94 Caprice Wagon 5.7L project--46 MPG so far

[Hersbird]

For anyone wanting to try this at home, this car is outside of Spokane WA.
https://missoula.craigslist.org/cto/5679563731.html

[HHOTDI]

lol HB, i was just telling my wife about one of those the other week as we're looking for another vehicle that will seat 8...she took one look at it and said NO, it looks like a bathtub! This one you posted is just down the street from my house!
:{)

[freebeard]

She says that like it's a bad thing?

Buy it and paint is camo.

[Hersbird]

Tell her it's a woody bathtub though, like a Viagra commercial.

[funkhoss]

Sorry it's been a while since I've posted--summer is by far the busiest time of year for my job.

I really haven't driven the wagon much at all since the initial post of this thread. After the 46 MPG trip, I left the car parked for several weeks. We didn't have anything that we needed it for, and I can't really justify driving it (even just to "test" it) when I can take the Metro and get 80+ MPG.

However, when I went to use it again more recently, I started it up, pulled out of the driveway, and when I hit third gear the car started shuddering pretty violently. I drove it around a bit and found that the shudder/vibration happened in all gears, but that it was worse at lower RPMS and higher loads. This sent me on a quest to figure out what the problem was...

My initial thought was that since I had done all of these drivetrain mods, using junkyard parts, the problem must be driveline related. I knew that I had a small oil leak dripping down where the engine meets the bellhousing, so I though that perhaps some oil had gotten onto the clutch disc and was causing it to slip. When I got the car up on stands, though, I saw that the leak was engine oil, so the trans wasn't leaking, and I saw that it wasn't a RMS leak either. The flywheel and clutch were completely dry, so that ruled out a slipping clutch. I also checked the U-joints and transmission mount while I had the car up, and they were both good.

What threw me off was that there was no check engine light--so I didn't suspect an engine problem, initially. However, what I've learned is that since this car is pre-OBDII, it won't throw a code for a misfire. So after lots of trial, error, and guesswork, I finally figured out that I had a misfire due to a bad spark plug. I replaced the plug and the car now works fine.

I have no idea why the plug went bad, as it was an OEM-type replacement (with a 100,000 mile service life) and it had less than 10,000 miles on it. At least it was a simple to fix once I figured it out.

I'm hoping to get the "towing" axle set up and in the car sometime in the next few weeks. I have several projects to do with our 6X12 trailer, and it will be a good opportunity to test it out.

[funkhoss]

Some responses to some of the thoughts and questions that have been shared...

Originally Posted by Frank Lee

How much ratio change do you think is needed? Perhaps swapping on a set of smaller diameter wheels and tires will do the trick. It might look funny but then again the skirts might hide it. Put air shocks or air bags on the rear to level it out again- helps with the load, aero, and looks.

Originally Posted by Vigo

As far as swapping the axles out, my first thought would be to use a rwd transfer case with a very mild low range (~2:1) and no front driveshaft. With your current tire size, 5th gear, and rear gear, a ~2:1 low range would have you doing about 2000rpm @ 55 mph, which sounds ideal for towing since you'll have abundant torque and probably not want to go much faster anyway. I'm not sure how this would fit under the car, but without a front driveshaft to worry about you could probably rotate it to suit with a little work. Seems like a more permanent solution than a 'theoretically quick'-change rearend. If you only used it rarely you wouldn't even need to make the shifter very convenient. Even jacking up the car and shifting the T-case by hand would be less effort than a rearend change, by far. I know you've already considered this but unless it requires a completely different main case for the nv3500 or major floorboard mods, it seems like the simplest long-term solution to me.

Yes, both of these solutions could theoretically work. But the problem with leaving the 2.14 ratio 7.5" axle in the car, and getting lower gearing though another means (such as an auxiliary transmission or smaller tires) is that the 7.5" axle really isn't up to handling the weight, torque loads, or braking of serious towing. It's fine for hauling passengers, but I wouldn't want to use it for much else.

Even the 8.5" axle that came in the car from the factory has it's limitations. GM used the same rear end in 1/2 pickups and SUVs, and it's been known to fail towing at full capacity (6000 lbs. plus). The 9.5" rear will make the drivetrain pretty much bulletproof, and give me better rear brakes than stock.

