Hi all-

I've got a 1999 F-550 with the 7.3L and a ZF 6 speed. It had a hauler bed that I swapped out for a 9' flatbed. It is a great truck.... I've got a question for ya'll.

There is an Overdrive mounted between the ZF manual transmission and the 4x4 transfer case it is electrically activated by a switch on the gear shift lever (just like an old style split rear end shift switch on big trucks). I've checked the power to and out of the switch... it works, and at least one of the solenoid inputs at the OD is getting power.... but the OD does not respond to the switch. It does a funny thing on engine start... the OD solenoid, uncommanded, switches on and then off.

I've talked to some transmission shops in the local area and they all shrug their shoulders. Any idea if this is a factory item... do I dare take it to the Ford Dealer to get it working again? I'm open to ideas.......

Thanks!
scott

 

Doubt it is factory option.
What you have sounds like gear vendor that gives you OD and sometimes underdrive. Just like additional transfer case. Those things are not cheap, but you have to find name of the manufacturer and call them.
There should be a label on it. When it is hard to read, I take small camera and take several pictures with flash and without.

 

Thanks, probably a good suggestion. It's not a GearVendor item... I installed one of those on a 72 Chevy I restored a few years ago.... totally different item.

scott

 

Ford didn't offer an overdrive like that. It is definitely and aftermarket item.

 

Mark-

Would it be possible to convert the manual to an automatic? And if so what would your recommendation be..... could you put one of those new auto 6 speeds the current trucks have?

 

By the way for those interested... my overdrive is a US Gear item and I got it working.... it drops the rpm at cruise by 500 revs and my milage went up to 17.5... pretty cool!

 

Yes, you can, and the only choice is a 4R100.

You could, but it would be so expensive to make this fit and work that it would cost less money to scrap your truck and buy a brand new 2012 with the six speed auto. This isn't even close to a plug and play swap.

 

Mark-

thanks... is the 4R100 a good transmission... good for towing, etc? Thanks!

 

why replace that awesome 6speed for a soso 4speed automatic? The 6speed gives your more gearing options, and a much better 5 and 6 gears for better highway, plus its ten times stronger then the 4R100

 

I've had very good results with a 4R100. I towed a 9100 pound trailer with mine and never had to do anything more than change the fluid.

I'm not saying it's bad, but let's examine what you said.
5th in the manual is 1:1. 3rd in the automatic is 1:1.
6th in the manual is 0.72:1, fourth in the automatic is 0.71:1. Not enough difference to get excited about, but the automatic has a very slight edge.
Seems like a draw here.
Got any facts to back that up?

The 4R100 is rated for 1000 lb-ft of torque after the torque converter multiplication. That equates to about 550 lb-ft at the flywheel. So you're saying the six speed is able to handle an engine producing 5,500 lb-ft of torque? Or was that just an exaggeration to make a point?