C4 Linkage Adjustment - Lost D, 2, and 1

[TorchRedTulsan]

Okay brain trust:
I drove my '76 C4 the other day and, out of the blue, it wouldn't go into park and just kept rolling backwards. I aborted my day and drove it home. I tried the linkage adjustment outlined by Viperwolf1 on another thread as well as these instructions

Now, when I put it into Drive, it's like it's still in Neutral. For 2 and 1, you can feel the transmission engage, but have very diminished power. Not even enough to get up my driveway.

I still have Reverse and it will start in Neutral and Park

The few articles I've been able to find mention "You may have to fine tune it", but I'm not 100% sure how to do that. I've tried moving the shift rod a little bit, but no change. It does feel like the manual lever is fully engaged with the selector level against the D stop, so I'm a bit out of ideas. I also don't have a 2nd set of eyes/hands to be under the vehicle while moving the selector level to see what's happening at both ends. Any advice would be rewarded with a virtual beer and high five.

 

[diggs00]

Okay brain trust:
I drove my '76 C4 the other day and, out of the blue, it wouldn't go into park and just kept rolling backwards. I aborted my day and drove it home. I tried the linkage adjustment outlined by Viperwolf1 on another thread as well as these instructions

Now, when I put it into Drive, it's like it's still in Neutral. For 2 and 1, you can feel the transmission engage, but have very diminished power. Not even enough to get up my driveway.

I still have Reverse and it will start in Neutral and Park

The few articles I've been able to find mention "You may have to fine tune it", but I'm not 100% sure how to do that. I've tried moving the shift rod a little bit, but no change. It does feel like the manual lever is fully engaged with the selector level against the D stop, so I'm a bit out of ideas. I also don't have a 2nd set of eyes/hands to be under the vehicle while moving the selector level to see what's happening at both ends. Any advice would be rewarded with a virtual beer and high five.

Does it go into park if you manipulate the c4 lever at transmission by hand?

 

[TorchRedTulsan]

Does it go into park if you manipulate the c4 lever at transmission by hand?

Actually, no it doesn't. I hadn't considered trying that. My searches all indicated it was the linkage adjustment, and I got tunnel vision. Since it starts, I assumed it was in park. Is this an internal tranny problem? (Re-researching as I type this question)

 

[diggs00]

Have you checked the fluid level?

 

[TorchRedTulsan]

Have you checked the fluid level?

I haven't. Had to run an errand. Will do that this evening

 

[TorchRedTulsan]

Have you checked the fluid level?

Well now I feel like a proper idiot. I haven't run low on tranny fluid since freshman year in college. It was definitely too low.

I'm going to do a full diff/tranny/engine fluid change next weekend (have to wait for the filter) and see if that resolves it

 

[Broncobowsher]

If it is low and not leaking excessively onto the ground...
Pull the hose off the vacuum modulator. If fluid runs out of the hose, you have a hole in the modulator and the engine is sucking transmission fluid in and burning it.

 

[brewchief]

Well now I feel like a proper idiot. I haven't run low on tranny fluid since freshman year in college. It was definitely too low.

I'm going to do a full diff/tranny/engine fluid change next weekend (have to wait for the filter) and see if that resolves it

Personally I would add fluid and check the vacuum modulator and see if it fixes it, if not then you aren't wasting more fluid and a filter to find out you have bigger problems. In the big picture a couple quarts of trans fluid is pretty cheap.

Sent from my SM-T510 using Tapatalk

 

[TorchRedTulsan]

If it is low and not leaking excessively onto the ground...
Pull the hose off the vacuum modulator. If fluid runs out of the hose, you have a hole in the modulator and the engine is sucking transmission fluid in and burning it.

Personally I would add fluid and check the vacuum modulator and see if it fixes it, if not then you aren't wasting more fluid and a filter to find out you have bigger problems. In the big picture a couple quarts of trans fluid is pretty cheap.

