c-6 no reverse

[Zookie400]

my brothers truck has a new (few years old but very low miles) c-6. the fluid level is good, and the fluid is still very fresh. the problem: it wont go into reverse. forward gears are perfect. when you put it into R from N/P it will torque the driveshaft as if it engaged into R but then immediately goes neutral. throttle application doesnt change anything. you can repeatedly go from P/N to R and it will continue to engage R and immediatly drop it. with my mechanical knowledge and experience i have NEVER had any of my c-6's fail......EVER! i am a bit in the dark on this one. HELP!

[jk080]

I had a late model C6 in the shop a few weeks ago that had no reverse, fluid good, ect. We found the low reverse piston had cracked and couldn't hold the clutches from spinning, causing it to slip. I have seen these pistons crack before, other things would be the snap ring that holds the low clutches.

If the low-rev check ball in the valve body has blown through the plate it will have reverse problems also, sometimes rubber or plastic check balls will wear down.

While the valve body is off air check the case for the cracked piston and you should also be able see the snap ring thats in the case for the clutches.

[Zookie400]

thanks for the response. i didnt get a chance to do anything with it today, but i DID get my hands on a '79 service manual (i assume the c6 is the same from 79-88?) that coupled with your advise should help us greatly!

i will post my findings....

[Zookie400]

ok so the reverse low clutch goes "thud" and i cant hear any leaks when pressure is applied to the port. the book didnt say anything about testing the reverse high clutch though, should i be testing that as well? its still pissing fluid so i didnt try yet.

also, if i jack the rear end and apply the low clutch, could i have someone spin the driveshaft to be sure that its actually holding? or will that not work?

[Zookie400]

transmission is out and apart, all looks perfectly new (as it should). i took the valvebody apart but dont see anything out of place. not sure what to do now. i hope someone has been here before.....

[jk080]

Weird, reverse is the direct drum (one behind the pump) and the low clutches.

How many check balls do you have in the valve body?, not counting the one on the spring.

[Zookie400]

i want to say 2 in the body, one on the spring, and a funny shaped plug on a spring. whatever was in the ford service manual is exactly what we have. i was trying to figure out if any of the spool valves in the body have anything to do with reverse, the manuals dont talk about those at all really.

[jk080]

Here is a break down of the c6 valve body, I wouldn't think the problem would be here.

Have you air checked the direct drum on the pump?

If I come up with something else I'll let you know.

[Zookie400]

i didnt check the pump because we have all forward speeds working properly. just no reverse. am i wrong in my thinking? i can check the pump either way.

[jk080]

Yea the pump is working if you have forward gears, but you still may want to take it apart and check for wear, its easy, just put the bolts back in to put it back together, no alignment needed.

Reverse requires more line pressure to operate than the forward gears, if the pump cant create enough pressure to operate reverse but makes enough to go forward is a possibility. The pressure is controlled in the valvebody, but the pump has to be able to keep up with the demand.

So the pump is worth a look.

Also you might want to take the pistons out of the drums and case just to make sure its not something simple.

[madrockwyo]

A leaking or worn piston seal? Make sure you accurately torque valve body bolts. Top loose or too tight and pistons in the valve body can bind. trust me, i learned the hard way!

I only got 250 miles on my last rebuild of a c6, the rear output snap ring broke and caused much damage. I have never heard of a snap ring breaking before and it is one thing the do ot list in the troubleshooting guides.