[DrStang]

Well we are onto the next step in the investigation of why I have lost two thrust bearings on a new engine break-in. Both times the engine was installed in the car with everything attached. The thrust bearing did not wreck until the clutch was applied.

Since then engine was successfully broken in on an engine dyno effectively ruling out the engine as the source of the problem.

So the next step is to find out what the problem is. From inspection, it's not the T5. So what we are left with is the JMC hydraulic clutch, the SPEC stage 2 disc and pressure plate, and the Mcleod scattershield.

The mechanic thinks the scattershield is warped, from inspection it looks fine, but you never know.

Your help and thoughts would be deeply appreciated as I can't afford to wreck another thrust bearing.

Steve

 

[blkfrd]

Not again!!!!!

That's terrible! I'd be freaking out! My post about missing my car for 3 months does not compare...this IS a PITA!

When I took apart my engine to fix the crank journals, I checked my endplay. I have 3 years and about 4000 miles on the engine. Before I could check endplay, I had to release the throwout bearing preload because it was pushing the crank forward (just slight pressure to take up some slack in clutch pedal). I've got a heavy duty throwout bearing that can handle the preload which means it's always spinning. My endplay was .008. It was .006 when I assembled the engine. I have a JMC clutch setup.

The only things that I can think of that can cause your problem are (and excuse me since some of these have probably already been mentioned or their bogus...just brainstorming):

Nose of T5 too long pushing on crank

end of crank where pilot bearing goes not true

not enough oil pressure to handle pressure on thrust bearing

thrust bearing face too small (what kind of bearings?)

Crank thrust area not true or not flat

Crank thrust area too rough...polished?

clutch pressure too high

Mains not true especially the face where the thrust bearing fits

clutch pressure not being released...something binding

Scattershield not true (ditch the scattershield if you have an SFI rated clutch and flywheel...you'll never spin it high enough to frag). How did it feel when you depressed the clutch? Hard to press or not smooth?

throwout bearing binding

 

[pabear89]

Not wanting to sound like a broken record but,
I suspect that your hyd clutch is over pressing the plate fingers and pushing the flywheel towards the eng block.

As you stated the engine was fine on the break in on a stand, but trashed your thrust bearing when you used the clutch.

Just my 2cts

 

[ductman]

Did you check the depth of the input shaft to see if it was bottoming out in the hole in back of the crank? We had that happen with our Hemi race engine and we machined off a little of the input shaft and the problem was gone.

Ductman

 

[DrStang]

Thanks for your thoughts fellas. The input shaft is at a safe distance from the crank, so no chance of it bottoming out. The hydraulic clutch riding on the diaphragm fingers may be a possibility. What do I do? Go to a cable clutch? We adjusted the H-clutch so the throw out barely touches the fingers.

 

[pabear89]

Start with giving some space between the throwout bearing and the pressure plate.
Yes you will have some petal travel before it ingages but it won't be putting so much pressure on the crank as your petal bottoms out.

you only need enough pressure put on the fingers to allow the clutch plate to spin freely.

 

[roadracer]

In order to have "normal" pedal stroke for your clutch you may have to change master cylinders.

The ratio of pedal movement to clutch pushrod movement is probably too high with a stock pedal arrangement. This is probably why the thrust bearing is moving too far and causing engine thrust bearing too wear out. I have heard of this before.

If this is the problem,... you'll need a master cylinder with a smaller diameter piston in it to reduce the volume of fluid sent to the slave cylinder. On a good note... this will make the clutch pedal easier to depress.

If you know the stroke of the master cylinder pushrod and the seal diameter of the piston in it you can calculate the volume displaced by it.

You can then back calculate the resulting stroke at the slave cylinder if you know its seal diameter. This will tell you how far the thrust bearing is actually moving at the fingers.

Might be worth doing before your tear into it. Your manufacturer should know these diameters and you can measure the stroke you get from the pedal with a ruler.

regards,

Charlie

 

[Huskinhano]

Is the hydraulic fluid expanding when hot and adding too much pressure to the clutch and not having any free play???

 

[DrStang]

Is the hydraulic fluid expanding when hot and adding too much pressure to the clutch and not having any free play???

This is possible, also the point about to much pedal travel is also good. The only question is why don't we see more thrust bearing failure with JMC hydraulic clutches?

 

[Huskinhano]

Is the hydraulic fluid expanding when hot and adding too much pressure to the clutch and not having any free play???

This is possible, also the point about to much pedal travel is also good. The only question is why don't we see more thrust bearing failure with JMC hydraulic clutches?

