Murena high fifth gear

[michaltalbot]

So today I started with changing the gears (picures are here: http://michaltalbot.rajce.idnes.cz/Gearbox/#album ), but there were some problems. Those two big nuts were tightened so hard, I think that somebody in past (there were silicon gasket under the cover) tightened it by air pistol. I used everything, all my power but it was impossible to turn it off. So I had to use very destructive way to get them out  (picture DSC07930 - the small "blue" strips is what I used to cut the nuts - terrible work) but after that "piggy work", I changed the gears and wanted to finish the operation with mounting the synchro-wheel with fork. And next problem is here. Roy wrote that original fork can't be used, so I prepaired the fork from CX gearbox and though that it solve the problem, but not - hole for securing screw is on a different place on CX fork  (piture DSC07933 left is CX right is Murena) so I must to fix this problem now, but how? Do I have to brush the original fork, or do I have to bore next hole into CX fork?

[Anders Dinsen]

Interesting photos, Michal. I'm a little surprised you had to cut the nuts to get them off. I suppose you have spares from the CX box?

Do I have to brush the original fork, or do I have to bore next hole into CX fork?

I'd go for machining the original. Drilling another hole in the CX fork could reduce strength a bit. They look to be quite close to each other.

/Anders

[Jon Weywadt]

So today I started with changing the gears (picures are here: http://michaltalbot.rajce.idnes.cz/Gearbox/#album ), but there were some problems. Those two big nuts were tightened so hard, I think that somebody in past (there were silicon gasket under the cover) tightened it by air pistol. I used everything, all my power but it was impossible to turn it off. So I had to use very destructive way to get them out   (picture DSC07930 - the small "blue" strips is what I used to cut the nuts - terrible work) but after that "piggy work", I changed the gears and wanted to finish the operation with mounting the synchro-wheel with fork. And next problem is here. Roy wrote that original fork can't be used, so I prepaired the fork from CX gearbox and though that it solve the problem, but not - hole for securing screw is on a different place on CX fork   (piture DSC07933 left is CX right is Murena) so I must to fix this problem now, but how? Do I have to brush the original fork, or do I have to bore next hole into CX fork?

I know what you faced with the nuts. I took my gearbox apart today for the purpose of fixing the 1./2. shifting problem. The nuts are of the same type as on the wheel hub. You have to make a punch that will straighten the rim out, without damaging the threads. Even so the nuts would not budge. When I took off the wheels I used an angle grinder with a diamond blade to cut away the part of the nut that was bent unto the notch on the shaft. I did not want to do that on the gearbox and risk getting metal shavings into the box. So I went and cut off a 80 cm. piece of 3/4" water pipe to extend the socket wrench. After fastening the gearbox to the table and with the added leverage, the nuts came loose. I cannot imagine why it would be necessary to tighten them so hard, when you have the notch to secure them. (Photos are on their way.)

In the process I have counted the teeth on the 5. gear set. 33/45 standard    I also think I found the shifting problem, but that is a different post.

[michaltalbot]

I think that mechanics in service, when they are tightening this nuts, are using air pistols, because it's easier and they don't have to fix the gearbox wheels against turning, but it's too strong.
If You want those fast 5th gears, there is a solution Finally I bought only wheels + bearings + fork from CX for that 250,-EUR and leaved the rest at his garage (because - what I will do with CX gearbox? Nobody will buy it and I don't have enough space for saving it). Still it's much cheaper than new set from Citroen (cca 600,-E). So if You want, I can buy and demount all parts for You and send it by post. All You need is on the picture DSC07921. It is 31 x 46 teeths 

[michaltalbot]

I decided to brush the original fork, but question is, if 2mm (max. what is possible) is enough. Roy, do You have a picture of brushed fork? (hope that "fork" is right word)

[michaltalbot]

