1999 F250 vs F350 & what rear end is in a F350? - Diesel Forum - TheDieselStop.com
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1999-2007 General Questions General questions related to 1999-2007 Super Duty trucks. If it doesn't fit the other categories, post it here. Gas engine discussion that pertains to all models is allowed. Specific gas engine questions should use the Gas Engines forum.

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Old 07-15-2007, 11:58 PM   #1 (permalink)
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1999 F250 vs F350 & what rear end is in a F350?

Question #1: The difference between a 1999.5 F250 and a F350 - from my understanding, the only difference is brakes and springs. Please confirm.

Question #2: What rear end, as in identification - example 9" / 8" / 8.8". I understand the rations are either 3:73 or 4:11, but I am curious as to the rear end size or name of the rear end. The F350 I am looking at may have 4:11s and if so, I may consider seeing if I can change to a lower ration such a 3:55 or 3:36's if available. My desire would be to be at 2000 rpm or slightly less at 73 mph.

Thanks for all your help.

Scott
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Old 07-16-2007, 12:04 AM   #2 (permalink)
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Re: 1999 F250 vs F350 & what rear end is in a F350?

[ QUOTE ]
Question #1: The difference between a 1999.5 F250 and a F350 - from my understanding, the only difference is brakes and springs. Please confirm.

Question #2: What rear end, as in identification - example 9" / 8" / 8.8". I understand the rations are either 3:73 or 4:11, but I am curious as to the rear end size or name of the rear end. The F350 I am looking at may have 4:11s and if so, I may consider seeing if I can change to a lower ration such a 3:55 or 3:36's if available. My desire would be to be at 2000 rpm or slightly less at 73 mph.

Thanks for all your help.

Scott

[/ QUOTE ]sterling 10.5s and brakes are the same on the trucks. the rear ends only get diff when u talk about drw trucks. with 3.73 gears at 2000 ull be at like 69
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Old 07-18-2007, 05:29 PM   #3 (permalink)
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Re: 1999 F250 vs F350 & what rear end is in a F350?

[ QUOTE ]
Question #1: The difference between a 1999.5 F250 and a F350 - from my understanding, the only difference is brakes and springs. Please confirm.

[/ QUOTE ]

Assuming you mean an F-350 SRW (single rear wheels), there isn't much difference. Brakes are identical. Front and rear spring packs are identical on pickups with otherwise identical options. Standard tires are different, but the F-350 SRW tires were optional on the F-250.

Per the Ford specs, the only difference besides tires was the rating of the rear axle. Ford put in a slightly heavier-duty rear axle in the F-350 SRW than in the F-250.

But if by F-350 you mean the Dooley (DRW), then there is all sorts of differences.

[ QUOTE ]
Question #2: What rear end, ...

[/ QUOTE ]

Again, the F-350 SRW and the F-250 had exactly the same basic rear axle with 3.73 ratio. Optional was limited slip, but no optional ratio other than 3.73.

The axle is officially called a Ford 10.5" rear axle. But it's made in the Ford axle plant in Sterling, Michigan, so lots of old-timers call it a Sterling axle. And Ford sold that plant to Visteon a few years ago, so now it's called a Visteon 10.5" axle.

The 10.5" refers to the diameter of the ring gear. The OBS (old body style) Ford Heavy Duty pickups, '97 and earlier, had a Ford 10.25" rear axle, but Ford pumped it up to 10.5" for the extra horses in the '99 SuperDuty PSD.


[ QUOTE ]
I understand the rations are either 3:73 or 4:11, but I am curious as to the rear end size or name of the rear end.

[/ QUOTE ]

All '99-up F-350 SRW pickups with diesel engine have the Ford 10.5" rear axle with 3.73 ratio.

But the "one-ton Dooley" with a diesel engine has a completely different rear axle. It's a Dana 80 with an 8.25" ring gear.

3.73 open axle was standard, and 4.10 limited slip was optional.

So when you talk about the F-350, you have to tell us which one you are talking about. An F-350 SRW ain't no one-ton Dooley. No way. No how. [img]/ubbthreads/images/graemlins/wink.gif[/img]
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Old 07-18-2007, 06:11 PM   #4 (permalink)
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Re: 1999 F250 vs F350 & what rear end is in a F350?

I had an early '99 and I believe that the 10.5" didn't come till a few years later. I had my '99 speced out at 10.25".
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Old 07-18-2007, 09:13 PM   #5 (permalink)
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Re: 1999 F250 vs F350 & what rear end is in a F350?

[ QUOTE ]
I had my '99 speced out at 10.25".

[/ QUOTE ]

Whoever speced out your rear axle didn't know what he was doing. 10.25" was in the OBS pickups. All '99-up SRW PSDs have the 10.5".

The 10.5" is a beefed up 10.25", so there's not much difference. But there are some differences, including the ring gear.
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Old 07-18-2007, 11:46 PM   #6 (permalink)
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Re: 1999 F250 vs F350 & what rear end is in a F350?

Thanks - I am looking at buying a 99 short box, crew, srw, F350.
I was able to find a couple of websites that sell the ring and pinion in case I decide to change the ratio, unfortunately my only option is a 3:55 or 3:54 which does not do much based on my calculation. I was hoping to be able to drive 72 at 1800 rpm. Based on the 3:73, I will be right around 2000 rpm with the standard F350 tires. This seems odd to me since a friend has 99.5 and it alway seems we are in the 2300 rpm range and I know for sure he has 3:73 and not 4:10s. Maybe we are going faster than we think.

Thanks again, hopefully the truck shakes out to be a decent truck and not a POS.

SAS
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Old 07-19-2007, 09:25 AM   #7 (permalink)
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Re: 1999 F250 vs F350 & what rear end is in a F350?

[ QUOTE ]
I was hoping to be able to drive 72 at 1800 rpm. Based on the 3:73, I will be right around 2000 rpm with the standard F350 tires.

[/ QUOTE ]

Yes, my speedo has been calibrated to almost 100 percent accuracy at 70 MPH, and my speedo shows 2,000 RPM at 70 MPH with stock-size LT235/85R16E Michelin XPS tires.

With 3.55 rear end and my tires and calibrated speedo, you should have around 1,900 RPM at 70 MPH.

The next step would be taller tires and calibrated speedo to match the tires. A good choice is LT255/85R16. That along with the 3.55 rear end should get you down to 1812 RPM at 70 MPH. That's almost your goal without going to even taller tires.

Yes, they make taller tires, but they are also wider and that will kill your fuel mileage. So if the purpose of the longer legs is better fuel mileage, then you don't want more that LT255/85R16 tires.

BFGoodrich, Dunlop, and Cooper have LT255/85R16 tires with 3,000 pounds max weight capacity. If you put more than 6,000 pounds weight on your rear axle, you're going to be severely overloaded, so that size tire is good for your truck.
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Old 07-19-2007, 11:15 PM   #8 (permalink)
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Re: 1999 F250 vs F350 & what rear end is in a F350?

Thanks - the truck I was looking ended up being a DOG, luckily the previous owner called me back to give me a history. Dodged a bullet on that truck.
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