New here,
Does anybody know what would cause the c6 to slip and jerk in reverse? I can't back up even the slightest incline, it will not grab. Also, it over revs on the second to third shift. I have a new modulator and good vacuum from the card. The adjusting screw does make it shift later or earlier but it still over revs for a second then engages but only 2nd to 3rd gear. Every other type of shift is perfect like 1st to 2nd is fine, even downshifts fine. So, what gives? Anybody have any suggestions?

 

Welcome to the forums.

Sounds like it has serious issues. Sounds like clutches are not engaging, either pressure issue or wear issue.

 

Do you have the proper amount of fluid in the trans? Low fluid will cause it to slip. What does your trans fluid look like?

 

And smell like? Does it smell burned? Is it nice & red in color or brown?




John

 

Thanks for the reply, guys. Fluid level is good. Fluid color is dark red. it doesn't smell burnt, but if you ask me, all oil smells burnt. Oil was changed like 8 years ago with new filter, but truck was only driven about ten thousand miles. It is a camper special and had a camper on it but i sold it, now it is my daily driver. (I know, stupid with the gas prices, but no choice, it is my only ride.)

Here is where i am at: Should I change the oil as a shot in the dark (50 bucks, gasket and 6 or 7 qts again) or just chock it up to major wear and look for a used or rebuilt C6 and put the 50 bucks toward that. Basically, can oil quality make that much difference in shifting performance? There is oil in it and it shifts fine on all other shifts. The oil isn't black, but it is not pure red either.

 

also, I adjusted the intermediate band because that is the only one i found instructions to. No real difference. Where is the reverse band? Inside i bet. It seems non adjustable for the C6, because otherwise, there would be instructions.

 

Thanks for your input, Freightrain. Do you know where can i check the pressure? Probably the fluid line that goes to the rad? What would be the ideal pressure at idle?

 

ol blu, I am a pretty darn good carpenter or I used to be, but a transmission repair man I aint. I suggest taking it to a rep. local tranny shop for good advice. A good shop will advise on correct assessment.




John

 

Like John, I'd take it to a reputable shop and get some advice. Doubt it is an easy fix. Maybe it will only take an adjustment to the bands? Maybe not. I'm not an automatic kinda guy, so can't assist much.

If it had gears and levers, I'd be all over it!

 

I think i will do that, thank you. I just thought that since C6's are so common that maybe others have had similar experiences or that those symtoms would point to a specific problem like governer or whatever, but I'll give a transmission shop a call to see what they say. Thanks again.

 

I am by no means an expert, but I will give you my two cents anyway. I just rebuilt my C6 transmission. Truth be told I am restoring my truck and have the whole front end pulled of and the cab stripped so I can not tell you if my job was worth the effort. My gut tells me I did a good job and that it is going to run great.

Like I said I am no expert. I did a lot of research be for I rebuilt my C6. From the information I got the band is only used for second gear. The reverse clutches are located near the back of the transmission. There is what is called a reverse piston that when shifted in reverse trans fluid pushes against the piston which causes the reverse clutches to engage. It could be that the clutches are worn out or on of the two seals that are on the piston are blown.

If it was not your only ride and you had the time I would say tear it down yourself. This was my first time to ever rebuild a transmission. You will need a special tool called a universal sprig compression tool to get to that reverse piston.

I got prices around here (Magnolia Texas) and was told if I brought it to them it would be around $650 or more. I did it myself for around $300-350. That included the tool which cost me $120. One good thing about the place I got the tool from gave you a video of the rebuild to a couple transmissions. I of course chose the C video. I took my time and think I did a good job. I got a complete rebuild kit off Ebay and I found the place that sold the tool by searching on you tube.

I hope you figure it out and it turns out to be something easy, but I think you will be looking at rebuilding it.

 

The clutch pack in the rear is the low/reverse pack. Sounds like you've got a trans that has hard seals and thus, worn clutch discs (if the fluid level is correct). Reverse has higher line pressures than does 1st gear (which sounds like your symptoms). I rebuilt mine for about $165, with a TransGo shift reprogrammer kit.
Torque converter was extra. Save yourself the hassle and replace the converter with your rebuild as well as send your radiator to the radiator shop to have the cooler cleaned out to avoid contaminants and particles from going into your fresh trans.

 

I'm no C6 expert, but I did just rebuild my first transmission, a C6, and it turned out great, I'll throw in my 2 cents.

Definetly sounds like you need a rebuild. Either a pressure issue, or your high/reverse clutch pack is shot like mentioned above, or both. Also like mentioned, make sure your radiator is flushed out or you will smoke a rebuit tranny. Also get a new converter or have yours serviced for the same reasons.

Buy a video and watch it before you buy any parts, or take your truck apart.

I suggest purchasing a transmission to rebuild instead of taking your truck apart and rebuilding that one. I ended up having my truck apart for awhile because I had to replace certain hard (sun gear shell) parts to get my end play perfect. I didn't shim it like many rebuilders will do. For me, only able to work on it on the weekends, every time I had to purchase another part, it cost me another week. Also, when I got my trans apart I found out it was a light duty trans with minimal friction disks and I bought the parts to add additional clutches and steels.

If you don't have a parts washer, buy one. I thought I could get away with cans of carb cleaner, but I could have paid for the parts washer with the amount of cans it took to clean the trans to my satisfaction.

Also, make sure you get the correct striped modulator and if your vacuum lines aren't new, replace them all. My old trans was crap and didn't realize how bad it worked until I rebuilt it. There was a slight lag in it's shift that bothered me and turned out I had a bad vacuum cap. My truck uses a black stripped modulator. That one is designed for trucks.

Good luck!

 

OP has a 1968 F250: C4AZ-7A377-B .. C4 & C6 Modulator Valve ~ white stripe ~ threaded type (Motorcraft TM-2).

Applications: 1968/71 F100/350 C6 / 1972 F100/350 C6 before serial number P60,001.

1965/71 F100/250 C4 / 1972 F100/250 C4 before serial number P40,001.

1964/72 ALL C4 Passenger Cars / C6 1966/72 Galaxie/LTD; 1966/72 Fairlane/Torino/Comet/Montego; 1967/72 Mustang/Cougar; 1969/72 Thunderbird/Mark III & IV ~ ALL before 7/1/1972.

 

wow guys, thank you for the great info. I will use your advice. I have rebuilt a volkswagen engine that took me 2 years, I should be able to tackle a C6. At least now I have some confidence knowing what to expect.