What to do while changing rear main

79Vette

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My M1009 leaks slowly from the rear main seal, and I want to fix it. I had a 350 SBC with a 2 piece rear main do the same thing, and I ignored it for 10k miles until it suddenly spat all the oil out on the road. So I'm trying to not make the same mistake with the 6.2 in my CUCV.

I want to do oil cooler lines and the rear main together during my next oil change. Is there anything else I should do while the pan is off, like maybe the oil pump?

This is a good running truck with unknown mileage. I hear a lot of people say to change the harmonic balancer and timing chain. My balancer looks fine and it seems to run fine (no obvious timing problems), but should I do them anyway? I would probably change the front crankshaft seal, water pump, timing chain and harmonic balancer together if I am going to take it all apart. Or should I just do the rear main now and wait for the water pump to go out before I start messing with the front of the engine?
 

chevymike

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I would HIGHLY recommend replacing your balancer, since these fail not just from miles but due to age. Many times you cannot see an issue until you have it off.

Here was mine, that I just replaced, that had less than 15,000 miles but is the original '84 unit. See the area in the blue circle? That is the rubber just starting to fail and squeeze out. This never would have been seen if I had not pulled the balancer. Either put on an AC Delco unit (they sell on Amazon) or a Fluidampr unit (which is what I did). Replacing is cheap insurance against the possible broken crankshaft.

0105201129_HDR_LI.jpg
 

79Vette

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At the point I have the oil pan and balancer off, is it worth pulling the front cover and checking the timing chain for wear? Or is that a bunch of unnecessary work on an engine that seems to run ok?
 

cucvrus

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In my opinion. If the rear main seal is leaking change it and the front main seal. I have had the same CUCV vehicles for years. I live by if it ain't broke, don't fix it.
What's the meaning of the phrase 'If it ain't broke, don't fix it'?
If something is working adequately well, leave it alone.
What's the origin of the phrase 'If it ain't broke, don't fix it'?
Hand axe
Humans seem to have the urge to improve things. Prehistoric hand-axes were made by repeatedly chipping small flakes off pebbles of flint with other hard objects. Million-year-old examples of these have been found that give the impression of being ruined by being chipped just one time too many. That pang of regret we have probably all felt after spoiling something by adding that unnecessary final touch was first faced by Ugg in his cave.
If it ain't broke, don't fix it
The thought may be Stone Age but the phrase 'if it ain't broke don't fix it', which sounds as though it might come from the Roosevelt or Truman era, is more recent than that. This one is widely attributed to T. Bert (Thomas Bertram) Lance, the Director of the Office of Management and Budget in Jimmy Carter's 1977 administration. He was quoted in the newsletter of the US Chamber of Commerce, Nation's Business, May 1977:
Bert Lance believes he can save Uncle Sam billions if he can get the government to adopt a simple motto: "If it ain't broke, don't fix it." He explains: "That's the trouble with government: Fixing things that aren't broken and not fixing things that are broken."
So KISS also comes to mind. Keep It Simple Stupid.
Maintain the vehicle and repair as needed. If it leaks fix the leak. The balancer. I have ask respectable engine builders and showed them a few that were on the CUCV's when I had them out. He always says. Put it back on unless you have extra money to spend. if it is straight and tight it will last a long time. I became a believer after replacing everything and thinking I improved things. I just made things different. These old irons like to be coddled as much as a wild cat. Leave it alone and fix only what needs fixed. And fix that well. Clean and paint as you go. If I pull the engine I replace the water pump as a precaution. never just changed one because I wanted to spend money. Do as you wish. I have a few balancers I removed from HMMWV engines that were scrapped just to change them. That is the government. they have deep pockets. Good Luck. Report Back. Stay the Course. Be Safe. And the government changed the entire engine and scrapped it just because they can.
 

79Vette

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In my opinion. If the rear main seal is leaking change it and the front main seal. I have had the same CUCV vehicles for years. I live by if it ain't broke, don't fix it
So you would do the rear main (which is leaking now), and pull the timing cover to do the front main even though it does not currently leak (might be getting to the end of its life)? Or leave it alone because it isn't currently broke?

And you recommend reusing the water pump and timing set if they look ok? I can afford a new balancer and will probably replace it like others have suggested if I have to pull it off to get to the front main seal. Maybe that's crazy, but I've heard enough horror stories thar the cost is worth the piece of mind to me. Maybe it's a waste of money, I dunno.

I can turn a wrench ok, but am new to diesel motors and respect your experience. Thanks for your help
 

chevymike

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If you remove the balancer, replace the seal. That is the timing cover/balancer seal and that can be swapped without removing the cover. Use a seal puller to remove and I used my balancer installer to install, using a piece of plastic tubing and metal plate with a hole drilled in it. Oh, FYI, the balancer bolt thread is 16x1.5mm so make sure you have an installer that will work with that. Also, that bolt needs to be tightened to 200 ft. lbs. Just did all of this over the last couple weeks.

Here is how I put in the new seal.

0112201016_HDR.jpg
 

cucvrus

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So you would do the rear main (which is leaking now), and pull the timing cover to do the front main even though it does not currently leak (might be getting to the end of its life)? Or leave it alone because it isn't currently broke?

