Jump to content
red67

Trouble Downshifting to First Gear?

Recommended Posts

Newbie here. I recently purchased a 1971 240Z with a later model 5-speed trans..  Shifting into first is somewhat of a crapshoot, sometimes no problem, and more often it just does not want to go in, period. I've  had to take off in 2nd, if I'm at a light, which I do not like to do! I've done some searches, and come up with bleeding slave units and such. Just thought I would bounce it off you guys, before I started. Thank You!

Share this post


Link to post
Share on other sites

Does it grind or does the lever just not move?  Also, does it go in to reverse easily?  Reverse is the true test of your clutch since it does not have a synchro.

Might just be worn bushings on the shift lever, letting things get out of alignment.

Share this post


Link to post
Share on other sites

Goes into reverse easily!  First is only issue. No grinding, just won't go in.

Share this post


Link to post
Share on other sites

Goes into reverse easily!  First is only issue. No grinding, just won't go in.

 

 

With engine off and clutch down:

 

Try going into second (and push hard home) then try getting into 1st.

 

If it works: try again with engine running.

 

If not working at all: S14a time!!

Share this post


Link to post
Share on other sites

Does not seem to be a sloppy shifter, but when I get home I'll Try.

Share this post


Link to post
Share on other sites
1 hour ago, red67 said:

Goes into reverse easily!  First is only issue. No grinding, just won't go in.

Could be something to do with the check and interlock balls.  Balls that are pushed in to notches to keep the gears in the correct place.  I think that you can check those without removing the transmission.  EuroDat knows more @EuroDat

image.png

Share this post


Link to post
Share on other sites

I had a similar problem with a Ford transmission and while I was figuring out a solution I would just match speed and RPM when approaching a light to get in to first and just sit there with the clutch pedal down.  You've probably considered it already but just in case.

The solution wouldn't apply to your problem, it's a design problem with the Ford (actually Mazda) transmission I think.  In that case changing fluids to Pennzoil Synchromesh worked.  I've never heard of anyone having your problem though.  It seems mechanical, maybe a broken synchro or a jamming ball.

One thing you might do right off the bat is to check the fluid level, then drain the fluid.  Check the magnet for fragments.

Edited by Zed Head

Share this post


Link to post
Share on other sites

Hi Red67,

Not seeing it, hearing it or feeling it happen makes it hard to diagnose. From your description I think you have a problem with the teeth on the side of first gear.

 

A little background on how a borg warner type synchro works. 1st gear: The FS5W71B Synchro mechanism consists of:

Hub (26),  Sleeve (28),  Baulk ring (29),  3x inserts (30/31),   Constant mesh gear (19). 

The hub is connected to the main shaft. In the hub are three grooves for the inserts and springs the push the inserts outwards towards the sleeve. The inserts have a tab on the outside so they will "centre" in the sleeve.

The baulk ring has three slots where the inserts fit into. This makes the synchro turn at the same speed as the hub.

The constant mesh gear has teeth on the side and a cone that fits neatly into the baulk ring.

 

Now how does that all work when you change from neutral to 1st gear. Basic description: 

The sleeve moves over the hub and pushes the inserts and baulk ring onto the cone section of the constant mesh gear. The friction then causes the hub and constant mesh gear to synchronise by speeding up or slowing down the first gear to the same speed as the hub.

When you push further the sleeve slides over the insert tab and meshes with the teeth on the constant mesh gear. The teeth on the constant mesh gear are pointed to guide the sleeve into position.

Now first gear is connected through the constant mesh gear à Sleeve à Hub. The baulk ring and inserts have no function. The detent balls in the selector mechanism hold the sleeve in position.

 

What can cause your problem:

1. The baulk ring is worm and under minimum tolerances. It can not synchronise the hub and the constant mesh gear. Result is grinding gears.

