Differential 3.07:1 vs 2.88:1 vs 2.47:1
 

How do you guys like your rear differentials? Our driving consists of mostly fast local roads/highways, and I'd rather avoid repeating the Corolla's 55 MPH @2000 RPM in 5th. What RPMs do the 3.07s run at highway speeds (hopefully, I can find this out myself sooner rather than later)? What do the 2.88s and 2.47s run? How is the 2.47 in the city? Is the 2.47 a direct bolt-on to my '84? Is there anything else I should consider? How does a potential 4-speed swap affect his?

Oh, and could I take a camper 5-speed w/extra-low first and mate it with the 2.47 to ease city driving?

2.88 compromise
 

hi mate,

it depends which engine you do consider i.e I had some experience
with 300d n/a and turbo,manual or auto.... diff's act quite different under those two.

for the n/a manual I would not go under 2.88 as the starting will take forever
on the other hand turbo engine especially with auto will do nice with any
in range 2.24-3.07....only thing you have to decide what is the desired state
- low noise or top speed.

2.88 is my choice as you can see from the signature
2.24 is also from gasser and can be used also (quiet little thing
and a bit of a slow dog...2.47 will do fine IMHO)


edit; 2.47 w/o abs


380,500 1:2.47

380,500,560SEL 1:2.47 ABS

420SEL 1:2.47


as for the 4spd swap:

if you have 300n/a and a manual with 2.47 ...NO good. you have to go lower...3 point something...


.

also, most 2.xx diffs have the large flange that will need to be swapped for your vehicle's

I have a 2.88 diff I pulled from an '85 to put into my W126 with the 3.07.
I thought it was a direct bolt on. Are those flanges different?
Please tell me it ain't so!

Jeff

He meant to say "2.47". The 2.88 came from the '85 diesels and it is a direct swap.

I have put the 2.88 in the SD ('84) and it is, for me, a perfect setup.

I would only recommend the 2.47 to those who do extensive high speed driving (70 mph +) on relatively flat roads and will suffer the difficulty in launching the vehicle from a standstill.

The 2.47 does have the larger case and requires a change of flange. It also may require a change in axle shafts but I am not certain.

I've got no complaints about my 2.47. I bought it that way so I can't really compare it to the stock diff. It turns over at about 2300rpm when cruising at 100km\hr so its nice and quiet on the highways. It is a little slow off the line if your on a really steep hill but I think that might be an issue with the bowden cable not engaging 1st as soon as it should. Theres a delay before it down shifts and there shouldn't be... Over all it seems good to me.

I agree with Brian 100% on this.

My previous 617 had the 3.07:1 which seemed a bit high strung at 65-70mph on the freeway. The current SD has the 2.88:1 factory, seems about ideal considering the powerband of the motor and US speed limits. I suppose it could tolerate a 2.47:1 on the road, but with the A/C on and a locked fan clutch... I think it would be pretty sad around town.

These are econo cars, going 80mph is not going to permit good fuel econ regardless of which diff you have installed.

Yep.........80mph cost mucho fuel. I go 63 mph and the SD is currently getting a steady 29, even on the winter fuel.

I tend to run 85 on the toll roads around Austin... That will net you 19mpg in a wagon.

And that's with the 2.88

My 1978 300SD is driven 1,000 miles/week to and from work. With the 3.07:1 axle, 70 is 3000 rpm.

My 2.47:1 is almost ready to install, a 600 rpm reduction in cruise rpm...

Dude! That's worth it.

My car has the 2.88, From the graphs that I have seen the engine makes peak torque at about 2000 rpm. I don't accelerate hard and would be very happy with a 2.47.

I have looked at GM transmission adapter plates. The GM 4 speed auto has a .7 top gear. Might give similar effect if it would fit in the tunnel.

I am leaving my car stock unless a specific part quits.

The 2.47 actually doesn't make much difference in take off acceleration on a 300SD, it just holds each gear longer, and you don't need/use 4th under 50mph...highway acceleration in 4th does suffer a little, but the rpms are much lower and makes it very pleasant.

I have the torquemonster setup in my 300SD, a 1985 torque converter (2600 rpm stall speed) and trans + 3.07 diff. Front of the car practically lifts off the ground with takeoff torque. I dare say for the first 10-15mph it can take off faster than my 420....its great around the city, it just effortlessly takes off and gets up to 40-50 easily.

Overall the 2.88 is probably best for a diesel, and 2.47 or 2.24 for a gasser (of adequate power levels) The key with the diesels is the torque converter, it really makes a difference!

so what is the stock on a 84 sd?

am I imagining the w123 300 turbo D seems to have a taller or lower ratio rear end as it seems to rev slower.
cheers

[QUOTE=SD300;3099623]so what is the stock on a 84 sd?

3.07

Jeff