It would be interesting to see if everything was together, how much difference in torque or resistance in turning over the engine by hand with and without the clutch being depressed. I would expect some increase due the pressure of the clutch being pushed in but if you couldn't turn it over or was very difficult, this may give you some clues.

 

[blkfrd]

In order to have "normal" pedal stroke for your clutch you may have to change master cylinders.

The ratio of pedal movement to clutch pushrod movement is probably too high with a stock pedal arrangement. This is probably why the thrust bearing is moving too far and causing engine thrust bearing too wear out. I have heard of this before.

If this is the problem,... you'll need a master cylinder with a smaller diameter piston in it to reduce the volume of fluid sent to the slave cylinder. On a good note... this will make the clutch pedal easier to depress.

If you know the stroke of the master cylinder pushrod and the seal diameter of the piston in it you can calculate the volume displaced by it.

You can then back calculate the resulting stroke at the slave cylinder if you know its seal diameter. This will tell you how far the thrust bearing is actually moving at the fingers.

Might be worth doing before your tear into it. Your manufacturer should know these diameters and you can measure the stroke you get from the pedal with a ruler.

regards,

Charlie

Excellent advice. You may have to go with a different clutch pressure plate. My setup works fine even with some preload on the throwout bearing. I have a Ford Racing lightened billit steel flywheel. What kind of flywheel do you have? If flywheels vary in thickness, I suppose it is possible that the flywheel you have is thicker than most which may tend to limit throwout bearing travel before too much pressure is put on the thrust bearing.

 

[roadracer]

It would be interesting to see if everything was together, how much difference in torque or resistance in turning over the engine by hand with and without the clutch being depressed

Excellent idea!

Why not pull the plugs to remove the effects of compression, have someone stand on the clutch and turn the thing over by hand noting the difference with and without the clutch!

Excellent advice!

 

[Red68GT]

What about the thrust surfaces on the crank? Did they get resurfaced?

Thrust Bearing Failure Article

 

[DrStang]

Some great ideas, I'll try the engine turnover idea.

Tracy, I'm also leaning towards changing the pressure plate. I have a SPEC stage 2 in right now. Maybe the load transfer is too high or the plate is defective.

Also, the flywheel is a steel SPEC SFI rated flywheel. Not sure about thickness. I'll check

 

[blkfrd]

Very interesting article and I like that simple mod to increase oil to the rear thrust surface.

 

[DrStang]

Very interesting article and I like that simple mod to increase oil to the rear thrust surface.

I read that article a while back when this fiasco started. They have bearings now (including the ones that went in my engine) that already have the mod done.

Steve

 

[Mtrain]

I would go to a factory type Zbar setup. I have five classic Mustang with four being 65's some running a tko 600 with around 600+hp with no problems, one with a toploader 500+hp, one with an automatic trans, one with an older tremec that I cranked over today and went through the gears with no problems, and the last will be a tko600 for the Eleanor project and it will have the zbar setup.
I prefer the zbar over the cable since I have owned many late model Mustangs and let me tell you its NO fun when that damned clutch cable snaps. The hydraulic system has issues to, I saw a car show on the tube where they had fitment issues due to the hyd thowout bearing so as someone said that might be your problem, but I still would go back to the zbar.
The trick with the zbar setup is to tie the engine down. I forgot to mention all of my Mustangs are a little different so I have just about all of the setups steering wise an headerwise and none have issues with the zbar.
I have one tc manual rack with a toploader and 393 with Hooker supercomps, one with a 431w with the tko600 and tc power rack, one with a randell power rack 347w and Hooker headers, and another with the tko 600 tc power rack and twin turboed 482fe.......
I hope I havent rambled on, but the only other thing I can figure is that the flywheel, or rotating assembly might be out of balance................Mike U.

 

[ductman]

If you still have the engine and tranny in the car bolted up try this if you can. Get a dial indicator and set it up on the front snout of the crank and set it to "0". Have someone watch the dial and you need to step on the clutch as you normally would while driving. Record how much the crank moves when you apply the clutch, do this several times to get an accurate reading. Even try rotating the engine at 90 degree intervalls to see waht happens. This may tell you how much the flywheel and crank is moving when you apply the clutch.

Ductman

 

[DrStang]

If you still have the engine and tranny in the car bolted up try this if you can. Get a dial indicator and set it up on the front snout of the crank and set it to "0". Have someone watch the dial and you need to step on the clutch as you normally would while driving. Record how much the crank moves when you apply the clutch, do this several times to get an accurate reading. Even try rotating the engine at 90 degree intervalls to see waht happens. This may tell you how much the flywheel and crank is moving when you apply the clutch.

Ductman

Thanks Ductman, I'll pass this onto the mechanic.

Steve