How To Replace Rear Main Seal On Chevy 350? [ Easy Steps]

If you have a vehicle sitting in your garage with a chevy 350 engine, then chances are that it’s either too old and grumpy or the rear main seal is broken. Now the question is, how to replace rear main seal on Chevy 350?

It’s quite simple. Firstly, you’re going to have to drill two diagonal holes onto the seal gasket. Then tighten the gasket using two screws. Use a claw hammer to gently pry out the rear main seal. Clean it using brake cleaner or simply replace it with a new one.

That’s how you replace the rear main seal of your good old Chevy 350. Interesting isn’t it? Stick with this write-up for the ins and outs on this topic. We would also be discussing the costs related to replacing the seal. So, stay tuned!

How Do I Know I Have To Replace Rear Main Seal On Chevy 350?

We all know that nothing comes perfect. This could be said for the rear main seal of your Chevy 350 as well. Let’s move to the common symptoms which may possess a warning.

Oil Leakage

If you notice oil puddles on your garage floor or the driveway when your car is parked, then you know what to blame. It is the most common sign of damage on the rear main seal, leading to leakage.

However, it’s wise to diagnose the root of this matter properly as oil can leak from different regions of the engine itself.

Smoke Given Off From Underneath Vehicle

Fluid from the leaking rear main seal would often drip on the exhaust and form smoke that comes out from underneath the car. This can be confused with the smoke coming from the tailpipe. But it’s easy to differentiate if you pay close attention to where the smoke is coming from.

Formation Of Dirt

You all know that oil could act as adhesive when you let it accumulate. Over time dirt and debris get stuck onto regions covered with the leaking oil. 

Hence, if you notice the accumulation of dirt and debris between the transmission and the engine, you probably know that it’s due to a leak in the rear main seal of your chevy 350. Thus, it requires replacing.

How To Replace Rear Main Seal On Chevy 350?

We’ve arrived at the cherry on top. Replacing the rear main seal could sometimes become a little too tedious. But don’t worry cause we’ve got you covered. Follow the steps below for a clearer insight:

Step 1: Preparation

Let the oil drain overnight as you would want a clean oil-free service as you replace the main seal. Remove the transmission and take off the flex plate bolts and keep the flex plate aside carefully. 

You could also remove the starter motor if you want your workplace to be more spacious. Make sure to unplug any wires connected to it rather than pulling it all out. Also, remember to disconnect the battery before removing the starter.

Step 2:  Removal Of The Main Seal

Then get a drill machine and drill two diagonal holes into the seal gasket. Wheel in two screws to tighten the gasket. If the seal doesn’t come out of the crankshaft on its own, then pry it out using a claw hammer. Make sure to be gentle!

Step 3: Replace The Main Seal

If the main seal that you removed is deteriorated or shrunk. Then the best option would be to replace the seal. So you can get yourself a new seal and use a seal installation tool to install a new seal after properly cleaning the seal housing.

Can You Drive With A Rear Main Seal Leak On Chevy 350?

You would be lying to yourself if you think that you can’t ride your vehicle with a leaked rear main seal. But within this possibility lies a few problems. Let’s discuss the problems in detail, shall we?

Increased Consumption Of Engine Oil

A leaking rear main seal would leave oil puddles almost everywhere you go. Thus, making you refill the engine oil quite frequently. This may become a burden on your pocket over time.

Dirt Accumulation Underneath Vehicle

Nobody likes a dirty car, even if it’s underneath. The dirt underneath could accumulate on the leaked oil and start interrupting with brakes and the tires. Hence, deteriorating the overall look of the car itself.

Engine Problems

As the oil keeps leaking from the punctured seal, the rotation of the crankshaft would make matters much worse and increase the leaking. This leads to a drastic decrease in engine oil.

Furthermore, resulting in friction and wear in the engine. This can cause serious damage to the engine and also cause the common issue we all know as engine knocking.

How Much Does It Cost To Replace The Rear Main Seal On Chevy 350?

Replacing the rear main seal on your Chevy 350 can be a labor-intensive job itself. However, the cost of replacing it with a new one can be quite expensive as well. Since none of the parts come cheap. 

Furthermore, the costs may vary depending on the number of parts that need to be replaced. An estimation may suggest that it should cost between $650 to $850. Although the main seal comes pretty cheap, about $35. The rest of the amount is for the mechanic.

If you’re on a tight budget you wouldn’t want to spend money on a mechanic. But don’t worry because this write-up has got you covered. A simple drilling kit for the screwing part would cost you around $60 so adding it with the cost of the seal brings it to about $95 only!


Whether you’re an engine enthusiast or a newbie mechanic on their learning schedule. If you’ve kept yourself glued to this write-up till now you should become more confident about replacing the rear main seal on your chevy 350 engine or any other engine by yourself. Since the process is quite similar.

However, the replacement process does come with a cost and is quite labor-intensive. But hey! Old school parts do cost more as they have served way past their age threshold with excellent performance. So for the sake of that attachment, you should be willing to spend a few bucks.

You could ask why is there nothing about the seal gasket? Well, as easy as it gets, you just have to wheel out the screws and replace the seal gasket with a new one as cleaning won’t help a deteriorated gasket.

So here it is. Hopefully, this write-up has been of great help to you. Till then, take care of your vehicle parts.

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