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VINTAGE FORD PANTING
I have a ’78 Ford F-150 4x4 with a 400 cubic inch engine (168,000 miles) which I bought new in June, 1978. My question concerns RPMS/gear ratios. My axle numbers are as follows: Front- 350DTATE 6100 49-5, Rear- WTE-A5 8CC 3L50 9 394B. The local mechanics state the gears are as high as possible for this year and that the axle housing does not allow other gears. At 65 mph I’m turning 3600 rpm. Any recommendations for verifying the info from the mechanics and the actual gears installed at the factory? Am I stuck with the low gearing? After 28 years, it shouldn’t matter, but it does.
Jim Gibbons, Via e-mail
From your numbers, Jim, you have a front Dana 44 (the very desirable reverse rotation unit) and in back, a Ford 9-inch dropout... both with 3.50:1 ratios. Your rpms don’t compute. Unless you’re running go-cart tires on that Ford, or have had lower gears installed, your rpms at 65 should be around 2600 with the factory tire size (L78-15, about 29-inch dia.). If you are getting that number (and the others you listed and I edited) from your tach, then it may be reading way off. You can go taller on the ratio. You already have the right carrier up front for a lower gear ratio and the Ford 9 inch will accept any gear ratio. Finding a reverse rotation ring and pinion taller than 3.54:1 is difficult. They were listed as tall as 3.00:1 that year, but I could not find any available today with a quick search. Finding taller 9-inch gears for the back isn’t a problem, so call around for a Dana 44 reverse rotation in a 3.00:1 ratio (or 3.07:1 which is close enough) to see. There may be an old set around. They aren’t desirable because most people want to go lower, so they oughta be cheap! A 3.00:1 ratio would drop your rpms at 65 to 2260 with 29 inch tires. An easier solution is to go with taller tires, but the results are not as spectacular. My books show a ’78 F-150 should be able to mount a 31-inch tire with no lift. That would drop your rpms to 2465 at 65. With a 2.5-inch lift, you could run 33s and that would drop you to about 2300 revs. However, if mileage is what you are after, the reduced aerodynamics of the lift and tires, plus the increased rolling resistance may cancel out any mileage gains from the rpm drop.
HOWLING EXPLORER
I have an ’00 Explorer with a 8.8 rear end. I recently upgraded to a 4.56:1 ratio and added a LSD to suit my 33 inch tall Super Swampers. There is a whining noise coming from the rear end at coast/deceleration. This noise was heard right off the bat. We didn’t overheat it. I put friction modifier in with the gear lube. The pinion preload was set at 25 inch pounds and the backlash was set at about .008-.009-inch. We put marking compound on the teeth to see how the gears were swiping and the pattern looked good. It was right in the middle, not too far down and not too far up, possibly a little closer to the toe side. We set it up according to stock Ford specs from All Data, The instructions said to set the backlash at .004-inch but they didn’t say for what axle. What can I do to get rid of this whine?
Drew Palmer
Mechanicsville, Virginia
Several things popped out at me here. First, my books show 14-19 inch pounds preload for new pinion bearings and backlash set at .011-.016-inch for the 8.8 Ford. Also, you mentioned the pattern being centered between the heel and toe but said nothing about the face and flank. The heel-toe position is the least important part of the pattern and pretty much non-adjustable because it’s a product of machining the diff housing. Yes, backlash changes will slightly move the heel-toe position, but if you stay within the correct backlash range, it usually ain’t enough to make any large movement in the pattern. In your case, you say it was nearly centered at .009-inch backlash (which is probably close enough to not be a problem in itself). The face to flank distance is vital. If you have that centered, you know the pinion depth is correct and that means no noise. If I were you, I would go back through it and set everything exactly to spec and read the pattern again... on both the drive and coast sides of the ring gear this time... and make adjustments accordingly. The problem is that if it’s a setup issue, once you’ve driven it any serious distance, you may not be able to get rid of the whine because it will have taken a set. If it turns out to be defective gears (very possible) then you also have warranty issues now for waiting so long.
BIG TIRE BLAZER
I’m looking at buying a ’77 Blazer. It has 36 inch tires on it. Are the axles strong enough to hold up to these tires.
