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FastWoman

Synchromesh worn out?

48 posts in this topic

ID: 1   Posted (edited)

Hi all,

OK, this is bugging me, so I'll ask you guys what you think.

I have a '78 280Z with a 5 speed. When the PO showed me the car, he warned me that the clutch engaged very close to the floor. It did -- VERY close. I later found the lock nut on the clutch pedal's push-rod had come undone, and the rod had screwed itself looser and looser. I corrected this and adjusted to specs.

When I bought the car, the transmission shifted a bit stiffly, but there was no gear bump/crunch between any of the gears. After I drove the car for a while, the transmission shifted a tiny bit more easily, but at the same time it developed a small grind when going into second gear from 1st -- perhaps a couple or three teeth. I resolved to change to change the transmission fluid to get a hint what was going on. Unfortunately the plugs were practically welded in place. I couldn't budge them and put off that job.

Later when I had the local Z specialist install an exhaust for me, I had him change the transmission fluid and asked for his opinions about the problem. He changed the fluid with Mobil 1, and he no problems with the fluid (no filings or debris). He identified a slow oil leak out the front of the transmission into the bell housing and said that was the cause both of my clutch chatter (I doesn't chatter when I drive it) and the 2nd gear grind/bump. He said I might also have a clutch issue, whereby the transmission doesn't fully disengage. He insisted that the transmission was fine and that my suspicion that the synchromesh was worn was probably not true.

The fluid change and further usage have done nothing to help this issue. The transmission continues to bump/grind every now and then when going into 2nd gear, even with the clutch pedal to the floor, and shifting continues to be rather stiff between all gears. (Caveat: I've been used to driving an original Saturn stick since 1991, and that clutch shifts like butter -- easiest stick I've ever driven. So I might not remember the Z clutch too well.) If it means anything, the bump/grind problem doesn't occur until after a day or two of driving if the car has been sitting any longer than a week. (That's probably why the problem didn't show itself when I was first inspecting the car, prior to buying it.)

Anyway, as far as I can tell, the clutch DOES entirely disengage when I depress the pedal. I have to release the clutch an ordinary distance off the floor before I get any grinding/bumping when shifting lightly from neutral to reverse. Reading more about synchromesh, I find it can get worn out if the clutch is not entirely disengaged when shifting. Well, with the clutch pedal practically to the floor as driven by the PO, that could easily be the case.

So I'm again wondering, is it a clutch disengagement issue or an oily clutch issue, as the local Z specialist seems to believe, or is it a synchromesh issue?

And if it's a synchromesh issue, is it rocket science to rebuild the gear assemblies, or is that something I should farm out to a transmission shop? Or is it better just to swap for another good/used 5 speed?

Thanks, everyone! :beer:

Edited by FastWoman

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Mine shifts smoothly. One thought, have you verified that your shifter bushings are in tact? Mine were completely disintegrated when I purchased the car and the shifter was really sloppy and hard to get in gear. Replacing those bushings did wonders.

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It's not a shifter sloppiness issue, Cozye. I haven't looked at the shifter bushings, but they feel solid (surprisingly so). I had replaced mine a couple of times in my old '75, so I know what a difference that makes.

BTW my old '75 had the 4 speed like yours, and that shifted fine. Now I have the 5 speed, so really I have no prior experience with this transmission. I wonder if it's ordinarily any stiffer than the 4 speed. (I doubt it, but...)

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Missed the 5sp part. No experience here. Hopefully it's not anything major.

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I have a 5 speed from a 78 in my 76. I had a grind like you describe, a few teeth worth, when shifting quickly from 2nd to 3rd at high rpm (freeway on-ramp stuff). Different from yours, but the few teeth description is right. It was very consistent, and my clutch worked perfectly.

I thought I had a bad synchro also (maybe I do), but decided to try the Redlline MT-90 fluid to see if their "balanced slipperiness" claim had merit. The stuff really worked. I was surprised because I'm cynical by nature, especially when it comes to old well-known products like oil.

