'd be surprised at the fuel economy.

vstech · #5 03-28-2016, 06:09 AM

Stock 300D automatic is the 3.46 with a 4 speed, 3.07 should be fine. I have tons of them if you want one.

100 mph should be no problem with the 3.07 and a manual trans.

wstetson3 · #6 03-28-2016, 07:40 AM

I'm trying to get started on my manual swap soon. vstech....my 81 N/A would have what diff? My 82 turbo should have the 3.07, right? I keep thinking I need to put the 3.07 in the 81 N/A when I install the 4 speed manual if my N/A has the 3.46 or anything higher than a 3.07. Would you agree?

Jarod · #7 03-28-2016, 07:45 AM

Quote:

Originally Posted by vstech

Stock 300D automatic is the 3.46 with a 4 speed, 3.07 should be fine. I have tons of them if you want one.

100 mph should be no problem with the 3.07 and a manual trans.

I was under the impression that the 3.07 was stock in the automatic 300d turbo models, and the 3.46 was used in the 240s and non turbo models?

Either way I go back and forth on this, my big fear is towing the jet ski, I'll pm you and see if we can arrange a deal on a 3.07 anyway.

Thanks!

Dan Stokes · #8 03-28-2016, 08:46 AM

My race truck runs a 3.08 (Chevy axle) which works pretty well for LSR racing with a 4 speed manual. I think the 3.07 will probably be a good choice unless you're going racing. The 2.47 might be a little hard to live with for daily driving especially with a manual trans though probably OK with the auto.

Remember to change speedo gears as necessary. If you can't come up with the right gears any good speedo shop ought to be able to make you a little gear adaptor to fix the cal.

Dan

t walgamuth · #9 03-28-2016, 10:55 AM

Quote:

Originally Posted by Jarod

I was under the impression that the 3.07 was stock in the automatic 300d turbo models, and the 3.46 was used in the 240s and non turbo models?

Either way I go back and forth on this, my big fear is towing the jet ski, I'll pm you and see if we can arrange a deal on a 3.07 anyway.

Thanks!

240d = 3.69
300D not turbo 3.46
300D turbo 307, in 1985 2.88

Jarod · #10 03-28-2016, 09:19 PM

I send vstech a pm about a 3.07.

I figure thats probably the best route to take.

it just feels like it needs taller gears to me, first gear runs out of usefulness as soon as I enter an intersection And I'm in 4th by the time im going 35.

With the auto it would do 75 but it felt obnoxious, my tach is inop so I cant tell but id guess it was around 4000-4500rpm comparing the engine note to that of the blue car.

I shouls crawl under there and see if the po did some kind of hackery with the diff like every thing else on the car... Speaking of which, I'm looking for a headlight switch so I can have dash lights again (I don't even know how or why, but that's whats causing them to be off though)

If I can get a 3.07 I'll use that for the summer and invest in trying a lower ratio at the end of my work season when I have a little money to spare.

Skippy · #11 03-29-2016, 08:02 AM

I have the 3.07 behind my 4 speed. First gear is a little short, and I think a 2.88 would be nearly ideal. I don't tow. With the 2.47, I'd be concerned about towing, and also about losing top end in 4th. With mine right now I can get to about 108-110 in top gear. Best of all would probably be a 5 speed with the 3.07, but those are hard to come by.

junqueyardjim · #12 03-29-2016, 04:18 PM

I just got my 83 240D back today after having it laid up for a year. I am to old to work on it much, so to make the engine switch to a pre 85 617 Turbo I had to ship the job to my friend Paul. He did a great job, I just put 15 miles on it with that 80 SD junkyard engine that I bought about 6/7 years ago. No smoke, runs cool and runs really good. I did have Paul do an overhaul on the turbo and it performs great. Almost instant 10 lbs on my boost gauge. I am running the differential from my 85 which is the 2.88. She will run that first gear in a heartbeat and 2nd, 3rd and 4th are pure delight. To my way of feeling and thinking, it probably was the best performing ride I have ever had in a W123 with a 617Turbo. Driveline is a little sloppy, perhaps not driving the 4 speed for 16 months gave the operator a little time to rust up also. Anyway, by the time I got it home, I feel that I really lucked out with the engine. As I reported a number of years ago on the post when I bought that engine, it was a hot afternoon in August and I jumped it from my W123 and without the glow plugs it fired up immediately, after sitting in the junkyard a couple of months. But I was running that 85 617 Turbo with a pilot bearing which I freeze shrunk to install and I was fearful it would lock up and and really be a mess to get apart. In this case, the clutch did disintegrate and caused a lockup, but the pilot bearing was still OK, after about 20,000 miles of city use. But now my new engine will take the pilot bearing, I have a new clutch and resurfaced flywheel, held my breath when first running it because again I put on the flywheel using only the factory balance, no marks, just put it on and I find it satisfactory. Now I am a little more heavy duty truck oriented then most of you guys and with trucks you just get use to the vibs at low rpm. If you don't like it, shift down a notch and you will be happy. I find the "drive" of my car, with both the 617's that I have used, to be extremely flexible, fast (for a 617) and very fun to drive. I would never put up with a 300D with an automatic and I just can't believe that Mercedes Benz held on to that old junk slush box for as long as they did. Amazing, and they continued right on with it until the early 90's I believe.

Frank Reiner · #13 03-29-2016, 04:59 PM

A few numbers may be of aid:

1st gear overall w/4-speed manual, & 2.47 = ~9.6:1. This will pull off from a stop comfortably.

If a 2.88 is replaced by a 2.47, and previous cruise RPM was ~3200, new cruise will be ~2700. 2700 is above the torque peak of 2400, so a headwind or slight grade will move engine speed towards increased torque, which tends to maintain speed.

NickCox · #14 03-29-2016, 05:08 PM

Pm sent

I'll be junking my 1985 300td soon. It's about done for rust wise. The engine and trans are going in another car, but the diff will be available.

t walgamuth · #15 03-29-2016, 06:02 PM

I have a 2.88 diff and a matching 2.88 speedo that I'll sell for $400 obo.