C4 transmission - No reverse or 1st gear

[High Pressure]

Just started driving my Bronco with a rebuilt C4. After only a 3-4 miles the transmission lost all "drive" at about 30mph. There was no noise associated with the loss. Tried reverse & 1st gear multiple times with no success. I have considered loss of the pump and removed the return line to the transmission and ran the engine for 30 seconds at about 850 RPM. The pump flowed a little less than 1 quart of fluid in a 30 second time period... Is this adequate flow?

 

[jdkin01]

I'm not a transmission man, but when that happened in our '56 Ford Pickup it was the first gear and reverse band that was broke. My friend fixed it while I watched. Looked pretty simple for him, but not for me.

 

[High Pressure]

Test for broken band?? If I try to readjust the band by turning the adjuster bolt "in"...say more than 4-5 turns with minimal torque (less than 120 inche lbs) might indicate a broken band???

 

[jedblake]

Refer back to the factory specs, I found them in the Haynes manual. The 4-5 turns you talk about seems like too much from my recollection. 1.5 for rear and 3.5 foward sounds familiar but double check and use a back-up wrench for final torque specs.
When adjusting mine incorrectly I lost reverse, 2nd and 3rd. Also adjust the bands w/ trans in nuetral use chalks for the tires.

 

[High Pressure]

Refer back to the factory specs, I found them in the Haynes manual. The 4-5 turns you talk about seems like too much from my recollection. 1.5 for rear and 3.5 foward sounds familiar but double check and use a back-up wrench for final torque specs.
When adjusting mine incorrectly I lost reverse, 2nd and 3rd. Also adjust the bands w/ trans in nuetral use chalks for the tires.

Jedblake... I believe you are correct for the amount of "backoff:" after reaching the 120" lbs of torque...but... I was thinking that If I tried to tighten to 120" lbs and did not reach torque in 4-5 turns "in" that would possibly indicate a broken band?

 

[jedblake]

You might be right, although the 120"lbs seems high. I'd have to refer to my manual for the torque specs. Try calling or stopping in at your local trans shops. Most seem to be pretty nice and very experienced w/ the C4, thats what worked for me at least.

 

[High Pressure]

Okay, just checked the Rev/1st gear band adjustment... I turned the adjusting bolt "in" approximately 3 turns to achieve the 120 inch lb torque.... then backed it back out again 3 turns... I guess the band is okay? Any other ideas?

 

[Broncobowsher]

Do you still have park? No, put the transfer case in gear. Yes, continue

Have you checked your transmission fluid level? Low, add some. Full, continue.

Do you have manual second gear? how about manual first?

For a C4 to drive forward the only clutch pack that needs to engage is the forward clutch pack. Low reverse band adds to the holding power of the low gear sprag, gives engine braking in first, and is used for reverse. If that band died you would loose engine braking in manual 1 and reverse.
Second gear band releases the hold of the sprag. still need the forward clutch applied to get forward motion.
Third gear is the forward clutch (if you didn't figure it out the forward clutch is what drives it forward in 1,2 and 3rd gear) and the reverse/high gear clutch engaged. Those two together lock the gear set into one complete mass. No gearing just straight through drive.
Reverse is the low reverse band and the high/reverse clutch pack.

What does all that tell us. No drive and no reverse is either multiple clutch failures or another problem.
I think a quart in 30 sconds sounds a little low.

Next step is to put a set of transmission pressure gauges on the test ports. Compare them to the service manual and see if you are getting the fluid pressure that is withen specs. My guess is that you are not.

 

[High Pressure]

Broncobowsher, Thanks for the information on how the C4 works.. I need to study that more.. I will try to locate a pressure gauge to take the readings. I guess the readings will change under various conditions? Idle vs 1,000 RPM etc..

 

[High Pressure]

I think a quart in 30 sconds sounds a little low.

I found an older thread...that says the oil flow should be 1 quart in 15 seconds at 1,000 RPM Still planning to check the pump pressure... in search of a 0-300 psi pressure gauge for a good price....

 

[BwoncoHowie]

Okay, just checked the Rev/1st gear band adjustment... I turned the adjusting bolt "in" approximately 3 turns to achieve the 120 inch lb torque.... then backed it back out again 3 turns... I guess the band is okay? Any other ideas?

