7.3 idi with c6 trans.

[88f3507.3idi]

I have a ford with 7.3 idi and c6 trans. I would like to swap trans out for a 5 speed or even an overdrive trans. This truck runs wide open at 3300 rpms at 60 mph and I would like to get the rpms down. Any suggestions would be great appreciated

 

[USNENFTS]

Ha, I converted from a C6 to a ZF 5 speed for the EXACT same reason. The swap is not hard at all! The hardest part is drilling out the holes in the firewall for the master cylinder. I tried to submit a tech article on it but I guess who ever approves them didn't like it. I can help you with anything you need. LMC truck sells the pedal assembly you need or just find it at a wrecking yard. I can PM you with all the parts you will need. The other thing you could do is install a Gear Vendors overdrive. If I were you, i would put a ZF 5 speed in there, you don't need to change your driveshaft at all. If you install an overdrive, you need your driveshaft changed.

 

[88f3507.3idi]

Thanks man that's what I'm looking to do is switch to the 5 speed but will it fit right in or do I have to change trans crossmember or drive shafts?

 

[USNENFTS]

It will fit right in, the cross member is same with the exception of the brackets that attach to it, just find a 88 to 91 with the manual in a wrecking yard and your good to go, no drilling needed. I used the same driveshaft. The ZF 5 speed is only half an inch shorter or so and that isn't near enough to make a difference. You want me to send you a list of what you'll need?

 

[cpdenton]

I think we need a little more information. Are you 2wd or 4wd?

The 2wd c6 uses a slip yoke, while the zf5 has a fixed output. Different end. If you are 4wd, the shafts stay the same because the transfer case swaps over.

 

[88f3507.3idi]

Sure send me a list. The truck is 2 wheel drive f350

 

[USNENFTS]

Yeah, if it's 2wd then you will need a driveshaft from a donor truck, thanks for catching that cpdenton. I dunno nothin bout the 2wd's. Okay, other than that its an easy swap, list stays the same, just need to find your same truck, just with a manual for the drive shaft and cross members. I will get that list to you tomorrow.

 

[PwrSmoke]

Gee, what gears does this truck have? What tire size? 4.10:1 was the lowest factory gear ratio and 2.35/85R16 was the tire size (about a 32). My truck is a C6 with 4.10:1 and even with the shorter original tires (it has 33s now) it would do 80mph flat out before the governor kicked in at 3300 or so. If you are indicating 3300 at 60 mph, either the tach is way off, the speedo is way off or somebody installed 4.88:1 axle ratios (which is approximately the ratio require to do 3300 at 60). I'm all for the OD swap but I am pointing this out to indicate you might have another problem and to clarify.

 

[88f3507.3idi]

Truck is supposed to be 4.10 ratio I have the c6 with 235/85/16s. I'm almost positive the tachometer is right as the engine is whinding out. Transmission shifts through the gears so I'm just stumped over why it does go faster at lower rpms

 

[cpdenton]

Someone had installed a c6 in my truck in place of the original e4od. I had similar rpm readings with my 4:10s and the same size tires. The c6 doesn't have a locking converter so it slips even in high gear. You might be having some other problem internally, but the c6 with 4:10 gears isn't a good combo for a 2wd not having lathe off road tires.

 

[88f3507.3idi]

Yes I guess this truck wasn't meant to go faster than 65 without redlining the engine. It is a bad combo.

 

[Hydro-idi]

Yep, something doesn't seem right. Your rpm's are a bit too high for that axle ratio/wheel size you have. I suspect that maybe you have a slipping torque converter that's not functioning correctly. Sometimes the veined wheels inside the tc can distort due to excessive heat and cause slippage. This happened to my truck with the PO when he was towing his enclosed car trailer up that steep grade on I-5 incline near Shasta. He said the rpm's were always higher at cruising speeds after that happened until he eventually got it rebuilt.
My 3.55 gears and same size tires will see about 2450 rpm at 55. Bump it up to 65 and it's right around 2850 rpm. Redlining these engines will not do any harm.

 

[88f3507.3idi]

Makes since.. I notice when I put in drive it takes a second before it actually kicks in drive. I'm thinking front pump and torque converter going bad. Just more reason to do the swap to 5 speed. Imho the 3 speed transmissions aren't meant for heavy pulling that's where the heavy duty standard trans comes into play

 

[Hydro-idi]

These C6 transmissions can handle up to 500hp/500ft. lbs torque in their stock form. They are more than capable of towing and hauling well beyond the trucks "legal" limits and do not need to be serviced often even if they are abused. And when the time comes for a rebuild, they are about 1/3 the price of an E40D overhaul. Now having said that, the zf5 will give you better performance while towing, better mpg, and lower cruising rpm's. Stating that the zf5 is a heavy duty standard transmission is somewhat debatable. Some have had great luck with them and some haven't. Keeping fresh oil in them is very important from what I have heard.
Here's a cool article that I found. "Top 10 off-road transmissions of all time"


http://www.4x4review.com/the-top-10-off-road-transmissions-of-all-time/