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Discussion Starter · #1 ·
So I got my '67 running today. Car was sitting for about 12 years. New distributor, rebuilt carb, new plugs/wires, changed all fluids. Car ran quite well. Still have a few bugs to work out. Anyways, i seem to have no reverse at all. With the shifter in reverse, I can rev the car like its in neutral. Park and drive both work as they should, but nothing going backwards. Any ideas? I checked the fluid, and it is fine. I've got no experience with ford transmissions, so any help or suggestions of what to check are appreciated!

Matt
 

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Hello 67Galaxiefor6,

I'll be happy to offer some advice. On a C6 for reverse to occur, there are 2 clutches that need to apply. First is the Reverse/high clutch (also called the direct clutch) and secondly is the Reverse/low clutch.

You mentioned you had forward speeds. You can do a bit of diagnostic testing to see which clutch(es) are not engaging by driving the car.

I'll assume you have the later '67 trans with "Select Shift" or the 'PRND21' gear selector and not the "green dot" drive "Dual Range" earlier '67 trans.

To test the Reverse/high clutch, put the trans in 'D' and verify that the trans does indeed go into 3rd as your accelerate up to appropriate speed. Count the shifts if you have to as 3rd gear uses that Reverse/high clutch.

To test the Reverse/low clutch, while moving forward put the gear selector in '2' or '1' (depending on your speed) and verify you have engine braking and it's not just overrunning (seemingly in neutral when you release the accelerator).

Results check:

If you have no 3rd in 'D', some items it could be:

* Bad seals(rubber) or worn frictions in the Reverse/high clutch,
* Broken seal rings(metal) on stator support
* Stuck check ball in the stator support
* Bad seals on the intermediate servo piston (accessible from outer side of case)
* Improperly torqued valve body or faulty valve body gasket

If you have no engine braking in either '2' or '1'

* Bad seals(rubber) or worn frictions in the Reverse/low clutch
* Improperly torqued valve body or faulty valve body gasket

Hope that helps a bit...
 

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Discussion Starter · #3 ·
Hello 67Galaxiefor6,

I'll be happy to offer some advice. On a C6 for reverse to occur, there are 2 clutches that need to apply. First is the Reverse/high clutch (also called the direct clutch) and secondly is the Reverse/low clutch.

You mentioned you had forward speeds. You can do a bit of diagnostic testing to see which clutch(es) are not engaging by driving the car.

I'll assume you have the later '67 trans with "Select Shift" or the 'PRND21' gear selector and not the "green dot" drive "Dual Range" earlier '67 trans.

To test the Reverse/high clutch, put the trans in 'D' and verify that the trans does indeed go into 3rd as your accelerate up to appropriate speed. Count the shifts if you have to as 3rd gear uses that Reverse/high clutch.

To test the Reverse/low clutch, while moving forward put the gear selector in '2' or '1' (depending on your speed) and verify you have engine braking and it's not just overrunning (seemingly in neutral when you release the accelerator).

Results check:

If you have no 3rd in 'D', some items it could be:

* Bad seals(rubber) or worn frictions in the Reverse/high clutch,
* Broken seal rings(metal) on stator support
* Stuck check ball in the stator support
* Bad seals on the intermediate servo piston (accessible from outer side of case)
* Improperly torqued valve body or faulty valve body gasket

If you have no engine braking in either '2' or '1'

* Bad seals(rubber) or worn frictions in the Reverse/low clutch
* Improperly torqued valve body or faulty valve body gasket

Hope that helps a bit...
Thank you for the help. I've finally gotten around to driving the car a few times to check the trans issues. I still have no reverse, and now that I've driven it, I've found I have no 2nd or 3rd as well! The car will not shift out of 1st gear when in "D" no matter what I do. If i put the car manually into 2nd, it stays in 1st.

I see in your write up that both problems could be caused by the valve body. My question now is, should I yank the valve body out, clean it, and re-torque it, or should I just yank the trans and take it to the shop. I've been working on cars all my life, but have never torn into an automatic trans. Thanks for your help, it is very much appreciated!
 

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Pull the valve body if you'd like, but I fear that an overhaul is really what needs to happen.
You can check that the modulator works and has a hose hooked up properly (that won't help your reverse issue tho)
If you are dead set against that, you can always check fluid pressures in the none working gears. Air checking the offending gears is another option to help you narrow it down.

The good news? an overhaul kit is absurdly cheap. Of course if I have to pull a transmission, I'm going to do a full rebuild, just cuz.

Other good news? I'm 100% certain if you decided to tear into a c6, myself, Desert and a handful of others can walk you through rebuilding it. (It really isn't that hard, and very rewarding)
 

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Hello,

+1 to DeepRoots, if all you have is 1st there is still a slim chance it's the valve body but more of a chance it's either blown or hardened seals or worn frictions and a piston moved past its limit and damaged a seal.

If the seals are original it's time to replace them anyway to be reliable.

Sorry I didn't have better news.
 

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I had the same problem and after re-sealing my gearbox the three speeds work but my reverse works only when the gearbox is cold once I’ve rolled back a little bit do you have any idea? Thank you


Hello 67Galaxiefor6,

I'll be happy to offer some advice. On a C6 for reverse to occur, there are 2 clutches that need to apply. First is the Reverse/high clutch (also called the direct clutch) and secondly is the Reverse/low clutch.

You mentioned you had forward speeds. You can do a bit of diagnostic testing to see which clutch(es) are not engaging by driving the car.

I'll assume you have the later '67 trans with "Select Shift" or the 'PRND21' gear selector and not the "green dot" drive "Dual Range" earlier '67 trans.