2. Poor quality oil makes the baulk ring inefficient. Oil does make a difference.

3. The teeth in the constant mesh gear and sleeve are blunt and rounded. That way the sleeve hits the blunt teeth and you require more force to engage the two. You have to force the gear a little left or right to get it home. Occasionally they will line up and it go in easily.

 

From your description, I would think the 3rd problem is the main issue and maybe some of it comes from the other two problems.

I would try changing the oil for starters. The rest will require dismantling the transmission.

A member on this forum "Chickenman" recommends an oil from AC Delco or GM. The part numbers are AC DELCO USA part number is: 88900399. GM USA part number is: 12377916. I can not order the GM or AC delco oil here in Europe so I have no experience with it. I'm using Redline MT 75W-90 and find it very good. Here is a thread on the oil subject

https://www.classiczcars.com/forums/topic/51698-how-should-a-71-240-4-speed-feel/

I don't think your selectors are an issue atm.

 

 

 

1st Gear.JPG

Share this post


Link to post
Share on other sites

So today, with engine off went thru gears, with no problem. Weather would not permit a drive, so I didn’t start it. 

Thanks all for the help. How many quarts do I need. I know...search.

Edited by red67

Share this post


Link to post
Share on other sites

I've used only Mobil1 or Amsoil synthetic gear oil for years in my 280ZX Turbo.  Makes a significant difference in ease of shifting. Make SURE that you use type GL-4, NOT GL-5. 

Transmissions need the GL-4 type gear oil. 

Incidentally, when I looked up the gear oil for my '83 ZXT on the Amsoil site, it shows an ATF synthetic for the '83 5-speed. I'm pretty sure that is wrong!

Redline is an excellent lube, one of the very best. I believe this gear oil is correct: https://www.redlineoil.com/mt-90-75w90-gl-4-gear-oil

Edited by Pilgrim

Share this post


Link to post
Share on other sites
37 minutes ago, red67 said:

So today, with engine off went thru gears, with no problem. Weather would not permit a drive, so I didn’t start it. 

Thanks all for the help. How many quarts do I need. I know...search.

FSM says 1.5L.

Share this post


Link to post
Share on other sites

8 hours ago, jfa.series1 said:

This is a highly recommended transmission oil, perhaps the same one referred to by @EuroDat

SAM_1843.JPG

Yep. This is the one. Part nr 88900399.

I couldn't find that here in Europe, so I went with the Redline MT 75W-90. It works fine in these old transmissions.

Share this post


Link to post
Share on other sites
10 hours ago, EuroDat said:

What can cause your problem:

1. The baulk ring is worm and under minimum tolerances. It can not synchronise the hub and the constant mesh gear. Result is grinding gears.

2. Poor quality oil makes the baulk ring inefficient. Oil does make a difference.

3. The teeth in the constant mesh gear and sleeve are blunt and rounded. That way the sleeve hits the blunt teeth and you require more force to engage the two. You have to force the gear a little left or right to get it home. Occasionally they will line up and it go in easily. 

One other problem I rthought I would mention here. It could be playing a roll in this problem.

4. When the springs behind the inserts get old and weaken they don't apply enough pressure for the insert in the sleeve. When this happens, the inserts don't apply enough force on the baulk ring to synchronise the hub and constant motion gear. The sleeve slips over the inserts and hits the gear before it reaches the same speed as the hub. Result is gringing into gear and rounding the pointy end of the teeth.

A good quality oil with help this a lot and extend the usable life of the transmission.

Share this post


Link to post
Share on other sites

Also loosen the fill plug before draining it!

They can be stubborn. Aweful to drain it then not be able to fill it.

  • Like 3

Share this post


Link to post
Share on other sites
On 10/3/2020 at 4:47 PM, Patcon said:

Also loosen the fill plug before draining it!

They can be stubborn. Aweful to drain it then not be able to fill it.

Let me chime in on the transmission FILL and DRAIN plugs...

