Transmission Advice Please

[Richard2112]

I could sure use some advice on a noise (sort of a grinding sound) coming from the trans.

I am installing an NV4500 in place of an SM465. I have used the cast iron bell housing from the SM465 and drilled and bolted the bell housing to the NV case so all internals within the bell housing should be the same. That geometry shouldn't have changed much with the exception of a reground flywheel and a thicker clutch disc.

The NV is rebuilt stem to stern and the input rotates freely, all the gears engage smoothly...while the truck isn't running. When I start the truck the four forward gears and reverse engage easily enough but 5th won't engage.

Moreover, If I start the truck while it is in gear and move the clutch pedal a bit up or down, the grinding noise will occur.

I do not have a drive shaft connected and there is no drag on the transmission yoke. It spins freely in all gears. There appears to be some clutch drag as the yoke will spin in neutral also but again, there's no drag induced at the yoke so I suspect that even slight clutch contact will cause the input to turn and consequently the output yoke will spin.

With my tunnel cover removed, I can see the yoke turning while in neutral and I can actually reach down an grab it and it will stop turning. This is why I think that some slight clutch contact is causing the shafts inside to rotate while in neutral.

Does there need to be some drag on the output yoke to control the spinning motion of the internal shafts? Could this be why there is a grinding sound when the clutch pedal is lifted and depressed slightly?

I have had the flywheel ground (not turned), installed a new bronze pilot seemed to go in nice/tight/straight, installed new clutch disc and T/O bearing.

Just not sure why it would make a grinding sound when the clutch is moved. Could sure use some advice. Thank you

[geezer#99]

How did you align the input shaft of the tranny with the crankshaft?

[68c10airstream]

I think part of what is going on when you can grab the yoke from moving in neutral (i'm assuming that the clutch is engaged and your foot is off the pedal) is the fact that when the input shaft spins it will cause the output to spin because of close clearances inside the trans and the fluid acts as a coupling device. If your driveshaft was hooked up i doubt the truck would move.

In the 70's as a subaru mechanic in minnesota during sub zero temps warming up the car in neutral and letting out the clutch out would cause the car to creep ahead on level ground. Amzoil synthetic lube would stop this tendency

I say hook up your driveshaft and go for a spin.

[Captainfab]

While in neutral, your output is turning simply from the oil inside the trans being circulated. Did this NV4500 originally have an external slave or did it have a hydraulic release bearing?

[Richard2112]

Originally Posted by geezer#99

How did you align the input shaft of the tranny with the crankshaft?

While I had the trans on the bench I placed the cast iron bell over the front bearing retainer, marked the location of the hole and drilled/tapped the tranny to accept 9/16-12 bolts. It seems to have lined up. Put in a new crossover and mounts.

[Richard2112]

Originally Posted by 68c10airstream

I think part of what is going on when you can grab the yoke from moving in neutral (i'm assuming that the clutch is engaged and your foot is off the pedal) is the fact that when the input shaft spins it will cause the output to spin because of close clearances inside the trans and the fluid acts as a coupling device. If your driveshaft was hooked up i doubt the truck would move.

In the 70's as a subaru mechanic in minnesota during sub zero temps warming up the car in neutral and letting out the clutch out would cause the car to creep ahead on level ground. Amzoil synthetic lube would stop this tendency

I say hook up your driveshaft and go for a spin.

Yes the yoke spins while in neutral and the clutch is engaged or disengaged. It's easy to reach down and stop it turning I used the fluid that gm specs (got 5 quarts from Summit).

[geezer#99]

Originally Posted by Richard2112

Yes the yoke spins while in neutral and the clutch is engaged or disengaged. It's easy to reach down and stop it turning I used the fluid that gm specs (got 5 quarts from Summit).

If it's still spinning with the clutch disengaged that tells you the input shaft is still turning. It shouldn't be. You likely aren't aligned correctly and the input shaft is hanging up on the pilot bearing.