To test the Reverse/high clutch, put the trans in 'D' and verify that the trans does indeed go into 3rd as your accelerate up to appropriate speed. Count the shifts if you have to as 3rd gear uses that Reverse/high clutch.

To test the Reverse/low clutch, while moving forward put the gear selector in '2' or '1' (depending on your speed) and verify you have engine braking and it's not just overrunning (seemingly in neutral when you release the accelerator).

Results check:

If you have no 3rd in 'D', some items it could be:

  • Bad seals(rubber) or worn frictions in the Reverse/high clutch,
  • Broken seal rings(metal) on stator support
  • Stuck check ball in the stator support
  • Bad seals on the intermediate servo piston (accessible from outer side of case)
  • Improperly torqued valve body or faulty valve body gasket

If you have no engine braking in either '2' or '1'

  • Bad seals(rubber) or worn frictions in the Reverse/low clutch
  • Improperly torqued valve body or faulty valve body gasket

Hope that helps a bit...
 

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I had the same problem and after re-sealing my gearbox the three speeds work but my reverse works only when the gearbox is cold once I’ve rolled back a little bit do you have any idea? Thank you
Hello Laurengee,

Like I mentioned above for reverse to occur in the C6 transmission the direct and low/reverse clutch have to engage. Since you mentioned you have all 3 forward speeds we can assume the direct clutch is working so that leaves the Low/Reverse clutch assembly. You can further conclude this by putting the gear selector in 1. This should hold the transmission in 1st gear WITH engine braking, if you do not have engine braking this is the clutch assembly at fault for sure.

If I were you, I would remove the pan, remove the valve body and apply pressurized air up into the rear case port for that clutch and check for air leaks. Some small hissing is normal, but if it's hemorrhaging air internally then you'll need to remove the transmission and dissasemble down to the rear clutch piston (in the rear of the case) and see what happened. It could be the clutch pack snap ring wasn't secured and is partially off causing the piston to jump out of the bore, or you tore a seal installing the piston on one of the many sharp pieces in the case.

These would be my suggestions based off what you wrote.

Good Luck

Cheers
 

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Hello Laurengee,

Like I mentioned above for reverse to occur in the C6 transmission the direct and low/reverse clutch have to engage. Since you mentioned you have all 3 forward speeds we can assume the direct clutch is working so that leaves the Low/Reverse clutch assembly. You can further conclude this by putting the gear selector in 1. This should hold the transmission in 1st gear WITH engine braking, if you do not have engine braking this is the clutch assembly at fault for sure.

If I were you, I would remove the pan, remove the valve body and apply pressurized air up into the rear case port for that clutch and check for air leaks. Some small hissing is normal, but if it's hemorrhaging air internally then you'll need to remove the transmission and dissasemble down to the rear clutch piston (in the rear of the case) and see what happened. It could be the clutch pack snap ring wasn't secured and is partially off causing the piston to jump out of the bore, or you tore a seal installing the piston on one of the many sharp pieces in the case.

These would be my suggestions based off what you wrote.

Good Luck

Cheers

thank you for your answer as all speeds pass Si j’étais vous, je retirerais le bac, retirerais le corps de la soupape et j’emploierais de l’air sous pression vers le haut dans le port arrière du boîtier pour cet embrayage et vérifierais s’il y a des fuites d’air. Un petit sifflement est normal, mais si c’est de l’air hémorragique à l’intérieur alors vous devrez retirer la transmission et démonter jusqu’au piston d’embrayage arrière (à l’arrière du boîtier) et voir ce qui s’est passé. Il se peut que le mousqueton de l’embrayage n’ait pas été fixé et soit partiellement éteint, ce qui a fait sauter le piston hors de l’alésage, ou que vous ayez déchiré un joint en installant le piston sur l’une des nombreuses pièces pointues du boîtier. Ce sont mes suggestions fondées sur ce que vous avez écrit. well I will try your idea and breath of air thank you very much. Maybe I’ll damage a gasket by pulling up the box!
 

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thank you for your answer as all speeds pass well I will try your idea and breath of air thank you very much. Maybe I’ll damage a gasket by pulling up the box!
 

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Hello Laurengee,

Like I mentioned above for reverse to occur in the C6 transmission the direct and low/reverse clutch have to engage. Since you mentioned you have all 3 forward speeds we can assume the direct clutch is working so that leaves the Low/Reverse clutch assembly. You can further conclude this by putting the gear selector in 1. This should hold the transmission in 1st gear WITH engine braking, if you do not have engine braking this is the clutch assembly at fault for sure.

If I were you, I would remove the pan, remove the valve body and apply pressurized air up into the rear case port for that clutch and check for air leaks. Some small hissing is normal, but if it's hemorrhaging air internally then you'll need to remove the transmission and dissasemble down to the rear clutch piston (in the rear of the case) and see what happened. It could be the clutch pack snap ring wasn't secured and is partially off causing the piston to jump out of the bore, or you tore a seal installing the piston on one of the many sharp pieces in the case.

These would be my suggestions based off what you wrote.

Good Luck

Cheers
hello here I finally took the time to dismantle my gearbox and here is the seal was damaged and I now have a reverse gear which is great, on the other hand after a few miles I lost my third gear !!! if I put it on "D" it starts and stays first, but if I do it manually I have the first and second. what I don't understand is that everything has worked really well and now it's not working. do you have an idea?
 

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Sounds like modulator may have lost it's vacuum or an issue there , valve stuck maybe ?
+1

Rather than take it all apart again I'd also connect the pressure gauge to the line port and modulator port on the exterior of the case and see what your pressures are and compare to the service manual. There might be clues in your readings to lead you to a diagnosis. If the pressures are normal under conditions then you'll have to take the transmission apart and inspect.

Good Luck

Cheers
 
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