Hello,

I have a 85 F350 6.9 Diesel. I drive it everyday... it somehow became my commuter "truck" when my girlfriend decided she rather drive my car than her own. Anyway, I see thread after thread about swapping overdrives into gas trucks.... not a single one about swapping an overdrive unit into a diesel. What are my options if any. Keep in mind I plow snow primarily with this vehicle so I can't use some weak tranny. I would also prefer an automatic, but at 10MPG I think I could learn to live with a stick.

Dan

 

A buddy of mine had an 85 F350 dually he converted to a 4x4. He was having the same issue, a C6 with 4.10s... not exactly highway friendly. He ended up swapping in a ZF 5 speed out of a newer diesel truck. I too am in a similar situation with my 84 F250 6.9, I pretty much decided I can live with it for now. The only downfall I see is I can't comfortably push the truck over 65 mph on the highway. I too don't want to trade my bulletproof C6 for some wimpy overdrive automatic.

 

It really is tough too because my C6 is hardcore, and I push and pull a lot with this truck... but when I am not pushing or pulling my 90% of my driving is on the highway.

P.S. My current top speed, floored is 74MPH

DG

 

Oh most definately, IMO the Ford C6 is the strongest 3 speed automatic ever put in a pickup truck. I plow with my truck too, and sometimes have to get pretty rough with it, the ol C6 has never let me down. Im a stick shift guy, mainly because I have had bad luck with automatics in the past... of course they weren't C6s either. A couple weeks ago I pulled a stuck semi out with this truck, it was a full on OTR truck with a big sleeper on it and a 50' trailer with 9,000 lbs of cargo in it. Tell me that ain't bragging rights! I plow snow for this guy who drives over the road and comes home on the weekends. He has an empty lot next to his house where he parks his rig, I keep it plowed out for him so he can get in and out of there. Anyway we got hit pretty bad over night and it snowed his truck in, and he got stuck.
Yep 74 mph sounds about right, I don't like pushing my truck that hard if I don't have to. I usually run about 55-60 mph on the highway, I just have to leave sooner to get somewhere if it's far away. No doubt about it, these trucks are beasts. The only other thing I have left to do to mine is I am swapping out the Dana 50 IFS front end for a monobeam Dana 60.

 

My 89 had the diesel with the c6 and 4.10's. I just swapped in a zf 5 speed, and it's a whole different truck, I highly recommend it. The only way I can describe it is picture your truck being towed by a large spring(this is the way the c6 moves the truck) or the truck being towed by a solid bar(this is the way the zf moves the truck). You really can appreciate the torque of the diesel engine with the zf, the c6 seems to hide most of it, even though it's still there.

I have a very steep gravel driveway, and with the c6 I had to get a running start to be able to get up the drive without spinning. With the zf I stop at the bottom and put it in 1st gear and it slowly crawls right up.

If you are going to do the swap I recommend you get a donor truck. I got a 89 donor with a zf, and I was able to use the pedal assembly, the manual floorboard cover, the manual wiring harness, the clutch master and slave, the crossmember, and also had to use the rear driveshaft and yoke out of the rearend. The driveshaft was about a inch shorter, and was made out of thicker material and had larger u-joints. You will also need the flywheel and clutch, unless you are going to convert to a solid mass flywheel.

 

I put a Gear Vendor behind the C6 in my old 6.9 F350. Not cheap, but an easy swap and it made it nice on the highway.

 

It's crazy how much power an automatic robs from an engine, I know the C6s really slow things down quite a bit. The gearing in a manual tends to be qite a bit deeper than an automatic. I actually concidered swapping a T19 into my truck but the ridiculusly low reverse gear would make snowplowing a PITA. I prefer a manual for towing, especially heavier towing... you have more control for going up and down grades and stopping.

 

I push snow also, and I thought I would not like the manual tranny, but going from reverse to 1st many times a hour isn't as bad as I thought it would be. The automatic was good for running into large piles of snow with the plow, but the manual is just as good if you push in on the clutch before you hit the pile and let it stop the truck.

I am amazed at how much quieter the truck is on the highway with the lower revs of the engine in overdrive.

 

I suppose so, I have a few buddies who also plow with gear jammers and love it. I have never tried it myself, I may like it too... it is a lot more pedal work but that could be fun sometimes.
My truck isn't too loud on the highway, although it does have that steady growl that sings you to sleep. Anyone who rides with me especially with the heater on starts dozing off, it's really kind of funny. Not a very good vehicle for long trips because of this.