Hey guys, I've got a 953 76Y that I've recently had some issues with. I blew a hose and while I had the belly pans off I thought I'd take a look around. I knew the rear main was leaking, but I had planned to just get to it when I had a chance as it hadn't been losing that much oil. But as I looked up I noticed a gap between the bell housing and the transmission. Then I noticed some of the bolts were loose/broke off. So obviously time to bring it to the shop and pull the motor. Ive got the motor out with the bell housing, but here's the issue. The top lip of the transmission is busted from having all the bolts break off and just have a few still holding. I was looking at the bolts and they are 7/16 bolts, mostly grade 5 from a hardware store. The only ones not broken were CAT grade 8 bolts. But looking at other 953 20z bell housings, they are supposed to be 3/8 bolts. So I'm guessing someone drilled and tapped these? Then just maybe didn't get them tight enough and they broke? Or maybe got them way too tight and broke them? They are broke off deep in the bellhousing, so I'm kinda leaning that way but I really don't know what to think. Anyone have any ideas on how they'd fix this?
Plenty of those 1U-3141 housings available used if you want to go down the road of replacing it.
That would not be an easy fix. You could have a go with nickel welding rods. To use any kind of brazing method would require taking the transmission apart and you really don't want to be doing that. Cold stitching could be a possibility. To be honest if it were me, once I had the broken bolts out of the bellhousing I would just put it back together with the one bolt missing. The way that particular assembly goes, the tension is on the bottom bolts and the top is in compression.
I thought about that, but wasn't sure if I really wanted to pull it off and see what was on the other side. Haha
So I was considering welding the broke off piece by pre-heating the cast and then slowly allowing it to cool. But wasn't sure if that could be done while still assembled without damaging anything? Then to the right of the broken piece you can see the other bolt hole is damaged too. For this one, I thought about using a short 1/4in thick strap like a washer. All the other bolt holes look good. I have access to another bell housing, but it's the regular 3/8 threads. So I'm leery to put 3/8 bolts in the 7/16 bolt holes on the transmission because there will be some play in the bolt holes on the transmission. So if I use the other bell housing, I'm thinking about having it drilled and tapped so I can use 7/16 bolts and fill up the hole. Or would it matter? I know the ring carries the majority of the weight that the bell housing sits on, and the bolts just keep it in place, but just want to be sure to fix it right.
If you're going to put any heat into it, you don't want to get it so hot that the paint flakes off internally. Along with the risk of making the job worse with distortion and cracking, I personally wouldn't bother. Bolts are designed to work by clamping the faces together so that friction stops things moving around, not in shear. I wouldn't have any problem using 3/8 bolts in 7/16 holes as long as you have decent hard washers under them. If it bothers you, you could get some little bushings made up. Removing that housing isn't impossible, but if you replace it you have to shim the end float on the input pinion to suit the new housing. It would be tricky to do with the tranny vertical.
Good point, I didn't think about paint being on the internal side. Thank you for your reply and the picture! I thought about the bushing idea too, I might end up going that route. Would you go back with grade 5 or grade 8? Also, do you think the most likely scenario is the bolts just backed out over time/ weren't torqued to spec and that's what caused them to break? That's kind of the way I'm leaning now, just hard to say for sure.
Grade 8 FTW, every time. As far as I'm concerned, the only thing that's going to leave you with a mess like this is someone in the past has made a balls-up of putting the bolts in.
That's what I was thinking too, going grade 8. So my plan right now is to use grade 8 3/8 cat bolts and try to get some bushings. Not real sure where to get bushings that won't be too long but I'll figure that out. Here's another thought, would you use some blue loctite then torque them? I was planning on running it for a few hours and re-torque them but I know how hard they are to get to so not sure if I'd get around to checking them all down the road.
No loctite IMO. Make sure the faces are clean and flat. I like to give them a rub with an oilstone to highlight any high spots,
The original Cat bolts shown in the Parts Manual are Grade 8. I don't think Cat even sell anything less than Grade 8.
Alright guys so I got the motor back in and have been running all year. I re-torqued the bolts after about 40hrs and they were all still tight. I've got a little over 500 hours on it since then. Only issue I have now is I have developed a hydraulic leak between the bell housing and transmission. I'm losing about a gallon of fluid after 12 hours of run time. My guess is the seal where the input shaft goes has came apart? I changed it while I was in there but when we were putting the motor back in, we were kind of rough getting it in. I can see a trail of fluid where it's pushing it out of the vent on the bell housing so I'm pretty sure that's where it's coming from. I really want to get this fixed but I've got a lot of work lined up. So my question is, can I continue to run it until winter or is there a chance I'm causing damage and need to pull it sooner rather than later?