C4 No reverse gear.

[gumby77]

While out in the Arizona desert this past weekend I was in a wash. Got into 4-L and hopped out no problem. Once I got to the top only about 10 feet ish. It felt as if the parking brake was engaged. It was not. I got shit it off and got out of 4 because it felt bound up. Restarted the motor and drove fine in drive 1-3 on my c4 shifted as designed. When shifting into reverse however, I felt the trans shift and give me the light clunk as normal but after applying throttle no movement.. I contacted the shop owner that rebuilt it 2 years ago and before telling him he rebuilt it he stated I must have tore the band. I just drained the oil and it isn’t too dark or burnt smelling. Going to check filter and pickup tube and see if fresh fluid does the trick.
Also a question on how many quarts the c4 takes if doing only the pan. Stock c4 pan
Thank you in advance.

 

[Broncobowsher]

Probably lost the low/reverse band. While you have the pan off, look at the band. Mainly the anchors.

 

[phred]

With the low/reverse band broken or slipping you wouldn’t have low (1st).

 

[Broncobowsher]

With the low/reverse band broken or slipping you wouldn’t have low (1st).

Not fully correct.

You will still get 1st gear, in drive and manual 1 positions. But you won't get engine braking in manual 1 position.
1st gear has a sprag that engages in acceleration, but releases for engine braking. This allows the transmission to downshift into 1st gear as you slow down without a jerk. The sprag allows over running. But to get engine braking, it only happens in manual 1st gear, not in drive. When manual 1st is selected, the low reverse band engages. The locks the sprag, it can't over run. Now you get engine braking.

So you can still have 1st gear with a broken low reverse band, just not engine braking in 1st gear.

C4 has 2 bands and 2 clutches
The simplist is the intermediate band, it is 2nd gear. That is all it does.
The other band is low/reverse. It applies in reverse. It also applies in manual 1st gear to parallel the holding of the sprag during acceleration, and locks the sprag from overrunning during engine braking
Then there are 2 clutches. The forward clutch applies for all forward gears (1,2,and 3)
The other clutch is the direct/reverse clutch. This applies in 3rd gear and reverse

Select drive from a stop. The forward clutch engages. The sprag is holding, you have 1st gear.
As the 1-2 shift occurs the intermediate band applies and the sprag realeases. You are driving on the forward clutch and 2nd gear band.
The 2-3 shift is the hard one to do. The direct clutch applies as the 2nd gear band releases. Now the direct clutch and forward clutch are giving you 3rd gear.,

When you go to reverse, the forward clutch is released. Direct clutch (Direct/reverse) is applied. The low reverse band is applied. The forces on the band go the wrong direction against the piston, so the line pressure control is bypassed and reverse gets full line pressure.

When you lose all forward gears, but still have reverse, you have an issue with the forward clutch
When you lose 1st gear in drive, but have it in manual 1st, the sprag has failed.
When you lose 2nd gear, there is an issue with that band.
When you lose 3rd gear, the only thing extra that is the direct/reverse clutch. Can't be the forward clutch as that worked in 1st and 2nd.
There is a chance that a valve can stick in the valve body as well if it isn't an acutal clutch issue, that is where the line pressure test come to play.

 

[nvrstuk]

BBowsher--- you just quadrupled my knowledge on C4 symptoms!

I had a C4 in a Bronco I bought when I was rebuilding my '68 and when it almost left us (family on Fathers Day) stranded in a knarly place, I began my hatred of of C4's and auto's in Broncos... took a long time for advancement in auto dependability and tech for me to ever own another!

 

[bronco italiano]

I had same issue with my '74. Lost reverse but had all the other gears

 

[Madgyver]

C4 issues we are having is reverse gear takes awhile to engage.

 

[gumby77]

Thanks for the info. I called my guy that rebuilt it and before telling him that he built it only 2 years ago he stated oh yeah thats ur revere band and those go out onetime and said that they’re hard to find so he keeps them to reuse if there in good condition blah blah. Then i stated that he rebuilt it and he said well i will give you a good deal.. im contemplating taking it to someone else. It really dosent get driven too hard Or incorrectly.
also my work order from the build had a part on the list for about 65 buck that said rear. Band. Kevlar. assuming thats what actually made it in there who knows what broke. All the rest of the build was r&r old parts and super servo “race clutches” all that stuff. Not sure why just reverse went out.