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No reverse in my C4

Dne'

Dne'

Well-Known Member
Hi ya'll! nothing worse than going to moms in Wingnut('67 stang) and waving goodbye and not going anywhere! Reverse in my C4 just magically went out! The forward gears are ok, has always been a little sloppyg going from 2-3rd, but manual shifting, it works fine. I spoke to the man that overhauled it 3 years ago, he barely remembered me, but he thinks the servo may be sticking? I put it up on my lift, and there is no way I am pulling that tranny back out unless IT HAS TO! The long tube headers headers are in the way to get the ttranny out see, I'm studdering now! lol

Also I noticed the modulator is leaking big time! So I may just take the car over to the guy and let him see if he can get it going again. I sure miss reverse!
However, if you have any ideas, I'd be ok with pulling the pan, valve body etc, if you can guide me through it ;)
dne'

Babysitting all this week, so may not be much time to play with my Wingnut! : (
 
IMG_8525-2.jpg
 
First things to do : check oil level = with engine warm and running and trans in "P" position , check oil on trans dipstick.
Check if the shifter linkage didn't came loose underneath the car.
 
THe first thing that I did do was check the fluid level hot in park. no problem there. Again, the modulator is leaking pretty good/bad. I've taken a pan off of a c4 but never any further than that. I don't know anything about adjusting bands or doing someting with the modulator. Or how to work on the valve body! step by step instructions would be helpful. ; )
 
Low and reverse use the same band. Low is engaged two ways in a C4, normally by a overrun clutch or one-way clutch. In drive, the tranny starts out in low and second overruns low. Manual low is different, using the Low/reverse band. You might have low, via the overrun clutch, but not low via the band, no easy way to tell driving it. Its possible the band broke on you. They break right where the heavy end piece is attached (spot welded) to the band. If it's the low-reverse band, the trans works using the one-way clutch for 1st gear. That would make it apparent only in reverse when the band has to work.
Adjustment is tighten down until snug, then back off about 2 to 3 turns out from snug. If it's broke it won't snug down.
It could be the servo. I would guess if it just quit working that it's the servo/piston. Bands rarely go out of adjustment or break unless its been slipping and abused. Servo's can dry/crack and leak and not engage the band.
It's the one on the same side as the shift linkage. It is difficult to check the servo itself without removing the pan and valve body to apply air pressure to the servo fluid apply passage.
Good luck!
 
neither of these explain why the modulator is leaking however. If it's leaking the vacuum could be sucking ATF into the engine. I guess it's separate from the reverse problem issue but I would change it as it is probably going bad. If it fails the car may lose drive (3rd) because it won't shift and if you go manual it will just be like neutral.
 
Good explanation Tarafied! hm, I may just drive it over to the guy who overahauled it, just need to make my path without having to backup! lol Or perhaps he could guide me through the process, but removal of the tranny kind of bothers me! I guess loosening all the header bolts excessively might give enough room for the tranny to be dropped through. I was thinking of a Summit racing tranny, it's not the money, just want a good dependable tranny.
 
"tarafied1" said:
Low and reverse use the same band. Low is engaged two ways in a C4, normally by a overrun clutch or one-way clutch. In drive, the tranny starts out in low and second overruns low. Manual low is different, using the Low/reverse band. You might have low, via the overrun clutch, but not low via the band, no easy way to tell driving it.
Click to expand...

Yes there is. Put it in low and see if you have engine braking while decelerating.
 
Think I found it!

While snooping around under the stang, taking photos, I come across this nut and stud, obviously loose and it's leaking right down onto the modulator! So, do I just tighten it as is, or torque the square nut on it. How do I proceed? ; )

IMG_9701a.jpg
 
http://image.customclassictrucks.com/f/ ... s_42_z.jpg

1970 Ford Bronco - Swiss-Watch-Precision C4
The low/reverse-band-adjustment nut can only be used once, since it has a silicone seal that gets compressed to seal upon tightening (prevents ATF from leaking past threads). Mike adjusted the low/reverse-band nut the specified three turns. The intermediate adjustment nut is shown in the foreground. It was next installed on the other side of the trans case. Its proper adjustment is 1.5 turns. Every time an auto trans is serviced, these adjustment nuts should be replaced and readjusted. View Related Article

Read more: http://www.customclassictrucks.com/tech ... z1PpmshlXB

looks like that might be your problem...
 
Well, for now, I just ran it back tightly. I got in and it went into reverse just like the good ole days! Funny, that I didn't have any problems with any of the forward gears. I generally run in by manual means, the "automatic" is just kind of sloppy, especially 2 and 3rd. Otherwise manually, I get second gear scratch. Maybe one day I'll get around to letting someone put a shift kit, but right now it's working ok and I'd like to get back on the Apache and make some progress.
I guess a lesson learned, is things aren't always what they seem! I thought for sure the modulator was leaking, but it wasn't. I was thinking how I was going to remove the tranny, when I should have been looking for the simpliest cause! I was actually pricinng a new tranny from Summit and prepared to pay the price! ha! oh me!
I don't think I have 500 miles on Wingnut, just drive to the Nifty50ee's and back and sometimes to Moms, but it's there when I want to drive it!
thanks ya'll!
dne'



"midpack" said:
http://image.customclassictrucks.com/f/ ... s_42_z.jpg

1970 Ford Bronco - Swiss-Watch-Precision C4
The low/reverse-band-adjustment nut can only be used once, since it has a silicone seal that gets compressed to seal upon tightening (prevents ATF from leaking past threads). Mike adjusted the low/reverse-band nut the specified three turns. The intermediate adjustment nut is shown in the foreground. It was next installed on the other side of the trans case. Its proper adjustment is 1.5 turns. Every time an auto trans is serviced, these adjustment nuts should be replaced and readjusted. View Related Article

Read more: http://www.customclassictrucks.com/tech ... z1PpmshlXB

looks like that might be your problem...
Click to expand...
 
wow, that's great! That is the adjustment for the band. Nice that it just backed off rather than anything being broken. That explains the leak too. I didn't think the modulator would be related.
 
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