4 spd. manual trans ratio - PeachParts Mercedes-Benz Forum

kip Foss · #1 01-29-2004, 02:43 PM

Does anyone know, or know where I can find, the final drive ratio of a 1972 Euro 350slc 4 spd. manual trans? I have one in one of my parts slcs and am thinking of putting it into my 1977 450slc in hopes that it will improve the mileage. If the ratio isn't much better I won't waste the effort.

ctaylor738 · #2 01-29-2004, 04:01 PM

I believe that the final drive in all of the 1970's 4-speeds is 1:1 in 4th gear, at least that's what Haynes says.

dpatterson · #3 02-05-2004, 04:23 AM

Pretty sure the ratios in my euro 350SL manual are:

4th = 1:1
3rd = 1.44:1
2nd = 2.34:1
1st = 3.96:1
R = 3.72:1:1

And someone feel free to correct me but from some research I did a year ago the 5 speed box from an M110 engine (ie the 280 6cyl twin cam) has the same ratios for gears 1-4 as listed above and there is some speculation that this will bolt up to the bellhousing for the V8. Of course those 5 speeds are hard to come by so I havnt been able to buy one to test this theory .... sure would be heaven to have a fifth gear hanging off that V8.

ctaylor738 · #4 02-05-2004, 09:07 AM

Here is what I can add. I am not making this up.

There were two 5-speeds made in the 1970's, the G76/18/5 and the G76/27/5. I believe that they were the same except for minor differences in the internal gearing. They are physically different from the 4-speeds only in their length to accomodate the .87 overdrive unit on the back.

I have had a /5 and and /4 unit sitting side-by-side on my workbench, and this is the basis for my statement above.

I believe that these units will bolt up to any bellhousing/engine that took the equivalent "/4" box. You would need to find linkage and shorten the driveshaft.

But I am not sure about your assessment of the M110. Some time in the 1980's, Mercedes started using a different 5-speed in the 201's and 124's and some 110's. I personally saw one in a 1985 280SL that I almost bought. It can be identified quickly by the little fins on the bottom of the case. I do not know if this trans takes the same bellhousing/clutch stuff as the earlier units.

So bottom line, I think an earlier "/5" would work in your car, and maybe the later unit if they didn't change the bellhousing.

It's very hard to get information on the earlier 5-speeds in the US because they were not officially imported here.

dpatterson · #5 02-05-2004, 04:34 PM

Thanks for the info Chuck - thats 100% consistent with advice from a local MB expert here in Oz. I was expecting the bellhousing to be a different volume (the clutch plate for the V8 is quoted at a larger diameter than for the six, about an inch more from memory) but I figured the bolting pattern would be the same, ie just a case of using the bell housing from the 4spd.

When I mentioned the M110 I was thinking specifically of a 280CE, '77 model which I had seen with a 5spd - perhaps that was one of the two gearbox models you referenced.

Although the manual trannys were officially available for the SL in Oz they are still as scare as Rocking Horse doodoo - I only know of four others and they are all 4s. The only 5 spd box I know of is not for sale so I'm not making much progress on this. I have found a brand new, old stock, 4 spd box which I have been promised for nothing but apart from replacing my still-perfectly-functional 4 spd theres not much advantage in that.

deanyel · #6 02-09-2004, 12:36 AM

He's asking about the final drive ratio - the correct answer would be something like 3.23 or 2.85 or 3.69. Robert Nitchke's Production Data Book usually has it, but the book seems to be getting hard to come by. Maybe your dealer parts guy could look it up. Also, can you get the rear end up in the air, turn the rear wheels and count the driveshaft revolutions? I would think the 4.5 would be geared taller than the 3.5, if different. This seems to be the MB philosophy - the more torque the taller the gearing.

kip Foss · #7 02-09-2004, 09:31 PM

To make this more confusing, what is the final ratio of the MB auto trans. and with a 3.06 rear end ratio will I be better off with the manual trans? I'm not interested in boiling the tires off the line but a bit better gas mileage wouldn't go a miss.