And smaller tires would have a lower load rating and lower ground clearance--both major drawbacks for towing.

Originally Posted by Vigo

I'm also curious if you've recorded any highway travel with no P&G or EOC and what it does under more or less 'normal' steady-state highway driving?

I posted about this car on the GM Wagon forum, and they had the same question.

This car would go 32 MPG pretty consistently with the automatic and 2.56's. So with the manual and 2.14's, I'm guessing it would do around 35 MPG highway with no EOC.

Running a tank with no EOC would ruin my 90-day average, though.

Originally Posted by serialk11r

If I were you though, I'd just go with a 2.74 final drive instead of the transfer case or a swappable diff, because your rpms are so low that you might actually do better P&Ging at a higher rpm. As you mention, you are already using 5th gear to pulse, why not just have 6th gear be like 5th and get a shorter 1st at the same time?

5th gear is the highest gear. It's a five-speed transmission, so no 6th gear.

Originally Posted by serialk11r

I cannot believe you went with manual steering on that car...makes me feel like a wimp for struggling to turn my steering wheel with the engine off.

Originally Posted by autoarcheologist

Did the S10 steering gear help the massive front end wander?

The manual steering really isn't bad at all, especially with the skinny, overinflated, LRR tires. My wife drives this car at least as much as I do, and she doesn't have any issues.

Originally Posted by autoarcheologist

If you do decide to tow close to 5000 lbs you should firm up the rear suspension, a Panhard bar would be a great addition.

In "towing mode," this car will have a rear sway bar (which it does not have stock), heavy duty shocks front and rear, heavy duty rear springs, and tires with a higher load rating. I would also plan to use weight distribution and sway control if towing that much. Hopefully it will be just fine.

Originally Posted by LioNiNoiL

Nice work Hoss, very nice.
Thirty-five years ago, I had an over/under/direct drive
auxilliary transmission in my old Jeep, made (I think)
by Gear Vendors (now defunct) that worked really well
for towing. It was a lot more convenient than swapping
pumpkins when I needed to pull a trailer.

A GV overdrive would be cool. There are only two problems. First, I wouldn't have the range of gearing that I will get with the two axles. And second, it would almost double the cost of the whole project.

[freebeard]

Might it be possible to terminate the brake line in a master cylinder and have a slave on each axle with a removable physical link? I'm not sure whether it would go before or after the flexible section. Maybe the slave could mount on a suspension bracket.

To save bleeding the brakes.

[funkhoss]

Originally Posted by freebeard

Might it be possible to terminate the brake line in a master cylinder and have a slave on each axle with a removable physical link? I'm not sure whether it would go before or after the flexible section. Maybe the slave could mount on a suspension bracket.

To save bleeding the brakes.

As I described in my initial post, I'm going to put a quick disconnect on the line that goes to the rear brakes (there's only one line that feeds both brakes). That quick disconnect coupling will let me swap axles without having to bleed them each time.

I'm also going to make a bracket that will let me do the same thing with the parking brake cables--I'll be able to just bolt them up without having to readjust.

[BabyDiesel]

This thread has so much win! Congrats on your accomplishments so far funkhoss!!!

You're giving me hope that I'll be able to eclipse 25 mpg in my 88 K5 Blazer when I get it back on the road

I can't get over how well the 5.7L does at 1000 rpm. I figured it would choke itself out.

[ThatDudeOrion]

So much awesomeness in this thread. I've got a similar project going, but haven't really documented or started a build thread.

I have a 95 trans am with the same LT1 engine in it that I use to commute almost 300 miles daily. I've done some very minor aero stuff, weight reduction, engine mods, and a trans swap from 4l60e to T56, so I've got a 0.5 6th gear in the trans and the 2.73 rear left over from the auto trans. I'm averaging around 35 mpg over the course of the whole commute with a high of 36.5 mpg, and I don't do any P&G, and I only EOC while going down big hills, trying to keep average speed around 75-80mph. So I think your estimates are spot on for what you'd get with more traditional driving style. One of my biggest wins has been running a laptop with the tuning software $EEHack, I can make fueling changes in real time and approximate a lean cruise which the stock LT1 pcm can't do. You may want to look into this if you haven't already.