Yes, that is the correct adjustment for the rear band.

front band is half the number of turns of the rear 1.5 turns out. This band is responsible for 2nd gear and manual 2nd, and is applied in those ranges only.

 

[High Pressure]

Have pressure readings... need advice....

Do you still have park? No, put the transfer case in gear. Yes, continue

Have you checked your transmission fluid level? Low, add some. Full, continue.

Do you have manual second gear? how about manual first?

For a C4 to drive forward the only clutch pack that needs to engage is the forward clutch pack. Low reverse band adds to the holding power of the low gear sprag, gives engine braking in first, and is used for reverse. If that band died you would loose engine braking in manual 1 and reverse.
Second gear band releases the hold of the sprag. still need the forward clutch applied to get forward motion.
Third gear is the forward clutch (if you didn't figure it out the forward clutch is what drives it forward in 1,2 and 3rd gear) and the reverse/high gear clutch engaged. Those two together lock the gear set into one complete mass. No gearing just straight through drive.
Reverse is the low reverse band and the high/reverse clutch pack.

What does all that tell us. No drive and no reverse is either multiple clutch failures or another problem.
I think a quart in 30 sconds sounds a little low.

Next step is to put a set of transmission pressure gauges on the test ports. Compare them to the service manual and see if you are getting the fluid pressure that is withen specs. My guess is that you are not.

Okay...Finally purchased and received a 0-300 psi pressure gauge...
1) Transfer case okay
2) Oil level okay while running.
3) Still No Reverse, 1st gear or 2nd gear
4) Below are the pump pressure readings at approx 1,000 RPM & 10" Hg vacuum applied to modulator via vacuum pump that is adjustable (based on the specs that I could find for testing)

Park = 105 psi Spec 50-90psi
Reverse = 175 psi Spec 150-175 psi
Neutral = 110 psi Spec 50-90 psi
1st = 110 psi Spec 90-105 psi
2nd = 110 psi Spec 90-105 psi
Drive = 110 psi Spec 60-85 psi

With no vacuum applied to the modulator......Park = 165 psi at 1,000 rpm

Please confirm that I have the correct line pressure specifications for 1,000 RPM at 10" Hg vacuum applied to the modulator?

 

[Broncobowsher]

I will want someone else who knows these to confirm, but the pressures actually look good. The slightly high pressures I am not concerned about at all. a hair more vacuum on the hand pump would probably bring them into spec perfectly. The hand gauge may be off just a hair. No big deal.

Pressure changes going into reverse, looks like the valve body is working. (I think there are a few other pressure ports that can be checked).

What does this leave? hard mechanical failure somewhere inside. Torque convertor stripped some splines, shaft broke, something not pretty

But please wait for another opinion before you call it.

 

[BwoncoHowie]

I cant see any reason why those pressures wouldnt work. does the speedometer on the vehicle work? Those pressures are about the range of a Transgo shift-kit(R) I cant see any reason why you have no vehicle movement. Do the rear wheels lock in Park?

Okay...Finally purchased and received a 0-300 psi pressure gauge...
1) Transfer case okay
2) Oil level okay while running.
3) Still No Reverse, 1st gear or 2nd gear
4) Below are the pump pressure readings at approx 1,000 RPM & 10" Hg vacuum applied to modulator via vacuum pump that is adjustable (based on the specs that I could find for testing)

Park = 105 psi Spec 50-90psi
Reverse = 175 psi Spec 150-175 psi
Neutral = 110 psi Spec 50-90 psi
1st = 110 psi Spec 90-105 psi
2nd = 110 psi Spec 90-105 psi
Drive = 110 psi Spec 60-85 psi

With no vacuum applied to the modulator......Park = 165 psi at 1,000 rpm

Please confirm that I have the correct line pressure specifications for 1,000 RPM at 10" Hg vacuum applied to the modulator?

 

[High Pressure]

Removed the valvebody & testing with air..

I cant see any reason why those pressures wouldnt work. does the speedometer on the vehicle work? Those pressures are about the range of a Transgo shift-kit(R) I cant see any reason why you have no vehicle movement. Do the rear wheels lock in Park?

