Truck Update #2

More successes than ever before and only one big disappointment for today.

Vacuum Problem Solved!

It has nagged me ever since I bought a vacuum gauge that the motor wouldn’t pull more than 15 inches at a reasonable idle. I came across this article which explains in great detail why you should probably use full manifold vacuum over ported vacuum. I had been using ported and that’s why my idle was just terrible.

I’ll try to distill that article for those uninterested in reading: lean fuel mixtures take a longer time to burn while rich mixtures take less time to burn. Having an increase in timing when running lean and a decrease in timing when running rich will be more fuel efficient and will help with curb idle, at least in my application.

How does it help with the curb idle? When my truck is just sitting idling, the motor will pull a vacuum which will pull on the vacuum canister on my distributor. This pull is called vacuum advance. The harder the motor pulls, the more timing the distributor will give it. The less the motor pulls, the less timing it shall receive. The motor pulls hardest under no load and most under heavy load i.e. acceleration.

What this means practically is that my motor idling is timed at about 33 degrees BTDC, but once you lay on the gas, that timing will reduce down to the static/initial timing I set at 16 degrees BTDC. When you are lightly cruising without much acceleration, the timing will also be higher than static. The result? My vacuum woes are solved! I was finally able to lower my idle speed to a perfectly reasonable 800 RPM while still pulling 17.5 inches on the gauge. It sounds better than ever.

I was overjoyed at how simple the problem really was, and have driven the truck with confidence to run my errands and jobs. I also installed this permanent vacuum gauge into my dash so that I can watch it all the time.

vacuum gauge

New Mufflers

I installed some two-chamber mufflers from Summit Racing to replace the old ones. The old mufflers were, I kid you not, only 5.25 inches in length. No wonder it was such a screamer. Now it has a nice low growl that isn’t at all offensive, but it is still a little noisy at 55MPH. I can live with it.

muffler comparison

Installation was a bit of a pain involving fairly precise cuts with a bandsaw upside-down. I should have welded them in, but with the way the pipes are bent, it isn’t possible to just remove them from underneath. So I had to use these weird lap clamps instead which aren’t making a perfect seal on my stainless steel pipes. Whatever, it’s good enough and doesn’t scream anymore.

Front Wheel Bearings

The truck had an inordinate amount of play in the front wheels themselves. By this, I mean if you jack it up and grab a front wheel at the 12 and 6 o’clock positions and wiggle, it moved about 1/2 inch. This is too much; it should have almost no play. Boring, greasy work, but necessary if you want to drive without a freakin’ wheel falling off.

Differential Disappointments

In the differential I have found something that I cannot do, at least without a lot more time, room, and effort. My truck has the 9 inch Ford differential, and I thought it would be a good idea to change the old gear oil out; heck, it’s probably original. I got 90W gear oil and slid underneath the truck only to find that the differential does not have a drain plug on it at all!

Next, I tried sticking a hose with an attached pump down the filler hole. The problem? The clearance between the hole and the gear inside would only allow for my 1/8th inch hose to fit. This simply wouldn’t work either.

Next, I decided I would open the darn thing. I started undoing the nuts, and chiseling off the copper washers only to later find out that the differential cannot be removed without first 1. Removing the tires, 2. removing the brake assemblies, and 3. removing the rear axle rod! Fuhgedaboutit!

I even considered drilling and tapping a hole in the stupid thing, but decided it was too risky. I buttoned everything back up and gave up on this pursuit until I am willing to do it the right, but very arduous way.

We’ve Hit Prime Time

Despite my frustration with the differential, I can confidently say the truck has hit prime time and can be driven with a greater measure of trust than in the past. I’m sure things will crop up, but I don’t think there is much of anything major that can go wrong now (I’ve fixed or replaced all of those!).

It gets plenty of time on the road, and I guestimate that the MPG are around 10-12, much better than 6. While that is still bad by modern standards, its about average for this motor, and I don’t drive terribly far anyway. It does make me plan road trips very carefully in order to squeeze as much economy out of those 12 miles as possible. Also, I doubt it will ever be my daily driver anyway, but whenever I need to haul, I can count on it.