[Greg Reid]

My son's '78 Bonnie is leaking oil at an alarming rate. Maybe a quart or more a week. I haven't had a chance to locate the source yet but I'm going to assume it's the rear main and hope the filter has a hole in it.
I need to know everything there is to know about replacing the rear main in the car while lying on my back on my garage floor.
After hearing the answers, I may be sourcing it out. He needs it back pretty quick.
Like the topic says...It's a 301.

[se428bandit]

Greg i would tell ya to drop a 400 in there but as i remember it has the small A/C compressor and the brackets are different for a 400,talk to dennis about dropping a 400 in it.if would have kept it that what i would have done.

[Greg Reid]

Russ, I really don't want to get into anything like that. This is his daily driver and I'd hoped to keep the expense of driving it AND repairing the leak as low as possible. So far, the 301 has been perfect for his needs and driving style..
Hopefully, it's something that could be fixed in a weekend.

[Tin Injun Tom]

Greg, I had a '78 Grand Am (Diamond Jim, from this forum, owns it now) with Y code 301. I had to replace the rear main in it, around 100K. The motor mounts had to be unbolted and the engine lifted, to remove the pan. Don't know if it's different with the B-body.
I recall it had a rope seal. The shop that did the work said it was a touchy job getting the seal in correctly.
You'll have to remove the Y-pipe also.
I would say it's worth getting done if the motor is otherwise in good condition.

[Greg Reid]

Yeah, I'm thinking I'll get it done.
Probably get Dennis to do it Russ.
I'm still hoping it's something else though. I looked down there today briefly..It's cold out...and noticed that the filter is covered with oil.

[Tin Injun Tom]

Could be the oil is pushing past the rubber gasket on the filter.....
I only had that happen once, and it was when the temperture was near zero. The only thing I could figure was the oil was too thick & I had a good oil pump. You're not running 20w50 by chance?
But if the inspection cover is open on that side, and the rear main leaking, it will sling the oil out to the right side of the flywheel. If that's what it is, I would recommend feeding it motor honey, until you have a block of time to have it fixed. A rear main leak is usually not as severe as it appears, and any cheap oil thickener will slow it down.

[455Grandville]

check the PCV valve or any oil breathers and make sure they are not clogged; Ive seen a few old Fords do that and blow seals out.

[Greg Reid]

Thanks for all the suggestions. I'm definitely going to try them out within the next few days. I'll pick up some Motor honey today. Running 30 weight right now.
The thicker oil won't hurt during this cold snap?

[srercrcr]

Too thick for the weather youre having the last few days. Thats the plus of a multiweight oil....good in winter or summer.

[Greg Reid]

Maybe, if I can find it, I ought to have him add some 10w/50 instead of the customary straight 30w?
I noticed that the leaked oil is very clean...I don't know if that means anything other than the engine is in pretty good shape because it's clean on the dipstick also. Runs great by the way.
The car in question is the car in the photos attached in SE428's posting above. I bought it from him for my then 18 y.o. son a little over a year ago.

[Tin Injun Tom]

Originally Posted by Greg Reid

Maybe, if I can find it, I ought to have him add some 10w/50 instead of the customary straight 30w?
I noticed that the leaked oil is very clean...I don't know if that means anything other than the engine is in pretty good shape because it's clean on the dipstick also. Runs great by the way.

Didn't mean to mislead you Greg, I'd only put the moter honey in if you for sure know the oil filter isn't leaking out the base gasket. Then maybe I'd wait till you get consistant weather above freezing.
Yeah, straight 30w is pretty thick in cold weather. It probably flows even slower than 20w50 when the engine is stone cold. That would give me confidence towards the rear crank seal issue. If you stay on top of it, I wouldn't think you would loose enough oil to hurt the engine. It'll just get the back of the car dirty.

Did you try looking behind the filter with an angled mirror? Wipe it off as dry as possible beforehand (and the block underneath) and watch as someone starts the engine. Bring the revs up to 2000 for a few seconds or more. My '78 GA had only 20 psi at idle, unless it was dead cold.

Footnote: The car I had experienced oil leaking past the oil filter base gasket was an '86 Z-24 2.8 liter, NOT the Grand Am 301.

[Greg Reid]

I didn't take it that way Tom. Good information. I will be checking these things as soon as I can coincide the car and myself being in the same place at the same time for more than a few minutes during the day time.

[Greg Reid]

Just to let you guys know how this came out....I took the Bonnie to a friend's shop. He has a lift. Rear main area was dry. All the oil residue was on the passenger's side. We changed the oil and filter, the op sending unit and valve cover gaskets. The gaskets were toast. That's where the leak was coming from. I couldn't believe how much oil was coming from the v.c..
Here's the clincher though. On the way down there, I noticed the fuel pump was leaking. We changed the lines and it stopped. A week later, it started literally shooting out of the fuel pump weep hole and the light went on for me.
Here's my theory....
The oil was thin because of the fuel pump...Sort of related to what was brought up earlier in this thread about thickening the oil to slow the leak.... The fuel pump leaking into the oil thinning it and the leaky vc gasket combined to make the leak more obvious.
Anyway, valve cover gaskets and a fuel pump fixed the problem. MUCH better than fooling with the rear main seal.
Thanks for the advice guys.

[srercrcr]

Looking real good!

[Greg Reid]

Yeah, it's a nice car. I'm thinking that if he can make it last, in reasonable shape, for maybe another year or two, I may take it back from him. He should be on his own and buying his own vehicles by then.

[2manyT/A'S]

Looks just like my Dad's car, but his is a 77 2dr Brougham,medium blue/silver blue 2 tone with NO rubber on the roof.
He bought it in the spring of 78 from the same dealer I got my new 78 T/A from.
Those cars drive BETTER than Cadillacs!

[Greg Reid]

Hmmmm....Maybe we ought to start a "Post a Pic of Your '75-'81 B-Body Cars" thread. lol

[Jack Gifford]

Nice to read a "happy ending" story- just gaskets and fuel pump- lucky guy!

[se428bandit]

Greg the Bonne still looks great,it's hard to believe in a few months you would have had it 2 years.

[Greg Reid]

Originally Posted by se428bandit

Greg the Bonne still looks great,it's hard to believe in a few months you would have had it 2 years.

Is that really right? I didn't think we'd had it that long...but I guess you're right now that I think on it.