429 rear main seal leaks

[Vinny6t6]

OK.  This is probably an age old topic, but I can't seem to get it straight.  I have a 66 DVC in which I replaced the rear main seal twice and it still leaks.  I replaced it once while the engine was out of the car (did not pull the pistons and crank) and once when it was in the car.  I can not get it to stop leaking.  By leaking, I mean LEAKING!  It drips alot.  I hear from people that I need a rebuild and I need the crank turned.  My motor burns no oil, does not smoke and I get a solid 185 on each cylinder in a compression test.  Now, the only thing I can think of is that when I replaced the half that goes in the block, both times I did not need the little shoe horn tool.  It slid right in.  Did I mabe put it in wrong? It's driving me nuts!!  My oil drips right between the flywheel cover and the oil pan.  Also from the little hole in the flywheel cover.  That's why I think it's the seal.  What else could it be?  My pan is not wet.  I really don't feel like putting the car on jack stands, pulling the exhaust, the front end and pan and doing it for a third time.  Especially now that it is going to be in the 90's here in NY.  Any help is greatly appreciated.

[gary griffin]

I dont know what seal you have but if it is a rope seal buy a "sneaky pete". Google it.  It gets a rope seal into place in one piece with only one joint. Loosen the main bearings a little bit  and work the old seal out and sneak the whole new one in. It will have excess material. Cut it at 45 degrees and leave it a little bit long so that the 45 degree ends are forced together.

If it is not a rope seal please excuse my intrusion onto your thread.

[Gene Beaird]

If you're using the rope seal, and didn't have to use the tool to pull or install the upper seal, it's not tight enough!  While I suspect that is where your leak is, have you verified there are no oil gallery plugs, or cam plug leaks at the back of the block? 

I'm not very familiar with the 429, but if they're at all like the 472, the oil pressure light switch is at the back of the engine, right where the trans bolts to it.  They can leak with age.  It could be possible you have a leaking oil pressure sending unit. 

Also, I'm not sure it you can take advantage of the neoprene seal that's an option on the 472, but if you can, I'd use that.  You do have to 'fit' the seal by trimming the ends properly, but if you get those right, they seal nicely, and don't rob much HP. 

[Vinny6t6]

Hi all and thanks for the reply.  I know it is not the oil pressure sending unit because i just replaced it because i put in a manual oil pressure guage.  My oil pressure id reading a solid 30psi.  I did not check the oil galley or cam plugs.  I am using a neoprene two piece seal from Best.  It is driving me crazy. 

[Dave Shepherd]

I 've mentioned  this before, if the journal surface where the seal rides is knurled, it can be difficult to get a neoprene seal to work, I assume you have the seal installed facing the right direction.

[Warren Rauch #4286]

 You haven't given us much of the history of this car. First , are you sure it is a 66 engine. The 64-early 65 ,427's had problems with these leaks. At engine #123045 (Serviceman feb 1965)they changed the rear main bearing and seemed to solve the problem. You mention the shoehorn tool. It was primarly used to keep the center (back bone, see Serviceman July1964) part of the LOWER seal in tack .  Back to the cars history. Assuming it is a 1966, was the rear main bearing ever changed? When the change was made in 1965 ,it was a small change. There was an extra oil groove added  on the rear edge of the bearing to channel oil back to the pan and away from the seal. The cap was changed so there was a connecting groove and the oil dumped in the pan. The Serviceman Feb 1965, tells how to file 63-65 caps so the new bearing can be used on the earlier models. In fact Cadillac dropped supplying the early type ,so you had to make the change. The problem is the older bearing will fit in the newer models and will cause leaks like you have .Warren

[Gene Beaird]

Vinny, you did 'fit' the seal when you installed it, right?  You can't just throw it in there.  It's been a LONG time since I've done that job, but with one end in the block even with the block, the other side has to be trimmed (best to use a bench grinder on the metal reinforcing ring and trim up the neoprene with a razor blade) to something like .003" (or something like that) above the surface.  I can't remember if both halves need to be done like this, or just one end with the other half flush with each end of the main cap.  You'd have to check. 

