Mercedes W114 250 Coupe - help!

[Charles Morgan]

Or...it is a 4sp box with a 5sp knob.

I hope not! I think this is the 5 speed of which Grober spoke

 

[Charles Morgan]

Not come out because of low light but the second casing (which is much more elongated than a 4 speed) serial number is 117 261 12 02. I think fifth is in there - it looks so similar to overdrive boxes (indeed to the 5 speed w124 auto 5th module).

I could be wrong though...

 

[grober]

Right 153 is 5th gear 75 is the shifting rod +selector fork that the broken shaft lever should act on via the follower on the shaft [you can just see the follower on the shaft in the picture Charles posted] . The other two shafts are of a different design in that they act directly on the selector forks via those round holes . The reverse gear/5th gear needs that extension shaft +selector fork to reach the gear set at the rear of the box. In the 4 speed it just selects reverse. There is of course an idler third shaft in order to reverse the direction of the final output shaft for reverse which you see at the bottom of the picture.
My guess is the 4 speed box has that self same lever+shaft thats broken ---its the extension shaft+fork 75 that may be different


Wikipedia explains it better than me

Reversing

An intermediate gear which does not drive a shaft to perform any work is called an idler gear. Sometimes, a single idler gear is used to reverse the direction, in which case it may be referred to as a reverse idler. For instance, the typical automobile manual transmission engages reverse gear by means of inserting a reverse idler between two gears. Since a driven gear (gear "A") rotating clockwise will drive a second gear ("B") counterclockwise, adding a third gear to the string means that gear "C" will be spinning the same direction as "A". A typical transmission is designed with "A" and "B" gears, so when the engine spins, the outputs shaft spins the opposite direction, which drives the vehicle forward. A reverse idler gear setup is actually typically an "A" and a "C" gear, which are not in contact with each other until a "B" gear is moved between them. Since the transmission is designed to move the car forwards when the output is spinning in the opposite direction from the input shaft, when you add the "B" idler gear, it forces the "C" gear to spin in the same direction as the "A" gear, and thus the input and output shafts are spinning in the same direction, which drives the car in reverse.

 

[Charles Morgan]

Most helpful and I think spot on Graeme. The broken part looks exactly the same as the equivalent from the 4 speed (140 in the EPC diagram below)

 

[Bellow]

Not come out because of low light but the second casing (which is much more elongated than a 4 speed) serial number is 117 261 12 02. I think fifth is in there - it looks so similar to overdrive boxes (indeed to the 5 speed w124 auto 5th module).

I could be wrong though...

Not wrong, I think both you G have identified that 5th gear is tacked on at the back. And this pic...

....shoes three detent positions - neutral, reverse and presumably, a 5th gear.

My guess is the 4 speed box has that self same lever+shaft thats broken --

I'd back that. Grind out the welds and reweld a shaft from the 4sp item at worst - the 4sp item may lack all three detents (as it only requires two and where the 5th detent is needed there may be a stop).

As much as I favour the auto option over the manual, the shorter top gear of the auto could annoy me. If I wasn't troubled by the prospect of three pedals in the footwell I think the taller gearing of the manual could win the argument.

 

[grober]

Unfortunately that shaft+ lever is only given a part no on the 4 speed diagram not on the 5 speed diagram ----tried to check/compare but unsuccessfull

 

[Charles Morgan]

As much as I favour the auto option over the manual, the shorter top gear of the auto could annoy me. If I wasn't troubled by the prospect of three pedals in the footwell I think the taller gearing of the manual could win the argument.

Yes.

I am not sure what my diff ratio is (probably 3.92 as it's an early 250CE) which is very low. With a .87 final gear ratio it would give an equivalent of 3.4, which is still a bit low. A diff from a later 250CE has 3.6 ratio, so 3.2 with the 5 speed. That would probably be a lot more relaxed at speed.

 

[Bellow]

Yes.

I am not sure what my diff ratio is (probably 3.92 as it's an early 250CE) which is very low. With a .87 final gear ratio it would give an equivalent of 3.4, which is still a bit low. A diff from a later 250CE has 3.6 ratio, so 3.2 with the 5 speed. That would probably be a lot more relaxed at speed.

I thought you had a diff from when a V8 was under consideration....
If you are intent on the 5sp manual (with whichever diff) and a 4sp part can be obtained cheaply and easily (though if buying new the 5sp item is the obvious choice) then just get one and even if it is not a direct replacement one of us can reshaft the original part (cannabilising the 4sp part). I say 'us' as there is at least one person following this thread who will be a more skilful welder than me (Druk will know who) but I will hapily tackle that task otherwise!

A bit of a toss up between auto or manual given the short gearing as it stands. Depends I guess how you intend using the car when it is finished. (As much as I despise a clutch pedal, I'm none too enamoured with short geared cars. The fuel efficiency will suffer also and given the motor all MegaSquirted and with sharp sparks should pull well from low down without histrionics, it would be a shame to make it perpetually scream for the want of a viable top gear ratio).

 

[Charles Morgan]

My V8 ratio is IIRC about 2.47. I think that would just overwhelm the 2.5 six even when megasquirted! But a compromise ratio between the two might well work well.

I too hate short geared engines. Much driving near me will be congested (so auto) or motorway (so long gearing preferential). Decisions...

 

[Bellow]

My V8 ratio is IIRC about 2.47. I think that would just overwhelm the 2.5 six even when megasquirted! But a compromise ratio between the two might well work well.

