Diff ratios

[jaymanek]

All I did was work out the difference in ratio as that was all that changed.

original diff 3.58
proposed diff 3.07.

3.07/3.58 = 0.857
0.857 * 3500 = 3001


Looks like you are indeed correct.

Just back working my maths shows I must have mis-keyed 3300 in as the original rpm. When I answered yes that was to the bit about the 2.25:1 diff.

Thanks..

Im still sat here with a post it note on my desk trying to figure out where I went wrong...
phew.

 

[Dieselman]

Im still sat here with a post it note on my desk trying to figure out where I went wrong...
phew.

You need a slide rule or abacus for Christmas...

 

[Dieselman]

^ much appreciate your answer. Although possibly 2.4 would give the car longer legs at speed I think the 2.7 from the pre-facelift 500SL is the way to go. Not least because the rear subframe mounting are the same and it should bolt straight up. The engine I'm using is the 606 turbo giving 180bhp although I'm swapping the 6mm elements from the electric pump into the earlier manual pump and rumour has it that the slightly longer internal stroke of that pump combined with the bigger elements will give nearer 200bhp. Either way the midrange torque should be fun with a 2.7.

Next question. Anybody got a 500 2.7 diff they don't want?

The W210 E300TD uses 1.87:1 diff ratio which gives ~30mph/1000 rpm, which is slightly under-geared.
With the same or more torque in your SL I would go for long legs as it will shift well anyway, especially as you intend to use a manual gearbox.

A diff ratio of 2.7 will give 26mph/1000rpm, which is rather short geared. Don't forget the OM606Turbo is a willing performer from below 1,600rpm.

 

[Druk]

Thanks Will. EPC shows W210 300TD to have 2.87:1 diff. Typo?
Which I could get from the scapper I got the engine from (probably) but I'd have all sorts of extra engineering to do to get it to fit the 107 subframe and axleshafts.

Another confession to make is I've gone off the manual gearbox idea in favour of the four speed auto from the 124 300D. Probably re-engineering it's pull cable and vacuum requirements are a lot easier in the long term than sourcing a flywheel/clutch and pedal box arrangement.

 

[Dieselman]

Thanks Will. EPC shows W210 300TD to have 2.87:1 diff. Typo?

No, not a typo, a brain seizure due to being tired.. you are correct, it's 2.87.

Before selecting a diff I would ensure I knew what gearbox I was going to use and it's ratios.

 

[krimat2005]

all true but W210 300TD has 5 speed autobox with final gear ratio 0,83:1, comparing to direct final gearing with 4 speed box from W124 300D. anyway is gearbox from W124 300D strong enough for this kind of power/torque?

 

[bolide]

all true but W210 300TD has 5 speed autobox with final gear ratio 0,83:1, comparing to direct final gearing with 4 speed box from W124 300D. anyway is gearbox from W124 300D strong enough for this kind of power/torque?

Early 5-speeds often had an additional overdrive gear leaving 4th as 1:1. The W124 box is a good example

I wouldn't want to push any more torque through a W124 E300 Diesel box. It struggles to shift cleanly at times due to the odd control mechanism which is designed to flare shifts. Faced with more power & torque I suspect it would struggle unless the control system was revised

The control system is based on vacuum pressures & restrictor valves. The technology always makes me think of Lamson Tubes and other Victorian-era pneumatic oddities

Nick Froome
www.w124.co.uk

 

[Druk]

Thanks. This is all great info and, for me, the best reason this forum exists.

So I'm back to my original manual gearbox choice. I have to decide between a 717 412 5speed overdrive box from an 80's W124 with long input shaft or a 717 430 Getrag 5speed close ratio from a 90's 320TE but with a short input shaft.

The 412 needs a single mass flywheel probably from a Sprinter of some sort and the 430 needs the dual mass flywheel I already have but don't know whether to trust with the torque. TBH, despite reassurance from some peeps I'm not altogether convinced the 412 will take all that torque either. There is some circumstantial evidence that the Finns are pushing 500bhp through these with W124 300TD's when fitted with enormous Holset turbos but no-one will say for sure. Can anyone put this to bed once and for all? That would be a great help. I wouldn't be dropping the clutch with 2000 revs on the engine but conversely I wouldn't like to change down to first on some hairpin bend and have it stripping a cog or two.

Can't get these guys to answer but this looks like a 412 bolted to a 606TD. mercedes om 606 bomba manual 6mm - YouTube

In fact, some of them are completely mad.

dori 606 turbo - YouTube

dori 606 turbo - YouTube




.

 

[kth286]

the original 124 Hammer was pushing out enormous power and was fitted with 'old' 126 S class auto boxes and performed well, contrary to bolide's thoughts.