Sent from my SM-T510 using Tapatalk

These are great points. I actually do have a pretty decent leak, but I seem to recall reading on here years ago that "they always leak". That was another reason to go ahead and put a new gasket on it. I'll try filling it up first though, then do a change if that fixes it

 

[mpboxer]

This helps to distribute pressure on the seal/pan.

https://shop.broncograveyard.com/C4-Pan-Reinforcement/productinfo/11105/

 

[TorchRedTulsan]

This helps to distribute pressure on the seal/pan.

https://shop.broncograveyard.com/C4-Pan-Reinforcement/productinfo/11105/

I love affordable improvements. Thanks! Just ordered that

 

[mpboxer]

I love affordable improvements. Thanks! Just ordered that

For sure, I have one and it is great.

 

[FordBronc]

Here is some advice I got for a 73-79 Ford truck C-6 that had an issue, should be about the same as far as trouble shooting.

"Check the vacuum modulator and the line that goes to it. Check the line for kinks or other problems, make sure it hasn't come off. If the line checks out, take the line off where it connects to the modulator. If trans fluid leaks out, its bad. If no fluid, it still could be bad.

They're simple to replace, disconnect the vacuum line, remove one bolt that holds the clamp in place and the modulator comes out. It has an o-ring seal. Modulators are identified by the color of the stripe. Pretty much the "go to" one is the black stripe. If they don't show that one in the catalog, go with the green stripe. Avoid the pink stripe. That one is a dual diaphragm version that has two vacuum line going to it.

If by chance you have one of these, replace it with one of the other two and use the vacuum line that goes to direct manifold vacuum, cap the other line. When you pull the modulator out, be careful. There is a pin that goes in the modulator. Sometimes it comes out with the modulator, sometimes it stays in the tranny. If it comes out, don't lose it."

 

[Rustytruck]

be careful when you change the tranny filter. when you pull the filter there is a spot where the filter has a thumb like protrusion on the filter. under that protrusion is a spring and a small metal valve that just falls out. they have to be put back in the same place and order for the tranny to work. many of us have pulled the filter not knowing and put it all back together to find ou what went wrong.

https://speedmaster79.com/instruction/ford-c4-deep-automatic-transmission-pan

 

[Rustytruck]

the c4 vacuum modulator if you remove it it will gush tranny fluid into your arm pit. be aware. once you pull the modulator there is a pin behind the modulator that wants to come out on you so catch it if necessary and put it back in before you put the modulator back in.

https://www.youtube.com/watch?v=R4sQTOo9bXY the video is a screw in modulator but broncos use a lock clip and push in modulator. just wanted you to see how the pin is in there.

 

[TorchRedTulsan]

Quick update from the last few days. Made sure the transmission had fluid in it, disconnected the shift rod and manually confirmed it was in park at the lever. Still rolled like a hippie at Woodstock. I'm afraid I'm going to have to pull the pan and see if I can access the parking pawl. Going to start researching that tonight.

 

[Rustytruck]

Parking pawl is inside te rear of the tranny in the transfer adapter. When you drop the pan check the shift lever shaft sometimes the shift lever and the shaft the factory weld fails then the shift lever moves but the shaft doesnt. If you have a problem like tat reach out to viperwolf on this site he has repaired those shafts. Unfortunately you have to remove the valve body to unbolt th shaft and remove or install it. The parking pawl is a purly mechanical function between the shifyt lever to the parking pawl. Good luck with your repair.

 

[TorchRedTulsan]

Parking pawl is inside te rear of the tranny in the transfer adapter. When you drop the pan check the shift lever shaft sometimes the shift lever and the shaft the factory weld fails then the shift lever moves but the shaft doesnt. If you have a problem like tat reach out to viperwolf on this site he has repaired those shafts. Unfortunately you have to remove the valve body to unbolt th shaft and remove or install it. The parking pawl is a purly mechanical function between the shifyt lever to the parking pawl. Good luck with your repair.

Thanks for all the great info