Car Questions

Clear all

Rear Main Time of Labor Estimate


Topic starter

Well, the other day I loaned my 2017 Mustang to my girlfriend and my parents had my DD 1999 Ranger to move something, so I had to drive my 1979 Pontiac Catalina with the Pontiac 301 and THM-200 automatic. I was going 55 on the highway and noticed some chattering valve noise. I got off on the very next exit, about a mile down the road, and checked the dipstick. Oil level was below add, but not off the stick. I threw the quart and a half I had in the engine, started it up, no chattering, so I went the rest of the way to work. I had my girlfriend bring 5 quarts of oil for the drive home, no problems. I had to use the thing again the next day, my parents kept my DD longer than they were supposed to. I heard chattering valves again, so I got off within a half mile and added more oil. Started the engine, it was quiet again, so I drove home, and the car has sat since Thursday night. 


In the daylight yesterday, I looked under the car and the transmission oil pan looked like a mirror. I fully suspect the rear main seal has practically gone out; it went through at least 6 quarts in 200 miles. The motor still sounds fine and runs fine, so I asked my girlfriend's parents to find out if their mechanics can do an old rope seal rear main. Other than a compression test, possibly a leak down test, and inspecting the filter media for metal, is there anything else I need to do to verify the engine's health? 


Here's a screenshot of the procedure to replace the rear main. Roughly how much time are we looking at, if a shop were to do this? I like the car, so I am willing to spend the cash to fix it. I should've done it sooner than later.



Does All Data have the information for a car this old, or should I offer the Pontiac service manual I have on CD?








2 Answers

What we used to do to replace those old-style rope seals is use a "Sneaky Pete" to do the job by dropping the pan and removing the rear main bearing cap. You'll probably need to find a greybeard to to the job. I don't think most of today's mechanics have ever dealt with those old rope seals.


You may be right about the new breed mechanics not knowing how to deal with rope seals. I'd try to do the job myself, but the engine needs to be lifted up a bit to get the pan to clear the bottom of the oil pump uptake. I'm glad I didn't brush that noise off and kept oil in the car at all times, or the situation would be quite different right now.

I'm surprised that Pontiac was still using rope seals in 1979. My '65 Rambler has a rope rear main seal in its 327 V8 (referred to as a "hemp seal" in the factory shop manual) and I thought that was pretty much obsolete even by mid-1960s standards. The database confirms it though as does your shop manual.,1979,bonneville,4.9l+301cid+v8,1246474,engine,crankshaft+seal,5604


Yep, I ordered that seal Friday morning. If the shop can do it, they let us give them parts and warranty the work, not the parts.

The Pontiac V8 dates from 1955, they were updated as time went on to improve fuel economy. The 301 in 1979 was referred to as a short deck engine. They're built with lightweight components to save weight. The block casting, connecting rods, etc. Are all lightly built.

I'm guessing that GM anticipated phasing out the Pontiac V8 and only updated it "just enough" to get better fuel economy until newer generation engines came out. I've heard these 301s are old man V8s, they're not made for speed. The 301 Turbo in the Trans Am was, but that's very different from mine, so the dinosaur technology would make sense. 

Posted by: @justin-shepherd

RockAuto didn't have any.

try these