Transmission Rebuild

[SteinOnkel]

Ahoy,

so we opened it up. Lots of things need replacing. Gasket and bearing kit, that's clear. All synchros are past their prime, so we are replacing those as well.

A few questions:

1) Is it usually enough to replace the brass synchros?
2) 5th gear popping out on decel, is that what I need this spring for:

https://mrfiat.com/fiat-124-600-fifth-g ... pring.html

That's it for now, more to follow surely.

Thanks
Steiny

[18Fiatsandcounting]

Steiny, I'm not sure that spring will help you. Usually, if the car pops out of 5th gear, it's because it wasn't shifted fully into 5th gear to begin with. This could be due to worn shifter forks, works synchronizer sleeves (hubs/collars), excessive play in the transmission shafts, or a restriction in the shift lever that doesn't allow full travel. For the latter, I have seen goofed-up shift boots or shift rubber seals that weren't installed right and prevented the shift knob from going all the way into 5th gear.

-Bryan

[SteinOnkel]

This transmission has definitely been messed with before. Blue silicone everywhere.

Hey - unrelated side note - you know what isn't oil resistant? Blue silicone ¯\_(ツ)_/¯

Anyways, just dropped a cool $600 on parts. I read somewhere that one can "flip"the 5th gear synchro?

I'm guessing it pops out due to excessive play in the shafts. The bearings are gone, all of them.

After this operation, everything will be new. From the pedal to the pilot bearing. Hopefully my partner (whom I teach to drive stick on this car) can appreciate it and be a little bit more gentle. It's not an 18th century mining cart, but she hasn't gotten that memo quite yet.

Cheers
Steiny

[18Fiatsandcounting]

I read somewhere that one can "flip"the 5th gear synchro?

I have not heard that, but I suppose it might work if the synchro is symmetric from one side to the other along the center axis.

I'm guessing it pops out due to excessive play in the shafts. The bearings are gone, all of them.

Yes, that could cause your problem, and my experience is that 5th gear is the gear where this is first noticed.

It's not an 18th century mining cart, but she hasn't gotten that memo quite yet.

There's gold in them thar hills!!! Or in this case, brass shavings in the bottom of the transmission from improper shifting...

Keep us posted. -Bryan

[Odoyle]

I read somewhere that one can "flip"the 5th gear synchro?

Yes you can flip the 5th gear synchro, I read about that when rebuilding my transmission last summer and tried it. It works. Though you said its popping out of 5th gear, which mine was not, so synchro might be too gone. Hard to say without a photo.

[SteinOnkel]

So, I'm knee deep into this thing.

I read n the manual not to mix up the selector springs underneath the retainer plate (there are three of them). My cat did not get that memo and now I don't know which one is which.

Critical issue or....?

[scrapironchef]

If you're teaching someone to drive a Fiat stick it helps to tape a thumbtack pointy side up on the top of the shift knob. It reinforces the idea that you don't rest your hand on the shift knob unless you're shifting.

[18Fiatsandcounting]

I read n the manual not to mix up the selector springs underneath the retainer plate (there are three of them). My cat did not get that memo and now I don't know which one is which.

Going by memory here, but I think you're talking about the 3 "shift detent" balls that are located behind a plate (& gasket) on the transmission. I think the springs and balls for these are all the same. Mix and match like you're a DJ at a Fiat rap concert. Yo, peep this synchro, homies!

-Bryan

[SteinOnkel]

Hmmm...they don't look the same.

The vendors are pretty useless in this regard. Only one that sells them is Mr. Fiat and they call it a "5th/reverse detent spring". The rep couldn't tell me what they are for or how many I need. For some reason I ordered two.

Anyways, I bet this is why my 5th gear doesn't properly engage.

[18Fiatsandcounting]

Could be, Steiny. From what I recall, you have 3 selector rods, one for 1st/2nd, one for 3rd/4th, and one for 5th/reverse. About midway on each of those selector rods are some indentations cut into the metal. You then have 3 balls (they look exactly like ball bearings) that are pushed into these detents by 3 springs, and those 3 springs are held in place by a metal cover (and gasket) on the side of the transmission, held on by two bolts.

When the transmission is shifted, the balls slide into those detents and hinder the shaft from slipping back out of gear. So yes, if some of your balls and springs are missing, this could make it easier for the transmission to pop out of gear.

-Bryan

[SteinOnkel]

So, here's the clarification on this according to the Fiat factory manual:

There's three springs and three detent "beans". The springs you can mix and match, the beans cannot. They are machined differently.

Seeing as we know this transmission has trouble properly engaging 5th gear, I decided to invest the cost of dinner on the town in a much more sensible thing: more parts.

Also ordered the 5th gear syncro, which I initially forgot. It'll take a week for all the stuff to get here, but it makes no sense putting known worn parts back together. We did start assembling the mainshaft yesterday with some head scratching. I think we missed a few spring washers. The drawings in the Haynes manual are useless and have a bunch of pieces missing and are full of mistakes.

Cheers
Steiny

[18Fiatsandcounting]

Sounds good Steiny. What I told you earlier very well could be in error, as I now recall those "beans" the last time I took apart my transmission which was in the late 1980s. However, (could be wrong here), my recollection is that the "beans" prevented the transmission from being inadvertently shifted into 2 gears at once. Kind of a lockout mechanism. My guess is that trying to shift the transmission into 2 gears at once (like if your shift mechanisms are damaged or misadjusted) would be a disaster, hence the need for the lockout pins (beans).

-Bryan

[SteinOnkel]

Yep.

So a few months ago my brother and I were driving around in the Fiat and it popped out of 5th on decel. He just calmly said "Yeah, there's springs in the shift rods and one of them is worn out." His intuition is spot-on 99% of the time when it comes to cars, so I'm pretty confident that replacing these springs will solve that issue. The beans are probably fine, but at $2.99 a piece? Fahggedaboutid.

The howling will be taken care of with the bearings.

And the synchros you may as well replace, even though it shifted fine...except for 4th.

All in all, chances are good this transmission will function like the day it rolled off the assembly line when we're done. I'm about $700 into it. Which is a lot of money, but what else are you going to spend it on right now?

Cheers
Steiny

[18Fiatsandcounting]

Worn bearings would definitely cause howling, and worn synchros usually cause a slight grinding of the gears as you shift from one to another. Sometime more than "slight" if the synchros are really worn. My experience with popping out of gear is that it's either not fully shifting into the gear to begin with, or bearings and such are so worn that things move around and it pops back out of gear when you get some loading (or de-loading) of the gears.

Anyway, you know all this. Good luck with it, and one of these days I want to see you drive up to my place in Livermore!

-Bryan

[SteinOnkel]

Ugh. So frustrating. Mr Fiat completely botched my order...still waiting on parts.

I'm also thoroughly confused about the 5th gear Synchro. According to all the vendors, that one is unique. According to what I have on the bench, it's exactly the same as 1-4th. Super strange.