Make sure the ends are not parallel with the main cap mating surface (offset the seal about 1/4" from the main bearing cap surface), dab a little blue silicone on each end, and assemble.  Make sure the seal lips point inward toward the inside of the engine. 

Hope that helps.  The neoprene seal was a 'secret HP trick' for the Pontiac 455.  I used it, but didn't know about the fitting part.  When I got the car running, the back of the car would disappear in a cloud of oil smoke whenever I hit second gear.  Scary.  I replaced the seal with proper fitting, and all was clean and dry.

[walt chomosh #23510]

Vinny,
  As Dave Shepard mentioned when he asked you about having the seal in the right direction,that's the first thing that came to my mind. It's easy to install the neopreme seal backwards. Crankcase pressure should apply pressure to the seal and if the seal is in backwards,it will blow by.....walt..tulsa,ok

[Vinny6t6]

Thanks guys.  Looks like I am ordering a new rear main seal and oil pan gasket set and I will try this for a third time.  Why does something tell me this went in backwards?

[Vinny6t6]

OK.  I ordered the oil pan gasket set and the rear main seal (both BEST Gasket Products) and they arrived yesterday.  Jacked the car up. Removed exhaust, center link, starter, flywheel cover and oil pan.  Removed the rear main bearing cap. I took a tiny screwdriver and gently pushed out the upper half of the rear main seal from the block.  It came out very easy.  This led me to belive I installed it wrong.  I took out the new rear main seal and removed all the flash from the edges.  I took out the shop manual and installed the lower half into the rear main cap just like it told me to.  I installed the upper half in the block alog with the help of the shoehorn I made to the shop manual's specs.  It took me a little bit of effort to put it in this time.  I remeber the two previous upper seals I put went in very easy.  I put a dab of silicone on each end of the cap and torqued it down to spec.  I cleand out the little slots in the block where the tabs for the real portion of the oil pan seals go in and put a little dab of silicone on all four cornors of the oil pan and installed the pan.  Put in starter, center link and exhaust.  Lowered the car.  All in all it took me 4 hours from start to finish (including arguing 15 minutes with my mom as to why I don't bring the grand kids over more). I let the car sit for four more hours before I filled it up with oil so the sealers have time to tack up.  I put in 5 quarts of Valvoline 10W-40 and the car started right up and held 28 PSI at idle on the oil pressure guage.  I ran it for 20 minutes and I shut it off.  No leaks!  Lets keep the finger crossed...................

[Eldoradoman]

Hi,
The old pan gasket is made in cork. you must have them in water some hour befor you install them. it is the same with valv cover gasket. The are to hard when they are dry. And it is easyer to install an soft gasket and will be much better.

You only need to try it 1 time.

Johan Hellsten CLC 13056

[n2caddies]

Vinny, Did the rear seal work?  Have the same issue on my 64.
Randy

[Vinny6t6]

Hey Randy.  Yes!  it works great.  no leaks at all.

[kwed2011]

Hey Randy.  Yes!  it works great.  no leaks at all.

Vinny, great to hear that you fixed the leak. I have a 63 CDV and replaced my rear main seal last year when I replaced the timing chain. Like yours, the upper seal went in easily but leaked immediately. My shop manual makes no mention of the shoe horn tool. Can you tell me the specs and maybe provide a picture? I HATE my oil leak but before I attempt to fix it again I want to make sure I have the tools and info to do it right.

Thanks,
Kurt

[Andrew Armitage]

From the 1966 Cadillac Shop Manual...

[kwed2011]

From the 1966 Cadillac Shop Manual...

Thanks Andrew!

[Scot Minesinger]

If you have a 1970 (probably 1968, 69 too) shop manual it discusses the shoe horn.  It says in the shop manual to make one and gives specifics.  The rear main seal kit I bought and installed included the little shoe horn.  I was carefull not to install the seal backwards.  The shoe horn was tough plastic disposable type, somewhat helpful but not essential to installing the seal.  It seamed like it would seal well after finished.  However, the engine will not be started for another month, so I'm keeping my fingers crossed.