I was using Valvoline 75-90W before. For about $25 it might be worth a look. I only bought two quarts and used the 75-90w to make up the difference, They will blend. Turned out that not all of the 75-90W drained out anyway so two quarts of MT-90 got me a full fill.

It's been in there for about 5,000 miles and I don't even think about the transmission anymore. It's not "notchy" in cold weather like the 75-90W was either.

http://www.jegs.com/i/Red+Line+Oil/816/50304/10002/-1

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If your clutch has not been fully disengaging as the cause of hard shifting in all gears, the synchros will be worn and thinned out. One stop-gap strategy is to use lighter transmission oil. That worked in my 1986 D21 Hardbody 5-sp. It takes special presses and pullers to rebuild your transmission. My 78 Z 5-sp has a slight clash in 2nd only when it is cold. Once warmed up, it is smooth and solid. Usually the 2nd gear synchro is the first to go. Did you mean that your mechanic noticed a chatter, but you have not? If he really pushed it hard and you normally don't, he could be right that the leak has really gunked up the clutch, and it is not releasing, causing hard shifting in all gears.

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I used Red Line in my Roadster. It did help the grind [a bit, not completely] but it is also a thinner oil. I have had a bit of seepage past the seals. If you already have a leaky seal, it will probably get worse with the thinner oil.

Have you bled the slave cylinder yet? That may gain you some travel in the throwout fork.

Also, I recently rebuilt a ZX tranny. It is not terribly difficult, but you have to be diligent about where you put all the pieces. I used a couple of dowels to simulate the shafts, and placed everything in the exact order as I took them off. The rebuild kit cost me $130.00- a shop would have charged me $600+. If you do it yourself, just study the FSM a number of times-especially the exploded diagram of the tranny guts, so that you understand where the pieces go and what they are called. Also be careful when you pull the synchronizers apart so that they do not detonate on you.

I borrowed a gear puller for the job, and it helps to have a vise and some pipes of varying diameter so that you can drive the new bearings into place without damaging them. I fabricated a metal bracket to hold the tranny in a vise which made the job much easier/possible at all. I'd be happy to send you the bracket if you paid the shipping.

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I used Red Line in my Roadster. It did help the grind [a bit, not completely] but it is also a thinner oil. I have had a bit of seepage past the seals. If you already have a leaky seal, it will probably get worse with the thinner oil.

Good to know. I was considering the red line for a maintenance item, now I have second thoughts. Not leaking now, but I don't want to start.

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ID: 10   Posted (edited)

Thanks, guys! I think what I'm hearing is that the transmission is weak/worn, but that I can possibly nurse it along for a bit longer with Redline. I might try bleeding the clutch too. I hadn't considered that a mooshy clutch could result in too shallow a lift, but that makes sense. Even so, I think all this just buys me time. Right? If I'm going to keep the car for a long time (which is my plan), it sounds like a transmission rebuild is in my future.

Until I can address this issue (probably in the spring), is the occasional bump/grind (by 2 or 3 teeth) is going to destroy the gears in the transmission?

Until then, I perhaps need to consider a rebuild, not only for the synchromesh, but also for the seepage from the front seal. A new clutch would also be an obvious thing to do. I'd probably find a transmission shop to do the work, all things considered.

Edited by FastWoman

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The other thing you can do is to double clutch on the way down. This will definitely prolong the balk rings.

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Some synchros don't like synthetic oil....period.

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I replaced the synchros and bearings in the 4 spd I had in my first 240z but I am no mechanic and knew that then so I took everything apart very carefully and laid it on newspaper in the same order it came apart. I also took a lot of pictures every step of the way as I wasn't sure I trusted myself to remember how everything fit. It worked fine after that with no spun bearing noise like it had before.

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Well, that's encouraging. I'll study it. Maybe I'm up to the task.

How hard is it, physically, to pull a transmission? Is it something a sturdy old lady can do? ROFL

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Well, that's encouraging. I'll study it. Maybe I'm up to the task.

