Conversion from a Automatic C6 to a ???

[USNENFTS]

So, I am tired of the transmission in my truck, 2800 - 3000 at 55 to 60 mph is wearing my engine down and eating me alive with fuel, 3 gears just ain't gonna cut it anymore. I am officially starting the conversion project this summer and would like some input before I start gathering all the parts I need. Should I go with the ZF 5 SPD, or 6 SPD? With the 5 I will technically only get 4 gears (granny) and with the 6 I will get 5. My current transmission is in excellent condition and I plan on selling it for a lower than average price once I figure out what they go for in good condition, that is, if anyone ever wants these darn things anymore...

 

[bookite03]

A ZF5 would be a simpler swap vs. the 6-speed. Relatively easy once you locate all of the parts. You'll need a 4x4 transmission, 87-91 pedal assembly, transmission tunnel cover, clutch, flywheel, clutch master and slave cylinders along with the line that goes in between the two. Since you'd be switching from the C6 you should be able to re-use your transmission cross member and the driveshaft ( the C6 is about 1/2" shorter than the ZF).
I just converted my truck from a C6 to ZF and ended up buying a complete donor truck for parts. Another option is switching out your front/rear gears...from the Rpm's you're telling me sounds like you're running 4.10's. 3.55's will help you out as well. The other expensive option is buying a gear vendors OD...

I can tell you from my experience if you have the 4.10's like I think you do, the ZF-5 will bring your highway cruising down to about 2k rpm @55mph...fwiw in my case I have a ZF5 + a Gear vendor with 4.10's and I turn around 1500 rpm @ 55mph.

Hope this answers some of your questions.

 

[79jasper]

The zf 5 first gear isn't a "granny low" gear. I use first in mine at every take off, unless I'm still rolling. (F350 7k lbs empty, 4.10's)

The zf6 does have a actual low gear. Goes L-1-2-3-4-OD.

Sent from my USCC-C6721 using Tapatalk

 

[bookite03]

1st gear is pretty short though...I find myself using it to get the truck rolling, then I short-shift into second.

 

[79jasper]

^yep. Usually. Sometimes I'll run it out.

The 88 f250 I had, 3.55's and zf-5. If I started in 2nd, it'd squeal the tires.

Sent from my USCC-C6721 using Tapatalk

 

[Eli]

Ditch the 4.10 gears, they're so ridiculously low that I don't know why Ford even offered them without an overdrive.

Eli

 

[Wyreth]

Ditch the 4.10 gears, they're so ridiculously low that I don't know why Ford even offered them without an overdrive.

Have you SEEN some of the things we drag around with these trucks? 4.10 isn't ridiculously low. That's a good ratio for heavy loads and heavier trailers on the stock tires. It's also a good ratio if you're putting larger tires on. You have to remember, when these trucks were designed the national speed limit was 55, so even empty you weren't supposed to go faster than that. It was also before OD gearing was offered on most cars or light trucks, even as an option. Hell the price of diesel was what, 50cents a gallon?

Can't judge the design thinking behind a 20+ year old truck by todays thinking. The world was very very different back then.

 

[PackRat239]

I never use first gear except to get the trailer moving or if I want to crawl somewhere. Normal driving I always use 2nd. Overdrive was available in the early 50's by the way.

 

[laserjock]

Someone else can confirm this but aren't the OD ratios on the 5 and 6 almost identical? You really just even out the gears a little and gain a granny low. It is not two overdriven gears. Did that research myself a long while back. These guys are great to educate you.

 

[Agnem]

Agreed. The real problem with the C6 is the lack of a lock up torque converter and an overdrive. That's why they invented the E4OD, because they knew that. However, a manual trans beats an automatic in my book any day, unless you spend much of your commute sitting in traffic jams. An auto is hard to beat for that application. But then sucky and sucky go together.

 

[icanfixall]

Overdrive gears in transmissions have been around since the early 30's. My 1937 Cord has a built in overdrive in the trans. They are the norm in every 36 or 37 Cord but not so well known in any other car around this time. Both Ford and Chevy had them as an option in the mid 50's as an option. 1989 was Fords big step to use the od in the auto trans. Problem was they left out some bushings as a cheap way to rush the E4OD to market. Those early buyers suffered and when out of warranty paid out of pocket for the repairs and upgrades to a working trans. The stigma of the E4OD trans being a pos stays with it today. But we know can modify the trans to outdo many others on the market. At the 2009 rally I took Mel for a test ride after he installed a Moose Pump on my engine. I manually shifted up thru the gears never once using the Gear Vendors to split a gear. He was so impressed he told me to remind him not to drag race and E4OD trucks at the drags we were going to... I have the Brians Truck Shop E4OD trans. When you ask it to move you better be hanging on cause its connected to the pavement like its on rails..

