Strange grind in 4th and 5th gear.

[ichorid]

Hey guys, so I'm curious if you have any insight on what could be causing this sound we are trying to fix.

Here are the symptoms, In 4th gear above 2k rpm a grinding noise starts coming from the tranny, sounds like it could be between the clutch or the tranny. Shifting into 5th noise is gone until 2k rpm and above, at this point if I remove my foot from the gas, the sound is there. Like a high pitched-ish grinding sound. Haven't really noticed it in 1-3rd gear. Another symptom that may be unrelated. Clutch depressed rolling forward with car in gear. Noise is there but sounds slower. Also the noise in 4th, and 5th goes away when the clutch is fully depressed.

Trouble shooting that has been done, Tranny is out, and the clutch/pressure plate are showing no abnormalities.

so only other things that could be causing this issue are tranny, diff, driveshaft?

Any one had a similar issue with some light to shine, really dont want to start replacing things bit by bit till its gone.

thanks for your help guys.

[hang_510]

TO bearing? usually consistant throughout the gears though...
always go for the easy things first

[ichorid]

thats what I thought, I dont think it is the TO though. I only notice the sounds in 4th and 5th gear. it could be there in the other 3, just too loud in the cabin to actually hear it.

also, should have mentioned, TO, pilot, pressure plate, clutch, and flywheel are all new. maybe 400 miles on em now.

[datzenmike]

Tranny is out? Remove the bottom drain plug and look at the magnet. Normally it will have a black 'paste' on it and maybe a few metal particles. (I pulled one once and it had a ball bearing stuck to it) It's very likely the counter bearing is in bad shape.

You can check both the main (top) and counter shaft (bottom) front bearings by removing the 5 X 12mm bolts on the front cover and removing it. Don't tap on the nose that the input spline sticks out through or you will snap it off. Save any shims that fall out and note their location.

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Here's the cover off. The main shaft input bearing is at the top, the counter shaft front bearing is just below it. This particular FS5W71B has the newer 62mm counter bearing. Yours, if from an L series, will have the 56mm bearing. Around '84, Nissan switched to the larger bearing to help eliminate the failure prone smaller ones. The front cover and 'bell' case was also modified to give better oiling to it as well.

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The bearing should be without looseness or slop and free to turn when the spline is turned. If you decide that either or both bearings are bad all you need to do is remove a snap ring from the input bearing, (right, and save any washers or shims) ...

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... and the reverse light switch (and top gear switch if applicable) just behind the clutch fork boot. Undo the 8 X 12mm forward facing bolts that clamp the front and rear case halves to the middle adapter plate.

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Tap forward on front case being careful to not dislodge the rear half:

[img]http://i138.photobucket.com/albums ... .jpg[/img]
[img]http://i138.photobucket.com/albums ... .jpg[/img]

Now you have full access to the front bearings. You can clearly see the groove in the main input bearing that the snap ring slips into. Use a gear puller to remove them and drive the new ones on with a suitable piece of pipe.

[img]http://i138.photobucket.com/albums ... .jpg[/img]

Be professional. Use a proper gasket making sealant like Permatex blue. Do not use RTV, it's suitable for Chevy valve covers only. It always leaks eventually.

[ichorid]

thanks a ton datzenmike Ill let you know what gets found.

[five&dime]

Sounds like my problem in my 5 speed. Mine is a roadster 5 speed. 5th gear is a two piece assembly that is pressed together. It is fairly common for the two pieces to become loose. Mine did this which at first was a noise very similar to what your describing. Soon after I was stuck in 4th and it wouldn't budge.

I had to send mine to a guy in Cali who welded it back together and set it back. $75 shipped. Much better than the $550 new 5th gear.