How hard is it, physically, to pull a transmission? Is it something a sturdy old lady can do? ROFL

I pulled the 4 sp out of mine and put a clutch in it in one day. You could do it by yourself using a floor jack to support the tranny, but you will have to balance it a bit on the jack as you pull it loose. An extra set of hands sure is handy for this job. Especially when putting it back in. I had an extra set of hands, but when it came time to putting it back in, the extra set of hands wasn't pushing the same direction my mind wanted them to go..LOL I ended up just getting under it and man handling it back in place.

After doing the complete suspension, I'd say the tranny is a breeze. You will have to drop the exhaust off the manifold, and take the drive shaft loose on the differential. Those are the hardest parts.

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I remember a wooden dowel guide of some kind I had to use to line up the clutch disk(?), some sort of specialty tool. I couldn't get the transmission back on without it.

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most if not all clutch kits come with the alignment tool. The transmissions on these cars are super easy to pull. last time I did this I sat under it pulled it out onto my chest. Install was the reverse. They do not weigh much.

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Well, it sounds worth considering. About how much does a 5 speed weigh, give or take? And about how much time should I budget myself for a transmission and clutch rebuild?

Tlorber, I appreciate the kind offer of your vice frame. I might take you up on it yet. ;)

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I want to suggest you try GM synchromesh rather than Redline MTL.

I put Redline in a Miata and felt no benefit. I heard the same from others. Then I heard a plug for GM synchromesh so I tried it in my other Miata that was being a bit difficult to get into third on the track. Boy, talk about an improvement!

You can now get Synchromesh from your local car parts place. It is more expensive but definitelty worth it to me.

From my notes: Do not put a GL5 fluid in your trans (ie Castrol syntorq) the sulfer content may be too high and eat the brass synchros. (Anyone, feel free to correct this info)

Al

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Thanks, Al, but isn't fiddling with the oils just a way of buying time? With a leaky front seal, 165k on the original clutch, and synchronizers that are that fussy, am I not at a point where I really need to pull the stuff out and rebuild it anyway? I'm not planning to do it tomorrow, mind you, but I think it might be a spring project, whether I do it myself or farm it out. (I'm leaning more towards attempting it myself.)

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Thanks, Al, but isn't fiddling with the oils just a way of buying time? [...]

Yes. It *might* buy you time and it is relatively cheap and easy. I was mostly addressing the fluids discussion that was going on in the same thread.

But I agree, with a 165k clutch and a front seal leak, pulling the trans is inevitable. Also consider replacing the engine rear main seal while the trans is out.

I agree that rebuilding your trans is the best solution. Finding a nice used one might be a good alternative. The problem is that most times you won't know if the trans is good or not until you install it.

I am sure you can handle the job from everything I have heard you say, as long as you have access to good tools.

Al

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I would estimate that the 5 speed weighs in at 60-70 lbs. As long as you can get the car up high enough, you can use some 4x4 blocks and work each end down/up bit by bit. That way you are only carrying 1/2 the weight at any time. To do this, you will need to jack up the front of the car, and place a support under the oil pan so that you can control the pitch of the motor as the tranny pulls the rear down. Just make sure you keep an eye on the fan blade so that it doesn't smash against the shroud.

This all makes more sense when you are going through it.

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Thanks, guys! It sounds about like our boat transmission in weight. Not fun, but I managed. (I farmed out the rebuild, though!) Anyway, I guess that's what I'll do, come spring. Meanwhile, I'm going to stay warm! LOL

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FastWoman- so any luck? I've got a similar issue- only 2nd gear grinds about 50% of the time, sometimes a little bump, sometimes a pretty gnarly few teeth. My clutch catch point is very high- only have to press in a few inches. Literally just got the car though, so haven't done anything yet. Sorry not trying to hijack your thread just hoping you've had some success short of a full rebuild :)

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Any luck? Not yet. There's SNOW on the ground outside! Yeeeech! No, it will have to wait for warmer weather.

FAIW, I've recently acquired a Miata and am also active on a forum for that car. This same problem occurs in Miatas (also 2nd gear), and the solution seems to be Redline fluid. So I might try changing out for Redline first, as well as bleeding/flushing the clutch. If that doesn't work, then I'll probably dive into a rebuild.

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