Speedometer pinion on different transmission not working

[jogirob]

This last weekend I was able to put the finishing touches on my 1978 A904 to 1977 A904 transmission swap on this 1974 Charger. The car feels solid and pulls good. Only problem now is that the speedometer is completely dead. Before dropping the old transmission I had a needle fluttering issue that was fixed by replacing the cable.

About the replacement transmission: I could tell something impacted the output shaft support housing just under the lip of the area where the pinion assembly goes into. I filed off the the imperfection because it was protruding into the mating surface. The rebuilder also got carried away with coarse grey spray paint and some of that paint got onto the mating surface and even on the output shaft where pinion worm gear is. I buffed most of the stuff off with a scotchbrite. I had to tap the pinion assembly in harder than I would've wanted too. No leaks fortunately.

Could I have broken something? If I pull out the pinion assembly will there be a lot of trans fluid to deal with? I did make sure to use the same gear ratio setting as before. I'm dumbfounded as to how simply turning the pinion assembly affects the MPH output by the way.

 

[67Charger]

Yes (maybe broken), Yes (fluid), and magnetic magic . There are at least 2 types of pinions depending on the year/application, so that is a possibility, misalignment is a possibility, and so is the incorrect orientation. Pull it over a clean pan, and just reuse it when you put it back together. You need to look. Are you sure the square end of the cable is properly engaged on BOTH ends?

 

[Dipstick]

Does your speedo pinion adapter look like this? If so you might have it clocked wrong, the numbers are the tooth count and it needs to line up with the raised dot at 6 o'clock.

 

[jogirob]

Does your speedo pinion adapter look like this? If so you might have it clocked wrong, the numbers are the tooth count and it needs to line up with the raised dot at 6 o'clock.

View attachment 680865

Yes it does. I made note of the gearing #'s when I took the adapter off the old case. Would a wrong setting or very slightly misaligned adapter result in no readings at all? I lined it up perfectly so that the "legs" for the clamp that bolts in falls into its 2 indents. On the old case it was slightly offset to where only one of the "legs" dropped into an indent.

 

[burntorng70]

You lose about a quart of fluid. Take it off and look at the gear. If it is good and it is set right for the tooth count then the issue must be the cable.Turning the pinion assembly engages the gear because different tooth counts are different diameters and the gear is offset to adjust for the difference.

 

[jogirob]

I just read the Haynes manual and it says if the pinion housing setting is not matched with the plastic pinion gear teeth being used, the teeth will sheer off and result in no readings at all. I'm 100% I installed the pinion housing in the same position I took it off on the old trans.

However, On the FSM I found this in bold lettering:
"CAUTION: Before installing pinion and adapter assembly,
make sure adapter flange and its mating area
on extension housing are perfectly clean and lubricated.
Dirt or sand will cause mis-alignment resulting
in speedometer pinion gear damage."

I bet that coarse overspray that got into the mating surface screwed me over. I should've taken a fine grit sand paper to the mating surface rather than a scotchbrite. The flange also wasn't in the best condition due to the impact area right below. :-/

 

[Garys1969RR]

Pull the cable off, and watch the end of the Speedo gear to see if it turns when you're turning the drive shaft. Then you will know if it's the speedometer or the gear that's causing the problem.

 

[jogirob]

Pull the cable off, and watch the end of the Speedo gear to see if it turns when you're turning the drive shaft. Then you will know if it's the speedometer or the gear that's causing the problem.

BRILLIANT! Will save myself the need to wait for the oring kit to get here or I can go ahead and buy the replacement pinion gear already.

 

[jogirob]

OK so I pulled the cable from the pinion assembly and it does turn when I turn the drive shaft. I put some pressure on the spinning insert with my thumb and it feels like one direction is a lot stronger than the other. Not sure what to make of that. If the weak direction is the forward direction maybe the pinion gear doesn't have enough strength to turn the cable?

While the cable was pulled I put a drill to it and spun it up. I do get readings to the speedometer just fine. The wire feels more difficult to turn with a thumb and index finger than when I originally installed it not even a month ago though. I pulled the inner wire out and squirted liquid graphite and the wire slid in and spun easily up until I had about 3 more inches to go. The wire would bind somewhere and I really have to force the wire in there. Once fully inserted I tried spinning the wire and again it feels too tough to turn. The cable was disconnected at both sides when I did this.

Gonna pull the pinion assembly and take a look at the gear and then I guess I'll buy another trans to servo speedometer cable if the gears look fine.

 

[miller]

spun easily up until I had about 3 more inches to go.

That binding would probably be in the housing itself. Three inches from the end? Look for part of it, that might be crushed a little, might be able to 'un-crush' it!

 

[jogirob]

That binding would probably be in the housing itself. Three inches from the end? Look for part of it, that might be crushed a little, might be able to 'un-crush' it!

I made sure not to have any sharp bends on the cable housing for this reason. Gonna try sticking the wire through the other end just for poops and giggles. If I get binding within 3 inches of the cable going in then it's the cable housing. If it goes all the way in up till the last 3 inches it's probably the wire that swelled up? I did noticed it's made of like a tightly spun tiny wire. Maybe I screwed it up when I took a drill to it and rotated it in the wrong direction.

 

[miller]

Maybe I screwed it up when I took a drill to it and rotated it in the wrong direction.

Yes, that's possible. Cable itself is made to turn one way, going by the direction of the twist. Backwards it will try to un-twist itself. Fixable? Can't say.

 

[jogirob]

Swapped out the speedo cable and no go. Oh well only $9 in the hole. Next up pinion assembly pull sometime this week. Will update you guys on the findings.

 

[jogirob]

Update: Solved. I pulled and examined the pinion gear. There was only slight burring on a few of the teeth so I reinstalled it. First, I polished off the bore with some fine sand paper and scraped off some imperfections and paint buildup off the lip surface. Then I duplicated from the old transmission the VERY slight misalignment of the gear teeth setting.
Speedo needle is steady and true now.