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Alrighty, I have a transmission problem, I think. 1986 F250 6.9 with a c6.
Driving back from lunch there was a clunk and then all neutrals. If it put it in park, the parking pawl engages, but all other gears do nothing. There is a whirling noise that seems dependent on engine speed, and I think it is in all gears including N. Nothing is leaking, fluid looks full and still a good red color. (I did shift the transfer case around, but it didn't change anything. Rear end appears fine.) Truck starts and runs as expected. The transmission is about the only major thing on this truck I haven't touched, as it has not given me any issues.
This has been a fairly low buck work truck so far. I got it cheap with a bad engine, I put a used engine in that runs and starts really well. I've replaced other things as needed to get it running and driving, and I plowed snow with it last winter with no issues.
Thoughts? Insights? What am I looking for to diagnose? Should I rebuild it myself, or should I swap in a ZF5 that I have (it might need to be refreshed as well)?
Mine did that, I have a 1989 and it had a c6 with the 7.3 idi. Just before I bought it the transmission went out, did the same thing as yours only it was in the middle of a intersection(I knew the guy I bought it from). He took it to the transmission shop, they rebuilt the transmission and said the torque converter had failed. I am guessing they rebuilt the transmission at the same time, since when one thing fails it sends metal through everything else.
It ran fine for several years after that when I bought it, but I swapped in a zf 5 speed. Changed the whole personality of the truck. I got 3 more mpg, I can cruise down the interstate and keep up with modern traffic. It's so much quieter inside the cab, the 5 speed utilizes the low end torque better that these engines have. There are so many wins with a overdrive transmission.
What am I looking for to diagnose? Should I rebuild it myself, or should I swap in a ZF5 that I have (it might need to be refreshed as well)?
You are looking to diagnose if the torque converter broke, the pump broke, a shaft broke, the gearset failed, or other major part broke. No matter which one failed, the answer is that the trans has to come out and be rebuilt or replaced.
I'm currently having trouble with the C6 in my Bullnose truck. Be aware that if you are going to remove the transmission and rebuild it you might also want to have the VRV serviced. Looks like this is going to be your only option. I think I see the 4x4 locking hubs in front in your pic.
Nick has great customer service and provides the necessary skills to get your Bullnose truck back on the road. His website also has directions on testing your VRV which you can do at home with a vacuum gauge and hand pump.
If it shifts ok I would not mess with the VRV. You can't get them anymore and if you break it, too bad.
Mark Kovalsky can speak to this if he would like, but the VRV seems like a bandaid invented to mate a automatic that uses vacuum(and road speed) to shift, to a diesel engine that has no vacuum. It does seem to work ok, but I can't see it working the same as it would with a gas engine. On the gas engine the vacuum will vary directly with engine load. On this diesel setup, it's going to vary according to throttle position only.
Mark Kovalsky can speak to this if he would like, but the VRV seems like a bandaid invented to mate a automatic that uses vacuum(and road speed) to shift, to a diesel engine that has no vacuum. It does seem to work ok, but I can't see it working the same as it would with a gas engine. On the gas engine the vacuum will vary directly with engine load. On this diesel setup, it's going to vary according to throttle position only.
Yes, that's correct. Do you have a better way to do it?
Yes, that's correct. Do you have a better way to do it?
No I don't.
Now that I have you on the line, can you speak as to why they made a oddball bellhousing pattern just for the diesel? Of course they used a international engine with it's own different bellhousing pattern, but International or Ford, don't know which one, made a adapter that bolts to the back of the international diesel to change the bell pattern. Why didn't they make the adapter to the standard big block Ford 460 pattern? And then you could have used all the transmission castings you already had for the big block.
Just curious. I worked in industry for years, and know sometimes the reason for things are a little convoluted.
Mine did that, I have a 1989 and it had a c6 with the 7.3 idi. Just before I bought it the transmission went out, did the same thing as yours only it was in the middle of a intersection(I knew the guy I bought it from). He took it to the transmission shop, they rebuilt the transmission and said the torque converter had failed. I am guessing they rebuilt the transmission at the same time, since when one thing fails it sends metal through everything else.
It ran fine for several years after that when I bought it, but I swapped in a zf 5 speed. Changed the whole personality of the truck. I got 3 more mpg, I can cruise down the interstate and keep up with modern traffic. It's so much quieter inside the cab, the 5 speed utilizes the low end torque better that these engines have. There are so many wins with a overdrive transmission.
That does have a certain appeal to it. I think I am leaning the ZF direction. The flywheel I have came from a 7.3 idi, will it bolt to the 6.9 with no issues?
Last edited by DowneyB; Jun 18, 2024 at 01:51 PM.
Reason: add content
You are looking to diagnose if the torque converter broke, the pump broke, a shaft broke, the gearset failed, or other major part broke. No matter which one failed, the answer is that the trans has to come out and be rebuilt or replaced.
I kind of figured that I was going down one of those paths... Not that I am planning on it, but out of curiosity, how new of a transmission would bolt to this motor?
