Ok, while driving back, the M20 transmission would sometimes pop out of 4th gear under heavy acceleration. Any ideas on what causes this?

Thanks!

John

jgoglick38840.6571527778

Joel will let you know soon.  Mine pops out of third on deceleration.longhorn29438840.6731944444

I want to hear about this too...

Mine will sometimes drop out of second on easy deceleration but mostly going downhill...

Also will occassionally jump out of 4th at heavy accel too...

There are two areas that can cause any transmission to pop out of gear.  The first is the shifter adjustment.  If the linkage is out of whack, the car can pop out of gear.  This is just a simple adjustment to repair.

The other area is internal.  There are internal linkages and shift forks.  It they are worn, the trans will act just like the out of adjustment linkages.  Replacement parts are in order.  But there also the possility that the shift coller splines and gear splines are worn.  These are actually tapered just a light bit so when torque is applied, the gear stays engauged.  When the wear, the torque can actually force them apart instead of together, and the trans pops out of gear.

Which One is the problem?   First realine the linkage.  If that does not fix it, the trans needs to come out and torn down to inspect for wear/damage inside, and go from there.

Don't try to second guess which one it is.   Some may say that if it is only in forward or reverse, and not the otherdirection, its spline wear inside.  But due to engine torque, linkage adjustment can still create the condition.  The engine torques up, tugs the linkage, and it moves.

 Unfortunately, I think mine falls into the internal catagory. When I decel in third, I can hold it in but feel a sort of bump or clunk several times. If I wasn't holding it in on those bumps, it would jump out.

Sounds like spline or shift coller problems.  Not fun.   In reality, one the trans is out of the car, it's really not too bad to repair.  I don't advise internal repairs for a first timer, but with decent mechanical skills and a good manual, it can be done. 

Ken is right in suggesting to check the shifter linkages first. The shifters on our cars are actually bolted to the trans crossmember, so any movement of the trans/engine, due to bad mounts, will create a problem.

Jumping out of gear under accelleration is usually an indication of worn synchro teeth on the respective gears.
Jumping out of gear(or "falling" out) when decellerating is indicative of excessive endplay, usually caused by worn bearings. If it just falls oput of gear while you're just cruising along(not under power), then there is wear on the teeth of the gears.
The synchro teeth on the main gears have a slight undercut, or angle cut in them. This keeps the gear and coupler connected under power. If the teeth wear, it won't be able to "hold" the coupler onto the gear, and it falls out of gear.

These problems can also be caused by worn forks not allowing the synchro "slider" to fully engage in the teeth of the drive gear.

Lots of folks have a habit of holding onto the shifter while they're driving. This creates pressure on the fork that would not normally be there. This wears more forks than any other issue, and creates a jumping out problem in fourth more than any other gear.

Also, while you're checking your linkages, make sure your lower shift boot(the rubber one) is not damaged in a way that will hinder the movement of the shifter handle/linkage.

Give up yet?!

 Nope, I don't intend to try. Most all of my mechanical skills lie in lawnmowers, which I'm up to my kyster in right now. (no pun intended )

Ken and Joel - thanks for the tips! I'll check out the linkage and shifter boot. When in fourth gear, I force myself to keep pressure on the shifter - which, of course, goes against everything that is right. I remember dad ingraining in me about the damage that causes.

Don't feel bad, John!! I do it too! I grab the very bottom of the shifter, tho. I do it more to keep it from rattling than anything else!