Reply
 
Thread Tools Display Modes
 
Old 08-15-2015, 11:52 AM   #1
Junior Member
 
Join Date: Aug 2015
Posts: 24
3.55 for 7.3L or...?

Hi folks! I am new to the forum and very happy to have found it! My rig is a 2001 E350/EB full SMB build w/ PH top. It has the 7.3L PSD with DANA 60 LSD rear w/ 3.55 gearing. It is just fine the way it is but unfortunately I am wanting to do a 4X4 conversion . It has 245x75x16 now and I'll probably limit myself to an upsizing of 33"/ 17" tire/wheel combo. The lift will be either a 4" or 6" undecided yet. This diesel has great low RPM torque. I am very satisfied with the present performance-economy setup, and am therefore very tempted to choose the same 3.55 gearing on the new-to-be front axle. The wheel size upsizing from the present 30.5" to the 33" does give me pause. I could disable Overdrive when not at freeway speeds to offset the lower RPMs, or when towing or in hilly terrain - is what I'm thinking. Any advise, especially from those with the 7.3L PSD, is very much appreciated.

Again, greetings to all! Will introduce myself again and post some pics at the new member topic.
__________________

__________________
2001 EB-350 7.3L SMB/PH Quadvan 4x4 285x70x17 orig. owner.
Vindisl is offline   Reply With Quote
Old 08-15-2015, 12:16 PM   #2
Senior Member
 
schluchtenflitzer's Avatar
 
Join Date: Jun 2012
Posts: 425
Re: 3.55 for 7.3L or...?

Gratulation for your new rig!
I had 285/75-17 on mine with 3.7:1 and i found out that it was to long in my mind. On flat highways perfect for a great mpg but in the hills i do not like it. And than the consuption goes up fast. With 3.55 i definitly would not drive it!
I now have 37x12.5-17 on it and went to 4.56 gears. I like this combination. You can feel that the engine is always in his comfort zone.
BTW my rig is about 9500lbs
__________________

__________________
www.Dieda-unterwegs.net
2001 SMB E350 4x4 7.3 Powerstroke
1968 Pontiac Firebird 400 Convertible ,1978 Peugeot 504 Convertible,1988 Porsche 911 Carrera 3.2,KTM 300 EXC,BMW G/S Paris Dakar,BMW "Diabolo"
schluchtenflitzer is offline   Reply With Quote
Old 08-15-2015, 12:18 PM   #3
Senior Member
 
BajaSportsmobile's Avatar
 
Join Date: Sep 2011
Location: Rancho Nuevo (Cabo/Todos Santos) B.C.S. and San Diego, CA
Posts: 1,952
Re: 3.55 for 7.3L or...?

We have converted several vans identical to your's to 4x4 and have customers that have kept the 3.55's and others we have re-geared to 3.73,s and 4.10's - all running 33 inch tires - we have done at least one of each in the last several weeks.

It is interesting to me that everyone is satisfied with their particular gear choice - a testament to the torque and power of the 7.3L.

My personal preference is 4.10's as I often find myself towing heavy trailers and I also like the option to run a 35" tire.

3.73 is probably a good compromise...
__________________
Four time Baja 1000 winner, four time Baja 500 winner. Solo'ed the Baja 1000 to LaPaz/Cabo twice.
4-Wheeling since 1972, Desert Racing since 1989.

AgileOffRoad.com
BajaSportsmobile is offline   Reply With Quote
Old 08-15-2015, 12:51 PM   #4
Junior Member
 
Join Date: Aug 2015
Posts: 24
Re: 3.55 for 7.3L or...?

To Schlu and Baja - thanks for your advice.

By way of personal experience on this very topic: I have a 4L Wrangler LJ which went from 30" to 33". I've decided to wait or maybe not do the gearing change on it. On the wrangler I use O/D only when at 65 mph or higher. I live in flatland Florida, and gas mileage remained a respectable 18 mph with a 4" lift!

About how much would the rear gear change add to the cost on the van? And could I expect the new gear ( 3.73. 4.10, 4.56, etc. ) to be as bullet-proof as the 3.55 has been for the last 14 years?
__________________
2001 EB-350 7.3L SMB/PH Quadvan 4x4 285x70x17 orig. owner.
Vindisl is offline   Reply With Quote
Old 08-15-2015, 03:06 PM   #5
Senior Member
 
carringb's Avatar
 
Join Date: Jan 2009
Location: Corvallis, OR
Posts: 4,560
Re: 3.55 for 7.3L or...?

What's your total wight when towing?

The factory GCWR for 3.55 gears is 16,000 pounds. I feel like it can handle more with stock tires. 4.10 gears is rated for 20,000 pounds. If you are pushing the stock ratings, I'd definitely recommend upgrading to 4.10 gears. The big issue with tall gears and the 4R100 is low speed maneuvering, like trying to back a trailer up a hill. It makes a lot of heat fast, and lower gears reduces the amount of slip on the torque converter.

If you're towing lightweight trailers (say under 6,000 pounds) its probably still fine with 3.55 gears, but it will be slower off the line, and you might not be able to stay in OD on some hills. This itself isn't a problem, but there is a fuel penalty if you can't hold O/D.

Gears run about $800 per axle installed, depending on local labor rates. If you have an open rear diff, you really should think about a locker or limited slip, and doing the gears at the same time is really just the extra parts cost.
__________________
2000 E450 dually V10 wagon
carringb is offline   Reply With Quote
Old 08-15-2015, 04:04 PM   #6
Junior Member
 
Join Date: Aug 2015
Posts: 24
Re: 3.55 for 7.3L or...?

