Vibration found..Pilot bushing!

[Bill75]

I've been tying to find the source of the clutch pedal vibration at higher rev's for a couple of weeks. I thought it was something with the Centerforce II clutch so today I pulled everything apart. After I pulled the tranny I was looking at the clutch fingers and I see the damn pilot bushing laying in there sideways!!! It had pulled out when I pulled the transmission!

This is a new Pilot from NAPA, when I installed it I put it in a freezer overnight and still had to tap it in with a hammer and a flat rod. Now it just falls out! The O.D. measures 1.085. The O.D. of a new needle bearing pilot I was chicken to use measures 1.095. So this thing has been turning somehow and ground off about .010 off the diameter. I can see the score marks around the outside and the back of the crank has some brass residue from the filings.

The I.D measures .590 and the input shaft on the transmission is about the same.

This is a new GM 350 crate motor with the GM bellhousing off my old 350. It just dropped right on the alignment pins but in retrospect I should have checked it for concentricity and parallelism, I just never thought it was necessary.

Could there be a problem with the bellhousing alignment that would cause this?? This happened in 500 miles or so of very soft driving.

Bill

 

[aapple]

I've been buiding trannys for 30 years, and I've never seen a bushing fall out like that!! You may need to check the inside diameter of the crank, and make sure it has not been machined slightly oversized.
The bellhousing/trans not being parallel wouldn't cause this. It might wear the inside of the bushing, and the end of the input shaft, and make it harder to shift, but I don't believe it would spin the bushing around like that.
Things that make ya go "hhhmmmmm?"

 

[Bill75]

You may need to check the inside diameter of the crank, and make sure it has not been machined slightly oversized.

It was a real tight fit when I put it in, I froze it in a freezer and still had to hit it in with a hammer and rod.

The transmission would not go in all the way either, that last 1/2" I had to pull it in with the bolts. I even depressed the clutch to center up the disk on the spline but still had to pull it in.
Later, when I started the car I couldn't get it in gear the first time with the motor running, I had to put it in gear then start it. After that first time it was fine but I'm betting that's when it spun. I had talked to the shop about the tranny not going in all the way and they said it was common and pulling it in carefully is the way to do it.

 

[GTR1999]

Bill that pretty odd,they usually are tight. One thing to check with those is to see if they are magnetic. A lot of them are and that can lead to problems of the input shaft "welding" to the bushing. Go to NAPA with a magnet and check on the ones for a camaro they worked on the last one I did.

 

[pgtr]

Did you check the fit of the bushing ON the pilot shaft BEFORE installing? That you had to use the bolts to mate the tranny makes me suspicious of this.

Over the years I've had many needle bearings fail on other cars that used them as OEM. In fact if I hadn't sold one of those cars, next time out I would have gone to a machine shop and had them make me a bronze bushing replacement. Bronze is a softer metal so any wear would have likely occured there and not the crank. Bronze may seem cruder and less sophisticated than a bearing assembly but given a choice it's the way I'd go.

 

[Bill75]

Bill that pretty odd,they usually are tight. One thing to check with those is to see if they are magnetic. A lot of them are and that can lead to problems of the input shaft "welding" to the bushing. Go to NAPA with a magnet and check on the ones for a camaro they worked on the last one I did.

Gary, I checked it with a magnet this morning and I didn't get any reaction. It is a NAPA part, when I picked it up I just asked for one for my car. I thought all 350 GM motors were the same from at least my era up.

I need to find out what caused this before I slap another one in, this is a pain!

 

[Hib Halverson]

It was a real tight fit when I put it in, I froze it in a freezer and still had to hit it in with a hammer and rod.

The transmission would not go in all the way either, that last 1/2" I had to pull it in with the bolts. I even depressed the clutch to center up the disk on the spline but still had to pull it in.
(snip)

Here's my guess as to what happended:
When you beat the new pilot in place you probably deformed its ID. Your clue to that was having to pull the trans back in the last 1/2" (which is the depth of the pilot) with the bolts. Esentually, by damaging the pilot when you beat it into place, you made the input shaft a press fit.

With the pilot a press fit to the input shaft and a press fit to the crank, the weaker of the press fits "lost" and the pilot began to spin in the crank. With the bronze bushing softer than the the steel crank, the bronze quickly wore .010 less than the crank ID then began to spin. When you tore the powertrain down, again, as you pulled the trans out, the pilot flopped over in the hole.

First, you need to insure the pilot hole in the crank is the proper size and undamaged. Then you need to install a new pilot (the GMPP needle bearing pilot is the best choice) per the service manual. Then you need to carefully inspect the trans input shaft for damage and repair as necessary.

Put the clutch back together using the correct clutch pilot tool then reinstall the trans and road test.

Good luck.

