Rick Hodgkins

What would cause a leak from the center of the yoke on a T400?
This staarted right out of the blue with car on a frame lift and wheels hanging.
Its not the seal, but dripping out of the center of the front yoke.

don71

Some yokes are vented like yours. Some are not. Being on the lift probably created a condition in which the hole allowed the fluid trapped in the tail to come out.

I know people have sealed that hole. Welded, epoxied etc. I like to keep in mind it was designed that way for a reason, but I'm no expert.


https://classicoldsmobile.com/forums...e-drip-148956/

Rick Hodgkins

I wondered about an oring on the tailshaft as mentioned in that thread.
This would have to be quite a way up inside past the output shaft splines.
Just did a fluid and filter change on this.
When its on the lift, the drive shaft is sitting on the exhaust pipes as the rear end drops down.
Wonderred if that lateral pressure is part of the reason, but this never leaked a drop till now.

OLDSter Ralph

Why is the driveshaft sitting on the exhaust pipes ?
Were the transmission and driveshaft correct ?


Does your output shaft have an "O ring" like above ?




The "O ring" should be in the machined diameter of the yoke. If the yoke is pulled back to far, a leak from inside the yoke will happen.

Sugar Bear

How long was it sitting on the lift? The torque converter may have drained back enough into the transmission to cause the fluid level to rise above the vent hole.

Good luck!!!

Rick Hodgkins

Thanks for that Ralph
The car has 2.5" SS pipes with an X pipe.
When the rear end hangs on the lift the driveshaft contacts the x pipe and the pipes which are larger.
No contact when on the tires.
I was under the car with the engine running looking for leaks when all of a sudden it started dripping.
It may be that the axle drop is pulling the yoke out enough that the oring is slightly out of place.

Sugar Bear

Just read it was running so Ralph may be on to something.

OLDSter Ralph

If there isn't a leak when the car is sitting on the wheels, I don't think you have a problem.

If you had that leak every day, I would suspect a bad "O ring" or a short driveshaft.

Ok, I have a question about these "H pipes" and "X pipes". Why are some people using them ? Many years ago when a few people were first trying them, there was no horsepower gain. The only thing they did was smooth the exhaust pulse..

Rick Hodgkins

Never had a leak till it was on the lift.
Good question on this x pipe
I have an 88 Monte SS with the same exhaust system but without the x pipe.
Yes 2 totally different engines, but also totally different sound at the rear.
Exhaust pressure balance is the main objective.
Efficiency or HP gains, the jury is out on that.
Interesting read on MT on this below.
https://www.motortrend.com/how-to/15...for-your-ride/

matt69olds

With the car on a lift, the rear end dropped enough to pull the yoke past the Oring. Once the weight is back on the tires the leak will most likely stop.

Transmission yokes without the vent will have one spline missing. The missing spline allows the yoke to vent air as the suspension cycles.

Rick Hodgkins

Thanks guys, not quite as alarmed as I was last night.
IT makes sense now, but also borderline.
Never ran the car on the lift, but it makes sense now.

OLDSter Ralph

Thanks for the link. The article was a little vague about any horsepower or torque gains. They mentioned "scavenging" exhaust gases, but thats what good "long tube headers" do. If an exhaust system is restrictive, it will be restrictive on both sides...how will that benefit the other side ? Sounds like negligible benefit and more "hocus pokus" than anything. I doubt I would spend any money on the X or H pipes.

Honestly, I don't think you have anything to worry about.
If you lift the car again, I would support the differential to keep the driveshaft from resting on the "balance tube". The weight of the differential and driveshaft resting on that "balance tube" (X or H) is exerting quite a bit of force on the yoke and your exhaust system. The balance pipe is acting like a fulcrum between the yoke and applied weight of the differential.
......Just my two cents worth.