This e-mail is a follow up on a previous post where you all straigntened me out on the fact that my '51F has an AOD transmission instead of a C4.

Then engine is a '68 289 with an early model AOD transmission (type with "rod" throttlevalve control).

The problem is that it is slow to shift between 1st and 2nd ... seems like it should shift soon. The same goes for shifting between 2nd and third.

Also, when shifting from 3rd to 2nd and from 2nd to 1st.

The scary part is that the engine rev's very high when it shifts out of one gear and into the other. If you take your foot off the gas it will go into the correct gear pretty quick but if you have a driver who isn't familiar with the problem and leaves their foot on the gas it feels like the transmission is going to explode!

We tuned the engine (new plugs, wires, points, etc.) and adjusted the idle, timing, etc.

Did some transmission pressure tests. On regular driving the transmission pressure stays like it is suposed to, between 55 and 70 psi. High rev's with the brake holding the car from moving will drive the pressure up in the 125 PSI, or more, range. At idle, the pressure is 45psi to 55psi.

One area of concern is at idle, in park or neutral, the pressue will sometimes slip down to 5-15psi for maybe 30 seconds or more and then climb back up to normal.

Lastly, the transmission doesn't lock into park correctly. For example, it park (without the parking brake on) on a slight hill, it will go ahead and roll and the transmission will "click, click, click).

As far as I can tell, the transmission isn't slipping in any gear.

Also, the transmission will downshift if you are cruising at 55mph and floor it.

We bought the two popular manuals and they tell in detail how to do the pressure test but don't really tell you have to troubleshoot or test for specific symptoms. They do tell how to rebuild the transmission but I don't think we are to that point yet (plus, although we are pretty confident amatuer mechanics deep into a truck restoration ... we need to get some confidence to really jump into a transmission rebuild).

As I mentioned before, I did post most of this message before in the Tranny section and got very little response ... so, anyone here that has a transmission experience, we would appreciate your input before we take our next step: 1) high rev's between gears, 2) 5 psi trans pressure in neutral, 3) park lock.

Thanks, Richard

 

Richard -

I'd say you got more than one thing going on here. It sounds like simple adjustments might fix it all. The clicking in Park is linkage adjustment. It just isn't fully into Park. The high rev's and slow shifts are definately adjustments and, maybe clutches. I'm not that familiar with the AOD internals. In fact, I'm in awe of anybody who would take any auto tranny apart.

In my case, I took my FMX to a local (small) shop that came well recommended. He diagnosed and fixed it all for cheap including adding a "shift kit", which dialed in my shifting speed. He also showed me how to adjust the shift points where I wanted them. I couldn't be happier. That was my solution. Best $160 I spent on my truck so far.

 

#3 Park lock: The early trannys used a park pawl. basically a pin that locked the output shaft. A hard bump while in park often broke the pin, I suspect that's what you are experiencing. You will need to diassemble the tranny to replace the pin.