Transmission issues

Bargain Box

Bargain Box

Stand back, I built this s*** myself...
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Joined
Oct 13, 2021
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476
Location
Raleigh, NC
I have had some strange rattling sounds coming from the bell housing area for a couple of weeks. They started to get noticably worse and I started to have issues with gear engagement in first, second, and third. It was hard to shift to those gears but no grinding. Less than 1k miles ago I changed the clutch and replaced the transmission fluid with MT90. The fluid did not look like this going in and I don't remember this much shaft play. There is a good bit of fine metal on the magnet. The oil looks silvery if I stir it with my finger. Flash light looks sparkly in it. How bad is it?
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The metal on the plug isn't overly alarming.

The fluid doesn't look good for only being 1k miles old.

The input bearing is definitely toast. Hope that's all it is.
 
freedom_in_4low said:
The metal on the plug isn't overly alarming.

The fluid doesn't look good for only being 1k miles old.

The input bearing is definitely toast. Hope that's all it is.
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With that level of metal do think the rest is ok? Did I just cook my fluid because of the heat from the bearing?
 
Bargain Box said:
With that level of metal do think the rest is ok? Did I just cook my fluid because of the heat from the bearing?
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I'm not sure the oil is cooked so much as the bearing is in the oil now.

If it's not your daily driver I'd be tempted to just change the bearing and oil and throw it back in, but my concern would be whether the hard shifting was related to damaged synchros due to the metal in the oil.

It's also a bit odd that it ate itself in 1k miles right after a clutch job. Is the pilot bearing present and in good condition, and did anything happen during the work that could have deformed the bellhousing?
 
freedom_in_4low said:
I'm not sure the oil is cooked so much as the bearing is in the oil now.

If it's not your daily driver I'd be tempted to just change the bearing and oil and throw it back in, but my concern would be whether the hard shifting was related to damaged synchros due to the metal in the oil.

It's also a bit odd that it ate itself in 1k miles right after a clutch job. Is the pilot bearing present and in good condition, and did anything happen during the work that could have deformed the bellhousing?
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The pilot bearing is ok. No visible damage and spins easily and smoothly. I will admit that I don't recall how much play the input had when it was out before but I feel like I would have been concerned if it was this much.
 
Follow up note, on the bench the transmission shifts easily into each gear. The input shaft seems difficult to turn with zero free spin in gear or in neutral. Seems like it should spin a little easier than it does.
 
Bargain Box said:
The pilot bearing is ok. No visible damage and spins easily and smoothly. I will admit that I don't recall how much play the input had when it was out before but I feel like I would have been concerned if it was this much.
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It's an easy thing to overlook while you're focused on the clutch job at hand. Hell, I just put a new Ax15 in mine and I put 50 miles on it with the fill plug only finger tight.

I only asked about the bellhousing because I once had a full size Bronco that killed flexplates. They'd crack around the bolts going into the crankshaft. Some sneaky interrogation techniques and I got the previous owner to admit to dropping the transmission off a workbench during a rebuild. Pretty sure it tweaked the bellhousing so the torque converter wasn't perfectly aligned with the crankshaft.

Bellhousing alignment is a common killer of input bearings, but the AX15 doesn't have a good way to check it and if your bearing survived all these years then it should be safe to assume that's not the problem.
 
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Anyone familiar with Zumbrota transmissions? They are sold by summit, lift kits for less, etc. They seem to have a good rep. The vendor I found on eBay out of Indiana is out of stock and no none locally wants to rebuild mine. Any input is appreciated, no pun intended.
 
Would appreciate any input on transmission brands or if I should just continue running what I have until I finish it off.
 
If it's an ax15, I'd look for a good used one or rebuild it. If it's an NV3550, if replace it with an AX15. If it's an NSG, I'd also replace it with an ax15.

The AX15 should be relatively easy to rebuild. No special fixtures involved and it's still being produced, so you can get the parts.
 
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Mike_H said:
If it's an ax15, I'd look for a good used one or rebuild it. If it's an NV3550, if replace it with an AX15. If it's an NSG, I'd also replace it with an ax15
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It's an AX-15 but I'm not confident with the rebuilding it myself part.
 
Bargain Box said:
It's an AX-15 but I'm not confident with the rebuilding it myself part.
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Find a decent used one... There should be plenty with as many jeeps as they made with that 5 speed. Swap it in and then rebuild your current one. Take your time, read the service manual, and it will be good as new.

Edit:. For an extra 400 ish dollars over the zumbrota, you can buy a brand new one from advance adapters

https://www.advanceadapters.com/transmission-ax15-4wd-new-unit-750-tip-boxed
 
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Mike_H said:
Find a decent used one... There should be plenty with as many jeeps as they made with that 5 speed. Swap it in and then rebuild your current one. Take your time, read the service manual, and it will be good as new.

Edit:. For an extra 400 ish dollars over the zumbrota, you can buy a brand new one from advance adapters

https://www.advanceadapters.com/transmission-ax15-4wd-new-unit-750-tip-boxed
Click to expand...

I'm finding reman units for around 1k so that is a big jump in price but it is new. Also, I'm not finding a lot of used units for a reasonable price.
 
Jeep put the wrong fluid recommendation in the owners manual leading to some ax15s getting gl5 that damaged synchros. My first one was crunchy into 3rd gear. For that reason I'd hesitate on a used one.

I just swapped my nsg370 for an Ax15 and have zero regrets about ponying up the extra for a brand new one. There's not much I loathe more than repeating the same work twice.
 
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Any suggestions on rebuild kits? I'm seeing a lot brands out there with wide ranges in price. No one seems to list their bearing brands in the kit either. I've decided to rebuild this so any help is appreciated.
 
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