Hi Carringb,

The rear diff is already a limited slip and I'm leaning towards keeping it that way. Will probable install an electric locker for the front axle. The most I have towed - and likely to tow in the future - are light utility trailers and light flats -style fishing boats ( 2500# max boat and trailer ).

The (3) comments so far have me leaning a little more in favor of keeping the 3.55 as is. I don't mind spending the extra $800, unless it would turn out to have actually made things worse. Regarding off the line performance, my experience with the Jeep with tall gearing is that, for daily driving with light/medium loads, acceleration is actually improved over stock ( 4L engine, 3.73 gear, going from stock 30" to 33" tires )!
__________________
2001 EB-350 7.3L SMB/PH Quadvan 4x4 285x70x17 orig. owner.
Vindisl is offline   Reply With Quote
Old 08-17-2015, 07:16 AM   #7
Senior Member
 
Bbasso's Avatar
 
Join Date: Jan 2012
Location: Western North Carolina
Posts: 1,258
Re: 3.55 for 7.3L or...?

I would suggest if you're keeping the 3.55 gears is to get a huge transmission cooler.
I have towed in the 8000 pound range (2WD) with 3.55 and the temperature does shoot up awfully fast and doesn't come down easily when using the stock cooling setup.
__________________
Rob.
Current:
2001 E350 PSD w/ a bunch of stuff.
And had three other E350s...
Bbasso is offline   Reply With Quote
Old 08-17-2015, 12:00 PM   #8
Senior Member
 
E350's Avatar
 
Join Date: Oct 2010
Location: Sacramento Delta, CA
Posts: 1,011
Re: 3.55 for 7.3L or...?

^^^ Bbasso

Go here:

http://www.ford-trucks.com/forums/forum31/

and search for "6.0 transmission cooler".

and look at these (drop your tank and inspect immediately):

http://www.ford-trucks.com/forums/11837 ... -tank.html

http://www.ford-trucks.com/forums/13872 ... iesel.html

http://www.ford-trucks.com/forums/12028 ... ainer.html

FWIW, I would keep the 3.55 (I went with 3.73 when I converted and I wish I kept the 3.55)
__________________
2002 E350 ext.; 160K; 7.3L; 4R100 (w/4x4 deep pan & filter); 4x4 conv. w/2007 F250/F350 coil frnt axle (oppos. dual Bilstein press. shocks cured DW) diff chg from 3.55 to 3.73 (bad!); BW1356 t.c. (bad!); LT265/70R17/E Michelin LTX M/S2; Engel MT60 Combi Fridge-Freezer; 4 BP 380J pv panels; Auragen 5kw AC gen. in top alt. position; Webasto Dual-Top; Voyager top. 1995 5.8L EB Bronco, bone stock.
E350 is offline   Reply With Quote
Old 08-17-2015, 12:26 PM   #9
Senior Member
 
Join Date: Jul 2011
Location: Flagstaff, AZ
Posts: 1,755
Re: 3.55 for 7.3L or...?

Really? You guys are recommending 3.55 gearing when the OP wants to add 4x4 and switch to 33" tires?

carringb's advice is sound and comes from experience. If you go with a 6" lift and you are going to want 35" tires for sure or they will look dinky.
__________________
2005 E350 RB 6.0 PSD for extended fun
1989 Landcruiser FJ62 for local fun
2011 VW TDI Golf for hwy fun
JoeH is offline   Reply With Quote
Old 08-17-2015, 12:41 PM   #10
Senior Member
 
E350's Avatar
 
Join Date: Oct 2010
Location: Sacramento Delta, CA
Posts: 1,011
Re: 3.55 for 7.3L or...?

Yup. After converting to 4x4 and going to 3.73 differentials. I have absolutely no overdrive anymore across NV, ID, UT flats and just burn and burn and burn way more fuel than necessary.

Increased RPM=decreased MPG

Most of my towing driving has been on the flats in Summer. Most of my mountain driving is in the Winter on ice or snow not towing. My personal experience with the 7.3L is that it has tons of low RPM torque in the 1200 to 1400 rpm range (and, yes, which will over heat the 4R100 going uphill at low speeds) and that torque is sufficient to pull a load across the flats at any legal speed with 3.55.

Yes carringb's advice is sound as it always is: "The factory GCWR for 3.55 gears is 16,000 pounds. I feel like it can handle more with stock tires."

I like the looks of my dinky stock size tires. I like a low 4x4. I don't like lift. Increased Lift=decreased MPG due to increased air resistance.

But I didn't build my van for appearance.

YRMV, so just one comment from one of the peanuts in the gallery...
__________________

__________________
2002 E350 ext.; 160K; 7.3L; 4R100 (w/4x4 deep pan & filter); 4x4 conv. w/2007 F250/F350 coil frnt axle (oppos. dual Bilstein press. shocks cured DW) diff chg from 3.55 to 3.73 (bad!); BW1356 t.c. (bad!); LT265/70R17/E Michelin LTX M/S2; Engel MT60 Combi Fridge-Freezer; 4 BP 380J pv panels; Auragen 5kw AC gen. in top alt. position; Webasto Dual-Top; Voyager top. 1995 5.8L EB Bronco, bone stock.
E350 is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Powered by vBadvanced CMPS v3.2.3
Disclaimer:

This website is not affiliated with or endorsed by Sportsmobile SIP or any of its affiliates. This is an independent, unofficial site.


All times are GMT -6. The time now is 12:16 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
×