I'm currently having trouble with the C6 in my Bullnose truck. Be aware that if you are going to remove the transmission and rebuild it you might also want to have the VRV serviced. Looks like this is going to be your only option. I think I see the 4x4 locking hubs in front in your pic.
Nick has great customer service and provides the necessary skills to get your Bullnose truck back on the road. His website also has directions on testing your VRV which you can do at home with a vacuum gauge and hand pump.
The current VRV seems to be working fine as long as the vacuum pump is working, but I have been aware of Nick's work. He has some pretty neat stuff that he has worked through.
Now that I have you on the line, can you speak as to why they made a oddball bellhousing pattern just for the diesel? Of course they used a international engine with it's own different bellhousing pattern, but International or Ford, don't know which one, made a adapter that bolts to the back of the international diesel to change the bell pattern. Why didn't they make the adapter to the standard big block Ford 460 pattern? And then you could have used all the transmission castings you already had for the big block.
Just curious. I worked in industry for years, and know sometimes the reason for things are a little convoluted.
I pretty sure the castings between the diesel and the 460 are nearly identical. The bolt hole sizes are different, and I think the dowels are different, but the shape and most of the bolt locations are the same. So they probably started with the same castings, and then made subtle changes for some other reason.
I pretty sure the castings between the diesel and the 460 are nearly identical. The bolt hole sizes are different, and I think the dowels are different, but the shape and most of the bolt locations are the same. So they probably started with the same castings, and then made subtle changes for some other reason.
If you run across a zf from a 460, it can be modified to work. But there is some precise drilling involved, you need a good drill press. They are different enough where it will not bolt up without some modifications.
On the flywheel thing, that is a can of worms I fell into when I did my swap. I knew nothing about a dual mass flywheel till I had the transmission out of the donor. I found out Ford used a dual mass flywheel with the zf behind a diesel. Apparently the diesel engine hits so hard when it fires, it shakes the driveline and the aluminum zf becomes very noisy at idle. It sounds like it has gravel down inside the transmission.
To get rid of this noise, they used a dual mass flywheel. It's basically a flywheel inside a flywheel, with springs and clutches connecting them together. It sends power from the engine to the transmission, while absorbing the shock from the diesel engine firing.
I found out these dual mass flywheels wear out, just about the same time the clutch wears out. And back then just the dual mass flywheel was $1000. But the aftermarket people have conversion kits to replace the dual mass setup. They give you a new solid flywheel and a clutch that has many springs in the disc. This takes place of the springs in the dual mass setup. It's not perfect, you can get some noise from the aftermarket setup. It all depends on how smooth your particular engine runs at idle. I found out also that I could turn the idle speed up just a little bit, and get rid of a lot of the noise.
No you can't use a solid 6.9 style flywheel with the zf. You said you had the flywheel from the 7.3. If the 7.3 had the zf, then yes you can use it, the zf takes a different depth flywheel. If your 7.3 flywheel is dual mass, you had better check it over and see how much play it has. Most of them are wore out by now unless it's a new replacement. Or someone could have used a aftermarket flywheel if it was with the zf and it's solid. All that will work on the back of the 6.9. It's just the 4 speed stuff will not work with the zf trans.
If you run across a zf from a 460, it can be modified to work. But there is some precise drilling involved, you need a good drill press. They are different enough where it will not bolt up without some modifications.
On the flywheel thing, that is a can of worms I fell into when I did my swap. I knew nothing about a dual mass flywheel till I had the transmission out of the donor. I found out Ford used a dual mass flywheel with the zf behind a diesel. Apparently the diesel engine hits so hard when it fires, it shakes the driveline and the aluminum zf becomes very noisy at idle. It sounds like it has gravel down inside the transmission.
To get rid of this noise, they used a dual mass flywheel. It's basically a flywheel inside a flywheel, with springs and clutches connecting them together. It sends power from the engine to the transmission, while absorbing the shock from the diesel engine firing.
I found out these dual mass flywheels wear out, just about the same time the clutch wears out. And back then just the dual mass flywheel was $1000. But the aftermarket people have conversion kits to replace the dual mass setup. They give you a new solid flywheel and a clutch that has many springs in the disc. This takes place of the springs in the dual mass setup. It's not perfect, you can get some noise from the aftermarket setup. It all depends on how smooth your particular engine runs at idle. I found out also that I could turn the idle speed up just a little bit, and get rid of a lot of the noise.
No you can't use a solid 6.9 style flywheel with the zf. You said you had the flywheel from the 7.3. If the 7.3 had the zf, then yes you can use it, the zf takes a different depth flywheel. If your 7.3 flywheel is dual mass, you had better check it over and see how much play it has. Most of them are wore out by now unless it's a new replacement. Or someone could have used a aftermarket flywheel if it was with the zf and it's solid. All that will work on the back of the 6.9. It's just the 4 speed stuff will not work with the zf trans.
Ah, that is the distinction I needed to know. The flywheel and clutch I have were in the truck together with the ZF I have at one point, so it should be good then.
The DMF sounds like a good idea, at least when its new anyway. I need to go grab the stuff I have off the shelf and check it out, but it may have already been swapped to a solid flywheel before I got it. If not, I might have to bite that bullet too.
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