I have a howl in my rebuild gearbox and would like anyone's insight. I have owned my Dino since 1974. In ’94 the clutch was slipping bad so I pulled off the bell housing to remove the PP/disk/TOB/flywheel to rehab. Since I was there I figured it was time for another valve clearance check and to closely examining the cam lobes. There was at least one low lobe on each cam so I pulled them to send to Megacycle. Short story- I decided to pull the motor and check all specs. While I was pulling the motor apart in my basement I sent the gearbox to a well-respected repair/restoration shop. The head mechanic pulled the gearbox down and said that all the needle bearing were acid etched as well as the Differential Drive Gear and Ring gear. He suggested I replace all and found the “last matched Drive Gear and Ring Gear” in the UK. $4K later I had a rebuilt gearbox- which sat for 10 years (with oil and turned over every few months by hand) before I got it back in my Dino. During my motor rebuild a good friend talked me into restoring my Dino. As those who have done this- it takes longer then you think. It took me 10 years. By the time I had my dino back together the shop had closed and the head mechanic took a job- I do not know where. Soon as I drove my Dino on its first shakedown ride I knew something was wrong. You can barely hear the exhaust note over the howl of the transmission. I have tried different lubes and no joy. The gearbox was always quiet before the rebuild. It is almost painful to drive my Dino. I am thinking that the so-called matched Drive Gear/Ring Gear set is not so well matched- or set up wrong. In a normal differential, you shim based upon blueing pattern on the teeth. I am not sure how the Dino gear set is adjusted- or if it can be adjusted. I do not see any shims in the parts diagrams. Before I break down and pull my motor/gearbox out again- does anyone have any thoughts (or has experienced) on what the cause of the howl/whine could be from. All new bearing as well as DG/RG. Does it mainly under power/load— more so under 3K rpm. Does not howl when on a lift running through the gears. For me, this points to the DG/RG. I still have my old set which does not look bad to me. Open to all theories and plans of action.
Here’s a thread on Ferrari mechanics in NC: https://www.ferrarichat.com/forum/threads/ferrari-mechanics-in-north-carolina.528015/ Good luck! Freeman
Thank you Freeman-looks like GMT and Son is the closest. I will probably end up pulling the gearbox apart myself and if I do not see anything obvious I will bring the gearbox to GMT. Wish I could hear the whine spinning up the gearbox on the floor so I could swap out the Drive Gear/Ring Gear set--spin it up to see if the whine goes away.
You have a good point-- Although if this is not a common problem then even a mechanic may not be able to pinpoint the problem even by hearing it. I have never heard anyone else on the forum or any other Ferrari mechanic speak about Dino gearbox whine so it may be a process of elimination starting with putting the old drive gear and ring gear set back in the box.
Is the noise still there when you push clutch pedal? Have you had it on a lift while the engine is running and someone runs it through the gears? You might be able to isolate where the noise is coming from. Having a good mechanic experience it, at the very least, gives you an extra POV.
The drop gears tend to whine if worn or incorrect lined up. Operating the clutch with the wheels suspended while listening should verify if this is the culprit. Best Peter
Yes- had on my lift many times hoping I could determine what section of the gearbox the noise is coming from. Put it through all of the gears and all different RPM. Tried to give it a load by applying brakes when in each gear. Only does it under load/power-- only when the clutch is engaged. Put the clutch in and noise is gone.
Thank for your thoughts Peter-- tried that both on the lift and jacked up by the frame on the floor --with the rims off and on and the lower A-arms supported by flat top jacks so I have a normal angle of the shafts. The drop gears are pretty noisy but do not change pitch at different RPM's. This is a singing high pitch which changes a bit at different RPM's.
