HOW MUCH TO REBUILD A 348 GEARBOX IF WORN

It's a 92 348 with 36K miles on the clock. The specialists had tried changing oil and adjusting cable to no avail. They took the gear box apart and found all gears in good condition but two syncros "glazed" up and needs replacing.

 

What is a Glazed synchro? I thought they are either in or out of spec???? The diagnosis is made with a micrometer isn't it?

 

Not knowing much about gear box, "glazed" was the word that the mechanic referred to the condition of the syncro

 

I've seen that quite a bit on the iron Ferrari syncros. Most of the time when I get into a TR or 512 box for syncro problems the syncros actually have little wear but the surface is cooked looking like an overheated flywheel. It is from using an improper oil (like the Agip garbage they used to have us use) and forcing the shift much like when you hear of people complain when those boxes are cold and baulky. If you force shifts in that situation that is what will happen.

Lapping the surface with valve lapping compound works quite well in restoring the syncro ring. I lap all syncros new or glazed to make them fit the taper better, makes them shift great.

 

4days of labour £1500 and £480 worth of hardware. IMO it sounds very excessive to change two syncros.

 

Rifledriver,

Thanks for the education. When you lap does that speed the break-in wear that I would have just from use or is lapping supperior to breakin wear? Also, when you do this I assume you use compound on the synchro right against the shaft. The shaft is harder than the synchro so you don't put any wear on the shaft? Can you take the new balkyness out of a 2nd gear with this method?

 

When you lap no break in required, Shifts great leaving the driveway the first time.

Compound between the ID of the syncro and the OD of the gear taper.

The iron syncros in Ferraris are pretty hard so I would assume you are removing some material from both but no more or less than during the break in period of the syncro.

It gets rid of a lot of the baulkiness. If you have ever noticed the iron syncro boxes take many miles to really break in. I have seen TR boxes take 20k miles before they shift smooth. Lapping makes that quality of shifting happen today.

 

Rifledriver, thank you. I find this tip very timely and interesting. Can you share the spec for the lapping compound you use? I would surmise it must be a very fine grit size. Perhaps similar to the “fine” lapping compound used to final lap intake and exhaust valves to seats. Thanks again.

 

It's not critical. I start with a coarse valve compound and finish with a fine and just look for a consistant pattern the same as you would on a valve.

The square area on a syncro as compared to the square area on a valve is so large you have to start with a coarse grit to keep the job from turning into a career. Also wrap the syncro with a rag so the dog teeth won't rip the skin on your palm to shreads.

 

Great tip Rifle driver. I don't know why I have never thought of this. I may get to rebuild a friend's 348 gearbox soon so I am anxious to give this method a try. You are correct. on the breakin wear. I had to start racing my gearbox (even though I heel-toe) to get it smooth. Now it is better than it has ever been. You are a credit to the real mechanics. This should be standard Ferrari operating proceedure. But then the gearboxes would shift so nice people would think there was something wrong!