Park = 105 psi Spec 50-90psi
Reverse = 175 psi Spec 150-175 psi
Neutral = 110 psi Spec 50-90 psi
1st = 110 psi Spec 90-105 psi
2nd = 110 psi Spec 90-105 psi
Drive = 110 psi Spec 60-85 psi

With no vacuum applied to the modulator......Park = 165 psi at 1,000 rpm

*** Next steps that were done on 23-Feb-08

5) Readjusted the column shifter to the transmission... seemed okay... but just wanted to repeat an earlier trans installation step from several weeks ago.

6) Reconfirmed the band adjustments for the 2nd time...

** Still no forward or reverse***

7) Removed the pan and did not find any thing concerning.. the fluid was new from a few weeks ago..

8) Checked the valve body fastener torque with a torque wrench set to 48" lbs... they were all torqued to a higher value...Was hoping to find some of the valvebody fasteners with a low torque... no luck

9) Removed the valvebody to inspect the bands...both seemed okay...

10) Conducted the air pressure tests for the servos to move the bands...they seem to be fine.....used the below video + a ford manual as reference for the air pressure checks..

http://www.youtube.com/watch?v=ucTqlOHhCxM

Still working through the air pressure tests...

 

[High Pressure]

Update ... I believe I have lost the forward clutch... When 40 psi of air is applied to the forward clutch hole I don't hear a "thud" like I hear when air is applied to the reverse-high clutch hole. Should I hear the same sound?

I pulled the transmission... the torque converter and input shaft looks fine. I rechecked the "pull back" spacing for the torque converter to flexplate which measured .110".

I'm also questioning when I install the input shaft into the transmission... the shaft "ratchets"! and rotates with minimal torque... Is this correct? The input shaft 24 spline end seems fine... I wonder if the forward clutch housing ID spline is stripped?

 

[BwoncoHowie]

It is possible that the splines in the fwd drum are stripped. You may be able to check them by removing the input shaft and looking down the hole with a flashlight.

All the symptoms described throughout this thread point toward some sort of mechanical disconnect of the input, especially if the direct clutches and rear servo air check well. and there is no pressure loss in all the gear ranges. The fwd pack doesnt always come on with a loud thump with only 40 psi, but it is important that it doesnt leak too much air.

Update ... I believe I have lost the forward clutch... When 40 psi of air is applied to the forward clutch hole I don't hear a "thud" like I hear when air is applied to the reverse-high clutch hole. Should I hear the same sound?

I pulled the transmission... the torque converter and input shaft looks fine. I rechecked the "pull back" spacing for the torque converter to flexplate which measured .110".

I'm also questioning when I install the input shaft into the transmission... the shaft "ratchets"! and rotates with minimal torque... Is this correct? The input shaft 24 spline end seems fine... I wonder if the forward clutch housing ID spline is stripped?

 

[PaulS]

The input shaft should rotate but I have never had one "ratchet" unless the splines were bad. You may have to remove the drum to inspect it for cracks. Used drums are still fairly easy to find and you can buy after-market drums that are welded or have a bushing pressed on to eliminate failures of the splines.

 

[High Pressure]

BroncoHowie & PaulS,

Thanks for the quick responses. I truly appreciate your advice and counsel. I looked down the input shaft hole with a light... Of course, you can tell from my questions that I'm not familiar with all of the internal features of a C4... I was suprised to count 22 splines with 2 missing at 180 degrees apart in the I.D. of the drum. I believe that a couple near the missing 2 splines seem to be damaged... but will have to tear it down to truly confirm.. Are the 2 spaces (or missing splines) for oil feed or return?

PaulS - thanks for the info about the availability of welded forward hubs.. I have seen one of your other posts for suppliers of transmission parts on another forum. Is "Broader" a good supplier for a reinforced hub? They want $75 for it.

This post will go quiet for about 14 days.. I'm headed to the UK and on to India...The things I have to do to fund this Bronco project! Though I will be able to access the internet. Hope to complete the tear down of the transmission shortly after I return.

 

[Broncobowsher]

When you get it apart, post pictures. I would like to see what went out. I have a suspesion that the 2 missing teeth are where the hub split at.