1974 T Top, 4 speed T10 (Sep car), 3.36 rear

My speedometer is not working. using a brown gear 18T, purchased new transmission fitting (driven gear sleeve) old sleeve bearing was egged out. Thought new sleeve would fix the issue , it works for a few hundred ft then stops.

At the transmission there is a 90 degree fitting that feels stiff, does anyone know if this is a stock fitting? I dont see one at vendors or in 74 shop manual. my service manual shows cable as a direct connect to driven gear sleeve but it only shows munci 4 speed trany not the BW T10.

If cable will reach I plan on trying the direct connect, thanks for any comments .
bg

 

I went to a direct connect on my '74 and got rid of the 90 degree adapter. The one I had, actually separated in half, despite being made of all metal pieces. Didn't like the action of it or the quality of it. Got rid of it. No problems since.

I had the same problem you did, with the 'egged out' or rounded out speedo drive gear in my BW T10 trans and had it replaced. Just a few thoughts. Make sure the speedo cable is locked into the speedometer. Secondly, once you affirm that, jack up the car, unplug the speedo cable from the trans and put the end of the cable into a variable speed drill. I believe it's a CCW rotation. Have somebody sit in the car and watch the speedo. It should be registering something.

Next, put a square bit into the trans side of it, plugging it into the plastic speedo gear and see if you can rotate it by hand. You shouldn't be able to, if the plastic speedo gear is meshing with the output speedo gear on the transmission shaft. Have somebody rotate the wheels and see if you have rotation as well.

Finally, here's what I had to do, I put my snake camera into the trans and that's when I discovered the inner speedo drive gear was rounded out. But you already replaced that, so the only thing to check, is to make sure they put the correct one on there, unless there's only one specific drive gear on that period. Someone feel free to chime in, as I'm not an expert on T10 internals. Ultimately, as you see, it's going to be a process of elimination and careful examination.

 

I suppose the cable could be broken from age somewhere inside the cable housing and the broken cable pieces at the break sometimes binds enough to turn speedo needle.

My 74 Camaro l82 and BW does not use a adaptor ....it has the 3.73 axle...as shown in AIM
Other ratio applications maybe diff.

My 74 vette 3:36 /Muncie DOES use the adaptor gizmo .

 

Thanks guys thats all good stuff, I'm going to try the direct connect and inspect the 90 d fitting / adapter carefully (maybe get a part number to determine if stock).

If it works without it, it might go in the box of stuff for future reference like my old master cyl, water pump, fuel pump, rotors and orginal caliper pistons.

Will let u know how it works, replacing the dash so will also check speedometer connection then. its got to work before new dash pad goes on.

 

A few photos, after closer inspection the adapter spins free its the cable or worse the speedometer that pacing resistance on the setup. further inspection needed. Btw part #6478879 & ratio 1: .882 , might keep it the in line up.



note numb 6478879 & ratio 1: .882

 

Update on what i found:
I disconnected the cable from transmission adapter and the two cable supports (under car) to bring the cable into the engine compartment.
2. With cable end accessible I cleaned up the squared end with a file so it would fit adapter better.
3. I placed speedometer gear on cable end and rotated it by hand CCW while observing speedometer, got needle movement and 3 tenths of a mile on odometer. (also
spun it up with battery drill got 20 mph)
3a. Installed the adapter into the transmission with square stock tried to rotate gear , could not rotate gear so gear was engaged. (Did not wiggle the adapter, i should have)

4. reinstalled 90 degree adapter on cable end rotating gear produced same results at speedometer.
5. the above steps proof the speedometer, cable, odometer and adapter.
6. reinstalled the cable lineup into transmission , speedometer worked briefly and quit.
7. there was a slight play at the adapter, it sagged a little, i could lift it around a 1/16", I stuffed a rolled up rag between frame and adapter to eliminate the 1/16" play.

Test drive.... speedometer works !

Questions
1. How difficult is it to remove transmission tail piece and replace internal gear?
2. My gear diameter is .7970 , is there a larger diameter 18 tooth (brown) gear?





ment

 

 

Listen Bob, before you go pulling the tail shaft, why don't you just plug the speedo cable into the transmission without the adapter? I've been running mine like that for many months and it works just fine. Or at least until you get another adapter. Personally, I'm not getting one, anytime soon.

 

I wanted to try that, didn't look like enough cable to make it happen. Looks like the sweep turn is gona take -12". I need to get car on lift to work it, right now speedo works and i know where the issue is.
Did you replace ur cable with longer one?
thanks for the feedback.
bg

 

Good question. I think it was the stock one, if I'm not mistaken. I'll check the routing tomorrow afternoon, because that definitely makes a difference.

 

I had the same problem with my 74. Had to use the 90 degree adapter. I also had to change the plastic gear, it only showed slight wear however when I put in a new on it made all the difference. Got the speed app on my phone to calibrate to see what gear to use. Also be very careful installing that gear, it can fall into the transmission. Ask me how I know.!!! I now have a spare inside the tail.

 

I have a tail piece spare too, hope i dont need it its a little hard to get to. I have new gear, o ring and driven gear sleeve (looks like civil war mini ball) in mine, the line up fits pretty snug but the speedo only works if i prop up the 90 degree adapter with a rag . Im going to get some lift time to see beter whats going on. So far the proped up adapter is working fine. Photo is of worn out driven gear sleeve.


note egged shaped hole its the bearing for speedo gear. my old worn out driven gear sleeve.

 

"but the speedo only works if i prop up the 90 degree adapter with a rag"

That brings back memories. What a floppy PITA! I'm going to have the C3 on the lift, late this afternoon, so I can take pics of the 02 sensor for another thread and I'll take pics of my speedo cable setup without the 90 degree adapter. I don't miss it, it doesn't seem to affect the operation and if it only lasts two years instead of four, I'll just replace it.

 

OK, it's up on the lift and here's a pic. I believe that's the stock speedo cable. It goes over the trans and runs along the firewall, goes through it to the inside and then turns another 90 degrees and plugs into the back of the speedo (wonder why there's no adapter there? ).

But seriously, you can see that it's not kinked in any way, nor does it look like it has to do a beyond 90 degree turn. Hope this helps!

 

Thanks for the photo, i'll try it.

bg