1989 f-150

Hey all,

I drive a 1989 f-150 4.9 6cyl 300. (4X4). I am currently running 31' tires, but am wanting to upgrade them to 35-12.5-15 mudders. What do you guys think would be wise to do to my truck prior to putting these tires on? I don't want them to rub or anything while turning, so I know i will probably have to lift the truck. Just don't know too much about it all, so any thoughts or suggestions would be great!

Havyek

IMO, jumping up from 31" to 35x12.5" tires you'll seriously want to think about regearing (if you haven't already). Especially on a 6cyl.

Lift choices I'm not very familiar with lifting F150s (Jeeps more my thing) but I'd assume a minimum of 4" (more if you have a wheels with a closer to stock backspacing).
Just remember that throwing on big tires is about more than just making them fit, you're going to need to make sure they can turn too!

EDIT:
Just took a quick look at the BDS site, they recommend 6" lift for 35s and a 4" lift for 33s
http://bds-suspension.com/product?ma...1&yr=1980-1996

Hope that's a bit helpful.

traxiii

You can get away with 33x12.5R15 without a lift. Or if you don't mind relocating all the junk on the inner wheel wells, just get some flaired fiberglass fenders from one of the desert racing outfits (Fiberwerx, Glassworks, etc.) in Southern California and you'll have clereance for your 35s without a lift. You will want at least 4.10 gears, probably bigger.

If I were you, I'd go with 33s, 4.10 gears with a Detroit Truetrac differential a set of Bilstein 5100 shocks and you'll go almost anywhere you want to go. The one thing you can't get away from is loosing a little turning angle as the tires get bigger, you'll notice them rubbing on the radius arms at wheel lock.

Another quick fix if you just want to bring the front up level with the rear end, install a set of 460/7.5L big block springs in front and get it realigned. It will lift the front about 2 inches and the spring rate stays pretty much the same, the springs are just longer. You will need to get the bigger offset alignment camber/caster bushings, no big deal, the alignment shop will do that, and it'll ride like stock only better because of the Bilsteins!

1989 f-150

Would it be better to just go up to a 4.56 ratio? Also, i'm not incredibly mechanically inclined, so how does the Detroit Truetrac differential differ from the stock differential? And what does it do exactly? Have you noticed how much additional clearance, if any, the Bilstein 5100 shocks provide?

PerryB

You are going to need a 4" lift to run those tires and do any real off-roading. As far as gears, I'd go 4.56 without question. For gears and a lift (professionally installed) figure on about $3000. Its a LOT of money but without the lift its going to rub terribly, and without the gears you'll have no power.

traxiii

I had 4.86 gears in my 1990 with 35" tires and they worked great. It was really close to the rpms I saw with the stock gears and tires and the speedo read almost perfect.

The Truetrac is a limited slip differential that is the closest thing to a locker, without the issues of adding the compressor for an air-locker or the weird traits of the Detroit Locker. (there are lots of threads out there on the web comparing diffs.) It works as a normal diff. until you lose traction then it delivers power to both wheels instead of just the loose one that a standard diff. does. It works great for DD trucks especially.

I've run with the Detroit Locker, an Auburn limited slip, the Ford Traction Lock and the Detroit TrueTrac. The Truetrac works as well as the locker for me, without the clunking, and chirping while turning issues of the locker and way better than the Auburn and Ford. Also there are no clutches to wear out like the Auburn and Ford units, and you don't need the friction modifier in the gear oil.

As far as rubbing, yes, 35" tires will rub the inner wheel wells and probably the wheel opening on the fender at times, 33" normally won't unless you do a lot of jumping/hucking.

The 5100 shocks won't add clearance, they are just a good off road shock that rides well on and off road, thats all. I guess I was just bringing some cheaper alternatives to 35 inchers and a lift kit. Good luck and keep us posted.

floversss

Hi every one . . have f 150 2006 larait ... i intend to lift 3in body lift on the original wheel . . . . but put a new toyo MT 305/70-18 ... any suggest from the house , need some help ...

PerryB

Yes, personal opinion here, but body lifts are a gigantic can of worms. Spend a little more and get a 4"suspension lift.Body iifts may be cheap from the standpoint of purchase price, but you'll pay the difference many times over making the thing fit/work.

1989 f-150

If I didn't have the money to drop on new gearing (in other words, I don't have a couple grand to re-gear my truck) would I be looking at any mechanical problems by dropping 35s on it without re-gearing? Or is it more of a, I will lose a small amount of power thing?

PerryB

No mechanical issues, but a huge power loss.