Clutches

robsad

robsad

True Classic
List,
After trying to drive my 74 after a yearlong restoration, the clutch wouldnt disengage. After dropping the trans it looks like I have the wrong pressure plate. Keep in mind my 74 has a 1500 engine mated to the original 4 speed trans. The clutch MC and slave are all working as they should. The first pic is of a 74 45 MM plate that I was told wouldn't work. The second pic shows the PP that wont disengage. I can see why. What puzzles me is the first pic shows the springs pointing upward as I'm used to seeing. In the second pic the springs on the one on the car not only are recessed 5 mm below the top surface of the PP, they do not have an upward slant but are flat so that even with the clutch rod fully extended the release bearing was not touching the springs. I do have a lightened flywheel from MWB but I can't see why that would make a difference. I'm guessing that I should be using the earlier PP. Fiat changed the design of the PP in 8/74 and my car was built in 7/74. Can anyone add anything ? Thanks in advance.

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It's the flywheel that makes all the difference. There are two 1300 flywheels, the early and the late, and they have a different step between the friction surface and the surface the pressure plate mounts to. You need the pressure plate that is right for your flywheel.

(However, the thicker pressure plate may foul the early bell housing. Fiat changed the bell housing, flywheel, and pressure plate all together in the middle of a model year to fix a transmission oil leak problem - I'll see if I can dig up the service bulletin explaining this, Brad Artigue has a copy online somewhere that I've been meaning to upload to the wiki).

You have an MWB lightened flywheel? Ask Matt which pressure plate you need. Also look at the inside of you bell housing. Is the end of the transmission driven shaft closed off with a big pressed-in steel plug (like a giant Welch plug) or is it cast solid metal?
 
Also check the inside of your bellhousing. If there is a metal plug on the inside covering a hole in the casting for a shaft, it is designed for the tall pressure plate. If there is no plug, it requires the short pressure plate.
 
I ran into this problem a few months back when I bought a clutch and pressure plate from MWB. Despite my car being a 74, it required the short pressure plate. Matt found out that the change was made at engine number 2050998 in July/August 1974 for the 1975 model year. Turns out my engine number was 2087506, build date 6/74, and had the later "no plug" trans. I bought this car new with this transaxle and engine so it was not a matter of things getting swapped out. My hypothesis is that it may have had something to do with the delayed introduction of the X1/9 in California.

The last time I bought a clutch and pressure plate, there was no Internet. I went into the auto parts store with the old parts and got replacements that looked like the old parts without ever knowing there were tall and short pressure plates.
 
EricH said:
Here's that service letter: http://xwebforums.com/wiki/images/6/68/Tranny.pdf
Click to expand...

Eric,
I did go over this with Matt and I thought we had things correct. I looked at the MWB lightened flywheel and it has " 75 to 78 " on it which would make it the later one. I measured it and it is approx 28 MM while my original is approx 32 MM but the service bulletin says the newer flywheel should be thicker ? Maybe the lightening process would account for this ? I read the service bulletin They use the term "serial number". Is this the VIN number ? If so my VIN ends with 20112 but this would imply I should be using the shorter PP which I have installed but has a problem. Since I'm the original owner I know this is the original trans and bell housing. I'm thinking of using my original flywheel but now I'm not sure what I should use. I will check my bell housing to see which one I have. This is getting really confusing. HELP !!!
 
robsad said:
I measured it and it is approx 28 MM while my original is approx 32 MM but the service bulletin says the newer flywheel should be thicker
Click to expand...
I think that the relevant measurement is from the pressure surface to the surface that mates to the end of the crankshaft - but I'm not sure.

While you are investigating, could you check the deck height, the step between the surface the pressure plate bolts to and the surface the disk engages? Is it the same on both flywheels? I think, but again am not sure, that the deck height is greater on the early style flywheel.

I've been confused about this for a while. I have several 4-speed flywheels on the shelf, all identical in weight, deck height, and thickness, that I believe are the later style. All came from cars with VINs above 20000.

I have one flywheel that came from 11453, with a higher deck height (but I don't completely trust the deck height because I don't completely trust the folks who reground it). This one is in a car now so I can't measure/weigh it, but I do know that the clutch wouldn't disengage with the thin pressure plate so I had to drop the transmission and install the thicker plate. I paid no attention to the bell housing (didn't know that there was a difference) but had no fouling problem even after I installed the thicker plate.
 
I remember now that whatever PP I had previously, I had to adjust the clutch arm to almost the extreme travel of the adjusting nut just to get things to work. ( I threw the old one away or I would have measured it ) At the time I just figured it was supposed to be that way. I'm going to do what you did and install the tall PP I have and see how and if it works.
 
Not just differences with flywheels, there are differences in 4 speed transaxle.

"74 casing is a little different too, the area where the pinion bearing fits in the post 75 gearboxes is taller inside the bellhousing, thats why the clutch pressure plate (38mm tall and 45 mm tall) and flywheel (for the different heights of PP) are different, to clear this area (has a coreplug fitted) whereas the later cases don't have the coreplug , it's cast over in alloy, and the casing has less clearance."

-Steve C.
https://xwebforums.com/forum/index.php?threads/transmission-modification.10068/


Bernice
 
Hi Bernice,
Can you tell from this pic if this is an early or late bell housing ? Car was built in 7/74 , VIN ends in
20112. I have no idea what the soft plug is or where it is.

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robsad said:
I remember now that whatever PP I had previously, I had to adjust the clutch arm to almost the extreme travel of the adjusting nut just to get things to work. ( I threw the old one away or I would have measured it ) At the time I just figured it was supposed to be that way. I'm going to do what you did and install the tall PP I have and see how and if it works.
Click to expand...

I know from personal experience what happens if the stack height (flywheel/disc/PP) deviates even only a couple 2mm from intended. Not good.

I would not put it all back together until you confirm the flywheel is indeed the correct height (surface area to crank mating surface) is indeed correct for the setup.

Got pics of all the parts stacked? New & original flywheels, etc? Would be good to see reference pics seen from a side view - “end elevation” (?) - can’t recall the proper term...
 
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