 

[IDIDieselJohn]

Never used 1st gear on my ZF with 4.10 gears, it's a useless shift, takes off in 2nd better than my F150 does in 1st!


I don't know what's your fuel economy with the C6 and 4.10's, but I been driving my cargo van for 2 years with the C6 and 4.11's, and don't mind it to much. I rarely go over 55 with it, but it always gets 16-18mpg (95% of my driving is highway). Does have a new IP, injectors and good timing on it.


As for putting more wear on the engine....my van has 420k miles on the original engine and C6, still going pretty strong to.



If I was you, I'd keep the C6, and swap to taller gears, but that's me. I like keeping my drivelines simple and reliable.

 

[franklin2]

A ZF5 would be a simpler swap vs. the 6-speed. Relatively easy once you locate all of the parts. You'll need a 4x4 transmission, 87-91 pedal assembly, transmission tunnel cover, clutch, flywheel, clutch master and slave cylinders along with the line that goes in between the two. Since you'd be switching from the C6 you should be able to re-use your transmission cross member and the driveshaft ( the C6 is about 1/2" shorter than the ZF).
I just converted my truck from a C6 to ZF and ended up buying a complete donor truck for parts. Another option is switching out your front/rear gears...from the Rpm's you're telling me sounds like you're running 4.10's. 3.55's will help you out as well. The other expensive option is buying a gear vendors OD...

I can tell you from my experience if you have the 4.10's like I think you do, the ZF-5 will bring your highway cruising down to about 2k rpm @55mph...fwiw in my case I have a ZF5 + a Gear vendor with 4.10's and I turn around 1500 rpm @ 55mph.

Hope this answers some of your questions.

I have done this exact swap also. To the list above I would add; Be sure to get the short upper crossmembers from the donor truck. The bottom crossmember is the same c6 to zf, but you have to slide it back to the other set of holes for the zf, and then the c6 short upper ones won't line up, there is only one set of holes in the upper part of the frame. But the zf upper crossmembers have more offset and will line up.

Also get the wiring harness. It unplugs underneath the brake booster. Unplug the c6 harness, plug in the zf harness, no wiring to do at all.

I have 35 inch tires with a 4 inch lift and 4.10's. All I could get was 12mpg with the c6. With the zf ,mileage jumped 3mpg to 15. If you calculate the fuel savings, it will take a long time to pay for the swap, but like was mentioned, cruising down the interstate keeping up with modern traffic is great now with the overdrive.

I work with a guy who has a completely stock 94 turbo with stock tires and 4.10's and the zf. He doesn't need and doesn't use 1st to start out. With the 35 inch tires, I find I need it to get started. I will warn you though, don't wind it out too much in 1st, there is a large difference between 1st and 2nd, and the synchronizers don't like trying to match the different speeds together so it can shift, It's easier on the tranny to short shift 1st gear.

 

[USNENFTS]

Sweet, you guys all just gave me most of the information I was looking for. Now for the hard part. To locate a decent transmission and all the parts around it! So both my drive shafts will have to be changed right? The front lengthened and the rear need to be shortened? That shouldnt be to hard. I wish I could find a single cab long box that had the ZF5 and was 4x4 that had a bad motor, then I would have everything I need Any hints as to a good place to look for all the parts I need. I would like to buy new if possible with the exception of the transmission.

 

[franklin2]

I found the cheapest way to go was to buy a wrecked donor. I found the exact same year truck as mine(by chance) but it had the zf in it, and was t-boned in the side. I paid $1000 for it which I thought was a lot for a totaled truck, but all the junkyards around here wanted $500-$750 for just the tranny. I got all the parts I needed, and was able to sell off the wheels, the transfer case, my old c6, and several other things and recoup a lot of money.

The front driveshaft you have now will work, even with the 1 inch or so difference. I don't know what to tell you about the rear shaft, this is what I ran into; When I was doing the swap, I pulled both shafts. The zf shaft was a little bit shorter, but I believe the c6 shaft would have fit. The rear joint has to squeak by the diff yoke so you can put it together, and I think it would. The problem I ran into was the joint cups where larger in diameter on the zf shaft, and the shaft was twice as heavy to pick up than the c6 shaft. Both will fit into the transfer case ok(I used my original c6 transfer case), but the larger cups on the joint would not fit into the diff yoke. I could have gone either way since I had both shafts, but decided to take the diff yoke off the donor and put it on my diff so i could use the zf shaft with the larger joints.