NV4500 clunk

[Frankenchevy]

I'll get the measurement in the morning.

Thanks!

 

[bucket]

True. I figured the rise of the crossmember from the bottom flange of the frame wouldn’t change though. I could be wrong, but I thought a W crossmember would be the same on a k20 and k30.

Your crossmember should mount on top of the bottom frame lip... inside the 'C' of the frame. A K20 will have it mounted to the underside of the frame.

 

[Frankenchevy]

Your crossmember should mount on top of the bottom frame lip... inside the 'C' of the frame. A K20 will have it mounted to the underside of the frame.

Really? I have the flat CM and it’s always been mounted under the frame...

I thought I’ve seen other cucv trucks the same way. I need to see if I can find some pictures.

 

[Frankenchevy]

Just like this guy’s

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[Frankenchevy]

The guy at the diff shop that did both of my axles said he’d put an ARB in for free if he got to keep the Detroit. Sounds pretty reasonable.

edit: actually he said he’d owe me money after the work.

 

[SquareRoot]

@Frankenchevy .

My x-member (w-style) mounts to the bottom of the frame rail.

The flat part where the trans mount sits is exactly the same height as the bottom of the frame rails. The trans mount is 3 inches high.

 

[bucket]

Really? I have the flat CM and it’s always been mounted under the frame...

I thought I’ve seen other cucv trucks the same way. I need to see if I can find some pictures.

My thought process isn't always correct. What I meant was, if you had the "W" style crossmember, it would mount up inside the frame.

The flat crossmember used through '84, and all CUCV's had two styles. A more flat one for K30's and one that had more curve on the ends for the 10-20 trucks.

 

[Craig 85]

Granted I have a 205 and a "W" crossmember, but it's above the frame rail. All my K10/20's have been below.

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[SquareRoot]

It's impossible for my x member to mount inside the rails. There's only 1 set of holes in the frame that corresponds with mounting it underneath the rail.

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[bucket]

It's impossible for my x member to mount inside the rails. There's only 1 set of holes in the frame that corresponds with mounting it underneath the rail.

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Right, but if it were a taller K30 frame, the holes would be there.

 

[SquareRoot]

Right, but if it were a taller K30 frame, the holes would be there.

Ok, makes sense.

 

[GRK82]

I have a NV4500 conversion in my 1985 K20. My trans is a 1993 GM unit. My tower would torque over and clunk my floor cut out. I had to make the hole larger. I know you’ve probably already thought of this and checked clearance. Have you checked your motor mounts? That could cause lots more movement than you would anticipate.

 

[Frankenchevy]

I have a NV4500 conversion in my 1985 K20. My trans is a 1993 GM unit. My tower would torque over and clunk my floor cut out. I had to make the hole larger. I know you’ve probably already thought of this and checked clearance. Have you checked your motor mounts? That could cause lots more movement than you would anticipate.

I was one of the things I considered. I checked clearance, but maybe I missed something. I’d be curious to see a truck with the 4500 in it from the factory to see how much perimeter clearance they have. How much space did you end up with around the edge?

I have an experiment to conduct as soon as my lift is complete to see if I can isolate the clunk to the Detroit locker disengagement. If it is the culprit, it’s coming out.

 

[QBuff02]

I glanced through the comments briefly after watching the video.. Didn't see if it was mentioned but that trans/shifter tower seems to move around an awful lot in that hole between accelerate and decelerate in my opinion. I'd be rechecking the mounts and verifying they are tight/to spec. And i'd also take a good look at your motor mounts as well. Especially since you just put brandy new trans mounts in, you really need to install all new mounts together. New engine mounts= new trans mounts and new trans mounts= new engine mounts. The torque has to go somewhere and it will find the weakest link. Dad taught me 30 years ago "If you feel it in your hands it's somewhere in the front end, you feel it in the seat of your pants its in the driveline or rear end" and I've used that ever since. I've seen rearends with excess play make it sound like its up in the trans. and it could be in the motor mounts emanating back through the trans. I saw locker mentioned but figured i'd throw my .02 in the ring.

 

[Frankenchevy]

I glanced through the comments briefly after watching the video.. Didn't see if it was mentioned but that trans/shifter tower seems to move around an awful lot in that hole between accelerate and decelerate in my opinion. I'd be rechecking the mounts and verifying they are tight/to spec. And i'd also take a good look at your motor mounts as well. Especially since you just put brandy new trans mounts in, you really need to install all new mounts together. New engine mounts= new trans mounts and new trans mounts= new engine mounts. The torque has to go somewhere and it will find the weakest link. Dad taught me 30 years ago "If you feel it in your hands it's somewhere in the front end, you feel it in the seat of your pants its in the driveline or rear end" and I've used that ever since. I've seen rearends with excess play make it sound like its up in the trans. and it could be in the motor mounts emanating back through the trans. I saw locker mentioned but figured i'd throw my .02 in the ring.

All valid points.

The motor mounts are new as well. I wasn’t super clear about that other than saying everything is new. At this point everything but the frame, body and axle tubes are new on the truck. Well, and I haven’t been through the transfer case yet, but the chain is tight and there’s no apparent slop in the bearings.

There was no clunk pre-locker, then some sense of it loading unloading behind the th400 and now it’s full on behind the 4500. The guy who rebuilt my axles concurs that they are in fact clunky SOBs behind manuals. That’s why I’m going to test the theory with the rear driveshaft removed.

I did check the mount torque again. Everything is really tight.