Diagnosis and Repair of Your Imperial's Rear Main Seal


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Question from Roger (318):

Has any one in club replaced rear main seal, is dropping pan very difficult and is there any tips to accomplish this task.


From Brad:

Try a bottle of CD2 and drive it for a couple hundred miles before attempting this task. I was dreading this job on my Ramcharger (and the pan removal was MUCH easier than yours will be) and tried the CD2 first. Within a week, no more leak. It's been over 3 months now...............still dry. My tip........pay someone else to do it! 

Question from Roger (318):

My 81 "Beauty" has developed a rear main seal leak. I maintain my car in near perfect condition. The leak is more than I can tolerate. I have been told that the seal is a two part seal and therefore very difficult, if not impossible to replace. I also have Bob Baker's experience of having a Chrysler dealer fix a similar leak. Does anyone have information or suggestions?


From DB Kemper:

A two piece seal is possible to fix according to the service manual. If you have this book it tells you how to go about it.......not an easy task but doable. The worst part is getting the transmission out and the torque converter. I helped a friend do one.....I cheated on my 81 and put in a new engine!

From Bill:

The way I have been able to accomplish the task successfully is by dropping the pan and then removing the rear main bearing cap and then loosening all the other mains to let the crank hang as low as possible. You then have to use a fine very stiff wire to move the old seal out of the grove in the block, you will work the new one in the same way. Make sure you lube everything generously when reinstalling. You should have more than one seal available in case you blow it. The manual is needed and follow the instructions. Obviously this is not the fastest way or the preferred way at a dealer, but if you do not want to take the whole thing out or totally drop the bottom of the motor this is the only way. Have lots of aspirin around. If you get flustered walk away and come back. Working on your back like this is a real bummer.

Follow-up question from Carl:

I still have a question about the seal itself. Is it one or two pieces? I understand that a two piece seal is very difficult to seat so that it no longer leaks. So difficult, that the mechanics I have been talking to decline the job because they do not believe they will have a successful outcome. If it is a two piece seal do you have suggestions for mating the two ends in a way that will form a solid seal.

Reply from Bill:

Unfortunately it is a two piece seal, but so are 80% of the rest of the engines on the road. Use at the bottom of each RTV sealant, a dab at the meeting points is what you want. Yes, success is a problem, but achievable. You may know I am also into Studebakers, and they have the worst rear main seals around. But you can do the job and make it if not 100% dry at least 97% dry. Its just such a pain job, nobody wants to do it. There is so much work to replace this relatively inexpensive part. If I was a mechanic I would think twice about guarantee for this type of job. The last one I had done because I did not have time was about 9 years ago and cost me $250.00. But I also learned something, make sure you check the pan before you reinstall, because they can be warped, thus making the seal useless on reinstallation. This can happen for a number of reasons. Hitting something, a floor jack, or torqueing it up improperly. Again, not a job I like but it can be done very effectively, just make sure its right before you button it up.

Reply from Kne:

One or two "tricks" that may make the seal seal better. If you can get the two halves of the seal to mate a little bit off from the parting line of the main cap and block that will help. What I mean is keep the parting line between the cap and block and the parting line of the two halves of the seal meet a bit off from each other by pushing on one end of the upper seal half when it is in the block. Hope someone can explain this better than I. Also, make sure the seal is lubed with some grease when you bolt it up. Sometimes people put it in dry, and like most seals it will "wear out" in those first few moments of running dry. Have to have some first-start-up protection to prevent this. And of course put a SMALL amount of sealer on the mating surfaces of the seal halves.

Question from Bryan (413):

I thought maybe I could get some advice on installing the rear main seals on a 413 that I'm rebuilding. The issue is with the two rubber strips that mount along each side of the main-seal cap. The FSM doesn't mention using any kind of sealant, yet an engine-builder I know suggested using a cement-type sealant. The FSM instructions dictate slathering them with diesel fuel (to swell) and to install ASAP. Can anyone offer their expertise regarding proper installation? I'm curious if there have been changes in the materials over the years that might render the FSM instructions inaccurate.


From Bob:

I'd suggest you look for a book "How to Rebuild Big-Block Mopar Engines: Covers All Years and Models of B/RB Series Chrysler, Dodge and Plymouth Engines" by Don Taylor. It has more current, detailed engine rebuilding instructions - and pictures! It's listed on amazon.com.

