NV4500 Throw Out Bearing

[Captainfab]

I did search the forums and could not find a thread that is relevant. I'll try and get to the point but I will give some of the history behind the issue.

Back in December I started driving a '92 GMC K2500 with a NV4500. A couple months ago I started hearing a faint and intermittent metal on metal squeeling sound in the mornings when I was letting the truck warm up. I initially thought it was the belt idler pulley. As time went by the noise got a little louder and more frequent. I then determined that the noise was the throw out bearing which seemed to be lightly touching the pressure plate fingers, while the trans is in neutral. It seemed to be bouncing back and forth, hence the intermittent noise.But at this point, when pushing on the clutch pedal, the noise would stop and I could not feel any indication of a bad bearing thru the pedal. Then a couple days ago the TOB finally took a crap. So now that the bearing is definitely bad and much louder, I can hear that the TOB seems to be turning even when driving sometimes.

I do not have a lot of experience with these factory hydraulic clutches, but the TOB turning when the clutch is engaged, just doesn't seem like a good idea to me. I used to have a '90 with the NV3500, that drove for 3 years and did not have any issues with the TOB. My question is, is this normal or is there supposed to be a return spring somewhere that likely is missing in my truck? I am hoping to find a good solution to this issue before I tear into this to replace the TOB. Hopefully it has not damaged the pressure plate.

[mongocanfly]

I'm not sure on yours...mines a mechanical clutch..but we setup a buddies hyd clutch the other day and it gave instructions for shimming the throw out bearing by measuring from both directions to get the needed clearance..but your hyd may not be retracting the bearing back off the p-plate fingers enough to keep it from scrubbing..may need to check that as well

['63GENIII]

Hey Captain. I had never seen a return spring with any of the stock clutch configurations that Ive run. Even on my current set up with the Adv Adapters BH, the entire deal is hydraulic. No return spring.

Is there a chance that either the master or slave is hanging up somehow?

It is kinda weird though that its making enough contact to spin it with the pedal out yet when you disengage the clutch, it was silent? I get what you're saying in that its "not a good idea" for the TOB to be spinning while the engine is running all the time. Sort of like riding the clutch would wreck a TOB.

I can't see how a return spring would hurt. Especially if it was on the outside of the BH where you could take it off if needed.

I do know that the "inspection plate" for that is virtually useless for any kind of "inspection".

Id also say that while you're getting into it, change out the magic elixir trans fluid for new stuff and add an extra quart through the shift tower for good measure.

[mongocanfly]

Just be aware if your changing trans fluid the nv takes a special kind.. (aka expensive)

[B. W.]

Hydraulic clutch systems are designed to run with the TOB in contact. I agree, not a great idea.

[mongocanfly]

BW..I've never heard that before..the one we setup the other day by the directiins doesn't touch

[B. W.]

To my knowledge (lot of gaps there!) all domestic OEM hydraulic systems are constant contact, both the concentric (internal mount) & the external mount slaves. I'm sure there are probably some exceptions. The aftermarket (racing) slaves allow for adjustment. With that said, every time I think I know something I prove myself wrong!

[Marv D]

Cap-en (said in my best interpretation of a drunken sailor). BW is dead on!
My 94 with NV4500 and hydraulic clutch is definitely constant contact, and is supposed to be. Like 63GenIII is saying,, there is no return spring,, just like disk brakes, they are designed to have a very small residual pressure keeping the TB in contact. OTHERWISE, you would have 'lash' like we had in the old mechanical linkage. That would be insane and a down right safety issue if you had to 'pump the clutch up' to get it to disengage at a stop light!

This page has a small section on the constant contact 'self centering release bearing; (what a tecnical bunch of BS for 'constant contact' bearing)
http://www.morris4x4center.com/knowl...tch-basics.htm


Oh and like mongo said, you MUST use the specific GM GL4 lube or you toast the carbon fiber syncro rings. About $120 a gallon and HARD to find. THIS is the only reliable source I've found for it. There is lots of chatter on the Mopar equivalent over at Pirate4x4

https://www.amazon.com/dp/B000QIR1V2...=2K7QIL76TDLFX

[mongocanfly]

Interesting..I didn't know about the constant contact throwout bearings..my nv4500 is mech clutch and it doesn't ride on the p plate..has about 1/4" gap...as far as the oil goes I got mine from gm dealership....

