Hey guys, years ago I put a used C6 in my '68 T-bird w/ 429. The guy I got it from claimed it was rebuilt by his uncle, but who really knows, right? Been restoring the car and haven't driven it yet until recently. I've put about 50 miles on her now.
Anyway, I only payed a couple hundred bucks for it, so no big loss, but anyway, I was out driving around town last evening, and while taking off, I went to give it some moderate throttle, not heavy enough to break the tires loose, just good and firm and almost instantly, I heard a very loud POP from the trans under the floor. More like a very big THUD like something popped apart in the trans. All forwards gears are the same; still goes forward, but slips real hard. It would never make it up a moderate grade (which was ahead me, so I had to turn around). Fortunately, I was just down the street from the house (2/10 mile) and gently limped it back (though I have Hagerty road side assistance anyway). It's not slipping really bad on level ground, under very, very, very light load, but it's slipping even then. Reverse still works great. I can feel a major difference when I put in R vs forward gears. It's very firm and positive in reverse just like forward was before the loud THUD happened.

Major repair or did a band blow apart and something I can fix without tearing deep into trans, or no way of knowing, until I get in there? Just wondering if this screams like something obvious to someone. Thanks guys.




This sucks, cus I was gunna take her back out for a nice long cruise today. I guess I'll install the new rear coil springs instead, maybe drop the trans pan to look for something obvious and if nothing, I'll get back on here to see if there's any suggestions before removing the trans. This car is way more fun than I expected. It can get scary quick. It's a good thing I'm old enough now not to be too stupid anymore.

 

It sounds like it did something to the forward clutch. You'll have to take the whole transmission apart to get to that because it is inside of the direct clutch. When the C6 is in reverse the direct clutch is applied to put power through the sun shell to drive the low/reverse planetary sun gear. The reverse clutch holds the planetary so that it can drive the ring backwards, forward clutch is not used.

Maybe they didn't have the snap ring in the drum correctly. Maybe the transmission has a problem where the line pressure is going too high. This can cause the forward clutch to destroy itself/blow apart. In a C4 the modulator valve can be installed the wrong direction and cause this to happen to the forward clutch. I would assume that C6 is the same. And you said that the transmission had been worked on....

 

Yeah, I figured it probably hurt something that wasn't going to be a quick fix. I'll get another trans for it then. Thanks man.

 

One sure way to tell if it is the forward clutch is to put it in D1. In D1 you have the forward clutch holding and the low/reverse clutch holding. If it doesn't slip in D1 then the one-way clutch is bad. If it slips in D1 then the forward clutch is bad. In D or D2 you only have the forward clutch and the one-way clutch (sprag to GM folks) holding.
Either way it's got to come apart.
Nice T-Bird! It's good to see someone saving one of those most people just walk by them.
If that is the original transmission it might be worth rebuilding most of those old C6's behind 429's had 5 friction forward, 4 friction direct and 5 friction low reverse clutches. If you decide to re-build it adding the E9TZ-7D164-B kit will reduce the internal friction by replacing the #9 thrust washer with a bearing and get you a better one-way clutch.

 

I don't build automatic transmissions for a living but I've always wondered how Ford and other manufacturers determine stuff like clutch pack count in a particular transmission. When I built a C6 for my truck about 25 years ago I put in a new CJ direct drum which held more clutches, stock that transmission had 4 in the forward and I think only 4 in low reverse. Either way, that transmission came behind a 460 in an F350. 20 years later I built an E4OD for the truck to replace the C6. I had a core and a big block case from a friend who does transmissions, my core was a small block or 6 cylinder version and it had a low clutch count in all positions except for low reverse where it has 5. Seems weird. Maybe all E4OD's had a lot of low reverse clutches, I don't know..

 

It seems Ford had a different clutch count for every occasion. The old CJ stuff along with Police and Fleet transmissions had the best parts. The 5 friction forwards are still around but the old 5 friction directs are about all gone now, the 5-friction direct C9OZ-7D044-A was replaced with a Ford Performance part M-7044-A in the mid 1990's but none are available from Ford anymore.

 

I got the 5 friction direct from Transtar I think but I didn't change the clutch count in the forward on my C6.

My monster truck customer ran 2 trucks for many years, Big Dawg and Tailgator which were both Ford powered and for a long time he used C6's built by a guy named Matt Heady. Sometimes a transmission would go into the truck when we freshened the engine and it would last a whole year and that's a lot of monster trucking. If there was a problem that came up it was easy to swap out the transmission with a fresh one, I think he owned about 10 transmissions after a while.

What I found interesting was how "stock" most of the transmission actually was inside. The thrusts were rollerized but the planetary gear sets were the regular stock aluminum ones and some of the transmissions used the 3 gear and some used the 4 gear. I think that it he maybe broke 2 or 3 planetary sets, not many. They used 2nd gear a lot and the greatest weak spot seemed to be the band. They had a band that was made of steel with ends welded on and it was as wide as possible. It applied with a billet aluminum R style servo and I don't remember what arm. When air checking using about 120 psi when the band would apply you could see it flex the case. Using a cast aluminum pan helped with that and I don't think he ever broke a case. Matt told me one time that if a C6 is breaking parts it is almost always a shift timing problem. The transmissions used the stock Borg Warner and the clutch packs were modified to hold a greater number but not a tremendous amount. It didn't have any of those special thin clutches.

 

Forward clutch must have gone then because D1/D2/D all slip. Only reverse is left. It's not the original trans to the car. I'm not sure if it had the original trans when I got it (possibly) but it was acting up, so I replaced it with something I found locally. A bit latter, like '72 or something. I had to trade over shift linkages. I almost think the guy said it came from a van originally but it's been 7 or 8 years or something now. It worked well enough for moving the car around the yard, back and forth from the garage for new exhaust at least.

Once I pulled the trans that was in the car to replace it and swap over the shift linkage, I noticed loose valve body bolts, and probably why it was acting up. If I remember right, it just wasn't shifting and if it was, I had to help it, by lifting off the gas. I'd continue to swap the trans anyway, rather than snugging up the valve body, because I noticed something far worse; the case was cracking around the bellhousing bolts. Someone probably over-tightened them over the years (I've long since scrapped than one.)

I'll try another used trans; they're cheap enough. If it doesn't hold up, I'll order a rebuilt one next time. Meanwhile, I'll dig into this one. Back when I was a kid, I rebuilt a C6. That's been so long, I don't remember anything about it now. All I really remember was, that since it was pre-internet, I had just a big manual to go by. Maybe I'll look it over and see if I can get this one back together and keep it on hand. If it truly is a reman already, it very well will be worthwhile to investigate further, rather than just scrapping it. Well of course I wont scrap this one no matter what. If I decide not to do anything with it, I'll see that someone who wants a good parts trans to rebuild, gets it. That someone just might very well end up being me though. Though I don't remember much about it now, I do remember having a lot of fun rebuilding one back when I was 17 I think I was. Took me all winter and I went over every step again and again to make sure I got it right. A little bit is coming back to me now, the more I reflect back on it.