Transmission leaks can be significant, causing potential damage and expensive repairs. One common culprit is a failed front seal, which allows fluid to leak out around the input shaft. Replacing a worn-out or damaged front seal is a common repair to stop leaks and prevent more significant problems in automatic transmissions.
In our guide, you can learn more about properly replacing the front transmission seal on an automatic transmission or a 2WD rear wheel transmission vehicle.
Seals wear out whether you drive a truck, car, SUV, or other vehicle. Following along, you’ll learn to inspect for leaks, purchase the right seal, perform the replacement yourself, or know what to expect at the repair shop.
By the end, you’ll better understand how to remove your transmission and replace a leaking transmission front seal before they lead to significant transmission repairs. (Read RV Furnace Fan Runs But No Heat)
What Causes A Front Seal Leak?
The front seal (sometimes called the front pump seal or input shaft seal) seals the transmission input shaft, where it enters the transmission case. Its job is to keep transmission fluid from leaking around the input shaft.
Over time, the constant rotation of the shaft can wear down the seal. High fluid temperatures and pressures can also degrade the rubber. Transmission fluid can leak out once the seal loses its flexibility and sealing ability.
You’ll notice the leak as a puddle under the transmission or droplets of fluid on the underside of the transmission. Left unchecked, leaking fluid can lead to inadequate lubrication and will eventually require a transmission rebuild or replacement.
When Should You Replace The Front Seal?
It’s best to address a Chevy front seal leak as soon as you notice symptoms of one. Waiting allows more fluid to leak out and increases the chances of internal damage.
Signs that the front seal needs to be replaced include:
- Fluid dripping or puddling under the transmission
- Low fluid levels that require frequent topping off
- Oil leaks at the front of the transmission
- A burning or smokey smell from leaking fluid hitting hot exhaust components
Any time the transmission is removed for rebuilding or replacement is also an ideal opportunity to install a new front seal.
How To Replace The Front Seal – Step-By-Step
Replacing a front seal involves:
- Removing the transmission.
- Disassembling it enough to access the seal.
- Removing the old seal.
- Installing the new one.
- Reinstalling the transmission.
This is an intermediate DIY repair that requires automotive know-how and specialized tools. Use caution when trying to fix a transmission front seal leak and working with heavy components. (Read Overdrive Light)
Here are the basic steps:
Raise and support the vehicle
Use a car lift if available; drive up on ramps or jackstands. The transmission needs to be accessible from below.
Drain the transmission fluid.
Locate the transmission fluid drain plug on the transmission pan and drain all the old fluid into an oil drain pan.
Disconnect drivetrain components
Detach all linkages, mounts, wiring connectors, cooler lines, and exhaust components from the transmission.
Separate the transmission from the engine.
Remove any starter components or brackets in the way. Separate the torque converter from the engine crankshaft. Then, unbolt the transmission from the engine and lower it out of the vehicle.
Remove the old seal.
There are two main types of front seals – a two-piece seal with rubber o-ring or a single lip seal. Carefully pry out the old torque converter seal using a seal remover tool or screwdriver. Ensure to remove any small pieces of the old seal. Clean the sealing surface before you replace the torque converter seal around the housing.
Install the new seal.
Don’t forget to lightly coat the old seal replacement with transmission fluid (don’t use silicone). Be gentle and slowly work it into the bore using hand pressure – be careful not to damage it. Ensure it is fully seated flush to close any gap.
Reinstall transmission and refill fluid
Once the new seal is in place, carefully reinstall the transmission, reconnect all components, lower the vehicle, and refill with the proper type and amount of fresh transmission fluid.
Start the engine and check for leaks.
Leave the engine running for a few minutes and inspect the seal area closely for leaks. If no leaks are seen, the repair is complete. (Learn How Long Does It Take For Brake Fluid To Circulate)
Finding The Correct Transmission Front Seal
Since the seal fits into a precision-machined housing, purchasing the exact OE replacement for your make and model of transmission is critical. Seals are not universally interchangeable. Bring your VIN to the auto parts store, or use online fitment guides to look up the seal you need by year/make/model.
Common seals part numbers are:
- GM 4L60E – #24206476
- Ford 4R70W – #F3TZ-7A168-AA
- Toyota A340E – #93527-20002
Aftermarket brands like Timken, National, and Victor Reinz also make quality seals. Stick with a reputable brand name to ensure proper sealing and fit. Models of Nissan will have their own model numbers.
Should You DIY Or Go To A Shop?
For those with auto repair experience, replacing a transmission seal at home using an automotive lift or jack stand is very doable. Ensure you have the required tools like torque wrenches, seal installers, pry bars, pans, etc.
However, transmission work can be complex. If the job is beyond your skill level, or you don’t have the space/equipment, take it to a transmission shop or dealer service center. Though labor costs will be involved, a pro shop already has the expertise and tools to properly replace your seal.
Conclusion: Fixing a Seal Transmission Leak
While not the most complicated transmission repair. Replacing a leaking front seal or rear main seal on the th350 turbos and 700r4s is still best left to experienced DIYers or professional mechanics in the local garage.
Proper diagnosis, precision seal selection, and careful installation are all critical. But it will stop or prevent leaks to spell more considerable transmission trouble down the road. Pay attention to early signs of seal failure and address them promptly to maximize transmission life.
FAQ About Front Transmission Seals:
How much does it cost to replace a front seal?
Parts will be $10-$30 for the seal itself. Depending on transmission type, labor at a shop will likely run $200-$500+. DIY may only cost you the price of the seal.
What tools do I need to replace it?
Common tools include pry bars, screwdrivers, torque wrenches, transmission jacks, seal installation tools, drain pans, and more. You may also need transmission stands or bell housing tools for removal/reinstallation.
How do I know if the seal is bad or leaking?
Look for transmission fluid puddles under the vehicle, low fluid levels, or drops of fluid near the front of the transmission. Leaking seals will also show signs of weeping fluid or a dirty stain pattern around the input shaft area.
Does the transmission need to be removed to replace the seal?
In most vehicles, the transmission needs to come out to access and replace the front seal. Only partial removal may be possible on certain transaxle designs.
Is it OK to drive with a leaking front seal?
It’s best to avoid driving with a known leaking seal, except for very short distances to the repair shop. Driving with low fluid can damage internal transmission components. However, slow leaks may go unnoticed for a while before repair is needed if topped off. (Read Can I Use Transmission Fluid For Brake Fluid)
Should I replace the seal with the transmission off for another repair?
Absolutely – any time the transmission is already removed for overhaul or replacement, it’s recommended to go ahead and install a fresh front seal since access is easy. This prevents leaks down the road.