NV3550 bellhousing to 4.0 engine block bolt sizes

IkariBattousai

IkariBattousai

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Pulled the NV3550 transmission from my 4.0L 2000 TJ and a few of the bolts were missing. Someone posted an image from some manual with a list of bolt sizes from the AX-15 transmission and assured me that the bolt sizes were the same. I bought those bolts and went to put the transmission back in and the bolts were absolutely NOT the same sizes.

Does anyone have a list of the bolt sizes that attach the bellhousing of the NV3550 to the 4.0L block? I'd like to get this thing running again this coming weekend.
 
IkariBattousai said:
Pulled the NV3550 transmission from my 4.0L 2000 TJ and a few of the bolts were missing. Someone posted an image from some manual with a list of bolt sizes from the AX-15 transmission and assured me that the bolt sizes were the same. I bought those bolts and went to put the transmission back in and the bolts were absolutely NOT the same sizes.

Does anyone have a list of the bolt sizes that attach the bellhousing of the NV3550 to the 4.0L block? I'd like to get this thing running again this coming weekend.
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Something is odd since both the AX-15 and NV 3550 use the same bellhousing. Likely the issue is the wrong bolts were used by someone doing a swap or a clutch job.
 
IkariBattousai said:
I bought all new bolts based on what I saw on the list and they did not fit the holes at all.
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Can you share the list that led you to the wrong bolts? The two transmissions use the same bellhousing so something is not right with whatever was given to you. I'm looking at the parts manuals now but it would be handy to know what you bought that didn't work.

As Blaine said, different bolts in all the locations (each size is used in pairs), so if you bought one bolt x6 or so, that will not be right. Need to know what you bought, what led you there, and Blaine told you what you really need.
 
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IkariBattousai said:
I bought all new bolts based on what I saw on the list and they did not fit the holes at all.
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Not sure what that means. The top pair are 3/8-16 by the length which I can get later and the two on the sides are 7/16-14 by the length which I can also get later today.

The motor plate is held onto the upper parts with some 3/8" coarse thread sheet metal screws and the lower two larger holes are 1/2" bolts that just through bolt.
 
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The correct bolts are 7/16"-14 x 3" long Grade 5 flange head for the two on the sides.
The two at the top are 3/8"-16 x 1 3/4" long E-torx flange head. If you substitute grade 8, do so with a flange head if possible. Reason being is if you run a regular hex head cap screw and put a washer on it, you are losing some thread engagement. (likely won't be an issue though, just me being pedantic)
 
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mrblaine said:
The correct bolts are 7/16"-14 x 3" long Grade 5 flange head for the two on the sides.
The two at the top are 3/8"-16 x 1 3/4" long E-torx flange head. If you substitute grade 8, do so with a flange head if possible. Reason being is if you run a regular hex head cap screw and put a washer on it, you are losing some thread engagement. (likely won't be an issue though, just me being pedantic)
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Appreciate it! Thanks!
 
Yeah no clue what's up with that diagram posted but it's way wrong. I couldn't even find an equivalent of that page in the 2000 manual I was looking in. Who knows, looks like you're straightened out now which is what matters.
 
Looking at the codes in the parts picture all those metric bolts are for the 2.5.
 
Lou said:
i am going to guess the 2.4 engine uses metric threads into the block.
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Weirdly enough that page was from prior to 2000, indicating it was for 4.0/2.5. It's showing 2.5 in the top flat-top bellhousing and AX15 below.

I'm sure you're probably right about the 2.4.
 
machoheadgames said:
Weirdly enough that page was from prior to 2000, indicating it was for 4.0/2.5. It's showing 2.5 in the top flat-top bellhousing and AX15 below.

I'm sure you're probably right about the 2.4.
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I edited my response after looking further and seeing the engine code says it’s for a 2.5. I’m a little shocked the 2.5 is metric.
 
Lou said:
I edited my response after looking further and seeing the engine code says it’s for a 2.5. I’m a little shocked the 2.5 is metric.
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I am shocked too, although it could be due to the fact that the 2.5L originally derived from the GM iron duke engine in the CJ days, rather than an AMC design like the 4.0.
 
I’m gonna ask why might amount to a dumb question, but I’m ok being educated.

When OP said the bolts were absolutely not the right size, I assumed he meant that they would not thread in. But everybody was surprised by that because the two transmissions use the same bellhousing. But the bellhousing isn’t the the threaded part, the block is. So why is it relevant that they use the same bellhousing? Should we not instead be surprised that the bolts fit because we all have the same engine block, rather than because we all have the same bellhousing?

Or I am missing something.

Unless he meant that the bolts wouldn’t even slide through the bellhousing holes….an M12 is possibly too big to fit through a 7/16” (11.11mm) hole, but we didn’t know he used M12 until later in the thread.

Just curious is all. Obviously it doesn’t actually matter at this point.
 
hear said:
I’m gonna ask why might amount to a dumb question, but I’m ok being educated.

When OP said the bolts were absolutely not the right size, I assumed he meant that they would not thread in. But everybody was surprised by that because the two transmissions use the same bellhousing. But the bellhousing isn’t the the threaded part, the block is. So why is it relevant that they use the same bellhousing? Should we not instead be surprised that the bolts fit because we all have the same engine block, rather than because we all have the same bellhousing?

Or I am missing something.

Unless he meant that the bolts wouldn’t even slide through the bellhousing holes….an M12 is possibly too big to fit through a 7/16” (11.11mm) hole, but we didn’t know he used M12 until later in the thread.

Just curious is all. Obviously it doesn’t actually matter at this point.
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You missed it. OP has NV3550 and picked bolts from a diagram that lists the AX-15. So, he thought that might be a problem. It’s not.
 
Mike_H said:
You missed it. OP has NV3550 and picked bolts from a diagram that lists the AX-15. So, he thought that might be a problem. It’s not.
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No, I saw that. And he said they didn't fit, so it in fact was a problem. If somebody tells me a bolt doesn't fit, I guess I assume that the size is close, but the threads are wrong. Everybody here assumed that the bolt wouldn't fit into the hole, which I found interesting is all. OR the bell housing is threaded on the manual, which would be surprising but would explain (to me, anyway) why everybody focused on the bell housing rather than the block.
 
hear said:
No, I saw that. And he said they didn't fit, so it in fact was a problem. If somebody tells me a bolt doesn't fit, I guess I assume that the size is close, but the threads are wrong. Everybody here assumed that the bolt wouldn't fit into the hole, which I found interesting is all. OR the bell housing is threaded on the manual, which would be surprising but would explain (to me, anyway) why everybody focused on the bell housing rather than the block.
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As far as I can track, he followed the parts manual posted in a different thread. The parts manual told him to use a bunch of M12s. The 4.0 doesn’t have any M12s for bellhousing bolts. The not fitting part was the threads.

The bellhousing is not threaded at all except for the 3 spots (10:00, 2:00, 6:00), which is how the cover plate sandwiched between the flywheel and motor secures.

AX15 and NV3550 have the same bellhousing. The parts manual did show in the cartoon a pic of the 4 cyl bellhousing, with the flat top. That is from the GM Iron duke pattern that the 2.5 derived from from its early days. However, the misleading part is that the parts manual listed M12 bolts and called out both EP0 and ER0 (2.5 and 4.0) as using them, but that’s definitely not true because the 4.0 doesn’t have M12 threads at the bellhousing bolt bosses. The 2.5L is still up in the air, I don’t know the size of the 2.5L bellhousing bolts.
 
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