Grinding when going into 3rd

[TheErictag]

Hello folks I'm kinda new here I recently bought a 240 z made in 9/71 the original transmission has been swapped for a 5speed and under hard acceleration when I grab 3rd gear it grinds for a sec and I think I should be able to get it in gear easier without the grind. I love my z it's been my dream car for the past 30 years or so since my godfather had one when I was young I've been hooked ever since. Any info on the trans is appreciated

 

 

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[Mark Maras]

 We've run this problem up the flag pole in the past. It's not uncommon. First and foremost be sure the clutch is releasing all the way. If the clutch pedal releases and engages the clutch down close to floor, the hydraulics may be suspect. If hydraulics can be ruled out, the next suspected cause and or cure could be gear oil. Many opinions on which one is best. In my notes from the last conversation, I have A/C Delco Friction Modified Gear Oil (recommended by @Zup) as the one that I'm going to try next. I'd try that before the dreaded trans tear down. Let us know the results if you try it.

[Zed Head]

I had a high RPM 3rd gear grind with a 1978 5 speed.  Changed to Redline MT90 from Valvoline 80/90W and it went away.  The AC/Delco product is probably good also. 

You might check to be sure that the fluid level is right first.  Or just go ahead and switch to a better fluid.  Make sure you remove the filler plug before the drain plug.  Heat, PB blaster, breaker bar.

[TheErictag]

Thank you all for your quick responses. I'll try the gear oil first and let y'all know how it goes. The good thing is haggerty just gave me my insurance and my "what it's worth " I'm super juiced time to RUN her through her gears ! $15k!!!


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[Chickenman]

2 hours ago, Mark Maras said:

 We've run this problem up the flag pole in the past. It's not uncommon. First and foremost be sure the clutch is releasing all the way. If the clutch pedal releases and engages the clutch down close to floor, the hydraulics may be suspect. If hydraulics can be ruled out, the next suspected cause and or cure could be gear oil. Many opinions on which one is best. In my notes from the last conversation, I have A/C Delco Friction Modified Gear Oil (recommended by @Zup) as the one that I'm going to try next. I'd try that before the dreaded trans tear down. Let us know the results if you try it.

Yep, AC Delco Friction Modified trans oil that's what I'm using in both my Audi and my 280Z 5 speed ( 83 ZX NA 5 speed ). Both cars shift like butter now. The AC Delco stuff saved me a rebuild on my Audi transmission. 2nd gear synchro was slightly damaged due to a failed pressure plate. Notchy shifting into 2nd after clutch repleced. Redline MTL, MT90 and Amsoil Manual Trans oil all failed to solve the notchy shifting. The AC Delco stuff did the trick. Solved some notchy shifting on a friends Infinity G35. he couldn't believe the difference it made. Good stuff IMHO. 

 

 

[Zed Head]

High RPM grinding when trying to make a quick shift at high RPM, like shifting up through the gears for acceleration, and notchy shifting aren't the same thing.  Don't get them confused.  

To add some detail to my 3rd gear situation - mine made a short "buzz" that I knew was a synchro problem.  Kind of like rubbing 10 teeth on a comb against a desk edge.  It only happened when trying to shift quickly at ~5000 RPM or higher.  The AC Delco might do the job, I'm just saying that I had what sounds like the exact same problem with the same model of 5 speed, and MT90 fixed it.  Details for clarity.  

I use a different blend of fluids in my transmission today because I had a mid-range notchy/grindy problem that Redline wouldn't fix.  Swepco 201 and ATF.  I'll probably just keep using that for all future transmissions because it works so well. But Swpeco is hard to find and you have to blend it and not many people use it and somebody's transmission ruined the synchros (probably coincidentally to the fact that they were in the middle of a race) when they used it.  So it's controversial.  JMortensen recommended it. He's also done some comparisons of the various fluids out there, I think.  Maybe he'll comment.

@jmortensen

 

[TheErictag]

Ok sweet now all I have to do is find where to drain the old fluid out of .. and find where to put the new fluid in!


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[rcb280z]

Just like what was said above, be prepared to fight the fill and drain plugs. If they haven't been removed for awhile they are going to be difficult. Just equip yourself with the right tools before you get started.

[SteveJ]

Tell us where you are. There might be someone near you with the correct tools to remove the fill plug. I was lucky that when I needed to remove the fill plug on mine, it cooperated. 

[TheErictag]

I am in Fairfield California between Sacramento and San Francisco. Just about in the middle


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[SteveJ]

I know there are several people here from the Bay Area. 

I was at Travis AFB in the mid 90s. That's where I bought my first Z.

[gnosez]

Any Datsun/Nissan tranny (1970-83) normally used in an S30 weren't made to use new style gear oil which is why Redline M/T or Swepco & ATF is often recommended (the late John Coffey said either was what he used).

Several places sell it such as -

http://www.paragon-products.com/Swepco-201-Transmission-Fluid-p/swepco-201.htm

Grinding could be a clutch fork or slave issue if it's just one gear change  but a synco can't be ruled out.

As to getting the filler and drain plugs loose, the drain is the easiest with a 1/2-inch breaker bar and a short section of pipe for leverage while the filler plug seems to resist just about anything you throw at it. With the car on jack stands I use a small Sears jack that has a cup which hold a 17mm wrench within the cup and the other end on the plug. Jacking up the wrench usually does the trick.

Now filling can be an issue especially if you are under the car pumping away waiting for gear oil to spill out. Instead I fill from the top using just the right amount of gear oil which I measure out before starting.