Tranny Piping Out Of Third

[Zed Head]

 (without berating me)

Wasn't trying to offend, just make a point that there was plenty there to get the job done.  Tried to take the edge off with my edit.  It would be nice if you could post at least one picture to match the eight that EuroDat has posted.

 

Good luck with it.

[Chickenman]

OP. You may want to check one simple thing before you go taking anything apart in the Transmission.

 

F4W71A ( early style ) and F4W71B ( late style ) have different shift lever attachments and shift levers. The shift levers are positioned slightly different in the transmission tunnel shifter cutout.  There are different shifter plate boots that fit in the tunnel to allow for the difference in positioning.

 

Now, either boot will physically fit, but if you get the wrong combination of shifter boot and transmission you will get the shifter boot compressing ( Bunching up )  too much when it is in 3rd gear.

 

When this happens it is like you are driving with your hand on the gear knob and constantly pulling back with a little pressure. Now, if you get the right " Coast " or unloaded conditions, the force of the shifter boot pushing back on the shift lever will be enough to pop the tranny out of gear.

 

I had this exact problem waaaayyyyyy back in the late 70's when I used to Race D- Production ( CSCC ) 240Z's. Car kept popping out of third gear whenever I let off the gas.

 

Problem turned out to be the new shifter boot that we installed for that weekend. We put a new one in because old one was torn. But we got the wrong part number for the matching tranny. Careful examination showed that the shifter boot was " bunching up " in 3rd gear. We put the old boot ( it was torn. Failed Tech. Through some Duct tape on to pass Tech ) back on and problem was solved. It was surprising how little backwards force was required to make the lever pop out of gear.

 

Then again, any one who has driven Dog Boxes (  like those in Formula cars or even Big Rig trucks ) knows that you can up-shift without the clutch, using very little force when you unload the transmission correctly. With race cars you just make a slight lift on the throttle and quickly ( and effortlessly ) grab the next gear. Now you can get WOT ( No Lift Shift )  systems for any Dog Box that have a very sensitive pressure switch attached to the gear lever. At the slightest pull back they will initiate an short ignition cut or timing retard and  you grab the next gear. No clutch disengagement needed at all.

 

Now Synchro boxes don't shift as easily as Dog Boxes, for clutch-less shifting. But it can be done. I can tell you from experience, if you have a the wrong shifter boot installed, it can cause enough backward force on the shift lever to make the Tranny jump out of 3rd gear.  1st gear doesn't seem to bunch the boot up enough to cause the issue and you are usually always accelerating in 1st gear. It's only under " light coast " situations that the Tranny Synchro hubs can disengage without use of the clutch.... and you don't " Coast " in 1st gear much.

 

BTW... the same issue exists with 5 Speeds. If you've swapped a 5 speed into your 240Z you must use the correct shift boot.

 

Might be something to check carefully. Easiest method is to just remove the shift boot and go for a drive. If Tranny doesn't jump out of gear anymore then you've found the issue.

Edited April 2, 2015 by Chickenman

[Chickenman]

BTW, unless you have Interlock balls or springs missing, it is very unlikely that they will cause a jumping out of gear problem from my experiences. YMMV.

 

Other than the wrong shifter boot, most jumping out of gear problems will caused by worn Synchro hubs and the Blocker inserts ( Dogs )  that engage in the Synchro hubs. The Blocker insert dogs and springs should be replaced when a Tranny is rebuilt.

 

The blocker dogs are the main part that lock the Synchro hub in gear. Torque transfer " LOCKS " these dogs in place, but if they wear down, the Synchro hubs can jump out of gear. You may also have to replace the Inner and Outer Synchro hubs if they are worn.

 

Picture of Blocker Dogs and springs below. F4W71B ( F4W71A is similar ) . Numbers 30 and 31 in picture.

 

Synchro hub assemblies consist of #28 ( x 2 ) " Sleeve Coupling "  and #26 and #27 " Hub Synchronizer in this example:

 

http://www.carpartsmanual.com/datsuns30/DatsunZIndex/PowerTrain/TransmissionGears/4Speed/FromSep-71/tabid/1711/Default.aspx

 

Edited April 2, 2015 by Chickenman

[ericjump]

EuroDat: Thanks, that clears it up, just wanted to make sure what I was doing was the right thing. I'm ordering the springs today and will give you a blow - by - blow when I finish.

Zed Head: I was always taught to ask if you weren't sure, especially in my line of work

Pictures coming.

Eric

[ericjump]

Springs are installed, problem Fixed! Installed the springs in the 3/4th and Reverse housings (couldn't reach the 1/2nd bolt) and that fixed the problem of it popping out of 3rd. Thanks so much for your help. I'll install the 1/2nd next time I have the console/shifter boot off. I made a little hook to remove the springs, (Remember the hook has to go inside the spring to remove it). I's post a picture but can't figure out how to do it. Thanks again.

Ericjump

[EuroDat]

Thats good news. Easy fix. Chickenman explanation about the hubs is probably also contributing to the problem, but the new springs is enough to fix it. To do the hubs, you need to fully dismantle the tranny. These transmissions are getting old an all the parts have wear on them.

If you want to load photos, click on More reply options and you will fing it there.

Chas

[ericjump]

Here is a picture of the spring I replaced in the 240 transmission,and the tool I made to remove the spring, it solved my popping out of third (into neutral) problem. This is a easy fix and would recommend it to anyone who has this problem, the springs are cheap and it only takes minutes to complete. Thanks again for the help.

Ericjump

[cbuczesk]

When we disassemble transmissions for rebuilds we use a strong, little magnet on a stick to pull out the spring and ball.

 

Chuck