The DREADED 1st-to-reverse, Have developed a process that is straight forward to prevent the 1st to Rev Options

[ctc911ctc]

914-6 all original - rebuilt the transmission

This is part of the rebuild thread - http://www.914world.com/bbs2/index.php?sho...3371&st=100

Transmission - Shifter -> This is my working theory, I am probably wrong.... (IMG:style_emoticons/default/biggrin.gif) (IMG:style_emoticons/default/dry.gif)

While I am chasing the 'carb-spitting' issue, I am also chasing the shifter being.....OFF

This is manifesting itself as the DREADED 1st to reverse problem.......As to the condition of the 901, gears are all within spec, new syncs 1st and second, new slider for 1st reverse - new dog teeth for 1st and second.

Let me explain,

When I put the car into 1st or reverse, I (as well all of you) push the lever from RIGHT to LEFT and feel the spring pressure of the shift plate.

About 1/4 of the way to the full extent of the spring compression the there is strong resistance. BUT i can CONTINUE to push to the left. I believe that I have reached the limit of the various linkage components and that what I am REALLY doing at this point is torquing the linkage. I can then continue to torque the linkage until I have reached the full travel of the shift lever spring plate



What happens is; when the shift comes out of 1st, there is no SPRING BUMP to push the selector in the transmission from the 1st-reverse position to the 2nd-3rd or middle position.

I have cut pictures from Clay Perrine's excellent 901 cut-away to depict what is happening

Transmission is in Neutral on the other side of the selector bars is a vertical channel, there is a knob that is in ONE of the THREE channels - when moved the selected bar moves left to right



Now, the knob is in the channel of the lowest bar AND the bar is slid to the left for FIRST GEAR



My shift LINKAGE - not the shift lever - when moved forward never gets the BUMP from the spring and as a result STAYS in the LOWEST position THOUGH the shift lever HAS moved to the right and you think that the shift is in the correct place BUT NO, it ends up pushing the SAME slider BACKWARD into reverse



OUCH!!!!!

What should happen is the selector should get a bump to the next position from the spring and end up here.




MY PLAN

I am going to adjust the Shift bar about 20 degrees to I do not get any mechanical loading, not sure if 20 degrees is correct......feels right.......

[Front yard mechanic]

Just remember it’s not gear grinding it’s gear polishing

[brant]

Is this the same box you found in gear when you installed the shift linkage?

[ctc911ctc]

Yes it is

Currently it does shift through all gears, I can shift around this problem but would rather make this right

Thank you

Is this the same box you found in gear when you installed the shift linkage?

[ctc911ctc]

There may be a short shift kit in the car - more to come!

(IMG:style_emoticons/default/shades.gif)

[ctc911ctc]

Trying this tomorrow

https://www.pelicanparts.com/techarticles/9...0into%20reverse.

[ctc911ctc]

*******UPDATE***********

Did you ever have the feeling that you were making a situation 10X more complicated than necessary? Yea, that is what I am feeling now.

My sense of the transmission linkage is that the engineers in Germany added components to natively connect a 901 transmission to engines that have been 'turned around' where the back is not the front and the front is now the back.

In the early 1970 914s, either 6 or 4 this involved the following:

Hand to Shift Linkage transform
Lateral Adjustment transform - at the fire wall
90 degree transform - at the tail, changes rotations from Front/Back to Lateral
90 degree transform - inside the 901, changes lateral to Back/Front - end of 180 deg transform
Selector Transform - selector Rod to Gear-channel-Gear selection

Each of these transformations introduces 'lash'
In a new car this lash is within SPEC

**********End of Analysis**********

So, I wanted to make certain that when the spring plate was unloaded all of the transformations resulted in the gear selector (final stage in the transmission) was in the 2nd/3rd slot........

Sooo, I started by selecting Reverse and then getting the various components in the 1st/Rev position.


