D2 Traxcavator differences of 5J & 5U

Both units have the 5 roller long track frames. On the unit I'm looking at getting shipped the dozer blade was welded to the lower bucket arms & the Cyl is mounted about even w/ top of the radiator on the original framework. Do you think the bubbles in rad. could be a bad head gasket or a leaky injector cup ?
Are these bad about cracking heads?
The rough 5U is pretty much complete (gonna look at it again tomorrow) has electric start pony on it also. Everything is locked up on it though. Original style track pads are all beat up. Bent & broken. Is there major differences between the 5J & 5U series other than motor?
Roby

Well from the # of views & lack of answers I guess I'm on my own on this. The trailer is loaded w/ a #7 autopatrol serial # 6D7, a 5J D2 running per description above and a 3J D2 for parts. I have also made the deal for the 5U D2 w/ T2 traxcavator. I was wrong it didn't have electric pony start. I looked at the 5U and it appears the T2 just bolts to the 5 roller track frame. I'm hoping I can find some manuals on this.
Roby Whitehead

Re the loader part of 'em, I can't address that end of it but as you noticed, there's a difference in engines between the J and U models. Also, there's a difference between the tranny lids. The J is a one piece unit while the U is a two piece. Also, the input shaft into the tranny is in one piece in the J while the U has a split coupling so the clutch can be removed w/o splitting the tractor. From memory, it seems the U has a longer clutch housing to accommodate the coupling on the tranny input shaft. It seems (again from memory) that there are a few internal differences that reflect the upgrades Cat made to 'em over the years.

I haven't been around a D2 of either model for a few years but like I said, that's what I remember about 'em.

As long as no one else is posting I will throw in my $0.02 worth. I have several D2's including a 5J with a T2 Trackson. As far as I know everything from the 5U should swap right over to the 5J. The engine is completely different but from the engine back all the castings are pretty much the same. There are some internal differences in the rear pinion and finals.

I like the D3400 in the J series. They are a good engine. I have one that is missing and bubbling on 2 cylinders. I plan to start with a leakdown test to see if I can find where the compression is going. I have blown many precups on the D311 but this is the first problem I have had with the D3400.

Congratulations on finding a Cat with a good undercarriage, that is a good place to start.

Thank you, I'll take all the .02 cents I can get. It's gonna take awhile to get back to even... Let me know how you plan on finding the problem (leakdown test). Best I can tell it's not missing on any cylinders. It also looks like there won't be a problem with clearance for the air breather intake above the hood to the underside of the framework for the T2 gearbox and winch. I will post some more pics.

Well I got the 3 units home now. Little bit of a fiasco but it's done. Next thing will be some kind of a loading dock. The d2 pony fired instantly. Need to adjust / work on starter pinion control as I have to hold it engaged during cranking ritual. Followed directions and she fired up easy. Purrs like a kitten. But after a few minutes starts pushing water out top of the radiator (more than just bubbles). I'm going to search through previous threads here as I'm sure this has been addressed before. Happy with deal though. # 7 autopatrol fired up on 3rd pull.

Well read through previous threads and have come to the conclusion that I am going to start with flushing the cooling system. He told me it has been parked in the barn for 3 - 4 years with no coolant in it. I'm looking at the tubes from the top through filler hole and see rust , etc in them. Think I'll drain & flush run some cleaner through and flush again. I'll see what I can get out of it. If that doesn't work then I'll look @ injector cups, head gasket, cracked head

Hi Texasbest,
blowback can also be caused by not bleeding air from a bleed valve on the top cover of the pony as per the pic below.
The trapped air expands when hot and some of it blows back out the filler neck.
Hope this helps.
Cheers,
Eddie B.