 

[bolide]

the original 124 Hammer was pushing out enormous power and was fitted with 'old' 126 S class auto boxes and performed well, contrary to bolide's thoughts.

I am sure it was. Shame that box & control system wasn't fitted to the E300 Diesel

The Scandiwegians are pushing lots of torque through unlikely boxes but they have all been rebuilt to handle it. I have no doubt that a standard, old E300 Diesel box, when faced with an engine of double the torque, would wilt quite quickly

Nick Froome
the independent Mercedes Estate specialists

 

[Druk]

Nick. Appreciate your input. Can we confirm we're talking about the same gearbox. Mine is a 722.345. When you say above that it has "vacuum pressure and restrictor valves" I'm wondering if you're referring to a different box to mine? All I have is one control cable and one vacuum line to the modulator valve. Looking on EPC there is a box which has another two extra lines + valves to the right rear but that's not mine.

However, I'm still thinking towards the dog-leg Getrag box except I'm very suspicious of it's dual-mass flywheel (which came from a petrol car). There are some SMF on the market but none of them explain how the gearbox input shaft is supported once the DMF spigot bearing is gone. It might be possible to swap for a longer input shaft but where would it come from?
(As alluded to on another thread)

 

[Charles Morgan]

How about a Torqueflight or similar? That would handle virtually anything...and having done something MB didn't do once, why not twice? Edit - or thrice, if you count the seats..

 

[Dieselman]

When you say above that it has "vacuum pressure and restrictor valves" I'm wondering if you're referring to a different box to mine?

However, I'm still thinking towards the dog-leg Getrag box except I'm very suspicious of it's dual-mass flywheel (which came from a petrol car). There are some SMF on the market but none of them explain how the gearbox input shaft is supported once the DMF spigot bearing is gone.

Bolide means the vacuum control valve mounted on the engine of a W124 300 diesel, the only valve on the box is the shift slur modulator.

For the spigot bearing just have a machine shop bore the flywheel and install one.
My preference would be to use either an auto box out of a 5 litre petrol engine car or use a manual box and maybe uprate the bearings before installation as it's the bearings will suffer, not the gears.

 

[Druk]

Thanks Will. I have the vacuum valve you refer to and it mounts directly to the manual IP I'm using. Surely that would still be needed if I went for a 500 box?
The problem with the Getrag box is the first motion shaft is too short enough to reach a crankshaft mounted spigot bearing, and not that there's not one there. In the DMF the spigot is flywheel mounted. If I use the Getrag box without the DMF there is nowhere for a spigot bearing to go, just thin air. Actually, I've just tested my DMF and it's OK so I was wondering if I welded it up and just used it as a SMF would that be OK but with a proper spring driven plate instead of the unsprung DMF one. ?

 

[Druk]

This could be salvation. Just made contact with this gent who has developed his own controller for the 722.6 gearbox. Quick dash back to the scrappy before the original 'box disappears. :bannana:

722.6 gearbox mercedes manuel mode - YouTube

 

[Dieselman]

Get the diff and propshaft as well.

Looks a good fix, he's also tried an Arduino controller for the rack position, so far without success as it uses PWM instead of simple voltage.

 

[Druk]

Get the diff and propshaft as well.

No such luck. Phoned the scrappy and they think they have the box and TC but the car is crushed and gone. So I'm now in the market for a gearchanger and some of it's wiring loom. Another complication is the need to install some sort of propshaft rev counter cos his device needs a speed input. Not sure quite what format as yet but he is very helpful with suggestions and is keen to make it work.
Am I correct in thinking the 210TD has a diff ratio of 1:2.87 so I could still go after the 500SL diff? It would fit better to the subframe.

 

[Druk]

Got the box and TC this morning :bannana:. £100...can't be bad. Cables have been cut an inch or so from the connector and whatever the little thingy is on the back of the box that stops it coming out of Park has been broken, but other than that...looks good. No shell left though so now I need a change lever and associated cables. Working the lever on the box it only has four positions so I'm wondering if the later 211 changer would work with it?

 

[Druk]

Question for the mathematicians out there.

If my car does 3500RPM at 70MPH with a 3.58 diff ratio what would the revs be at the same speed with a 3.07 diff ratio?

Bump!

Same question but with a 2.24 or 2.47. What would be the engine revs @ 70MPH?


.

 

[Dieselman]

Bump!

Same question but with a 2.24 or 2.47. What would be the engine revs @ 70MPH?


.

Assuming no other gearing changes;

2.24 = 2189rpm.
2.47 = 2414rpm.

Looks like the 2.24 is a good match.