MatraSport Forum

The model type (I assume that is what it is) on the gearbox in my 2.2 says "AC 506". I have heard that it should be a Citroen CX box, but I have been unable to find any references to  AC 506 in connection with gearboxes.

Can anyone tell me what it corresponds to in Citroen partnumbers, if that is where it's from?

Also, if it is a Citroen, is it using the same gear ratios in the Murena?

Finallly, are there any other gearboxes that will fit the 2.2 engine in the Murena?

Yes!.. the gearbox from a peugeot 505 turbo will, and possibly some of the older chrysler 180's.. but these are all front engine rwd cars so it won't do you much good.


Some citroens had higher 5the gear.. thus the long 5th gear conversion that Roy has pioneered.


Personally I wouldn't bother... Simon has an extensive parts catalogue of the gearbox, and I doubt that there is much saved by asking citroen to find such old parts.
 

It wasn't so much that I wanted to shop at Citroen, but it may be easier to find a Citroen with a usable gearbox at a junkyard, than finding a Murena. ;)

The gearbox was used on several fw cars: Citroên CX, Lancia Thema, (Alfa Romeo 164). I know the final drive of the CX-unit is different giving lower rpm and less acceleration.
The gearbox is connected to the Chrysler engine by a special Matra badged bellhousing.

I had my gearbox refurbished a couple of years ago as the inside switching arm for the reversing gear had broken.

That's strange if you have a '506' in a 2.2.  The 506, 511, 2GE14 and 2GE16 were all Murena 1.6 units whilst the 510, 2GE15 and 2GE17 were fitted to 2.2 models.  The differences between the two groups was the differential ratio.  I wonder if someone has fitted a 1.6 unit to your 2.2?  The only other explanation I can think of, is that the box itself was nominally marked 506 but that the complete unit would take on the correct designation after it was assembled with the diff.  However, I have never actually seen any designation tag on any Murena transaxle, so I don't know where it would be found.

According to the information I have, 506, 2GE14, 510, and 2GE15 are all Lancia units, whilst the others are Citroën.

All the Murena gearboxes have the same 1st to 5th gear ratios, and the only difference is the diff. ratio - 62:13 in a 1.6 and 61:14 in a 2.2 (they are the crown wheel and pinion teeth numbers)  The gear ratio set is not the same as any other Citroën and I have records for I think all the models including the commercial vehicles that also used these units.

The 1st and 2nd are the same as some but with different 3rd, 4th and sometimes 5th.  Some have different 1st and 2nd, and the same or similar 3rd and 4th and exactly the same 5th, but the diff. ratios are different.  Part of the reason for so many differences comes from the fact that Citroëns usually had much larger wheels and tyre rolling radii than the Murena so they required a different figure to give the right overall gearing.

That was how I came to realise that if I changed the 5th gear to that used in the CX GTi Turbo and Diesel models, it would make an ideal 5th for the Murena.

So the first thing you need to find out for certain is, exactly what diff. ratio is in your unit.  Since your unit should be a Lancia version, it simply means it came from an Italian factory rather than a French one I think.  The parts microfiche details where the internal parts used differ.

What do you need to  know?  My own gearbox parts list is fairly comprehensive one as I have combined all the Matra and Citroën information over the years.  Many of the items are simply no longer available anyway, and others take an age to obtain - it took me seven months last year to get some bits!

The ideal box to get from a scapyard is a diesel or GTi Turbo unit as it has the best set of ratios including the high fifth for a Murena but the diff ratio will be incorrect.  However, these are like 'hens teeth'!  So good luck on finding one.

Roy

Hi Roy.
This is where I have to admit that I, at this moment, do not know what model is actually on my car.  :-[ I was told that it was the same as a spare gearbox that we have lying around and it is a 506. But since my car is a 2.2 I will verify if it says 506 or 510 on the one in the car.

I suspect that you have had one of these gearboxes taken apart a time or two  ;D, so perhaps you can explain the function of the two adjusting screws that can be accessed from the clutch housing and the adjusting screw that is in the end housing with the 5. gear. I am talking about the ones that protrude from the box, are slotted on the end and have a lock nut to fasten them in place. There is no explanation of these in the shop manual, except that they are for 3./4. and 5. gear. Are they perhaps end stops for the shifting rods, or are they for aligning the claws on the selectors? I am hoping that it is the latter, so I perhaps can fix my 1./2. gear problem.  ???

I am really impressed by your extensive information and research. It gives me more options to perhaps find replacement parts. I will definitely try to change the 5. ratio while I have it disassembled anyway. Thanks. :)

These are the end stops for the selector shafts and once set should never need, or be adjusted.  It would be extremely unlikely that you would ever get enough wear on the shaft ends to require re-setting!  These stop the shafts and therefore the synchros at the correct point so they don't go too far and balls start popping out.

If you look carefully at the end casing where the fifth gear is, there is a small casting 'pip' inside that is the equivalent of those adjustable stops, but in this case is fixed.  However, it relies on the case being fitted with the correct paper gasket.  If you were to fit a thicker non-standard one for example the pip would be too far away and allow the 5th/reverse shaft to travel too far.

The setting up procedure for the shaft stops is in the manual.

Roy