Then a misaligned drive / ring gear might be the next suspect as you mention yourself. Also check the diff planetary gears for wear / pitting. I had to replace the entire diff due to extensive pitting on the planet gears and that reduced "gear" box noise significantly.
thank you for relating your experience. Interesting-- do you recall if the pitted diff planetary gears caused a higher pitched whine-- I have to open my windows to have any pleasure at all driving my Dino. Just hard for me to believe that these Helical gears can be this loud. I was hoping they would "bed in" and tone down the whine. But in '73- my brand new gearbox did not sound this loud so I am skeptical that more miles on the box will make a big difference. Having not been in this box I would like to know if there is shimming adjustment to set the correct tooth contact pattern between the diff drive gear and the ring gear. I do not see any adjustment shims listed in the parts drawings that I have. Are the two gears meshed/lapped at the factory assuming that their centers will be the same in any gearbox they are installed into?
I remember the sound from the worn diff to be more of a lower howl than a high pitched whine. Have you tried to listen intensively to the drop gears box with a screw driver or similar placed between the box and your ear? This might indicate if the sound is from this end of the gear box assembly. The whole diff assembly, and hereby also the ring gear, is shimmed in order to optain the correct pre-load of the diff bearings. I had to fabricate extra shims to fit the aftermarket diff since this was approximately 2 mm smaller than the original (See pictures also including a picture of all internal bearings in the box and the pitted satellite gears). Best Peter Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login
Do you have the workshop manual available by the way?. Gearbox and diff assembly is covered quite detailed herein.
Thank you for your thoughts-- Checked the drop gears sound many many times--- also-the whine occurs only under load so I eliminated the drop gears as the cause. I have a translation of the factory manual I bought from Angelo Wallace in 1976. It gives a nominal clearance of .03-.04 mm-- but I have noticed a few incorrect specs when I was rebuilding the motor-- is this the clearance you set your differential gears? His manual mentions roller bearing pre-load washers and ring gear positioning washers but I have not found any part numbers for various thicknesses so I assumed that the factory assumed that you did not adjust- you just reassembled and checked if you did not exceed the "wear clearance" of .12 mm. My fear is that my set may not have been OEM and the mechanic just reassembled using the original "washers". If the clearance was tighter then .12 mm he assumed all was good with the box. If the gears were tighter then .03 mm I think these gears could be loud
Remote diagnosis is impossible especially because can't hear what you hear. I have rebuilt many 348 boxes a 308 box never a dino. But I have worked on dinos many years back. 1st thought is are you double damn sure it is not low hanging fruit like a throw out bearing? Clutch in and out noises that's the 1st thing you think about. It can be gear whine. You could open the box and prussian blue the gear set and see how far off it is. You may be able to isolate the noise better on a rolling chassis dyno if you can't duplicate it on the lift not under load.
I had a similar noise from my gearbox many years ago and it was a high pitched howl /whine as you describe which seemed to disappear when you took your foot off the gas, stripped down the engine and gearbox for a rebuild and found the taper roller bearing on the diff were worn. Fitted new ones and checked the preload by making up two 200mm dia circular discs and bolting these to each output driveshaft flange, connected with a bar between the two. I then used the top half of the diff casing (inverted) to fit the crown wheel and diff assembly complete with new bearings without the shim in place. I then added a 3kg weight to the joining bar between each 200mm dia disc. I then tightened the flange( no shim) until it moved freely. The gap was 1.8mm (old shim was 2.30mm) Doing it this way you don't need to strip out the gearbox internals and more importantly each shaft moves in unison with each other so the diff doesn't counter rotate. Problem cured.........for me anyway! Tony
Thank you for experience on this-- all symptoms point to the differential bearings or the drive gear/Ring gear. All of the bearing in the box and differential were replaced with new- but there is always the chance a bearing was bad out of the box. I tend to agree that the symptoms point to the differential bearings. To be sure--- before I do any teardown ---I am buying a few small microphones and placing them on different points on the gearbox/diff as well as by the drop gears and make a few digital recordings on the road. This way I can define/compare the overall levels and run a few FFT's for comparison. Having done this on the bench- do you think that if I pull the headers and remove the trunk wall I could get enough room to pull the top off of the differential housing? I am thinking I could check the tooth pattern as well as run the clearance check using your procedure. I am sure that the tech simply reused the OEM shims which may be the issue. Did you take pictures of the setup you used? Even a sketch would be helpful Thank you again.