From Bill: 

Do as the FSM says! Never use sealant on any rubber pieces is the safe bet!

From Mark:

Well, the material HAS changed, though I'm not sure just when. Whenever I get an old gasket set with the "rope-based" rear seal, I soak it in motor oil over night to get it swelled-up and pliable, but the rubber-based ones I just install with nothing on them. I always make sure there's plenty of motor oil or assembly lube on the lip of the seal before I install the crankshaft, though.

From Ron:

Unless the NEW gasket/seal set has specific instructions to contradict the FSM, do as the Manual Instructs. I have rebuilt a lot of these and the original method works fine, Fel-pro, McCord, Detroit Gasket all make their gasket set to OEM specs. I have read several of the responses you have received on this and first off a few of them have missed the target gasket, this is not the "rear main seal" but the (2) side seals for the lower rear main seal housing. These seals are made loose, and will move in and out of their respective slots, they are made of a material which swells (a lot) in oil, thus providing a good seal. DO NOT GET THEM WET WITH WATER, if you do you must dry them very well, or if they got "soaked" get new ones. I find WD-40 to work better than diesel fuel (diesel fuel has many more additives in it now then when the FSM was written) for getting them oil soaked, have the crank fully installed BEFORE you soak them, install the lower rear seal into the housing (if using a rope type pre-fit it and check drag, if using a rubber 2 piece just install it) install the lower seal holder and tighten to spec. When you are satisfied that you do not have to redo anything, this is the time to soak the side seals, about 1 minute (WD40, or #1 Fuel oil) slid them in right away and drip or spray them for a few minutes. This works well, the reason for presoaking is to STOP fresh start up leaking, engine oil keeps the seals swollen, but if put in dry, you would have a leak for a little while, about 1/2 - 1 Qt. on average then it would self seal.

Unless the NEW gasket/seal set has specific instructions to contradict the FSM, do as the Manual Instructs. I have rebuilt a lot of these and the original method works fine, Fel-pro, McCord, Detroit Gasket all make their gasket set to OEM specs

From Steve:

While you have the oil-pan off...a good move would be to check the bearings on the crankshaft. Reason being: If the main bearings are worn and are allowing the crank to "wobble", the rear-seal will be unable to do it's job. Back in '86 when I worked in an auto repair shop, a '64 Newport came in with an oil leak which was coming from the seal. Two of the mechanics tried to fix it...to no avail. The car was then sent over to me to fix, a MoPar fan with a '69 NY'er. I checked the main bearings and found them to have too much clearance. I then replaced both the main and rod bearings and also the rear main seal. Needless to say...the car did not leak much to the dismay of my co-workers.  Don't forget the thrust bearing!

If you checked the bearing clearances like I mentioned, and are going to replace the main bearings while you have the oil pan off while you replace the rear seal also...a helpful thing to do to get the #1(front) journal top-1/2 of the bearing out is to loosen the belts. Hopefully the crankshaft is not worn too badly. 

Story: The first Chrysler I owned was a '69 NY'er that was driven by the previous owner until the "Oil" light came on...then he added 1 quart to make the light go off. :o( ! The main bearings wore out to the point where the seal leaked. The new seals that I put in would not help...so I replaced the main bearings AND the seal and cured the problem for about 20,000 miles or so. It would have been a permanent cure but the crankshaft was worn and grooved also and one of the main bearings had "spun" within the block and cap. I wasn't about to change the crank. That was in '85 when I was 18.  

Question from Lance (413):

I took my Dad's old 65 and drove it to Albuquerque from Santa Fe. Drove great with the new tires. I then took it to Jiffy Lube to change the oil. An hour and a half later I noticed the oil was dripping and I returned the car back to Jiffy Lube. They told me that my rear main seal gasket needed replacing. I ordered it from the parts store and now I am faced with what to do. I understand ( I have little auto mechanical skill ) that they will have to remove the tranny to put this gasket in? Should I take this to a Transmission store? Or the garage around the corner? Last question....what are your guesses on the cost?


From Roy:

A leaking rear main seal can be a minor nuisance to a down right inconvenience, but never a real problem! Before you go to a lot of expense make sure that the crankcase wasn’t overfilled! Also take the car to a car wash and thoroughly clean the area between the engine and transmission that will let you see how much oil actually leaks over time and from where. What looked like a main seal leak on one car I had, was actually oil seeping from the corner of the valve cover and running down the back of the block!

