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December 2011 Techline Tech Questions

Posted in How To: Tech Qa on December 1, 2011 Comment (0)
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Ratio Right
I have an ’86 Ford Bronco. This past year I put a 4-inch lift and 35s on it, but it is still running the stock gear ratio. What would be a good ratio to get back the lost torque?
Brandon Hansen
Redlands, CA

Yep, your Bronco has to be pretty much a lame dog with 35s and a stock axle gear ratio. In 1986 the Bronco had either a 3.07:1 or a 3.50:1 axle ratio. I can’t even imagine driving it with the 35s and 3.07 gears. As to the proper gear ratio, well that depends on what transmission you have, and how much highway driving you plan to do. If you have the T-18 four-speed or the C6 automatic, then I think I would not go any lower than 4.11 if you spend much time at the maximum speed limit. If the Bronco sees lots of trail usage, I say go with some 4.56s. Now if you have one of the AOD four-speed automatics, then it has a 0.67 Overdrive in Fourth gear and I think 4.56s would be ideal for the road. Same goes for the four-speed manual Overdrive trans that has a 0.71 Overdrive gear. The biggest problem with this manual trans is its relatively high 3.25:1 First gear ratio, so again 4.56s are the ratio of choice.

Clutch Burner
I have an ’82 Chevrolet K20 ¾-ton. It has a 4-inch block lift in the rear and lift springs in the front. It’s powered by a well-built 350 V-8 mated to a four-speed and an NP205. All this spins Thornbird 33x12.50 tires on PIA 16.5-inch wheels. With most of the specs out of the way I am having quite the issue deciding what clutch to put in it. I’m not sure what the specs of the clutch were when it was purchased. However, after the build I was out driving around (being a good little boy) and the clutch was destroyed within a few minutes. I replaced it with what I was told was an awesome mudding clutch (Perfection Hy Test CA 1909). Well this thing is a turd. I can’t even drive on the road at 50 mph and step on it without this thing just smoking. So I need a good clutch that will not slip. Do you have any suggestions?
Super_probie
Via fourwheeler.com

Pulling an SM465 trans and an NP205 transfer case is not my idea of a fun weekend— and probably not yours either. I suggest that you sit back and rethink your installation process and take a look at a couple of different aspects. First off, what is the condition of the flywheel? Did you put a straight edge across the face and check to make sure it was not warped? Does it have hard spots on it indicated by dark blue marks? Lots of people think that one can just machine the flywheel and get rid of these marks but in reality you cannot. The grain pattern in the steel has been altered and they will come back. It’s always a good idea to re-machine the flywheel just to make sure that it is flat and true and has no circular scratch marks. These scratch marks indicate high and low spots on the flywheel and prevent equal surface contact with the disc.

Somehow I get the impression that you are just replacing the clutch disc and not the pressure plate. One should always replace the disc, throwout bearing, and pressure plate as a matched set. You can install the world’s best disc but using a pressure plate with weak or broken springs will not allow the clutch to hold properly. Sometimes it is difficult without a very close inspection to see if a spring is broken.

Something that a lot of people don’t think about is the fact that the transmission input shaft may not be centered to the crankshaft. The bellhousing is what does this and the two alignment pins must be in place otherwise there is enough slop in the bellhousing bolt holes to exceed the 0.006-inch allowed misalignment factor. Even with the pins in place it’s not uncommon for this to be as much as 0.015- to 0.020-inch off. If the input shaft runs at an angle, hard shifting and early clutch and pilot bushing wear can take place. There are several websites available that show how to check this. One is www.powertraintech.com.

One should loosen the bolts an equal amount around the pressure plate as they are removed and tighten them in progressive equal amounts when reinstalling. Otherwise you can damage the mounting surface and actually warp the assembly.

