New Differential -- Wow
 

I just installed a 2.88 diff in my 84TD that had a 3.07 original. A lot of work but, wow, what an overall quality improvement in shifting, rpm and noise at highway speed.:)

Yep..........:D

........now watch the fuel economy.........29 is not unrealistic for a highway number (for the SD).........the W123 might achieve 28.

Or in my case 16mpg :(... WHERE is my prec chamber lock ring tool, pelican parts swore it'd be here on wed...... Gah.

Yep, at 16, you've got some serious issues.........valves.........timing.........prechambers...........cam timing..........compression..........all/some of the above.:mad:

Why would a 123 get 1 mpg less than a 126? Aerodynamics?

yea, the W126 had better aerodynamics

I am still on the hunt for a 2.88 diff if anyone has one.... :D I need to be ready for when my cv boots give up the ghost, then the whole rear end is getting swapped out. :D

Is the the 2.88 found in 85's?

Yes.....do you have one? :D :D

I used to. Sold it since it was attached to the car.;)

Oh well, I tried. :idea3:

I didn't get anywhere near 28 mpgs with that axle in the 85. Rarely even got near 25.
I think I know of a 2.88 axle that might be available in Portland though.

Really? How much? :D I'd possibly be interested....

This guy on CL might have one. His name is Rus, he's a Russian so don't believe any mileage claims.
http://portland.craigslist.org/mlt/pts/426474056.html

Well for what it`s worth, our 85, I guess it has the 2.88. we get 27 to 29+ on the highway. came home from portland last may, fueled up in Lodi,CA @ Flyn-J and got 30.86. best I ever got, ever:P.

Charlie

With the 'new' 2.88 diff, the 300td shifts like butter -- can barely feel them. And I made no tranny adjustments.

I'm just guessing at the 1 mpg, but, generally, the SD's do slightly better due to the better Cd of the body.

Well, you might consider an adjustment to get it to shift "crisply" if you wish the maximum life from the transmission. "Butter" translates into extra clutch wear.

Cold butter (not margarine) would be ok but, not warm butter. ;)

How would the prechambers effect fuel economy?

Scott

If the shaft falls out of the prechamber, the fuel isn't atomized properly and efficiency is lost.

Wow, my car must be in great tune because I got 28.2 with my last tank. As long as I keep the speed consistent - not trying to speed up and pass people with a lot of throttle, and keep it under 75 mph, I consistently average above 27 mpg. Road trip last month to my sister's - north Jersey to Lewes, Delaware. Return trip took me up 95 thru Philly because of traffic at the Del Mem bridge, across Jersey on the A/C Expressway and back up the GS Parkway at "speeds over 75 mph", windows and roof open on a 90+ degree day, I got 27.6 mpg on that tank. Over 500 miles and it only took 17.5 gallons when I filled it. I assume my 83 has the 3.07 rear ?

Are you talking about the ball at the end of the prechamber? If that breaks off, doesn't it fall into your cylinder and destroy your engine? Where does it go?

Thanks,

Scott

It's a through shaft with an elarged central portion that some folks characterize as a "ball".

It doesn't break off.........the shaft fails in the prechamber wall. If it falls out of the prechamber, it sits in the bottom of the prechamber and partially blocks the exit holes from the prechamber...........resulting in poor combustion in that cylinder.

Those are fantastic numbers with a 3.07 if the speeds are correct. They are usually not attainable at 75 mph. In fact, I'd be fortunate to achieve them with the 2.88 in the SD if I drove it that fast.

Hmmmm, interesting. I'll have to firm up the shift points a bit.

I have a 2.47 rear
 

I am going to have my guy install it before heading to Washington. I will check back with any mileage improvements. I am installing it mainly to get the RPMs down at 75mph. I got mine from eBay a year ago, for I think 80 bucks, but have not installed it. I think I will have my indy do it on his lift rather than trying to do it on jack stands.

I'll be curious to see how you fare on the typical hills in NY. I don't think you'll be able to climb certain highway grades at 65 mph in fourth.........you can certainly forget about 75 mph. But, a 4-3 forced downshift should clear up the problem..........I'm interested in the first time you need to do this. The engine will be turning about 3700 rpm in third which will offer plenty of horsepower.........and a bit of racket.

That was one reason I have been holding off on the swap. Of course I will be keeping the 3.07 so if it is too bad I can always swap back. I am thinking about doing it before moving to Va. I won't be climbing the Catskills any longer! Any hill climbing will be done on back roads so I should be OK.

I will let you guys know of my experience as soon as it is done.

Could you increase your top speed by quite a bit with a 2.47 or is there just not enough power to fight drag after a certain point in 4th gear to make a difference?

They along with the end of the prechamber go into the cylinder and eventually out the tail pipe. I just put up a thread about this. Replaced 2 of 3 faulty chambers and the car has some real power now. Can't wait to properly torque one of the 2 and redo the other one as well.

With limited highway grades, you'll be fine. The fellows on the flatlands love the 2.47...........but, it won't climb a decent grade at speed in fourth.

My 2.88 will need maximum power to hold 65 on two specific hills in CT........and I never considered them very steep.

2.47
 

I put one in my '83 300CD and love it! At 75 MPH the tach is about 2900. I am having no problems with hills. I expected that I would have to bump it down into 3rd much more often than I do. I drove it from High River, Alberta to Likely, B.C. and back recently. Google both locations on Google maps if you are curious what sort of a drive it is. 2 very full days in some pretty rugged mountains. I got such great fuel economy that I MUST have done the math wrong.(BUT it is GOOD) I couldn't be happier with the lower revs and quieter ride. Of course I really have to admit that I now would like more power too, but it doesn't need it. It isn't 'glacial' like I a 240 (no offense intended 240 owners) the urge for more power is just the kid in me.
I checked the speedo error today with a borrowed GPS. At 100 kph I am doing 121-122 kph. had thought it would be more like 124.+ kph but the speedo was probably reeding a bit low before the swap. Now I need a good speedo out of a 380sec or something else with that 2.47 diff
Good luck with your swap