From Rodger:

Take it to any garage that you feel good about. They will also need to replace the oil pan seal.

From Brad:

If it wasn't leaking when you took it into JiffyLube, it should not have leaked after the oil change. Are you certain where it is leaking from? If I had to go out on a limb, I'd say the halfwits at JiffyLube never checked the rubber gasket on the filter and the oil leak is coming from there. That is a common error among the inexperienced.

Personally, I will NEVER let any af these "pit stop" type places touch my car. If I can't do my oil change, I'll take it to my mechanic to do. That doesn't cost much more and usually takes just a little longer. I will also never take my car to the automotive department of a department store like Sears, WalMart, Canadian Tire, or Zellers. I've heard too many horror stories come out of these places.

A good mechanic is like a good spouse. They can take a while to find and once you do, you need to nurture the relationship. Respect what they do, their time and their talents. Pay them for what they do. Don't constantly squeeze them for a bargain. Check up on their work. After you get something repaired, take it home and inspect the repair. Have a buddy or even another mechanic periodically inspect their repairs just so you can either feel more and more confident in your mechanic's work or you will know when it is time to apply for a divorce and find a new mechanic.

I've got three mechanics that I have no problem trusting with my cars. If they say it needs doing, or even should be done, I trust them all the way. They know that I do enough of my own work that they won't easily slip something by me. I also pay them for their work. If they asked me to come in to fix their computer systems, I would expect my normal fee of $125.00/hour. If they didn't want to pay that, they could get the kid down the block to fix them up...and then watch where that leads them.

Anyway. This got a bit involved just because your statement sounds fishy to me. You didn't have a leak, got the oil changed, and now have a leak and suddenly your rear main seal is leaking? It just doesn't sound right to me.

From Ken:

First you need tools

Second you need jack stands

Third oil

Fourth rope type seal (do not take the bushing type seal)

Five fish line and needle.

Jack your car up and put it on stands. (Warning- if only using two jack stands, block back wheels or the car could fall)

Take off center link and remove right and left inner tie rod ends, take off idler arm. Move center link to the back, it will pivot on the pitman arm.  Drain the oil pan and take off the oil pan. After the last main cap on the crank, right at the back casting, there's a tiny cap flush with the block - take that off which will expose the seal.  It should be the rope type... grab an end, pull it down (I use vice grips). Now, thread the fishing line in the needle, put it through the seal, tie both sides of the line together (make it long) and this is how you pull the seal through. Push the line up and around the crank, push with one hand pull with the other. Make sure and oil the seal first, not a lot, a little everywhere.  Cut the line off and trim seal so they fit, slightly overlapping. Putting it back together you will need a pan gasket and cotter pins.

Question from Don (413):

Can a 1964 413 2-piece seal be upgraded to a full circle rear main seal. Is that do-able?

Reply from Steve:

The seal you are describing is not "do-able". The reason being is because the flange where the torque converters flex-plate bolts to, is of a much larger diameter than the journal (bearing surface) that the seal rides against.

If the seal was made one-piece like a rubber-band...then stretched over the end of the crankshaft and positioned on the journal...then the retaining cap tightened down..? Possibly someone can invent this. But I doubt it would be as fail-safe as the original design installed correctly.

Question from Jim (440):

I am in the process of tearing down my 440 (1968 HP). Got the ridges reamed and the pistons out this past weekend. I hit a roadblock when it came to removing the crank though. The rear main bearing oil seal RETAINER must be removed before the bearing cap can be removed. The two bolts that attach the retainer to the block are recessed in holes in the retainer so that they are below the mating surface with the oil pan. I cannot find a socket to fit the "unusual" heads of these bolts. They are not hex head and they are not Torques. They appear to have 12 points and valleys. The " How to rebuild" book I have says a 7/16" 12 pt socket will do the trick, but that is way too large. A 3/8" 12 pt fits better but still slips. I have a 11/32" 12 pt, but it is too small and will not fit over the heads. I was hoping someone on the list may have encountered this problem and found a solution that will not ruin the bolts. If not, I am considering trying to weld a conventional 1/4" bolt to the head of these bolts and see what happens. Failing that, I guess I could torch the thing out and end up buying a new retainer and bolts. Don't want to do that. I'm hoping there is a "special" socket that will do the trick, but I just don't know about it!! 