And you recommend reusing the water pump and timing set if they look ok? I can afford a new balancer and will probably replace it like others have suggested if I have to pull it off to get to the front main seal. Maybe that's crazy, but I've heard enough horror stories thar the cost is worth the piece of mind to me. Maybe it's a waste of money, I dunno.

I can turn a wrench ok, but am new to diesel motors and respect your experience. Thanks for your help
Then No I would not disturb the front seal. It is easy enough to replace if it does leak, And as mentioned it can be changed without pulling the timing cover. Do as you wish. I wanted to just let you know that it is better to let things work than tear into them to fix things that are not broken. That is my point. Rear main seal and an oil pan gasket. Back together in a few hours and ready to go. All is well. Something else will come up again. It's a 35 year old vehicle. it is bound to have issues on occasion. Good Luck.
 

79Vette

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Sounds good to me. Thanks everyone for your replies.

I'll hook up a mechanical oil pressure gauge and see how it looks, and do the rear main and pan gasket this weekend. If the oil pressure seems low I'll do the oil pump while I'm in there, otherwise I'll leave it alone. I'll change the balancer soon, but not now. It works, so I'll let it keep working until I get another free afternoon.

Will post back with an update when I am done. Thanks again.
 

Sharecropper

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Sounds good to me. Thanks everyone for your replies.

I'll hook up a mechanical oil pressure gauge and see how it looks, and do the rear main and pan gasket this weekend. If the oil pressure seems low I'll do the oil pump while I'm in there, otherwise I'll leave it alone. I'll change the balancer soon, but not now. It works, so I'll let it keep working until I get another free afternoon.

Will post back with an update when I am done. Thanks again.
Just so you will know, oil pressure is the measurement of oil resistance throughout the system, and not necessarily an indication of the efficiency of an oil pump. If your bearing surfaces are worn, the gaps between the moving parts will be larger and therefore allow more oil to move more freely through the gaps, consequently lowering the "oil pressure". In my 50 years of fooling with these things, I cannot recall ever having to replace an oil pump. I guess it may be due to the fact that there is oil moving through the pump at all times for constant lubrication of the pump gears. If it were mine, I would replace the rear seal and pan gasket like Rick recommended and drive the thing. If it ain't broke, well, you know the rest of the saying.

Hope this helps.
 

cucvrus

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Thank you. I would not replace the oil pump either. Most times I work on paying customers vehicles and they want them out on the road running and the less cost that is involved in the repairs the happier they are. When you open up engines you could just go wild and replace everything. But in a case of a leaking rear main seal I quote the parts and labor involved. Anything I find after that is extra and I will recommend it be replaced and most times the owner agrees. But to keep things simple and on budget I do the agreed repairs and notate other things I see even if the owner opts not to do the repairs at that time. Good Luck. I think you have this nailed and will be back on the road in less time if you plan the work and work the plan. Be Safe. Report back.
 

cucvrus

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I remembered I had pictures of changing the rear main seal in terminus M1009. I hope this helps. I done a lot of work on Terminus m1009 and I used it very hard off road. I tested it many times over. Very few failures.

 

79Vette

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So I finally changed the rear main, and I messed something up. Before it was leaking a drop or two after a long drive, but now I have a major dripping leak from the back of the bellhousing after only running the engine for a couple minutes. I followed the directions per the -34 TM, but clearly messed something up. Pics are after running for about 5 min in the driveway.

I was careful to use a little plastic "shoehorn" to install the seal halves so I dont think I cut the bead on the seal, I am pretty sure I installed it in the correct orientation (as marked "Outside", and I offset the ends of the seal from the seam between the block and bearing cap.

I did this last year on my 82 gas 350 blazer with no problems, but apparently I screwed up something on this one. I need to do this job again apparently, so if anyone has any ideas on what I could have done wrong I would appreciate any insights.

I did notice the crank had a 2 small grooves worn in it from where the old seal was rubbing. Is there any way changing the seal with a new one could cause it to leak there? Does anyone make an "offset" seal that would touch the crank in a slightly different place than the original one?
 

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cucvrus

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Not sure where you went wrong. I changed many and have been successful thus far. I use the Permatex Right Stuff in addition to the gaskets and the seal. I put a bead at all 4 corners. Are you sure you don't have valley leakage, valve covers, or vacuum pump leakage. I have seen this on several CUCV's. Look closely and locate the leak before tearing into it. Make sure the seal or pan are still leaking. Double check everything. Good Luck. Be Safe.
 

79Vette

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The leak went from fairly small to very large when I put it back together, so I'm thinking it's gotta be something I messed up.

I also use permatex Right Stuff. Best sealer out there. Wheich 4 corners did you use it on?
 

cucvrus

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The front corners where the pan meets the timing cover and the rear edges where the pan meets the main bearing cap and the rubber seal goes on. I put a generous bead on all 4 areas. I hope that helps. Unlike the other sealants The Right Stuff does not peel and get all jammed up inside. It adheres and stays where you put it. I don't even bother with RTV sealants anymore. Good Luck. Be Safe. https://www.steelsoldiers.com/threads/terminus-m1009.144523/page-10 I attached this for your reference.
 
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