It is my understanding that the 3.5 Euro engine had about 60 HP more than does the 4.5 US version. The difference between about 240 hp and 180 hp.

deanyel. The differential ratio is stamped on the rear end. If you are looking forward at the back of the rear end there is a flat tab on the left side just in line with the axle. It is on the surface to which the rear end cover is bolted. There are two numbers there. One I guess is the housing part no. and the other, which on mine is 3.06 is probably the ratio.

ctaylor738 · #8 02-09-2004, 10:58 PM

The final drive of any car is determined by the combination of the rear end ratio and the final drive of the transmission. I think that in the 107's the lowest final ratio you can get STOCK is in the 1980's cars with a 1:1 transmission and a 2.43 rear end.

That would mean that for 2.43 turns of the engine you would get 1 turn of the rear wheels.

A five-speed (.87 overdrive) 3.5 with a 3.69 rear would get you a final drive of 3.21 (.87*3.69).

And ,of course, you can further change the distance covered by each turn of the engine by varying the tire size.

kip Foss · #9 02-10-2004, 09:28 PM

Since I have a fixed rear end ratio (unless I want to go to the trouble of changing it-which I don't) I was hoping that the manual trans. I have might give me a slightly better gas mileage than the auto. trans. Considering the effort involved in removing the manual trans. and clutch pedal assem. from the parts car and installing it in my 450slc I doubt that the result will be worth the trouble. Gas here is about $1.50 a gal. and I doubt that I will drive the slc more than 5,000 a year so the difference between 14 mpg with the auto. trans. and probably 15 mpg with manual will not be a financial benifit. It will be an interesting project but not cost effective.

Gilly · #10 02-10-2004, 09:42 PM

Kip
The Euro 350SLC ratio is a 3.46:1. Your 450SLC is a 3.08:1, so the mileage would probably suffer if you went with the '72 differential, but it would accelerate better probably.

Gilly

PS OR if you mean what's the ratio of 4th gear in the transmission on the '72, yes, it's direct (1:1). You may pick up some mileage with the manual trans, but I agree it'd be too much work to do if that is your only goal is to increase fuel mileage.

ctaylor738 · #11 02-11-2004, 08:47 AM

But there is the benefit that the manual trans really wakes the car up - IME with my 280E that I converted, it was like getting another 20% in horsepower. To say nothing of being more fun to drive.

It was a lot of work, but the result was worth it.

kip Foss · #12 02-11-2004, 11:20 AM

Chuck,
The clutch mechanism in the slc is all inside the car. It only has a hose that goes through the fire wall to the brake reservoir. The master cylinder looks like one of those long thin cylinders that are used on car hoods or van tailgates. Was your similar? What problems did you have in the conversion? Is there any reason to suspect that the trans., flywheel and bell housing from a Euro 350 would not fit a US 450? Did you buy a new clutch plate and if so how much did it cost? I have a feeling that, even though I have all the parts, this could be one of these projects that starts out as a good idea and ends up costing $500 and endless hours.

ctaylor738 · #13 02-11-2004, 12:34 PM

What you are describing is the clutch master cylinder. All of that stuff should bolt into the 450, including the pedal assembly.

I have no idea if the bellhousing/flywheel/clutch assembly from the 350 will work in the 450. My guess is that it would, but the best way to check would be to compare the part numbers from a 4-speed 450 and 4-speed 350 for the critical pieces.

And you need to find out if the 450 automatic crankshaft flange will take a pilot bushing.

You will almost certainly have to change the length of the driveshaft.

My 280E conversion was a piece of cake, since I had a complete euro car as a donor. I also converted my 250C to a 4-speed by chasing piece parts and that was not a big deal either.

kip Foss · #14 02-12-2004, 02:08 PM

Chuck,
I spoke with a MB mechanic today and he said that his only worry would be that the apparently since the crank and the flywheel seem to be balanced as a unit that by putting a different flywheel on an existing crank there might be some vibration.

He said that he had replaced the crank on a 450 once and when he ordered it from MB the crank came with a flywheel as a balanced unit. He said that mostly it would be a trial and error deal but that the conversion should work w/o too many problems.

ctaylor738 · #15 02-12-2004, 02:22 PM

What I did on my 280E was to have the auto and manual flywheel statically balanced by a machine shop. You mark the crank flange and the auto flywheel and remove it. You then take the flywheels to the machine shop. They will balance them, removing from or adding some metal to the manual one, and give them back to you with a mark on the manual one that you line up with the mark on the crank flange when you install it.

If you can't find a shop in your area, Metric Motors in LA does it all the time.

Cost like $50 and it was smooth as silk.