From Robb:

This is a VERY special socket.. It IS a twelve point socket... However, if you are using one that is worn, forget it.  The newer the better!!

From Bob:

I just rebuilt my 440 and I used a 3/8 12 point socket on the bolts that hold the rear seal in. If that does not fit try a 7/16 one of them should work.

From Robert:

I also did this recently and I used a 1/4 inch drive as the bolts are not very tight and the 1/4 drive socket fit with ease.

From Rich:

One of the things where you sometimes need to pay attention to detail is in the area of quality sockets & wrenches in the smaller sizes. Years ago, I was in the Auto Body business up north in PA, where rust never sleeps. I have tried to remove a rusty shock absorber bolt with a Sears Craftsman socket & rounded the bolt. I have then but on a Snap-On socket of the same size, & removed the bolt. The reason ?? The less expensive hand tools are "punched" out, & the better brands are machined. The better brands also check their "class of fit" , & if things are getting out of tolerance, they scrap them. Years ago, Snap-On had a feature called flank drive, which caused the load to be put on the flank of the fastener, & not just on the tips of the fastener. That was a major selling feature. I believe that that patent has long since run out, as I have seen this design on other brands in the past couple of years. I suggest that you purchase or borrow a Snap-On or Mac Tools 12 pt socket, & you should be able to get this fastener loose.

From Dick:

In further praise of good tools: Snap-on and other premium brands use a better grade of steel, this allows them to get away with thinner walls on the sockets, even with increased strength. After over 50 years of wrenching on various vehicles, I'm now convinced that the only tool I will ever buy for my garage equipment is Snap-on, Macs, SK or other top line equivalent (in about that order). My Craftsman stuff, with its peeling plating and rounded off socket teeth, is in my travel kits in the trunks of various cars, and my offshore made junk is in my grandkids' toy tool chests.

Good tools are VERY expensive, but it pays in the end, when you can get that inner starter bolt loose with a 3/4 12 point deep well floppy socket when nothing else but some kind of open end knuckle buster would do it, or that header down pipe loose from the manifold with a butterfly driving a 3 foot extension 3/8 drive 9/16 6 point impact socket on a wobble drive adapter, where there is no way to even get a wrench in there with any normal thickness tool! (Don't tell Snap-on about using that long extension on my 3/8 drive butterfly impact - while I haven't busted it yet, I know it ain't kosher.)

I know the cheap brands are now advertising "Guaranteed for life - if you break it - we'll replace it FREE", but that ain't the point. If it won't do the job, what good is replacing it?

Follow-up from Jim:

I have the answer...these are "Ferry head" cap screws. I found a website for the Ferry Cap Screw company . If you look carefully, you can see the design of the head on the background graphics for the main page. (Apparently these bolts with the unique head design are used mostly on diesel engines.) All those who said a regular 12 pt socket would do the job were right as well. However, Rich has a good point, in that a well made socket sometimes performs better than a poor quality one. What actually happened (if anyone is interested) is this: 

- it was a 3/8" 12 pt socket that was needed, not a 7/16 as my "How to" book stated.  

- the first 3/8" 12 pt socket I tried was an off-shore cheapy and it was useless. 

- realizing that the off-shore socket was probably no good, I went out and bought a new 12 pt socket from a local hardware store. But it was just as useless 

- it was at this point I turned to the mailing list for assistance.  

- it turns out that the 12 pt socket I got at the hardware store was actually an 8 point!!! I never bothered to count the points ...I just assumed there were 6 pt and 12 pt sockets and that was it. It had more points that my 6 pt sockets, so it must be a 12, right? WRONG. (Kind of adds credence to that old adage - NEVER ASSUME, doesn't it?) 

- a millwright where I work loaned me a 12 pt 3/8" "PowerBuilt" brand socket and it worked great, even though I had beat up the heads of the bolts pretty badly by now. And what I found most interesting was the fact that even tough the Ferry head was beat up pretty badly, the proper socket still had really good engagement with the bolt and no hint of slipping! It appears the Ferry head is superior to the hex head if they are damaged.

This page last updated January 30, 2004.  Send us your feedback, and come join the Imperial Mailing List - Online Car Club