auto transmission shifter linkage and back lock
 

Hi,
My 1970 Formula gear selection is not working well. When the selector is in the indicated position on the shift indicator PRNDSL, the transmission is not in gear. A bit more travel of the shifter is required to find the gear. The transmission is a THM400.

At first I thought there was a problem with the shift cable, or the attachment to the selector crank and link into the transmission. I tried backing the shift cable lever pin all the way to one side but this didn't help.

Now I'm thinking the back lock bushing is the problem. Shouldn't there be a bushing, washer, and spring inside the frame to position the back lock rod? When the shifter is moved the rod flops around. The bushing and related parts seem to be missing from the metal cup in the frame. What do you think?

There is a white Nylon " cup" that sits in a bowl thats bolted to the frame. It does have a spring that keeps the back shift rod against the transmission.
AMES sells a kit for this I believe.

On Ames I see two possible kits:

1.
FR680B: 1970-81 BACKLOCK BUSHING KIT (RE)
BACKLOCK ROD TO STEERING COLUMN ARM BUSHING KIT. ORIGINAL DESIGN WITH RUBBER GROMMET & STEEL INSERT. INCLUDES WASHER AND PIN
No photo

2.
FR680J 67-81 BACKLOCK HARDWARE KIT(RE)
KIT INCLUDES PIVOT SPRING, PIVOT BUSHING, PIVOT BRACKET BOLTS AND WASHER.
attached photo

I tried removing the metal cup part from the frame to look in there. It's frozen in place. Maybe it rusted out and allowed the bushing spring and washer to fall into the subframe.

you will need the steel insert too then. Some are out there used if Ames doesnt have exactly what ya need.

I tried loosening the cup from the frame last night. It's frozen in place. I'll try to get replacement parts including the metal cup part at Carlisle next week, before removing/possibly destroying the original.

Tons of GM cars used that cup in frame design, but were mounted in different places and may hyave had a different bracet. BRING whats left of your with you.

I think your problem may still be your cable. All the after market ones never worked right for me. It wasn't until I got a GM one that it lined up right.
Not saying you don't need to fix up your back drive because getting the park neutral and reverse lights dialed in can be a pain too.

My original cable shifted properly, but it broke years ago, near the flange. I found a classified ad (remember those?) of misc Firebird parts, and bought a used (and appearing good) cable from that lot. I think I paid $10. That's the cable in question. From day 1 with that used cable on my car the PRNDSL quadrants and trans detents didn't align.

To my eye the used/good cable looks the same. But did GM have cables for other applications that look similar but differ? Say, for a Camaro, or Nova?

All 2nd gen firebirds should be that same which will be the same as 73 to 81 camaro. The earlier camaro used the horse shoe shifter.
I kept buying the pioneer brand cables and each cable would get me a different result. I finally picked up a genuine gm one and it finally lined up. I got mine back in the day from shiftworks but classic industries carries it too.

https://www.classicindustries.com/product/g8469.html

Get the bushing/spring kit you posted. I’ll assume the frame bracket is in good shape.

Then…dive into the service manual for the procedure to properly adjust/align everything.

When my cable seized I was amazed at what it took to set up. IIRC there’s two points of adjustment, the column back drive rod at the frame lever and cable end pin on trans selector lever. There’s also a specific starting point…trans and shifter in neutral.

* shrug * It’s been a long time for me..

I went to Carlisle a few weeks back, and brought a photo of my back lock linkage and frame bracket, and pages from the Parts and Illustrations catalogue, and illustration from the 70 Assy Manual.

Several people I spoke to were not familiar with the bracket. I grabbed the bushing and spring kit from Ames.

A guy at Firebird Central said they had the back lock frame cup bracket coming soon. I don't yet see it on their web site. But on their listing for the white plastic bushing, they have a good photo of what looks like the 2nd design cup bracket. I posted a photo of my 1st design cup bracket, above.

My interpretation of the cup bracket parts listing from the Firebird parts & illustration "catalogue" is:

Group 4.040
Bracket, transmission equalizer shaft to frame
3982394 first design - uses 2 screws
3998691 second design - uses 1 screw, when replacing the 3982394 discard the 2nd screw

Type 2 and 3, original GM.

url=https://flic.kr/p/2oyapBA]https://live.staticflickr.com/65535/...179369c4_b.jpg[/url]GM shifter backdrive cup with bolt hole (1) by Ben, on Flickr

https://live.staticflickr.com/65535/...6766cb3a_k.jpgFirebird backdrive mechanism cup bush spring linkage (3) by Ben, on Flickr