With the couple of posts recently of Thrust Bearing Failure(TBF), i thought i would write this up real quick. It was convenient for me as i had just smogged my car and was underneath removing my cats again. It was fresh in my head.


I AM SO GLAD I TAKE THE TIME TO CHECK THIS..

ANYONE...ANYONE WITH AN AUTOMATIC SHOULD DO THE SAME.

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In a nut shell.....YMMV. The goal is to get access to the bottom of the rear bell housing cover so you can remove it. I removed the entire exhaust system...you may be able to just swing/move it out of the way AFT of the cat.


1) raise car. Preferably all for corners.

2) If you have a cat by-pass go to step 13 you already have access to everything.

3) Soak header to cat bolts with wd40 (NOT while its piping hot..DUH!!)

4) remove, rear muffler or RMB

5) loosen 2 clamps behind the CAT that secure the exhaust. If you have a cat bypass go to step 13 , you already have access to everything.

6) One at a time remove the bolt that holds each muffler to its respective hanger (its back near the differential area)

7) remove each exhaust system by twisting and pulling it aft.

8) take a large open end wrench and loosen the air pump fitting that leads to the cats. Its on the passenger side header area.

9) loosen the 3 bolts on each header to cat flange.

10) Perhaps get some blocks or a couple of jack stands to help support the cat as you lower it. You will only be able to lower it a little bit as the O2 sensor is still attached.

11) Hopefully it will lower far enough where you can turn it 90' (perpendicular to the Torque Tube)..if not you may have to go into the passenger foot well area and disconnect it in order to create some more slack...or just remove the O2 sensor.

12) With the cat supported and turned out of the way you have access to the bolts that secure the lower bell housing in place. I think there are 8 if i recall?

13) Remove the bolts that secure the lower bell housing.

14) you now have access to the front pinch collar and bolt as seen in the pic below.

15) get the bolt orientated so you can loosen it.... either blip the starter or preferably use a thick wide blade screw driver on the flywheel to incrementally move the flywheel around. Be sure you turn it in the correct direction, CLOCKWISE when viewed from the FRONT of the car.

16) Take an exacto knife and scribe a line at the end of the collar , across the splines. This will give you some reference to the amount of movement, if it should occur when you loosen the bolt.

17 ) take a socket HEX KEY and loosen the bolt. Hopefully the flexplate and collar assembly will not move. If it does then your mission was a success..you just relieved the pressure on your thrust bearing!

18) re torque the bolt to 72 ft lbs. (110% of factory specs of 66 ftlbs)

19) reinstall everything.


Below is how far mine moved!!
I knew it was going to be bad as i could actually see the forward bow in the flexplate!!

This is a little procedure i do EVERY YEAR or when i have access to the bottom of the car doing another job.

If you have a cat bypass it is SO EASY TO DO as you dont have to remove any of the exhaust. Simply raise the car, remove the bellhousing cover..lossen the bolt..retorque..install the cover!


This is how far mine moved!! Scary huh! Thats CM not inches on the ruler




This is a page on how to measure thrust bearign health.
http://members.rennlist.com/v1uhoh/cranksha.htm

 

Hey Tony, next time you do this cut aprox. 1/4 inch (measure how much clearance you need before removing the exhaust) off the rearmost bolts that hold down the cover. Now you can take the cover off in seconds without touching the exhaust. (at least it works on my 89) Kevin

 

Is that WITH THE CATS ON Kevin?
With the cats on there is no way you can get that lower cover off...is there? I guess ive never tried...ive always had the bypass on...or the whole thing apart under there

Actually I never put the aft two bolts back in...their is still 4-6 more holding it up..The aft 2 are the PITA compared to the others.

 

Re. scribing the splines to check for movement - doesn't the collar move back when loosening the pinch bolt, thus hiding your original scribe line on the splines? If so, how can you tell how far the movement was?

Maybe I have it backwards.

 

Tony,
You're right! - 3.5mm ~140 thou is plenty. Was this the first time you released the 'pinch'? How many miles ( since last time, if previously done) on the car?
Kevin's approach is the easy way - for the second time in! I tried to remove the back two bolts prior to dropping the front header connections - almost, but not quite!
The amount you shave off the back two bolts (and they come out easily with cats in place) depends on how much the motor mounts have collapsed.
For the first time in, open the two header flanges and the air injection line: a support, or small jack is req'd under the cat to prevent damage to the O2 sensor wiring as the whole, attached exhaust system is pivoted downwards.
BTW, I thought 66 ft-lbs was the 110% value; that's where I set it prior to committing to the loctite 290. Apparently, this isn't going to matter - sounds as if a thermonuclear device is req'd to move the loctite!

 

Does there come a point where the spline become completely hidden? I mean, if you do this check repeatedly, is it possible that the shaft will keep moving further and further into the collar? I guess I'm curious about whether the shaft will eventually stop moving forward before it runs out of room in the collar.

 

Actually, 'tis the other way round: the collar moves/is moved forward on the splines - leaving a preload on the flex plate (cupped inwards towards the crank): it is this established preload that is linked to TBF, as the flex plate tries to rest in the 'unflexed' position - this creating the forward force upon the ring gear/crank.
The prop shaft, as long as it stayes within it's elastic limit, will wind/unwind X-degrees axially - like a torsion bar: However, the shaft remains of constant length in normal operation.

 

in case some of you havent seen a thrust bearing....



this one is worn, but not to the block.

Click the link here to see the entire bearing in the block and assoc. pics. Its from a motor of a local 928 owner in Vegas.

I forgot i had the link.
http://home.earthlink.net/~jherhold/thrust.htm

 

Yikes!

Tony, can this bearing be replaced and the engine saved at this point, or is TBF imminent and unavoidable?

 

So the shaft is gradually coming out of the collar, and therefore gradually exerting more pressure on the flexplate?

 

Actually the shaft is being pushed INTO the collar...out of the tube...and thus INTO the flexplate..and thus INTO the Thrust Bearing...if it fails/wears away thus INTO the block!

The pic of the bearing shows a worn one....failure hasn't occurred YET, he got to it in time. How much time he had left, who knows??? Im sure if an oil analysis was done copper would be found...but who does oil analysis on there motors regularly..if at all. I know of a couple. The problem occurs as i know it when the the bearing surface protecting the block is actually worn away. From there the next stop for teh crank is to wear away on the block. THEN YOU ARE SCREWED.

The object of relieving the pinch bolt is to allow any tension built up on the flexplate and pressure on teh thrust bearing surface to be relieved.

causes of this? Several ideas and i think they are all factors

1) Converter ballooning
2) drive shaft winding and unwinding, changing its dynamic length.
3) poor installation of a Torque tube during replacement.


This leads me to an idea i was thinking about...

Why cant a thrust bearing surface be built/engineered into the torque tube itself. It could sit at the front end, very near the exit of the shaft where it meets the collar and flexplate. Any expansion AFT of that point wouldnt go any farther forward. I guess a ridged running surface there would pretty much make a flexplate pointless and would load up tension elsewhere...probably on some component in the tranny?

I imagine it could be engineered so the flexplate would see some minor movement in everyday use, but if the travel got too much, it would ride on the thrust bearing surface in the torque tube instead of the bearing in the block?


Crude i know..Thats the idea in principle, not application.....just a thought.