[68c10airstream]

I had some exposure to s-10's with throwout bearing noises usually followed with only partial clutch release (slight grind in reverse) and probably not your case, but a multifinger pressure plate as it ages it has a tendency to end up with one of the fingers sitting higher than the rest and the TOB was a dead ringer for a full clutch job. Basically a heads up to look over the pressure plate for all of the fingers being level. Good luck diving in!!

['63GENIII]

Originally Posted by Marv D

Cap-en (said in my best interpretation of a drunken sailor). BW is dead on!
My 94 with NV4500 and hydraulic clutch is definitely constant contact, and is supposed to be. Like 63GenIII is saying,, there is no return spring,, just like disk brakes, they are designed to have a very small residual pressure keeping the TB in contact. OTHERWISE, you would have 'lash' like we had in the old mechanical linkage. That would be insane and a down right safety issue if you had to 'pump the clutch up' to get it to disengage at a stop light!

This page has a small section on the constant contact 'self centering release bearing; (what a tecnical bunch of BS for 'constant contact' bearing)
http://www.morris4x4center.com/knowl...tch-basics.htm


Oh and like mongo said, you MUST use the specific GM GL4 lube or you toast the carbon fiber syncro rings. About $120 a gallon and HARD to find. THIS is the only reliable source I've found for it. There is lots of chatter on the Mopar equivalent over at Pirate4x4

https://www.amazon.com/dp/B000QIR1V2...=2K7QIL76TDLFX

I didn't even think about having to "pump the clutch" if there was a lash or clearance there. Heck, pumping the brakes and the clutch at the same time would look like I was doing the Jitterbug while coming to a stop! Or had Fire Ants in my pants!

FWIW, and not trying to start any kind of "lube war thread", I couldn't find any of the Syntorque (I think that's what they called it) when I went through my 4500. I went to the Amsoil store and they had an oil which stated "For NV4500 transmissions". The guy swore up, down and sideways that it would be fine for the newly rebuilt transmission. After a little over 12,000 miles, I guess he was right. No issues so far, was easy to get and IIRC, it was just under 100$ to fill it and add the extra recommended quart. Just an option if you have a hard time locating it.

[Captainfab]

Thanks for the replies guys. Marv D and BW confirmed my suspicion, but that still seems like a bad idea to have the TOB turning all the time. 68c10airstream, yes I will be checking the pressure plate and disc. I am a little concerned that the clutch will need to be replaced as it is not really in the budget right now. The engine was replaced not too long ago (1000 miles according to the PO) and I would think that the clutch would have been replaced at that time.....it only makes sense to me. But if that was the case, why did the TOB go out so soon? As for the trans oil, I did replace that with the correct AC Delco synthetic trans oil back in December when I put the truck back on the road.

https://www.summitracing.com/parts/ado-10-4059

[Marv D]

I wonder WHY THE HECK I never thought of searching slummit for the gl4 GM synthetic. I'm liking that $18 a quart MUCH better than the $31 I've been paying through Amazon. Because I WORK my trans so hard pulling a 10,000 pound race trailer I change the fluid every 25,000-30,000 miles (it's a lot cheaper than the rebuild to replace those syncro's) . It's coming due so THANKS for the head-slap and Summit link.

[Marv D]

mongo,, I'm guessing here, but I would assume this is somethig that came about when they went to the hydraulic clutch vs the mechanical linkage. On my 4x4 the drive shaft between the transfer case and front diff (along with the exhaust) would make linkage a tough proposition. The hydraulic slave is on the passengers side of the bell housing. Typical GM engineers of the 90's trying to pack 10 pounds of $#!+ in a 5 pound bag.

[Captainfab]

Yeah, $31 a quart is ridiculous......

Originally Posted by Marv D

I wonder WHY THE HECK I never thought of searching slummit for the gl4 GM synthetic. I'm liking that $18 a quart MUCH better than the $31 I've been paying through Amazon. Because I WORK my trans so hard pulling a 10,000 pound race trailer I change the fluid every 25,000-30,000 miles (it's a lot cheaper than the rebuild to replace those syncro's) . It's coming due so THANKS for the head-slap and Summit link.