(begin rant) I have no clue why people tighten these SO TIGHTLY! It's un-necessary. In my former life I was a licensed Journeyman Plumber (Ret.). Actually, I guess I still am a licensed Journeyman Plumber - just not employed as such... What in the crap does this have to do with transmissions you ask?? THOSE PLUGS ARE PIPE FITTINGS (well, they have pipe threads...)

So, now that you know that I am eminently qualified to speak on the subject: 

- Go the Home Depot. Plumbing Department. BUY an entire roll of TEFLON TAPE.

- Go home. Properly apply (ya, just wrap that sucker up with tape) the teflon tape following the manufacturers directions to the male threads of BOTH PLUGS - BEFORE you install them.

- Tighten the plugs (BOTH PLUGS) ONLY ENOUGH so that they don't leak! There is NO pressure inside the transmission (like there is in your Natural Gas line or your galvanized water pipe) SO THE PLUG DOESN'T NEED 80 FT/LBS OF TORQUE. Seriously, you can practically screw them in by hand if you use teflon tape or good pipe dope (just kidding (exaggerating really) you need to snug them up.) But you really, really can stop over tightening those plugs.  How do I know? Come and remove these plugs from MY transmission. Be a plumber - even if you don't want to - for me...

(end rant);

  • Like 4

Share this post


Link to post
Share on other sites

@cgsheen1, consider it done! Thank you! Will report back with results. picking up fluid(AC) tonight. Hopefully change tomorrow!

  • Like 1

Share this post


Link to post
Share on other sites

Changed trans lube today! What a difference! Used 2qts AC Delco 10-4014. No problem downshifting now. Thank you!

What I did discover, was the speedo cable connection appears to be leaking. How do I correct that issue? Or should I start a new 

thread?

  • Like 1

Share this post


Link to post
Share on other sites

Great news.  Curious...was it low?  Asking for future reference.  Your problem doesn't really fit fluid change but might fit low level.

Regardless, your transmission will be much happier with that fluid.

On to the next problem.  There are threads about the speedo connection O-rings.  Can't find them right now but they do exist.

Share this post


Link to post
Share on other sites

Grats. Poor quality oil or low level can cause a lot of shifting issues. Yet another happy AC Delco/GM gear lube sucess story.

 

Speedo leak: Where exactly is the oil coming from? Leaking out the side of the adapter, then it's an o-ring seal between the adaptor and the transmission housing. If it is leaking through the cable itself, than it is a leaking lip-seal in the adaptor where the speedo pinion shaft goes through.

The speedo has an o-ring seal and a lip seal. It is easy to change both. They cost less than $10 for both seals. You will need to tap out a small roll pin, but with basic tools it's is not much work.

Simply unscrew the speedo cable and the 10mm hex (m6) bolt and locating tab. You can pry the adaptor out using a flat screwdriver in the locating tab slot. You will see the roll pin passing through to the side of the pinion shaft. It holds the pinion in place. You can tap it out with a small hammer and a blunt wood nail.

See tech article for the part numbers. You can also source the parts at a local (hydraulics) parts store. Make sure you ask for NBR, HNBR or Viton rubber. Don't use EPDM or Silicone.

 

  • Like 1

Share this post


Link to post
Share on other sites

Blown away! Thank you, thank you! 

I think fluid was a bit low from speedo leak, and was quite nasty.

After leak fix, it’s on to Diff. Fluid change, what juice do you recommend ?

 Thank you, again!

ABBCE35A-209A-45AE-A402-8897155B1D01.jpeg

Share this post


Link to post
Share on other sites

I've never seen a sticker like the one on yours.  Might be a replacement or rebuilt.

image.png

Share this post


Link to post
Share on other sites

Here's that speedo washer i bought from local Nissan. P/N #32709-14600. They don't stock them but can get it overnight.

Speedometer cable grommet (@ trans) - Open Discussions - The Classic Zcar  Club

It goes down in here.

Speedometer cable grommet (@ trans) - Open Discussions - The Classic Zcar  Club

Not sure if @EuroDat posted these numbers yet but I found them on one of his old post.

 

  • Like 2

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use. We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.