Another 348 gearbox takeapart...

I was lucky... For a 2 dollar part I could have lost the whole box.
This is my spare gearbox. I took it apart as I needed to change the pin that drives the gearbox oil pump which was broken. To do this you need to take the oil pump side casing off, followed by the ring nuts and then the whole cage. This will then expose enough of the main shaft to get you to the little hole where the pin fits. To block the gears you need to remove the face place and engage the reverse and 2nd gears.

I had to buy a GBP 70 ringnut tool from hill, 2 SKF BA2B 636151A's (GBP 90), 2 ringnuts (one left turning and one right turning), a tube of Locktite 271, and yes the pin for a single pound.

Aside from being nutty irritated at the waste of a whole morning and 200 pounds to replace a tiny pin, I was very happy to find that the ringnuts were somewhat loose. At arm power I managed to tighten them by about 10 degrees of turn (then I found out I got them backwards and tightened instead of loosening.

There was NO locktite anywhere, though the ringnuts were staked (but not very well I may add) - this was an October '93 box SN. 1416856915. The bearings in there were the later type - BA2B 636151A, matching the ones I had in "stock" perfectly (so I did not have to mess with the spacers) - so I took the liberty to replace the bearings. The original ones were perfect, so no problems to start with. The sealant was a white sealant, so I am assuming this box was not opened since manufacturing.

Can someone tell me what the correct torque setting for the ring nuts should be? I don't have an impact wrench, but I can tell you I have enough strength to break a 25mm socket, so I must be good for some 400nm on the biceps... I'm going to drown them in locktite (which is best? red 271, or blue 243?)

Nothing new, but here are some pics for anyone who needs them. P.S. the red "stain" is copper grease spray.


Marco
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It is about a day of bench time with all the necessary spares. A half day to take it out and a half day to put it back in ( buying you some spare time both ways). I'm in London too... I have a '90 and a '93 box at hand. I'd be happy to help you if you want. 2 people can do this in a garage with two bottle lifts and two stands. If you tell me the age of your box, and I could shift it cold & warm while listening, I can tell you if a) there is a reason to open it, and b) if the bearings or ringnuts need doing.

So far none of the ringnuts have been pinged or loctited properly... Probable yours is in the same situation.

Remember when loosening the ringnuts, that they have different threading. The frontmost (towards driver) shaft (lay shaft) loosens clockwise, the rearmost (towards the clutch) loosens anticlockwise. This is counter-rotational and designed to prevent the loosening of the ringnuts. (The same is true of the opposite side, but no need to take them out.)

As I said, happy to help... my number is 0777 037 3029 and I am in west London (Ealing).

 

Good thing is that the only major issues are the main-shaft bearing by the oil pump and the drop gear splines both due to poor tightening at the factory. The fist produces a marked whine as the bearing races wear, and the latter a clear clunk most noticed when in first gear and at walking pace you tap the throttle on and off - usually in start-stop traffic.

The '93 box, I believe is the last generation of 348 gearboxes (the one in the pictures below is one of them) with all the improvements to deal with most of the early box issues.

I'd be very happy to test yours and hear if it is something to worry about. We can pull the sump plug, and while it is drained pull the inspection plate for a look-see... You can then take advantage if this to refill with Redline Ultralight Shockproof gear oil. I can get it for you in Chiswick if you want.

By definition I have a spare box that is available for anyone who wants to defend themselves from rip-off F-dealers. It is now completely refurbished and all the evidence is on-line ;-)

You can call me anytime for a chat.

Marco

 

It is the one you had a problem with when your gearbox seized. It is the clutch shaft and the bevel gear shaft. Those are connected by two gears, each fixed on by a ringnut. The one on the bevel gear is accessible by removing the small panel under the flange for the throwout bearing, the other requires the removal of the clutch shaft. The clutch shaft is hollow and has the prop shaft going theough it from the engine to the flywheel.

It is all in your old post http://www.ferrarichat.com/forum/showthread.php?t=163194&highlight=splined+shaft.

You can loctite the hell out of the geat onto the clutch shaft, then super tighten the ringnut. I have seen people actually weld the two parts together is the splines were too far gone. With the splines gone, both parts are throw aways anyway, so yo may try to do that. A good steel to steel weld can work wonders, but a bad one can misalign and ruin everything...

Marco

 

MaterMec,

You have a post where you took this part out as a result of a 400 ft burnout a week after you bought the car. The nut I am referring to above is the one that came loose on your shaft that caused it to move outwards and hit the throwout bearing flange. Did you just tighten it and put it back in without loctite? If so pull it back out, undimple the ringnut and you can try the below

I don't remember the loctite number. 242 is medium strength. If you have a "clunk" now it means your splines collapsed further. I had one for about a year until I understood what was going on. The spline recession on mine was half way between your pictures and Jack's above (all my posts are listed in http://www.ferrarichat.com/forum/search.php?searchid=2968401. The specific one is http://www.ferrarichat.com/forum/showthread.php?t=207294&page=2) and I had a main shaft bearing problem.

