Grinding M/T gears... uh oh

[slipnfall]

Hi there, I like to get opinions on these problems as they happen, so please excuse all the problematic posts of late. Anyways, I'm beginning to think that my transmission is a bit more worn than I'd like to believe. It's a '92, about 130k on it. Just changed to Redline MT90 fluid. On a cold start, my car is difficult to get into reverse. The shifter won't pull 'down' far enough, untill I let the clutch out a little, then depress the clutch, and it goes right in. Not too big a deal, b/c it only happens once in the mornings. No grindage. Worse yet is regular shifting. If I shift *slllooowly* into gear, I get a grinding, and it freaks me out. If I shift quickly, with a little extra force, it goes right it. Certainly a little resistance. Same with up as downshifting. If I take my time and baby it, it grinds. 1-2-3-4. I actually took it to a M/T shop, and he test drove it: I was getting a 'whiirrrr' in Neutral with clutch out. He said that was normal, and didn't detect anything wrong. I just recently noticed this grinding though. My fluid change yielded lots of bit's and pieces of metal, plus metalic sludge. Is this telltale sign of syncro's excessively worn? Exedy clutch/pp/throwout.

Thanks for any insite!-Jamie

[NISTECH]

first, is the mt-90 gl4 or gl5? gl5 is corrosive to the brass syncros.2nd the "whirrrr" is not normal if its loud enough to hear clearly at a stop with traffic going by. That indicates your bearings are worn,which you comfirmed during your fluid exchange finding metal bits in it. some on the magnetic drain is ok but flowing with the fluid is a bad sign.

[slipnfall]

first, is the mt-90 gl4 or gl5? 2nd the "whirrrr" is not normal if its loud enough to hear clearly at a stop with traffic going by. That indicates your bearings are worn,which you comfirmed during your fluid exchange finding metal bits in it. some on the magnetic drain is ok but flowing with the fluid is a bad sign.

Most deff. GL-4. I was very close to putting GL-5 in b/c the Parts Store clerk told me you can always 'go up in grade' with M/T fluid. Good thing I checked here 1st. The whirr is only noticable in my driveway, with windows up, stereo off, and shifter/radio trim removed. I'v never heard it in traffic, so it's not that loud.

There were probably a dozen or so 'chunks' in the pan when I drained the fluid. Rough guess was 1x1x1mm in size. So these pieces are likely from the bearing, and not the syncro's? I was told the slight noise was probably the input bearing, which I didn't think was even submerged in fluid.

Can a poorly adjust clutch pedal cause this hard shift or grinding? The car will not move with the clutch in and in 1st/Rev, but perhaps the transmission gears are still moving slightly(not disengaging fully).

This is something I'm going to check tonight. FYI, removed damper, new slave, DOT-3, vacuum bleed.

Thanks,-Jamie

[dgeesaman]

1) the thing about reverse not shifting is normal with many m/t vehicles. Like you said, pump the clutch and try again. It's a matter of the synchros not lining up perfectly, which is not an issue on a moving vehicle.

2) what color were the metal chips? Synchros typically have a bronze/brass color. If you have trouble shifting, try doing a double-clutch into that gear and see if that makes it shift smoothly. (Double-clutch example: clutch in, shift from 1st to N, clutch out, clutch in, N to 2nd, clutch out). Double-clutching will avoid loading the synchro, which allows you to pinpoint the broken synchro, and by double-clutching procrastinate the repair indefinitely.

Dave

[slipnfall]

The pieces in the fluid were not a brass or bronze color, they were a dulled silver/gray. I tried to double shifting, and although it's a little awkward, it sees to help. The shifter pops right into gear, although I havn't really been able to isolate a single gear. It seems to improve them all a bit.

When I shift normally, the shifter get's 'stuck' on the side of something, and pushing faster just makes it slide by. transmission's are something I really know very little about, but as I understand it, the syncro's are there to bring the next gear's 'gears' up to speed with the output? Do the syncro's 'load' up to the point that you shift, or when you push the clutch in(anticipating the next gear)?

Thanks for the tip, looks like I'm gonna be using this a lot untill I can afford a rebuild. (I can hear it now....$$cha-ching$$)

-Jamie

[dgeesaman]

Well, most of the time it's synchros that get damaged, 1) because they are the first moving part to begin engaging teeth during a gearshift and 2) because they are made of a softer metal. This is by intention, since gears are $$ and need replaced in pairs. However, damage to the synchros can be followed by damage to hard parts (the grey metal).

If you see greyish metal pieces of small size, it's possible that the clutch sleeves (the piece that slides over the synchro and onto the gear) have had their teeth chipped or damaged. Or the keys that this sleeve rides across. With damage to the hard parts such as this you're looking at reduced torque capacity. No burnouts.

I haven't rebuilt a Nissan transmission yet, but since you may live relatively nearby I'd be willing to help. They are fundamentally similar. I just finished an M/T rebuild on my RX-7.

Dave

[slipnfall]

Hi Dave, Well no news is good news eh? I'm not sure if I'm really able to afford a rebuild just now, otherwise I'd be tempted to take your offer. I don't know that I'd even have the apropriate tools(enought to rebuild my engine and install it, but I imagine there's some special pullers for trannies). What did you end up replacing in the RX7, and at what (total) cost? Just a rough guess, what do you think it'd cost me to *have* this rebuilt? Sad, because I always had the impression that Nissan transmission's are bullet-proof. In fact when I called Maaco, they said they've never worked on one, because they're so stout. I have a spare M/T at home, 120k, was hoping I didn't have to use it. :-)

I'm looking at the FSM now and I see what you mean(the sliding shaft sleeves as you call them).

-Jamie

[slipnfall]

Oh FYI, I really don't rip and tear in this car just yet, but I have easily laid rubber with 3/4tread all season's.

[dgeesaman]

A rough number for a rebuild is $1000. It depends on what needs replaced. Any decent transmission shop can do the rebuild.

It's probably better to replace all the synchros on the 120k spare and install that. I paid for OEM parts on my Mazda and the total came to $500, all labor being mine. I don't know if any special tools are required for this transmission - I had to make one or two for mine. You can see the writeup I did at http://www.davidgeesaman.com

[NISTECH]

several of the components are pressed on so you would need a hydro press to seperate and reinstall the components. There is also asleeve needed to go over the shaft when pressing gears back on.

a hot plate would be usefull as well to heat up some of the bears and spacers when installing them. It helps them just slide on instead of pressing them.