Well, having become completely unimpressed with hte stoplight performance of my truck, I decided to take a close look at it to determine what I really had.

My 99' XLT Supercab, shortbed, V6, has the factory 29" tires (235/70R16s) and, cough, the 3.31 Open rear differential (yeah, I know, I can only spin one wheel, and that's only when it rains ).

So, I was thinking, I want to fill up the wheel wells with rubber (these 29s look tiny in there!) and, I want a little more grunt off the lights. So, I was thinking of raising the gear ratio (3.55, 3.73, 4.10) and raising the tire height (31s are in mind). I ran the numbers and discovered the following...

1) If I put 31s on without adjusting the gear ratio, my effective gear ratio would be just a bit above the 3.08.

2) If I installed a 3.55 rear end with the 31" tires, I would have almost no effective change in my gear ratio.

3) If I installed the 3.73 with the 31s, I would effectively have a 3.55 rear end.

4) If I installed the 4.10 with the 31s, I would have a rear end around 3.80.

So, that pretty much rules out sticking with the 3.31 or going with the 3.55. I have also heard that a change of less that .5 in the ratio isn't really all that noticeable. I have also heard that some people have trouble getting their speedo's adjusted for the 4.10 (I have a 99, so, its in the computer now. I understand that the SuperChip I'm planning on getting can fix this).

So, I'm open to suggestions on the rear end. I want a limited slip (I'm so disappointed with the single track...). And, I'm really leaning towards the 4.10 rear end.

Also, does anyone have any suggestions as to what kit I should get for the gear swap? Who makes a 4.10 LS gear set conversion for the (I think its a ford 8.8) rear end in these F-150 4X2s?

Will this completely kill what little fuel economy I have? Will it help it due to better RPM placement for my primarily city driving?

Also (I think I'll have to ask this in the wheel/tire forum), does anyone know if 31X10.5 tires fit on the factory rims that came with the 235/70R16s this truck came with?

Thanks in advance

 

Smart research!! Excellent plan to go to a LS during a gear change if it's desired and calculate in future tire height. You should get your computer code and ask your chip dealer if they can positively adjust for your tire and gear choice. If you're "unimpressed with the stoplight performance", you should forget anything under 4.10s with a tire height increase. It is an 8.8"/31 spline axle, and .50 is moderately noticeable. 3.73-4.30 is a very sweet area on street vehicles. The 8.8" is lucky to include a step between 4.10s and 4.56s which the 9.75" doesn't; 4.30s. The overdrive gearing leaves plenty of top end and helps with the mileage. There are several "stages" of installation kits; adding differential bearings and/or axle bearings. There are several good differentials for the 8.8": the OEM LS(capable of being rebuilt) and the Auburn (high torque bias) are a couple. www.ring-pinion.com www.auburngear.com

------------------
2000 F-150 XL, RC, LB, 5.4L, 4R70W, 3.55LS,
Class III tow, Payload #3, & Convenience pkgs.,
4-wheel disc/ABS, Chestnut/Parchment 40/60,
Ford bedliner w/Paintsaver & gas/wheel/spare locks,
K&N F.I.P.K. w/Outwears pre-filter, Superchip,
Dynomax ultra-flow welded 3" cat-back w/ 3" Y-pipe,
Hellwig front & rear anti-sway bars, Rancho RS 9000s,
Mobil 1, K&N oil filter.

 

OK, so, I've been doing a little research (OK, its window shopping...) on Summit and Jegs and I have found that things aren't quite what I thought they would be.

I want to make sure that I'm getting this all right. To do the conversion from my 3.31 open differential to a 4.10 limited slip, I would need the following:

1) A ring and pinion set for the 4.10 gears for a Ford 8.8" rear end like these...
836-69-0310-1 Ratio: 4.10
Teeth: 41-10
listed at Jegs.

2) A track-loc/limited slip differential like this auburn...
109-542025 83-Up, 8.8" 31-Spline
that is listed at Jegs.

What other things would I need to purchase to get the job done? What other things should I purchase to do the job right? (i.e. Do I need to replace bearings while I have it open? Special pins? Seals? Bolts? Etc.)

Also, are there any less expensive limited slip differentials than the Auburn? I know that the V-6 is a half way decent engine, but, I don't need the world's most bullet proff diff. here. Something reasonable to get the job done that won't break the bank? I mean, at this point, the Differential is going to cost $320 and the ring and pinion is going to be $185. I've seen "installation kits" that include crush sleeves, bearings, gaskets, bolt lock, shims, seals, etc. These run at around $99 to $129.

That brings it to a grand total of $600-$620 + shipping and this doesn't even include hte fact that I'm going to chicken out and get a mechanic that I know to install this stuff for me.

Is this price reasonable? And, don't get me started on 31"X10.5 tires...

 

NOLA-Ford-guy- You're right on Target. The Ford Trac-Loc is slightly cheaper ($299);I'm not saying buy this. Adding the bearings to the installation kits increases their cost in 2 stages; carrier bearings, then axle bearings. It's nice to have all new stuff, but that said, each one can be evaluated for wear (we are talking a 99 vehicle right?) Do you have access to bearing separators, a press, pullers, dial indicator, soft blow hammer, high # torque wrench, low # torque wrench, etc.,etc.,etc?? It is very expensive, especially for 4WD guys. Shops can usually get a wholesale price on parts, evaluate bearing wear, and have all the tools and experience. Keep us updated !!

 

Definitely buy the installation kit and replace all the parts with new. I don't know of many good mechanics who would install new parts without using the install kit. On my Expedition, the front carrier bearings were shot a 10k miles. It would have been crazy to reassemble everything with worn parts.

You also need to include for the oil and friction modifier - the synthetic Ford oil (silver) is very expensive ($12/quart), so you might go to an aftermarket synthetic.

Also allow for speedo correction - on a 99 you need to get a superchip ($300) with speedo correction or calculate which factory ratio you are closest to and get the dealer to reprogram your computer ($50-100).

The Auburn unit is very good but also very expensive. I used to have one in the front of my old F250 and never regretted the choice but there are other cheaper alternatives for the 8.8". Check out any of the 4x4 magazines - there are always application charts for the different axles. If you are not going off-road the other choices might be enough for you.

Good Luck

Ian



------------------
99 Expedition EB
5.4l, 4x4, 4.10 LS
WMS Tube, Bassani Cat Back Exhaust, Superchip Flipchip

 

OK, well, I've got to get the money together for this stuff. Does anyone know of another brand, other than auburn, that sells LS differentials? I could probably go to ford and buy an OEM 8.8 LS, but, if I'm going to put out the cash for an OEM, and an auburn is that close to it price wise, I might as well get the Auburn.

As for the equipment you speak of, I don't have half of that stuff. I am definitely going to get the gears, LS diff and a swap/rebuild kit that includes bearings and either order them through a local shop, or order them myself and have a local shop do the work for me.