Every f-workshop I spoke to told me they were screwed and I would have to replace the shaft (not too expensive) but then the pair of drop gears as they were matched (VERY expensive) and throw on top a whole gearbox disassembly to replace the lower gear on the bevel shaft.

What I did after realizing I only had to gain (and making a change the bearing again very improbable) as the parts would require changing, was to clean the shaft, gear and nut in brake cleaner. I bought a high strength (I remember working out that an adhesive strength of some 100Nm per square inch over the square area of the assembly point would mean I'd have more than 500 or so Nm of torque resistance, which we don't output - no nitro!!!) bearing adhesive - not loctite but another brand with a 24 hour cure time.

I put a new bearing (you make it very difficult if not impossible to change it in the future) on, then a ring of gearbox silicone sealant on the base of the shaft where the gear rests on the bearing. I then covered the shaft and gear and assembled them. I also poured the adhesive in the little holes that would form on the worn edges of the splines, then twisted the shaft and gear so the worn edges were the mating line (that is where the torsion forces are applied in forward driving), then wiped off the overflow.

I filled the holes formed on the reverse side now with adhesive, and shoved steel wire in the gaps (found some steel wire of the right diameter about .3mm i I remember properly) to absorb the forces that happen when you take your foot off the gas and the momentum of the car puts opposite forces on the shaft, pushing on it instead of being pulled by it.

I let this cure overnight over a warm radiator. The day after I welded a ring around the ring nut end of the gear and shaft assembly permanently fixing the gear in place. I then drowned the threads of the ringnut and shaft with the same assembly and tightened it to 230 NM (maximum setting on my torque wrench). I then pinged the ring nut, but was unsure of the shallowness of the dimple. So I welded the base of the ring nut to the shaft.

I don't do burnouts so to not tempt fate, but I have NEVER hear another clunk since - and I have been putting off buying a new shaft and gear set for over a year and some 10,000 miles of driving the car across Europe and on several tracks including SPA, Silverstone, Brooklands Park and Nurnburgring... Even if it all went to hell tomorrow I still think I got something out of nothing.

I'll be swapping gearboxes in the next couple of weeks (the above is a rebuild I'm doing on my spare one) so I'll be able to tell you how the repair is holding up... But no clunks so far....

Marco

 

See, I think the key to the repair is to ensure the gear and shaft are fixed with the worn faces in direct contact. The natural tendency is to fix them on the unworn faces to ensure the right geometry. But that will also mean that the torsional forces in forward movement will act first on the loctite then on the faces (after it fails), leaving you where you started once the loctite loses adhesion. I used a specialized bonding agent that was both an adhesive and a high strength filler. Coupled with steel wire inserts to take up the slack on the rear of the rotational direction.

If the faces are at contact then there is a solid continuance - adding the welding of the gear to the shaft adds more strength against the torsional force (Eventually I expect the weld will fail too - hence why I bought an additional gearbox)

For my USD .02, I see the failure mode as follows:
The gear splines and shaft will have some natural play i them. Every time there is a switch of power from where the car is pushing the engine along (taking your foot off the gas) to where the engine is pulling the car (going on the throttle) there is the same effect as one face beating on the other. Repeat this a huge number of times, you have metal fatigue and compacting deformation leading to the gap becoming bigger and the play widening. With the widening, you have more inertia on the face of the impact and so on, until the rate of the damage incurred at each impact grows and eventually leads to failure.

The forces are distributed equally among the faces of the splines, and if the energy delivered on each impact per spline is greater than what the metal can absorb without fatiguing, you have the metal deforming. Increasing the number of splines (like the 355 shaft) increases the faces absorbing the impact and I would expect will reduce the energy absorbed per face to a level that is below the deforming threshold. I suspect increasing the number of splines was cheaper than having the gear be pressed hard onto the shaft (removing any play) and increasing the tensile strength of the metal (eg. using stronger but more expensive alloy or other metal).

The ring nut is only there to keep the shaft from moving in and out against the bearing. The needle and ball bearing races keep the shaft in place radially, and the clutch flange keep it in place longitudinally against the forces of the clutch springs.

But then again I could be very wrong... I applied deductive reasoning with very little metallurgical knowledge...

M

 

I just glued and welded the thing so I could fix it in a weekend and am still driving it after 1 year and 10K miles. FBB - the typical racer - wants it perfect and it would be ;-)

 

271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, what was it again? oh yes... 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, now I'm getting it... was it 271? yes it was, look I know it 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, woohoo!!!!

Hey Ernie, I meant to say I remembered the loctite number it was 243, shhhtit, I meant 271! (I'll get it right some day, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271, 271.....)

 

I did everything as I have low confidence in my welding skills (10K miles and still truckin' on is ok though). I thing FBB's experience and the fact it will all cost you less than buying the 355 parts sounds an excellent idea. FBB, they are directional, but just match the worn faces then you're fine. If you back the gear so the unworn faces touch then weld it in that position you're guaranteed good alignment.

But we need pictures for this!!!

M