Newbie with a question.

Reply Subscribe

Thread Tools

Search this Thread

Aug 15, 2011 | 01:04 PM

old-hermit

Thread Starter

New User

Joined: Aug 2011

Posts: 2

Likes: 0

Newbie with a question.

Newbie here and wanted to say hi. I got an '88 F350 crew cab last year and have been slowly fixing it up. It has the 7.3 idi non turbo diesel with a three speed automatic trans and a Classy Chassis conversion. I've been lurking around here reading the tech tips and info on my truck and have learned quite a lot. It sat for four years and the rats chewed up the wiring. I got the wiring straightened out, everything working and the old girl runs pretty good. My next investment is dual stacks which the local muffler shop has quoted me a decent price on. My biggest problem is the low gearing and high rpm at interstate speeds. Redline is 3700 rpm and she's turning 3400 rpm at 70 mph. Can I swap out the three speed auto for a four speed overdrive from a later model truck or do they make an over drive conversion for this truck. Thanks in advance for any info. Till later, Al.

Aug 15, 2011 | 01:25 PM

Lazy K

Post Fiend

Joined: Jan 2005

Posts: 8,402

Likes: 10

The OD trans for these trucks is the E4OD which is computer controlled so you would probably need to go with a stand alone controller to avoid a lot of computer wiring.
To avoid that you could either change the axle gearing or look for a bolt on overdrive unit for the C6.

Aug 15, 2011 | 01:27 PM

bashby

Post Fiend

Joined: Nov 2005

Posts: 7,437

Likes: 4

From: Charles Town, W bygod Va

You have a few options ... an e4od, fords 4 spd overdrive automatic. It is computer controlled so you'll need a computer. If you convert to MT a ZF5 could be installed, but then you have to deal with the clutch pedal, master cyl... Gear Vendors makes an add on overdrive that will give you 6 speeds. They are pricey, check ebay. You could change your rear end gears to 3.55's or so. BTW, what gears are in it now?

Aug 15, 2011 | 02:23 PM

84-6.9L

Posting Guru

Joined: Feb 2011

Posts: 2,216

Likes: 0

From: Princeton MN

Based on RPM it looks like he has 4.10's

Aug 15, 2011 | 03:03 PM

IDIDieselJohn

Post Fiend

Joined: Feb 2009

Posts: 8,005

Likes: 7

From: Ottawa, Ontario

That there looks like a super great looking Centurion conversion

What I'd give for one of those!

I'm surprised yours doesn't already have a GV unit on it. Most Diesel Centurion conversion i've seen already had those things on it, especially ones with the C6. Maybe someone removed it to keep it or sold it? hmmm...

Easiest thing to do is gear swap, expensive one to do is Gear Venders, complicated one to do is E4OD, and most labor one is ZF5.

So up to you on that one.

What kind of use do you have planned for this nice truck?

Aug 15, 2011 | 04:33 PM

old-hermit

Thread Starter

New User

Joined: Aug 2011

Posts: 2

Likes: 0

Thanks for all the info guys. I don't think expensive, computerized or converting to manual will work with my wallet. heh heh heh. Changing the rear gear sounds like my best option. I don't know what's in it now but guessing I'd say 4:11 or 4:56 just by the way it shifts. I was thinking as low as a 3.08 which should give me approx 65 mph at 2500 rpm. Just not sure what it would do to my standing start pull.

PS, I pull a flatbed equiptment trailer and a camper. I've pulled both with my half ton but it is a strain.

Aug 15, 2011 | 04:35 PM

IDIDieselJohn

Post Fiend

Joined: Feb 2009

Posts: 8,005

Likes: 7

From: Ottawa, Ontario

My motorhome has 3.54 with the C6 3 speed also and I love it for highway driving. Puts me about at 2300RPM @ 60mph.

Yours defenently has 4.10's not 4.56