I have to assume that you are using a clutch alignment tool when installing the disc. When reinstalling the transmission, it’s important that the transmission’s input shaft does not put excessive loads on the disc’s center hub. To prevent this I like to take a couple of long bolts and cut the heads off and taper them to a rounded point. With a file, saw or grinder, cut a screwdriver slot in the end. These are then screwed into the bellhousing. This way you can slide the transmission’s mounting holes over these bolts to support the weight as the input shaft slides into the disc. When the other two transmission mounting bolts are in place you can then remove the long bolts and replace them with the proper bolts.

Even if you did replace the pressure plate, could it be that the throwout bearing is not adjusted properly? When the clutch pedal is totally out, that is with the disc engaged; there should not be any contact between the fingers on the pressure plate and the throwout bearing’s face. I believe that 0.125-inch is pretty much the standard clearance. Could it be that the throwout bearing is actually pushing in on the pressure plate’s fingers and releasing some of the contact pressure?

Oh, one other thing while I am thinking of it—you did install the disc facing the proper direction, right? It’s always a good idea to also inspect the pilot bearing in the crankshaft for excessive wear. Here is a trick to remove it if it is necessary to replace it. Pack the inside of the pilot bushing with grease, even wet toilet paper will work. Then take a punch the same diameter as the hole and drive it in. The idea is to force the grease or toilet paper between the bearing and the crankshaft and in turn push the bearing out.

One other thing that is really important is that you keep all grease and oil off the clutch contact surfaces. This includes greasy fingerprints. A spray can of brake parts cleaner and a clean white rag works great.

As to a replacement clutch, well there are a lot of great clutches out there in the aftermarket including the brand that you used. Actually, a factory clutch should work just fine considering the size tire you’re using.

Full-Throttle Envy
I have an ’05 GMC 1500 HD. It has 243,000 miles on it. It generally runs great but lately when I mash on the fuel to pass, it seems to bog down. But when I back out of it, it seems to pick up and go. Any suggestions?
Threeeringcircus
Via fourwheeler.com

Wow, 243,000 miles! When was the last time the fuel filter was changed? That would be the first thing that I would take a look at as the vehicle has the symptoms of fuel starvation. Then a fuel pump pressure check is in order. Electric fuel pumps don’t last forever and from my experience they usually start getting tired at around 100,000 miles. If the pump is not working up to its demand pressure rating, then there is a darn good chance it also needs replacement.

Do keep in mind that there could also be other issues that are causing the problem you describe but the fuel system is a great place to start.

Dirty Air MPG
I have just recently put a 4-inch Superlift suspension lift on my ’96 Explorer. I have the 4.0L V-6 engine and the gas mileage sucks. I was wondering about regearing. I’m gonna be using this vehicle to get to and from motocross tracks towing a trailer with a couple of bikes on it. It’s all stock underneath running 33x12.50 tires on 16-inch wheels.
Matt Mahanor
Virginia Beach, VA

That is really a hard question to answer Matt because a lot of other factors are taking place. My guess is that you’re thinking that the engine is working too hard now that the overall gear ratio has been changed due to the larger diameter tires. Going to lower gearing, let’s say a 4.10 gear set, will put the engine back in the rpm range that the Ford people figured would get the best fuel mileage as well as improve the towing performance. So yes, you are right on that point.

However, you have to keep in mind a couple of other factors. One being that the larger tires have more rolling resistance due to more pavement contact as well as additional weight. The other is that your Explorer now sits higher exposing the underside to more airflow. The front axle, transfer case, and other components are now causing a lot more air turbulence or what I like to call “dirty air” that has a negative effect fuel mileage. Here is a classic example: A vehicle of mine started out getting about 18 to 22 mpg when driven on the interstate at a reasonable speed with 3.73 gears. A 3-inch lift and 31-inch tires caused the fuel mileage to drop down to the 15 to 18 mpg mark. More lift and 33-inch tires with a swap to 4.56 gears put the fuel mileage down to about 13 to maybe 15 mpg on a good day. Yes, off-highway performance was greatly increased but with a fuel mileage decrease. Life is nothing more than a big trade-off.

