T56 Magnum trouble

Ok, here is a good one. The T56 Magnum in our 1st gen with NA LS3 pushed the rear seal out at the drag strip. No biggie. We pull frame stiffener, driveshaft, and replace the seal. Nothing appears to be abnormal. Put the car on the ground and it pushes the seal out again 2 blocks from the shop.

This car has been together for years, LOTS of miles logged without issue. Tranny and clutch seem fine and I grabbed the vent tube and it did not appear tight or pinched. Also the vent cap sounds to be free and rattles.

Before we yank this thing (yuck) I want to see if others have had issues similar to this. Thanks, Matt

Quote:

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Originally Posted by btmatt

Ok, here is a good one. The T56 Magnum in our 1st gen with NA LS3 pushed the rear seal out at the drag strip. No biggie. We pull frame stiffener, driveshaft, and replace the seal. Nothing appears to be abnormal. Put the car on the ground and it pushes the seal out again 2 blocks from the shop.

This car has been together for years, LOTS of miles logged without issue. Tranny and clutch seem fine and I grabbed the vent tube and it did not appear tight or pinched. Also the vent cap sounds to be free and rattles.

Before we yank this thing (yuck) I want to see if others have had issues similar to this. Thanks, Matt

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Yup, I have heard this before. I pulled my all
rubber seal and installed a ford seal that has a metal body. I’ll have to see if I can dig up the part number. I was given the info from another member who had seals blow out.

https://www.pro-touring.com/threads/...-leaking-badly

Just saw this. Maybe I should try and search next time. Ha

I did remember that when I bought the yoke it will fit a C6 trans. On a hunch we went to the local autozone and bought a seal for 66-76 F150. Checked the dimensions and it was a match. As noted the seal is not rubber clad like the original. We installed today and so far so good.

I will update later. Thanks

Quote:

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Originally Posted by btmatt

Ok, here is a good one. The T56 Magnum in our 1st gen with NA LS3 pushed the rear seal out at the drag strip. No biggie. We pull frame stiffener, driveshaft, and replace the seal. Nothing appears to be abnormal. Put the car on the ground and it pushes the seal out again 2 blocks from the shop.

This car has been together for years, LOTS of miles logged without issue. Tranny and clutch seem fine and I grabbed the vent tube and it did not appear tight or pinched. Also the vent cap sounds to be free and rattles.

Before we yank this thing (yuck) I want to see if others have had issues similar to this. Thanks, Matt

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If you get the chance to check for this, look at the tailhousing before you put the new rear seal in. There should be two oil passages between the slip yoke bushing and the body of the tailhousing (see pic). Those are drainback holes to allow fluid that gets trapped to return into the main case. Tremec had a batch of these Magnum tailhousings that didn't have those oil passages machined into them. This allowed fluid to build up and eventually force the rear main seal out. If your's doesn't have these passages, you'll likely see this issue creep up again. Unfortunately the only real fix is to replace the tailhousing, but Tremec has been good about taking care of these for customers.

Attachment 172787

Thanks for the reply, Craig. I had read about the drain holes, but had not seen a pic with the detail you show.

We have installed the new seal and no issues so far. If it begins to weep I'll pull the seal and check for the drains. Thanks, Matt

We had the issue Craig stated and TREMEC sent us a new tail under warranty.
However it took too long (only a week) and the car was taking up space on the lift so we machined the tail with an end mill and never had an issue again.

-Dale

I had this same problem. Wish I had known about the drainback holes before a installed a new seal....I'll definitely check next time.

Interesting....I didn't know the tail housing may not have been machined. I know the metal housing seal I did install has a weep hole...I guess time will tell.