[Richard2112]

Originally Posted by Captainfab

While in neutral, your output is turning simply from the oil inside the trans being circulated. Did this NV4500 originally have an external slave or did it have a hydraulic release bearing?

That's a good question. I think I still have the alum bell housing laying around somewhere, I'll check it see if that tells me anything.

The T/O bearing I put in it is the same that came out of the SM465, except new.

Not being a mechanic, I do not know If I can do an accurate check on the transmission working correctly with no load at the output yoke.

Everything "seems" to work except 5th. The grinding sound doesn't happen when I shift, it happens when I push the clutch in or when I begin to let the pedal up from the floor.

Also, this is a 93 GM NV4500 for 2wd

[Richard2112]

Originally Posted by geezer#99

If it's still spinning with the clutch disengaged that tells you the input shaft is still turning. It shouldn't be. You likely aren't aligned correctly and the input shaft is hanging up on the pilot bearing.

Could the weight of the transmission hanging from the cast iron bell be causing a bind at the pilot?

[geezer#99]

Originally Posted by Richard2112

Could the weight of the transmission hanging from the cast iron bell be causing a bind at the pilot?

Nope!
Did you check the inputshafts are both exactly the same length.

[Richard2112]

Originally Posted by geezer#99

Nope!
Did you check the inputshafts are both exactly the same length.

Yes. Checked to length/diameter and the diameter of T/O bearing snout. Before installing the pilot I placed it over the end of the input shaft and checked for fit. It was exact, no wobble and slid easily over the end. When I removed the old pilot, it was sticking out of the crank about a quarter inch. I seated the new pilot bushing full depth, so it was flush. I tapped it in with a socket that was about the same diameter as the outside of the pilot bushing. The new bushing fit tightly enough that small hairs of bronze where scraped off of it's surface as it went in.

[geezer#99]

Did the tranny slide in unassisted(by hand) or did you pull it into place with the bolts?
Shouldn't scrape anything off the bushing during installation.

[geezer#99]

Maybe one of these might help. They're a little more forgiving for slight misalignment.
https://www.speedwaymotors.com/Chevy...aring,591.html

[Richard2112]

Originally Posted by geezer#99

Did the tranny slide in unassisted(by hand) or did you pull it into place with the bolts?
Shouldn't scrape anything off the bushing during installation.

I ran the tranny onto place by hand although it was a bit difficult to seat. I thought the index pins on the block to bell housing might be causing it.

I'll have another look at alignment. Don't really want to pull the trans again but I will.

[Richard2112]

Update on trans problem

The grinding noise and difficulty getting into 5th gear is a problem inside the bell housing, I suspect a bad pressure plate or I have the clutch adjustment way to tight.

I discovered today that by depressing the clutch pedal to the floor slowly, there is a point where the output yoke stops turning and shifting though the gears (all 5) is smooth and easy.

But if I continue to push the pedal, the yoke will spin, the grinding noise will occur and shifting into fifth is impossible.

It seems as though the fingers on the pressure plate will allow enough travel such that they eventually make contact with the raised dampening springs of the clutch disc, grind for a moment and begin spinning the clutch.

When I back the clutch adjustment off to reduce travel, my pedal then does not return to full height. Plus, it seems to take only a light pressure to to release the clutch.

The one component I did not replace was the borg/beck pressure plate because it seemed to work fine before. Fingers were even, there was good and even spring pressure at each of them, no loose components or rattles.

I'm going to try to re-adjust so there is less travel, providing I haven't already damaged the PP fingers or disc.

When I find out for certain what it was, I'll post it here. Also fixing my sloppy bell crank issue. Maybe that will help with pedal return

[Richard2112]

Thanks for the responses. Without the ideas put forth here I might still be in head scratching mode. But synthesizing the information garnered in this thread I was able to eliminate some possibilities and focus on others.