Somebody, Via e-mail
Not really. If it was used to cruise the drive-ins (do people even do that any more?), maybe. If you are going to ‘wheel it, you’ll break something... probably at the worst possible moment. You’d be safe with 33s, fairly safe with 35s if driven easily. But above that, you’re in the red zone. A lot depends on the driver. A smooth driver with finesse can go a lot farther with weak axles than a throttle-jockey.
COMMANDER WITH TROOPS
I own a 2006 Jeep Commander without the factory lockers. The unit is a V8 and Quadradrive II. I would like to install limited slips similar to those of Detroit’s helical gear setup, (I forget the name). The problem is I cannot find out what axles are installed and whether I can install aftermarket limited slips and/or lockers.
Richard Liden
Bridgeport, Ohio
Your Commander has a Jeep model C200F front diff with a 7.9-inch ring gear. At present, you are limited to the factory electronic locking diff and 3.73 gears. In back, you have the latest iteration of the venerable Mopar 8-1/4, which Jeep now calls the C213RBI and lists it as having an 8.3-inch ring gear. You have many choices in gearing and limited slips for that axle, but of course you need to stay with the same gears as the front. Interestingly, all ’06 Commanders with Quadradrive II and V8s were supposed to have the ELSD, (Electronic Limited Slip Differential) but teething problems caused them to be delayed until later in ’06, so not all ’06s have them. The LSD you’re thinking of is the Detroit Truetrac and it’s a sweet unit. There is an application for your rear axle but not the front (nor is there likely to be anytime soon). You’d be good to run the Truetrac in the rear alone, as it’s virtually seamless and wouldn’t interfere with your fulltime 4wd system.
UNLIMITED QUESTION
I bought a used ’04 Jeep Unlimited that I believe has its stock differentials, a Dana 44 limited slip rear and a Dana 30 front, both with 3.73 gears. Is there any problem installing front and rear ARB Air Lockers with 4.11 gears? Does anything need to be done to the transfer case? Should heavier-duty axles be installed?
Joe Perez, Via e-mail
You’re good to go on the ARBs, Joe, and also with the gears. No issues at all with the t-case as it relates to the axles. If you are lifting the Jeep, you may want to install a fixed yoke rear output kit. As to stronger axles, it depends on what tires you will run. If you are going to stay around 33 inches and aren’t a hard-core ‘wheeler or a throttle-jockey, the stock pieces should serve you well.
VIBBBRATING YJJJAAAAY
I have a ’92 4.0L YJ with a 2.5 inch lift and 32s. I just installed 4.56 gears front and back, a Posi-Lock cable to get rid of the Vacuum CAD and a Lock-Right Locker in front. I also changed all the ujoints and yokes. Now I have a vibration so bad I can hardly see out my rear view mirror. In about a month, I’m going to install a 4.5-inch Rubicon Express kit, SYE, CV driveshafts and 33s. How can I get rid of this vibration without redoing everything I just did? Since I put in the new gears, I’m doing 3000 rpm on the freeway and the speedometer is very far off. When I put on the 33s, will it make the freeway driving easier? I’ afraid I might hurt my 139,000 mile 4.0L.
From someone, Via e-mail
You have several issues here. The first is that Lock Right up front is spinning your front driveshaft via the driver’s side axle. Because you have no locking hubs, you can’t stop that from happening, even with the CAD disengaged on the right. Since most front driveshaft angles are not optimal, it’s typical that you have a vibration. For all I know, you also have a rear shaft vibration too from the 2.5- inch lift. Lower gears will increase the tendency to vibrate because the driveshafts are spinning faster. My advice is to get your other lift and tires installed, pay special attention to the driveshaft angles front and rear and re-evaluate. If your installer gets them perfect, you should have minimal vibration. I’ve never seen one vibration- free, though there have to be some lucky slobs out there and maybe you’re one. The sure cure is to install a Warn locking hub kit (www.warn.com 800-543-9276), which will make your YJ like the older CJ Jeeps. You’ll be able to lock and unlock them as needed. Hubs kinda negate your Posi-Lok purchase, but it’s really doing you no good at this point with the locker up front. With hubs installed, you should consider ditching the Posi-Lok and the factory, two-piece RH axles and upgrade to a stronger, one piece passenger side axle shaft. The only other option is to remove the Lock Right. As to tires, the 33s won’t drop your rpms all that much from 32s... about 100 rpms. At 3000 in 5th, you must be really moving, even with 4.56 gears!