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wereveriroam · 01-15-2010, 04:44 PM

Hello everyone, this is my first post on this forum and yes l do have a question that I can't find the answer too. I'm looking at buying a tow vehicle to pull my 5th wheel and since I can't break the bank on it I'm looking at used diesels. I've got my mind set on 7.3 PSD F450's or F550's between 99-02. I've done alot of research on these trucks so I'm pretty sure I know what there major problems are. My question is I found one that has had the rear gear ratio changed from 4.88 to a 4.11 with a locker, will this change the towing capacity? If so down to what? With the 4.88's the truck was rated to pull a little over 17000lb., my trailer is close to 15000lb.. Thanks...

mfire1339 · 01-15-2010, 05:00 PM

It should do fine. You may need to down shift a little sooner on heavy grades. but you will like the mileage.

Mike

a k · 01-15-2010, 05:18 PM

I pull a 18,000 race trailer with 99 F350 dually with 4:10, it pulled ok but I put a Banks kit on it anyway. THE 450 AND 550 HAS TALLER TIRES. MIGHT MAKE A DIFFERENCE.

Ray,IN · 01-15-2010, 07:40 PM

Go to Ring And Pinion Gears, Axles and Axle Shafts, Drivetrain Parts and Tools - Accu Auto Parts, then click on gear ratio calculator at top right of the page. This may be quite helpful in making your decision. You will know the exact ramifications of switching from 4.88 to 4.10/11(whichever you have).

wereveriroam · 01-15-2010, 11:11 PM

Thanks guys, those are some super quick responses. I checked the link that Ray IN posted and if I filled out the form right the results came back with just about a 19% decrease in RPM's as well as torque. I'm sure the decrease in RPM's will be appreciated but I'm not too sure with the decrease in torque. The truck is a 6-speed (including overdrive) manual with a banks 6 gun diesel tuner, a Banks power elbow with a 4" down pipe on the turbo. I'm not familiar at all with modifications but I've been told by some friends that those modifications are like steroids for the truck. The guy selling the truck is a diesel mechanic so I would think he knows what he's doing

Does anyone think that this is a bad setup? I'm guessing these modifications will make up for some of the lost torque.

450Donn · 01-16-2010, 08:25 AM

Depends on how hard it has been driven with the modifications. Personally I would not buy a used truck with mods. Never know how badly it was abused.

Ray,IN · 01-16-2010, 11:02 PM

The up-side is the 6-speed manual. Downshifting to 5 when needed is not harmful to the drivetrain. If the diesel mechanic certifies the truck is is good condition you should be ok. The truck should already have after-market gauges to monitor EGT, oil pressure, tranny temp, etc., since it has power enhancements and a larger exhaust system. If not__ Donn is right, stay away. After-market power enhancements can/will cause drastic engine damage if not monitored closely.

wereveriroam · 01-17-2010, 01:20 PM

Thanks again guys for your responses. I decided not to buy this truck after a good lookover, there were several (probably costly) issues with this truck.