 

[Bill75]

Did you check the fit of the bushing ON the pilot shaft BEFORE installing? That you had to use the bolts to mate the tranny makes me suspicious of this.

Well I can't say for sure I checked it on the shaft but I was pretty concerned about getting the right size and I remember measuring it. But I do agree that something was fishey about me having to pull it the rest of the way in with the bolts.

 

[Bill75]

Here's my guess as to what happended:
When you beat the new pilot in place you probably deformed its ID. Your clue to that was having to pull the trans back in the last 1/2" (which is the depth of the pilot) with the bolts. Esentually, by damaging the pilot when you beat it into place, you made the input shaft a press fit.

With the pilot a press fit to the input shaft and a press fit to the crank, the weaker of the press fits "lost" and the pilot began to spin in the crank. With the bronze bushing softer than the the steel crank, the bronze quickly wore .010 less than the crank ID then began to spin. When you tore the powertrain down, again, as you pulled the trans out, the pilot flopped over in the hole.

First, you need to insure the pilot hole in the crank is the proper size and undamaged. Then you need to install a new pilot (the GMPP needle bearing pilot is the best choice) per the service manual. Then you need to carefully inspect the trans input shaft for damage and repair as necessary.

Put the clutch back together using the correct clutch pilot tool then reinstall the trans and road test.

Good luck.

Hib, The front of the bushing has a huge countersink that leads to the ID that is pretty well below the outer plane. I can see a shiny ring around the very outside edge where the rod I was using pressed against it but it's nowhere near the ID. I didn't really beat on it to make it go in, it required a little persuasion but it wasen't excessive.

Think there's any chance there's an alignment issue here with the transmission shaft?? I'll check it dimensionally as you suggested.

Here a closeup of the bushing. The white piece is just to tilt it on an angle. You can see where the tool smoothed out the finish at the very edge.

Bill

 

[Hib Halverson]

Hib, The front of the bushing has a huge countersink that leads to the ID that is pretty well below the outer plane. I can see a shiny ring around the very outside edge where the rod I was using pressed against it but it's nowhere near the ID. I didn't really beat on it to make it go in, it required a little persuasion but it wasen't excessive.

Think there's any chance there's an alignment issue here with the transmission shaft?? I'll check it dimensionally as you suggested.

Here a closeup of the bushing. The white piece is just to tilt it on an angle. You can see where the tool smoothed out the finish at the very edge.

Bill

Ok. The earlier posts seem to indicate that hammering was used to put it in.

If you believe there's even a chance of the clutch housing mounting surfaces being perpindicular to the centerline of the trans and the mounting faces being parallel. You need to check that. The procedure to do so can be found in various places and requires some special measuring tools. Seems to me the McLeod Industries clutch catalog had a section in it on how to check a clutch housing.

If the housing is "off" it'll either need to be machined or replaced.

 

[Jack]

longest bronze pilot has most contact area w/crank

Bill:
Seems pilot bushing was installed properly.

Bronze sbc pilot bushings are available both short & long; we use the long ones ... long has more OD surface area contact within crank's ID pilot counterbore. Long fills depth of crank's counterbore; inboard bottoms out, outboard nearly flush w/counterbore. We don't use bearing sbc pilots. We do see bronze "wallow out" ID ... but I don't recall one that spun.

We typically R&I manuals by separating between BH & trans; it's more common than not that during install we have to pull the trans in the last 1/2" or so ... carefully tightening in pattern those four large bolts at trans' four ears ... remember, when doing so you're pulling the tran's steel front bearing support OD into & through the BH's bore ID.

Concentricity and/or parallelism may be an issue; understand it is a new block & new crank mated to old bellhousing. Understand old bellhousing must've worked fine with old motor; maybe there's a C/P issue when mated to new block/crank.

-edit- If you are running longest (can't tell from pic) ... and its OD is too small for crank ID ... before you install bushing, you can "dimple" the bushing's OD with a centerpunch ... raising the metal.
JACK:gap

 

[Bill75]

Hey Jack,

This is nuts isn't it?? I haven't run across anyone that has ever heard of this happening before. I believe this is the long style, it measures .755. I installed it to maybe .010 above the surface of the crank and it looked like it was bottoming out on the shoulder.
The bell housing dropped on the alignment pins and seated with just a couple of taps of my fist. If this were a non GM part I guess I could imagine it being off but it's not. In any event I'm going to borrow a dial indicator and magnetic base and check things out, might take me a couple of days to round things up or buy them.
OK on the dimpling method. This one was pretty tight going in, I wish I could remember if I really checked it or not in the transmission shaft. Something really made the shaft grab this thing to turn in in the crank it takes a lot of force to make that happen. Makes me wonder if the bushing had a tapered ID or something but that seems pretty impossible.


BIll