Sending units on transmission, what do they do?

[Texsardo]

I bought this transmission from a forum member. My tranny doesn't have 1st gear, won't go into gear period, stopped or running. So the forum member said he had one out of a later model spider that would fit my 1978. He did tell me one bolt hole was damaged.
Tranny arrived late summer and I only had time to open package and see if any major damage as box was pretty badly banged up. So it sat until a week ago. I found a mechanic that has worked on Fiats like this. His father actually had a repair shop specializing in Fiat. Anyway he agreed to swap the two out for me. In the meantime I ordered a gasket and seal set from Auto Ricambi. For 5 speed transmission.
Problems have arisen. I was going to replace gaskets in this replacement transmission but the new front seal looks to be slightly smaller than the one in replacement. On the back where the drive shaft connects there is a small rubber (??seal??) that fits immediately behind the spacer or ?? with the XXXXs. The rubber was in three pieces and pretty mangled. Don't know if I can find a replacement. Also there are 2 plugs, sending units that had 2 wires each (both plugs pretty much destroyed though, wires fell off when I unboxed it. Does anyone know what they are for?? Do I need them for a 1978. I have a replacement for the ruined back up light indicator so that one is OK, just don't know what other 2 are for or if needed. I am now thinking of asking mechanic to use my transmission but replace any worn or missing, broken parts using the replacement transmission. All gears look good to me. I have included photos. Any ideas or advice??
This is on top of transmission.

This is a close up of plug, sending unit on top.

Another plug/sending unit on passenger side of transmisssion.

Close up of unit on side.

Rubber seal was behind the XXX spacer and under the black ring keeping spring in line.

Bolt is on top of transmission, repairable or leave alone if I put this tranny in the car.

Gears in replacement transmission.

Thanks for any advice.
Texsardo

[76was124]

This will help http://www.fiatspider.com/f08/viewtopic ... up#p150204

[Texsardo]

Thanks, that answers the question about sensor on passenger side. Still trying to figure out what the first sending unit on top did. When I removed it, it had a short plunger rod, about half the length of the back up sensor on the back of the tranny. Wish I could remember what year spider it came from as that would provide some clues.
Texsardo

[wizard124]

That black rubber seal: http://www.midwest-bayless.com/storefro ... =284733795

I don't think you know which way to go until you open up and examine your current tranny. The 1st gear shift issue may be something as minor as a shift fork. Depending on the shop labor rate, buying new parts may be cheaper than tearing into #2 tranny.

I rebuilt my transmission because of a 4th gear syncro failure. http://fiatspider.com/f08/viewtopic.php?f=9&t=26031 I also have a second transmission, but of unknown working condition. I bought new bearings and syncros, replaced after tear down, cleaning and inspection. Rather than dis-assemble #2.

If you are confident in the running condition of #2, then it may make sense to use that one. Drill out that bolt hole, swap the sender over, buy a couple of seals. Again, the decision is based on what you discover.

Personally, I would tear down and inspect whichever tranny I planned to use. Not wanting to have to do the R&R twice.

[Texsardo]

Thanks wizard. You nailed what I was thinking on the head. I can take #2 transmission apart but I wouldn't know if it was better than the transmission in the car. I wish I could figure out if the gears, forks and springs worked on #2. Looks good inside, no debris when pan cam off. No fine metal powder slop. No noticeable wear. Just wonder how to check it before tearing it apart. With no shifter attached, I can't check if it would go into each gear. Frustrating.
Texsardo

[redcars]

The only 2 ways that I know of to see if a transmission is good Is to either put it in a car and drive it or take it apart. The parts that you need to see and inspect can only be done so when the transmission is apart. You can tell if a transmission is in really bad shape by removing the bottom cover, but you can not tell if it is good by doing so. You do not know when the oil was changed or the bottom plate was remove and cleaned.

[76was124]

Thanks, that answers the question about sensor on passenger side. Still trying to figure out what the first sending unit on top did. When I removed it, it had a short plunger rod, about half the length of the back up sensor on the back of the tranny. Wish I could remember what year spider it came from as that would provide some clues.
Texsardo

I believe the one with the plunger is the reverse/back up light switch, the other is the 3-4 gear idle switch also mentioned in the same thread previously posted.

[Texsardo]

I thought the plunger on the back of this transmission was like my 78. It also has a plunger in the back, exactly like and in same spot as the back up plunger in the 78. So I don't think that plunger on top is for reverse. But I am still trying to figure it out. I am really kicking myself for not getting the year from the seller. I am assuming it is a 1980 or later. So I have decided that if I have to take apart one of the transmissions, I might as well do mine that's in the car and when I figure what this transmission is that I bought from a forum member that said it worked while in the car and should fit mine as all 5 speeds are alike, sell this one. As I said. It looks great inside but I won't be taking it apart. It will put me a month behind in the schedule as I will have to inspect everything I take out of mine and hope I can put it all back together again. But lesson learned. No more nickel and dining. If it is defective replace with new or rebuilt. No more should be or might be from fellow forum members.
Thanks
Texsardo

[76was124]

Ok, I think I understand your question now. You have three sensors (pictures calls them plugs in some places). I have an '81 but it's in storage for the winter. When I get a chance I'll check, but I am pretty sure I only have two sensors and am only using the back-up sensor switch.

Just out of curiosity, how many actual plugs(not sensors) do you see on the passenger side of the transmission? There should be two, one is the trans oil fill plug, the other I am not sure of its purpose, but Its not a sensor. Could that be what you are seeing?

[Texsardo]

76was 124, in the photos above it is easy to see. It is a plunger identical to the plunger/sensor on the back of transmission that is the back up/reverse plunger/sensor. Only the plunger on top in photo #2 has a plunger rod half the length as the one in back. I just cant find out what it was used for. I have the same " plugs" on the passenger side as other transmissions. The only difference is a sensor(that you can see in above photos) that someone said had something to do with shifting between higher gears. These sensors/plunger or whatever, had 2wires at one time.. but they had been smashed and broken. Looks like this transmission had been dropped and rolled around on the floor at one time.
But that is OK as I am not going to use this transmission. It was bought with knowledge that it had worked before being pulled and that it had 1 broken/smashed bolt hole on top to bell housing. I am sure it is a good tranny but with these odd sensors shown in photos above I don't know if it would function properly in my78'. So I will have mechanic pull my old transmission, try to figure out why first gear doesn't work and then I will get any parts needed and using the gasket set from Auto Ricambi that I bought, repair and put it back in.
Texsardo

[Texsardo]

OK, still looking for someone to tell me what that plunger sending unit on top of transmission (see first and second photos above), it is just like the back up unit on back of transmission so l KNOW it is not the back up sending unit.
Also new question, how to I get the XXX marked ring on the back transmission shaft.shaft off? Do I need a puller, I don't see how it comes off. I think it is in 5th photo above. Keeps the spring and rubber washer in place.
Help please..........
Texsardo

[131]

OK, still looking for someone to tell me what that plunger sending unit on top of transmission

It's been about 25 years since I worked on 124s, but if memory is correct, the top switch is engaged when 5th gear is selected. You could easily confirm with a multimeter. There's a circlip on the end of the shaft that has to come off before the X marked ring can come off.

[Texsardo]

Thanks 131, the circlip I had already removed. Just can,t get that darned XXX ring off. O well guess I will have to buy a puller.
Especially thanks for info on that sending unit. That means I won't need to worry about it if I decide to use this transmission.