Shift fork material?

[FredWinterburn]

Hello, My wife recently bought a 1971 124 Spider. I drove a Lada Niva for 11 years and had the transmission off the car several times to replace bearings and other worn parts, mainly shift forks and synchro sleeves. This is 25 years ago now. I was given a Fiat Spider gearbox for parts and modified the Fiat 5th gear to fit into the Lada housing as the Lada 5th gear was poorly designed. Anyway, to make a long story of rebuilds short, I ended up grinding down a set of worn out shift forks and built them up with braze (likely brass). I then hand filed them to match a new set of synchro sleeves. That cured all of the wear problems and that transmission was finally reliable. Fast forward to today, and I dreaded what I might find when I drained the old oil from the 71 Fiat transmission. The oil was very old and I could see some very fine particles of brass (almost microscopic) suspended in the oil, but happily there was no real amount of collection on the magnetic drain plug. A bit of grey paste was all I found. So I filled it with GL4 and felt quite pleased about that. I fully expected the drain plug to be covered in silver fur and possibly bits of other stuff like on the first oil change with my Lada. My question for the forum: Did early cars have bronze or brass shift forks? If so, when did they switch over to the steel forks with a bit of bronze spattered on to them? The Fiat transmission I had for parts was either from the late seventies or early eighties and it had steel shift forks just like the Lada. I can't imagine the lack of wear evidence with steel forks considering they rub constantly against the sychro sleeves while in gear. This transmission was rebuilt but from records at least 25 thousand miles and I'll bet the oil hadn't been changed until I did it. Thanks, Fred

[18Fiatsandcounting]

My question for the forum: Did early cars have bronze or brass shift forks? If so, when did they switch over to the steel forks with a bit of bronze spattered on to them?

I can't speak for all the model years, but the shift forks that I have are iron. I just checked with a magnet (brass or bronze is not magnetic).

You would think that shift forks and sliding collars would wear, but the latter is hardened steel. The shift forks are iron, but excessive wear is usually seen with drivers that rest their hand pushing on the shifter which tends to push the fork against the collar leading to wear. If treated well, a Fiat spider transmission can go well over 200K miles without issue. My '71 transmission is the original and still works perfectly. Oil leaks and clutch replacements are a different matter of course.

The only brass component that I am aware in the Fiat transmissions are the synchro rings. Based on color, I'm pretty sure they are brass and not bronze. Note that since brass is not magnetic, synchro wear will not be picked up by the magnetic drain plug. Wear on the synchros is usually seen as a gold sparkly glitter effect in the oil. Not unusual over time.

-Bryan

[FredWinterburn]

Thanks Bryan. It could be that the Lada synchro sleeves were not case hardened while the Fiat sleeves were, even though dimensionally they are identical. One thing I never had to replace on the Lada were the brass synchro rings. Fred

[FredWinterburn]

The Lada transmission went with the car when I sold it. I have a picture of a worn fork that I saved for posterity. I would post a picture of it, but this forum format is confounding me so no picture. The wear groove is about 3/32" deep. The associated synchro sleeve would have been worn too. Once the gears jump, the spline ends on the hubs etc don't last long and more expensive parts need to be replaced. Fred

[18Fiatsandcounting]

I've torn down about a dozen transmissions, and some shift forks have almost no wear while some have deep grooves cut into the forks. Not sure whether it's an oil issue, different materials, or driver behavior. Or simply extreme age.

If the forks wear deeply enough, they won't push the sliding collars completely onto the gears and so the transmission tends to pop out of gear when under load. Extreme wear in the outer grooves in the collars can cause that as well.

-Bryan

[FredWinterburn]

BTW, I suspect that the forks and sleeves worn the worst used 20W50 motor oil as recommended by the Hayne's manual. Those forks and synchro sleeves need something more viscous. Although the Lada transmission came with 80W90 gear oil and probably Gl5 by the smell of it, and the forks still wore prematurely. I will say this for the Fiat design, and that is the synchromesh is very good. About a thousand times better than the synchros in my 56 Morgan with the Moss gearbox, and almost as good as a sixties Volvo Fred

[18Fiatsandcounting]

BTW, I suspect that the forks and sleeves worn the worst used 20W50 motor oil as recommended by the Hayne's manual.

Which Haynes manuals said to use 20W-50 motor oil? I thought all the manuals (Fiat or otherwise) recommended GL-1 for the transmission, which is a mineral oil-based oil about 80W or 90W viscosity.

By the way, the issue with GL-4 and GL-5 is that they contain sulfur additives, and while fine for the differential, such additives are not good with brass synchronizers.

-Bryan

[FredWinterburn]

GL4 is fine for brass and always has been, and probably modern GL5 formulations nowadays. Good luck finding GL1. The Haynes manual I have is well worn and came with the car. 'Fiat 124 Sport 1967 to 1974'. The recommendation is Castrol GTX 20/50. Wrong choice IMO, but my only experience is with Ladas which might look exactly the same, but in fact might not be due to better materials and heat treating etc by Fiat for the same design. Fred

BTW, I suspect that the forks and sleeves worn the worst used 20W50 motor oil as recommended by the Hayne's manual.

Which Haynes manuals said to use 20W-50 motor oil? I thought all the manuals (Fiat or otherwise) recommended GL-1 for the transmission, which is a mineral oil-based oil about 80W or 90W viscosity.

By the way, the issue with GL-4 and GL-5 is that they contain sulfur additives, and while fine for the differential, such additives are not good with brass synchronizers.

-Bryan