Low-Lift F-150
I have been trying to find information about lifting an ’89 Ford F-150. In the spirit of less is more I would like to go with a 2- or 2½-inch coil and new leaf springs. I would like to run 33x12.50R15LTs which I have run without a lift. They rub badly on the radius arms when turning and limit the turning radius a lot. I have contacted Rancho Suspension and asked if I could use the extended radius arms without a lift and they said that I couldn’t because the truck would need to be aligned. Obviously, modifying the suspension would result in the need for an alignment, so I ask you would it been possible to make a custom kit with 2-inch leveling coils, extended radius arms, radius drop brackets, traction beam drop brackets, and new leaf springs? Or how about any other combination to keep the center of gravity low but allow the fitment of 33-inch tires with no contact on the radius arms. Fender trimming is not required even in stock height.
Kelvin Mann
Minden, Ontario, Canada

Sometimes it is OK to mix and match parts from different companies and sometimes not. Can you use the Rancho radius arms with another brand’s coil springs? Generally speaking, yes, I see no reason why you can’t use them. I assume that you want to use the Rancho radius arms because they tuck in a bit and allow more tire clearance when turning. However, I don’t think Rancho offers the radius arms separately.

Something that you should also look at is the backspacing on your wheels. A large amount of backspacing will put the tires in closer to the radius arms and cause rubbing at full steering lock. Less backspacing will move the tire outward for more clearance; however, you don’t want to go to an excessive amount as this causes all sorts of steering and suspension geometry problems.

The same goes with wheel width. If you keep the backspacing the same but switch to a wider wheel, the bulk of the tire is moved outward providing more inner fender clearance. But this may cause outer fender lip clearance problems. With today’s tires having a lot of sidewall tread compared to earlier years, a specific tire size that used to clear fine will sometimes contact now due to the sidewall tread lugs.

Home Job Stroker
I got a great deal on an ’84 305 Chevy V-8 engine that I plan to install in my Jeep. I have heard that I can take the crank out of a 400 engine, which my friends tell me is a boat anchor, and drop it in my 305 to make it a 383 stroker. Just what do I have to do to do this?
Mark Dixon
Via fourwheeler.com

Well, your friend has got part of it right. With a 0.030 overbore to the 305 block and adding the 400 crank you will be just about 50 cubic inches short at 334 cubic inches. It takes starting out with a 350 block to get the 383 size configuration. First off, you’re lucky in that the engine you acquired has a two-piece crank rear seal just like the 400 engine has. I believe engines built after about 1986 use the later style one-piece rear seal. Yes, there are kits to convert it over but they are pretty expensive. To start off with, the main crank journals are too big so they have to be turned down to the 305/350 size. You have a couple of choices. You can keep the 305 pistons and use the short (5.565-inch) 400 rods, or you can also use the longer (5.7-inch) 305 rods with some custom aftermarket pistons. There may be some interference points within the block so some grinding there as well as on the connecting rods may be necessary.

I think that using the longer rod is the way to go as you don’t get as much sideways thrust by the pistons to the cylinder walls. You will also need the flexplate or flywheel as well as the harmonic balancer from the 400. Crankwise, I think that you would be better off buying one of the aftermarket cast cranks. It will likely be less expensive than paying to have the 400 crank’s journals turned and you don’t have to search for a good crank in the wrecking yards.

I really advise doing a dry run assembly of the engine to make sure everything fits properly. You may even have to make some minor oil pan clearances. When it comes down to power, why not just locate a real 350? It will save a lot of work on your part and make more power than your stroker 305.

Where To Write
Address your correspondence to: Four Wheeler, 831 S. Douglas St., El Segundo, CA 90245. All letters become the property of Four Wheeler, and we reserve the right to edit them for length, accuracy, and clarity. The editorial department can also be reached through the website at www.fourwheeler.com. Due to the volume of mail, electronic and otherwise, we cannot respond to every reader, but we do read everything.

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