I'd need to check, but from memory, around about 3:1 FD and 1:1 top gear gives 23mph/k rpm on 15 rims running 195/50 tyres. I can check if needed but as a ball park figure...

I too hate short geared engines. Much driving near me will be congested (so auto) or motorway (so long gearing preferential). Decisions...

The 5sp auto! But for pesky electronics.

 

[Charles Morgan]

I think it's much more the differential calculus that matters...

I'll get my hat.

 

[Bellow]

I think it's much more the differential calculus that matters...

Yes, integral to the plot....

I'll get my hat.

Get mine for me while you are at the hat stand please.

 

[Charles Morgan]

On which groaning note, time for bed!

 

[Druk]

I thought you had a diff from when a V8 was under consideration....
If you are intent on the 5sp manual (with whichever diff) and a 4sp part can be obtained cheaply and easily (though if buying new the 5sp item is the obvious choice) then just get one and even if it is not a direct replacement one of us can reshaft the original part (cannabilising the 4sp part). I say 'us' as there is at least one person following this thread who will be a more skilful welder than me (Druk will know who) but I will hapily tackle that task otherwise!

A bit of a toss up between auto or manual given the short gearing as it stands. Depends I guess how you intend using the car when it is finished. (As much as I despise a clutch pedal, I'm none too enamoured with short geared cars. The fuel efficiency will suffer also and given the motor all MegaSquirted and with sharp sparks should pull well from low down without histrionics, it would be a shame to make it perpetually scream for the want of a viable top gear ratio).

Druk is indeedee watching this thread with interest; unfortunately from the luxury of an iPad in Kent which can neither access the EPC nor the Excel spreadsheet that I have at home which gives the rolling diff/tyre/gear ratio combo that I used to work out the ideal ratio for the SLTD.
Graeme...can you enter the part number for the shaft from the 4speed into the EPC search box and see if it cross- references any other application?

 

[Mike Walker]

Welcome to the Garden of England Derek

This thread is a technical work of art if there is such a thing. So much more interesting than most of the stuff on here, even though a lot of it goes above my head. Keep going guys.

 

[Charles Morgan]

Certainly not me providing any technical art here!

The crack about differential calculus was of course not really a joke. Steady state engine revs to final drive is important, but so is the rate of change. Mercedes have very often used low geared diffs to allow for better acceleration at the price of higher revs at speed - anyone who has ever driven a multivalve diesel W124 in stock form with 4 speed auto will know why. One of the heartening things about the map on my SM is that torque levels are great from quite low revs - I'll dig out the rolling road printout to put it up, so it should be feasible if the map on the 250CE is similar to allow for slightly taller gearing, but I really doubt that a high ratio (such as my 2.47) will ever do anything other than make regular stop start driving very very sluggish.

Having converted the Allard diff* from 4.11 to 3.25, the effect on motorway driving was considerable, with acceleration more than adequate from a very torquey V8. Mugging up again, there are numerous options available as the car can use a W123 diff (as well as 116 and early 126 diffs). So the range of options is very decent.

*Ford diffs really. In the era of 3 speed boxes the final drive ratio was a real bugbear as the cars would really shake under full load. Being a highly inventive lot, one solution was the famous 1934 Ford Columbia 2 speed differential operated by vacuum that could be switched while in any gear. Try finding one in operating condition...

 

[Bellow]

Yes, an overly tall FD can be just as bad - stretches the gaps between the intermediate gears also. Not to mention giving a clutch a hard time on take-off. If the next gear down from top has a large (numerical) distance then a down shift for better acceleration can be a noisy uncomfortable experience.

I thought I'd encountered all the various transmission options used over the years (I thought the same re axle location until I tripped over how Bristol did their's on the 400 series) but had not seen the Ford OD axle. Presumably from the days before they abandoned chasing a multiplicity of ratios and plumped for torque-fat engines instead.
My car runs a 3sp gearbox with two FDs (the more things change....) but not the option to shift between FDs in any gear though (sequential - it runs through the 3 gears on the low FD then to select 4th it returns to the lowest of the gearbox ratios while selecting the high FD and repeats the process). Done that way in the interests of reducing overall gearbox length I think. None of this is helping the W114 get anywhere though...

 

[Charles Morgan]

None of this is helping the W114 get anywhere though...

Indeed - on which note, you have mail re dizzy. Time for me to crack on with important things!

 

[grober]

Druk is indeedee watching this thread with interest; unfortunately from the luxury of an iPad in Kent which can neither access the EPC nor the Excel spreadsheet that I have at home which gives the rolling diff/tyre/gear ratio combo that I used to work out the ideal ratio for the SLTD.
Graeme...can you enter the part number for the shaft from the 4speed into the EPC search box and see if it cross- references any other application?

When searched on the EPC Part no A1152601238 comes on numerous models inc 114.115,109,111 It occurs in both 4speed and 5speed gearboxes
and replaces numerous other parts e.g.
1152600883
and
1172600638
both from 4 speed boxes!

which implies the newest iteration of the part is backward compatible but not necessarily imply the old parts are forward compatible i.e. you can use the new part in an old box but not necessarily the old part in the new box for reasons Bellow has already alluded to his earlier post That said now pretty sure A1152601238 is the part no required I guess there is only so much "satellite reconnaissance " you can do from the EPC before confirmation by "ground truth parameters" i.e. having the two parts in front of you for visual comparison.

 

[Druk]

How desperate are you for the part Charles? If you mail me it and the lever I'll have a go at repairing it. Nothing ventured etc....