As the car gets older all of the soft components age and introduce more lash
In a small way all of the assembly components also introduce lash, roll-pins, U-Joint Bolt, etc.....





Now I unbolt the rod that attaches through the firewall and the nut is slipping......WHAT? I was a bit surprised - on my '74 this is not the case, the nut will stay in position........Soooooo

I had to fashion a tool to hold the nut, took a few hours of trail and error.



After the bolt was loosened, I then went and made sure that the gear-shift was in the position of Reverse, that the springs were fully loaded but not too much pressure.

This introduced about a 10-20 degree difference from where the rod entered the receiver as seen above.

Tightening this bolt was 10 times the pain as loosening, I will post a picture of the tool I fashioned to hold the nut asap.

Shifted better on the stands - not 1st to 2nd grind, but if may be going into 4th..... (IMG:style_emoticons/default/mad.gif)


Will test drive today.

More to come.

[ctc911ctc]

*****UPDATE ********

I have spent about 6-8 hours on this quest of a perfect 1970 tail-shifter shifter -AKA- when it was shipped from Germany, what was it like?

My initial premise is/was that if all of the gears are to spec (lash is within spec - check!) and they are. All of the sliders are smooth with sharp teeth that would make Dr. Evil jealous (super sharp! - BTW, Dr Evil is our #1 901-transmission authority ). New Sync Rings for 1st and second as well as very sharp and not warn-out Dog-Teeth - new for 1st and 2nd with a new 1st/reverse slider (yea, the expensive one).

With all of the above true, and bench tested then I should be able to get back to very close to factory spec. Right? (IMG:style_emoticons/default/dry.gif)

Here are the challenges:

1. there are many mini-transmissions of the shift forces prior to arriving at the sliders inside the transmission.
2. Each of these mini-transmissions ( I listed them earlier in this thread) introduce their own lash, which can introduce inaccuracies in the setup.
3. Minor deterioration in the different fasteners and guide-sleeves introduce more lash or inaccuracies. Special attention need to be made to the Roll-Pins and other fasteners.
4. Introducing a short shift kit into this equation, makes setting this to perform correctly a huge challenge.

I initially started on this quest using the "reverse-gear" method. Get the transmission to reverse and then put the handle where you want the reverse position to be and lock it down.

This will have you fishing for the correct tension on the Shift-Spring-Plate at the "Stick-Shift"

After many hours of trial and error - and also having to fashion tools to perform this job, - I have determined that the most accurate method is what I call the Neutral-2nd/3rd method.

Neutral-2nd/3rd method.


1. Make certain that all of the components along the path to the transmission are operating as close to new as possible; clean, lubricated and smoothly performing

2. loosen the collar that holds the two shift rods together just front of the firewall, you will need to work this collar a few times, get used to loosening and tightening this collar

3. place the shifter in the position of Neutral ready to shift to either 2nd or 3rd.
4. make certain that the shifter is resting firmly against the spring plate but not compression the springs.

5. Fashion a method of holding the shift rod in this position.

6. Go to the rear of the car and look at the transfer shift mechanism at the transmission - here is the look from AutoAtlanta's parts page.



7. The lateral ROD (Bell Crank) that sticks into the transmission should be in the middle position. In the picture below it is in the middle and the correct position for this procedure.




8. The rod that connects from the Firewall to the Bell-Crank should be in a vertical position.
9. If this is all true, then lock this position down with Vice Grips.



10. You now have the shifter in THE EXACT position it needs to be to select 2nd gear if you were to push the gear-shift forward. Or 3rd gear if you were to move the gear=shift toward the back of the car

When you move from 1st on your way to second, the shifter and the rear BellCrank MUST be in this position.
11. Fasten the Collar TIGHT while not moving the vice grips or the shifter position.



YOU WILL NEVER HIT REVERSE AGAIN......unless something in this long linkage loosens or fails.

DO NOT FORGET TO REMOVE THE VICE GRIPS!!!!