It was a hard day today
I picked up the brushed fork, than I completed the gearbox and went on the highway for test drive. I did more than 70 kms, but trafic was still so busy. But I've made some video as I promised. At speed 160km/h the rewmeter was bellow 4000 rpm. I've counted that for cca 230km/h I will need longer free road and on my way back there was one place, so I pressed the throttle and reached 220km/h GPS when rewmeter was a little above 5500rpm. Than I had to slow down because of traffic again but it works, so if it can reach 6280 rpm it must to make 231km/h GPS. So next time, maybe on sunday morning when roads are empty, but first I must repair my clutch, because 300m before my garage my clutch slave cylinder leaved its place! maybe because of weak old safety ring, I don't know... will check it on saturday.
I will load the video on youtube (but it takes nearly one hour with my internet connection   ).

Edit: video is here: http://www.youtube.com/watch?v=FGTe1mQRASQ and pictures are completed here: http://michaltalbot.rajce.idnes.cz/Gearbox/
I forgot to write, that driving experiences are that acceleration from 160km/h is worse but from 170km/h it's much better and the car goes up very fast, reaching 210km/h is very easy and travel around 170km/h is like eating sunday dinner   and I'm speaking about GPS values.

[Jon Weywadt]

... and travel around 170km/h is like eating sunday dinner   ...

You must be eating fast food on Sundays 

[Matra_Hans]

Congratulation with the well done "surgery" on the gearbox.

Hans

[roy4matra]

So today I started with changing the gears, but there were some problems. Those two big nuts were tightened so hard, I think that somebody in past (there were silicon gasket under the cover) tightened it by air pistol.

Yes, if people don't use the torque values when tightening nuts and bolts then others often have more trouble.  All those I have done came apart without using my impact wrench.  If the gearbox is locked in two gears, as per my instructions, you should be able to undo the nuts using a normal 18" breaker bar on a socket.

And next problem is here. Roy wrote that original fork can't be used...

Not quite true.  What I said was the original fork has to be modified, and I described how to do that.  The problem with trying to use the fork from the Citroën box is, as you found, the mounting is different, certainly on the early ones, which from the photos I can see you have.  It is better to modify the Murena fork.

Do I have to brush the original fork...

Yes, it can be machined either on a professional machine or by hand as I have done using a grindstone on a hand drill.

... or do I have to bore next hole into CX fork?

No because the boss for the hole is in the wrong place.  Citroën machined the fork to clear the larger gear but that fork is no longer available.  However, you can machine the original yourself, as you have done.

...so I pressed the throttle and reached 220km/h GPS when rewmeter was a little above 5500rpm. Than I had to slow down because of traffic again, but it works

So now you know what a Murena can really do! :-)

Roy

[michaltalbot]

Roy: yes, I know now but what I still don't know is - how to thank You for sharing this with us. Lot of people modify their engines and spend a lot of money for same target - to be faster. The worst thing (from my point of view) is that when somebody who will see Murena for first time in his life, won't know how it looked like when it was made in Romorantin and with engine from Alfa Romeo, Ford, etc. everybody can say: "hm you had to use a different engine in this sports car, to be faster than average familly car, so original engine had to be a trash" But this modification stays hidden and if I will beat somebody at topspeed on highway, then I can proudly open the engine bay to show him what Talbot-Matra produced

[roy4matra]

Roy: yes, I know now but what I still don't know is - how to thank You for sharing this with us...

We'll have to have a 'High Five' Murena club with a badge! :-)

Roy

[JV]

Congratulations Michal. The difference is quite clear.

Jan

[Anders Dinsen]

We'll have to have a 'High Five' Murena club with a badge! :-)

Indeed, Roy! Indeed!

[Oetker]

Nice job Michael, and defenitly wurth the trouble.
One thing I missed in youre tutorial.
a picture of the machined fork.

[michaltalbot]

Oetker: no, no, it is there - http://michaltalbot.rajce.idnes.cz/Gearbox/ picture 16072009.