Oil Leak

[Scoop]

I just got an oil change with a synthetic oil 10 W 40 with high zinc, before putting my 74 Challenger away for the winter. Soon after the oil change and there is a large oil leak just below the oil pan drain plug. The plug is tight but I'm thinking the leak is from the rear main seal? So my question is, if it is the rear main seal, can it be changed without taking the engine out? The Challenger has a 340 with a automatic 904 Torqueflite. It could be coming from the oil pan? I don't have a lift to under the car fully, so it just me trying to crawl under. From what I can find, the 340 was manufactured in 1968.

Thanks in advance for your help.

 

[moparleo]

First is to verify the leak. Can you access a lift ? You need to clean all oil and grease from the pan and lower block area.
Put oil leak detector dye in the oil and take for a short drive. put back up in the air and with a small black light or dye detector look for any traces of the dye. It will show where the leak originates from.

 

[Ricks72Chlgr440]

I just got an oil change with a synthetic oil 10 W 40 with high zinc, before putting my 74 Challenger away for the winter. Soon after the oil change and there is a large oil leak just below the oil pan drain plug. The plug is tight but I'm thinking the leak is from the rear main seal? So my question is, if it is the rear main seal, can it be changed without taking the engine out? The Challenger has a 340 with a automatic 904 Torqueflite. It could be coming from the oil pan? I don't have a lift to under the car fully, so it just me trying to crawl under. From what I can find, the 340 was manufactured in 1968.

Thanks in advance for your help.

Like Leo said, clean the underside the best you can to remove all oil that has leaked. Run the engine for about 10 minutes then stop and put jack stands under the front control arms and lift it as high as needed to crawl under. With a light look all around the underside for leaked oil. When you find it look higher to see where it came from. Synthetic oil was never designed for our older car engines so often what you're seeing is the result. Also, the 340 cars never came with a 904 automatic, only 727.

 

[mrmopar340]

Like Leo said, clean the underside the best you can to remove all oil that has leaked. Run the engine for about 10 minutes then stop and put jack stands under the front control arms and lift it as high as needed to crawl under. With a light look all around the underside for leaked oil. When you find it look higher to see where it came from. Synthetic oil was never designed for our older car engines so often what you're seeing is the result. Also, the 340 cars never came with a 904 automatic, only 727.

Yep on the 727.

 

[Scoop]

Thank you for your suggestions and help. The Challenger originally came with a 318. The 340 was put in some time ago, not sure when. Would the 318 come with the 904? Would the 904 be compatible with the 340?

Thanks again for your help.

 

[Chryco Psycho]

There are 3 possibiities , could be the oil pan , the rear main which can be replaced in the car or the oil sender by the dist leaking .
318/ 904 is the normal configuration , the 904 will work with the 340 for a while at least , the 904 is not a weak trans & can be used in racing behind 340/360 / strokers as it is lighter than the 727

 

[Ricks72Chlgr440]

Thank you for your suggestions and help. The Challenger originally came with a 318. The 340 was put in some time ago, not sure when. Would the 318 come with the 904? Would the 904 be compatible with the 340?

Thanks again for your help.

Yes, the slant 6 && 318's normally came with 904's. You can certainly keep the 904 behind your engine but be aware that the stock 904 does not have the strength needed to hold together behind a stout 340. With upgraded internals, the 904 is actually a coveted transmission due to its lightweight design & better 1st gear ratio.

 

[Scoop]

There are 3 possibiities , could be the oil pan , the rear main which can be replaced in the car or the oil sender by the dist leaking .
318/ 904 is the normal configuration , the 904 will work with the 340 for a while at least , the 904 is not a weak trans & can be used in racing behind 340/360 / strokers as it is lighter than the 727

Thank you very much.

 

[Scoop]

Yes, the slant 6 && 318's normally came with 904's. You can certainly keep the 904 behind your engine but be aware that the stock 904 does not have the strength needed to hold together behind a stout 340. With upgraded internals, the 904 is actually a coveted transmission due to its lightweight design & better 1st gear ratio.

Thanks very much for your time and explanation.