Re-adjusted clutch linkage so travel was limited to clutch release and not beyond. It worked. But my pedal operated with only about 2 inches of throw and close to the floor. I want my clutch pedal to operate at full height so tomorrow I'll re-adjust so pedal operates at full height and fab a bracket or a limiter to restrict the travel of the pedal.

Until now, I was unaware the PP fingers could be pushed into the clutch disc.

[Captainfab]

Did your clutch operate correctly when you had the SM465?

[Richard2112]

Originally Posted by Captainfab

Did your clutch operate correctly when you had the SM465?

Yes. The 465 set up worked flawlessly. The disc was worn down to the rivets though (didn't gouge the flywheel or pressure plate) so the adjustment had been backed off accordingly. It was that way when I got it and I haven't put 50 miles on it since so I never adjusted it. I changed the tranny oil because it needed it but the clutch was ok.

When I installed the disc/cover onto the flywheel, I noticed the fingers of the clutch cover were inset more than they were on the thin (worn) disc. I figured that since those fingers are levers and the disc was thicker, this was due to be the case. The three fingers on the pressure plate being more recessed into the cover, due to the thicker disc, seemed to cause significantly more travel in the fork and consequently in the pedal also.

Yesterday, I had my brother push the pedal slowly to the floor and I was under the truck watching the action of the fork and pressure plate. I could see it release. I had him press the pedal again (slowly) and I used a flat blade screwdriver to attempt to turn the clutch disc only. As he pushed the pedal there came a point when I could easily turn the disc with the blade of the screwdriver. I had him continue to push the pedal down and there came a point where at, though the pressure plate had released the disc, I could no longer turn it freely.

[geezer#99]

Keep digging!!
FWIW the fingers on a b&b pressure plate can't move far enough to contact the disc hub spring.
For that matter no pp fingers no matter what style will do that.

[Richard2112]

Originally Posted by geezer#99

Keep digging!!
FWIW the fingers on a b&b pressure plate can't move far enough to contact the disc hub spring.
For that matter no pp fingers no matter what style will do that.

Admittedly, I could be wrong about that and don't mind finding out that I was. Everything I've seen though, points me in that direction.

I'll keep digging as you suggest but with my limited experience, my options on possible causes are a short list.

It was peculiar (to me) that the disc would turn freely at some point in pedal travel then lock up at further pedal travel, even though the Pressure plate had released its hold.

Maybe I bent the fingers on the pressure plate by having my clutch adjusted up tight when I first actuated the pedal to the floor.

Honestly, I don't know.

I wonder if I could have the wrong clutch disc installed. I ordered ir from rockauto using the dimensions, outer diameter, spline count, input shaft diameter and the 168 tooth flywheel. They should have worked (I think) but I wonder if some discs were manufactured with the dampener spring hub sticking out further than others.

[geezer#99]

It's quite simple!
You're out of alignment. The input shaft isn't perfectly inline with the crankshaft.

[Captainfab]

Could the disc be installed backwards?

[Richard2112]

Originally Posted by Captainfab

Could the disc be installed backwards?

I know how easily that can be done and the T/O bearing. I tried to be extra cautious with those. I took photos in case this came up and I could reference them without disassembly. I believe the disc is correct...?? Disc hub with dampener springs faces the trans?

[Richard2112]

Those pressure plate fingers are recessed more than they appear due to the thickness of the new disc. And when I push the clutch pedal halfway to the floor, the yoke stops spinning.

Previously, I did not know the yoke would stop spinning at some point in the pedal travel because I was fully extending the pedal all at once. Then in later tests, I gradually pushed the pedal and watched the yoke. About halfway to the floor, the yoke stopped spinning as the clutch released. But If I push that pedal further (to the floor), I could swear those fingers on the PP are contacting that spring hub. It'll grind just before it catches and the yoke spools up. Then it'll grind again as I back off the pedal.

I can shift through the gears quite easily as long as I don't push the pedal to far.

[Captainfab]

Yes that disc is correct. So what else did you change besides the clutch disc, TOB and the trans? Is there more than one location to connect the clutch rods on the bellcrank?