51 single lever transmission wont go? or operate in reverse

Kdancy

I just went thru this transmission, one out of a 51 Commodore. The car is on a lift with the wheels off the ground. It shifts great into 1st, 2nd and 3rd.
The shift lever moves up into reverse but when I let off the clutch, the tailshaft nudges in the reverse direction, turn a time or two then nothing happens. This tranny has the od unit.
I'll double check the cable linkage but at this point it doesn't seem to be out of adjustment.
Ideas anyone?

Uncle Josh

Mace sure the Overdrive cable lever is all the way forward.  It's the rearmost lever on the left hand side.  Then try it

Kdancy

I made sure it was pulled out all the way. The housing has a stop cast in to the housing so I don't think the linkage can go into the OD unit but one way. I'll pull the cable off and see if I can move the lever any more to check if that does it. I have been thinking it seems like an OD related issue.

Geoff

 My Hornet does exactly the same thing, except that it works when I pull the  knob out to disengage o/d, then it will reverse.   Seems it has the wrong low/reverse shift shaft installed.   Too much work to pull apart and fit the correct part, much easier to just pull the knob.

Geoff 

SuperDave

The shop manual says to take it out of overdrive to go into reverse. Because "some cars" experience this malady. I feel that there is a problem with the detent in the shaft that moves forward and aft.  Some guys say it's the reverse lockout switch apply in forward pressure on the shaft. I took my switch out and it still would not stay in reverse. I had one 49 that worked every time, then the next two (51 and another 49) would not go into reverse. One of these days I'm going to take the good one apart and see why it worked so good ! I only took it out because the input shaft was damaged where it mated to the pilot bearing, causing a clutch chatter..

Park_W

When the cable's fully in (i.e., in OD mode) try holding the shift lever firmly into reverse, as it has to be pretty solidly in that direction before it locks out the overrun clutch in the OD.

One reason some of these critters don't want to stay in reverse . . . the OD trannys have a much stronger reverse detent spring, to keep the big spring in the OD from pushing it out of reverse.  If someone has mistakenly installed a reverse detent spring from a non-OD tranny, it'll not want to stay in reverse when the OD button is all the way in (i.e., in OD mode).  Al Saffrahn has had some of the heavier springs made, so can probably supply one to anyone in need.

Fortunately, the reverse detent spring is the one immediately under the top cover plate at the left rear corner, so even with the tranny installed, with just a little bit of knuckle busting one can remove the left rear cover bolt and loosen the rest, then remove and replace the detent spring.

Kdancy

For some reason today I am having trouble copy and pasting in the message box. Don't know what is going on.
 I am imagining all sorts of things I might have done wrong in the OD re-assembly.
I'm wondering if it is possible to re-install the control shaft 180 degrees out? (#22)
If so, can I pull the control lever back off and just rotate the shaft or does the od housing have to come back off?
I'm not with the car right now, so just want to get my ducks in a row before hand.

IvarSweden

The shift rail (21) needs to be properly aligned for the control shaft (22) to engage its slot (yes it can be turned in the wrong direction). You can't fit the tapered pin into the slot of the control shaft until it's all in position. It's also essential the shift rail retractor spring (20) is aligned with the hole in the OD housing, before attempting to install the housing over the shaft.

Kdancy

Ok, yes the spring was in proper position. If I remember right, the slot was a full 360 degrees around the control shaft, so if the lever is taken off, (not allowing the housing cast stop interfere with turning the shaft 180 degrees), can it now be turned the 180 or will the cam in slot prevent it from making the turn?
Is the only option pulling the housing?

IvarSweden

The slot is only on one side, if it's turned the wrong way it will not work. You can't turn the shaft without removing the OD housing. The below picture is from when I disassembled my gearbox.



I almost made this mistake myself, the picture below is from the reassemly and as you can see I had the shaft turned the wrong way at first!



Doug Wildrick gave me the advice to put permatex sealer on both sides of
all the gaskets between the gearbox and the overdrive. The bell housing
to gearbox bolts also need sealant or they will leak gearbox oil.

Kdancy

Update-
After pulling the trans cover and fiddle farting with it, everything seem to check out. I wound up shortening the adjusting rod and it now goes through the gears (running on the lift) just fine. Road test will tell us more. Later