Dogleg tranny very loud in 3rd and 5th gear

[ServeEm]

Hello all, new proud owner of a 71 510 4dr. Purchase was a great deal for this great car.

 

The only issue that is beyond me is the tranny. The engine's strong, clutch engages great and the tranny shifts without any issues. As I'm going through the gears shifting fine I go into third and it's a bit louder. The increased sound doesn't sound like grinding or knocking. The sound goes back to what I would think is a normal operating volume when thrown in fourth. Then shifting to fifth gear is sounds even louder than third. Again it doesn't sound like grinding or knocking, just loud like a big work truck. Any ideas or anyone else that experiences these sounds? Thanks in advance for any help or tips!!

 

Richard

[kiznook]

worn out transmission, under typical daily driving conditions, you normally spend the most time in 3rd and 5th, so it would make sense that they would wear the fasest. I would imagine if the transmission only saw a lot of hard autocross hours, the same would be true for 1st and 2nd.

 

As far as easy fix goes, get some redline MTL or similar synthetic high grabe gear oil. Or regular gear oil with half quart (?) or ATF...I'm pretty sure thats "the old datsun tranny trick" but it smells terrible!!

[Bleach]

it could be that it just is low on fluid I suppose. Can't hurt to drain the fluid and put in some fresh lube! :D

[kiznook]

oh yeah, there is that. the lube may not be reaching one end of the trany properly, so you would probably hear noise in 1st, 3rd, and 5th. But you aren't likely to actually hear any noise in first as things aren't spinning very fast.

 

Either way, service the transmission with some good GL

[tiltnose510]

As I recall, If fourth is quiet, it would mean that the bearings for the cluster gear are getting sloppy because fourth is a "straight through" gear and the others are on the cluster off to the side. When you get into those gears it would make noise if the bearings are getting worn. third and fifth are under a bigger load and would be louder than the others.

[datzenmike]

As I recall, If fourth is quiet, it would mean that the bearings for the cluster gear are getting sloppy because fourth is a "straight through" gear and the others are on the cluster off to the side. When you get into those gears it would make noise if the bearings are getting worn. third and fifth are under a bigger load and would be louder than the others.

 

Yeah. Not sure about ATF, it has lots of detergent additives to keep dirt in suspension. (so it gets on and between the gears and bearings) As long as you use it as a flush and drain, it would clean the insides. Then run a thicker 90W to cushion anything with too much clearance and muffle the noise. Or synthetic to reduce any more wear. The synthetic is very thin and won't muffle the sound as well, but may prevent it in the first place. Synthetic, will flow past seals that would normally hold back regular oils, so change the rear tail stock seal, $5 at Nissan. Be sure to pull the bottom bung and clean off the magnet. It will or should have a black 'paste' of metallic powder on it. Inspect for chips of metal. Wrap the bung and the oil filler bung with plumber's Teflon tape to prevent synthetic oil leaks.