AMC Pacer Revival

That's what I was thinking! The trans kick-down linkage on three speed Chrysler automatic transmissions controls internal fluid pressure as well as kick-down. It's like the TV cable on 700R4s and the AW-4. So get a TSM and make sure it's adjusted properly. You said you have the 4.0L head and EFI on the car now? How is the linkage connected to the throttle body? If it's not, that might be the whole problem. It needs to be connected and adjusted before you smoke the transmission. If the linkage won't connect properly get a cable for a Chrysler six cylinder/904 from Lokar. If a six isn't specified it will most likely be the longest cable.

Pacers came with 2.73 axles stock, with 3.08 optional, auto or three speed stick. A 2.53 was optional for the auto, 3.08 was the only axle for high altitude use. Sounds like you might have the 3.08.

Do you have a tach connected to it? If not, go to AutoZone or whatever and get a cheap electronic tach. Once that is connected and the trans linkage adjusted take it for a test drive. Verify rpm at a couple set speeds -- say 45 and 60.  A 195/70 or 205/70 x 14 tire was stock. If you have something close to that now the speedometer will be about right.

If you have a 3.08 axle you're running around 2900 rpm @ 70 mph (assuming 205/70R14 tire -- 25.3" diameter). That a bit on the high side. With 2.73 gears it would run just around 2600, which is more like it.  I like it to be no more than 2500 when cruising. In my car I can cruise at 75 mph @ 2400 rpm. So you can limit long distance cruising speed to 65-70 mph and probably be good, but higher speeds are going to be rough on gas! With 2.73 gears you'd be running just over 2700 rpm @ 75 mph. With a 205/75R15 tire (27" diameter) rpm would drop to 2550 @ 75 mph, 2400 @ 70 (assuming 2.73 gears). That would be much nicer with no more expense than changing tires. Take-off will be affected some (a little less quick), but not very much. A lot cheaper than changing the trans! With 3.08 gears and an early AW-4 (0.70 OD) the engine would only turn 2000 rpm @ 70 mph (2065 rpm w/later 0.75 OD AW-4). That is just barely enough for the engine to work efficiently.

I've found that most AMCs (V-8 and six) need to turn at least 2000 rpm to be enough in their power band (due to stock cam) to deliver good economy and adequate power. You want to cruise in the 2000-2500 band for the best compromise. Higher or lower and gas mileage will start to be affected in a noticeable manner. A torque (RV or towing) cam that "comes in" under 1500 rpm will let you run around 1800 rpm and still produce good economy without affecting the higher end much (can still cruise around 2500 and be okay).


Edited by farna - Jul/04/2012 at 8:29pm

About your trans..sounds like the trans kickdown linckage is not adjusted correctly to me. That will make it shift at the wrong times(more or less)

I have to agree on the mechanic. PCV will only hurt if the engine is badly worn and the carb is sucking way too much oil in the breather. If that's the case the engine needs rebuilding and disconnecting the PCV will only buy you a little time.

The trans has little to do with the horrendous gas mileage. Unless it takes off like a scalded dog right now an OD trans will most likely make gas mileage WORSE. The stock rear gears won't be low enough to pull OD at speed. If it takes off really good now it's because the rear axle has been changed to lower gears. That will improve in town mileage, but highway mileage will suffer unless you drive no more than 50-55.

People have the wrong impression about an OD trans. Most are used to give LOWER FIRST gear AND only a SLIGHTLY higher high gear.It improves gas mileage by giving a more efficient gear spread, keeping the engine closer to it's main power band and allowing it to take off easier and maintain speed at a mid rpm level. For example, most automatic equipped cars in the 60s came with 2.87-3.15 rear axles. Most cars with an OD auto come with 3.50-3.73 axles (and a few as low as 3.23, but all around 3.23 or lower). So why OD in the first place? It's a cheaper way to add a gear to existing automatic transmission designs. You need to view an auto OD trans as a four speed automatic instead of thinking in terms of an OD. With the high gearing typically used in non-OD autos you would get much worse gas mileage and only be able to use OD if you're running at high speed. Even then the engine isn't turning enough rpm to efficiently move the car through the air without working the engine hard. I tried using a 3.08 axle in my 63 wagon with a 4.6L EFI six and AW-4 trans. It worked fine, but I had to be going over 70 to reach 2000 rpm. Wind resistance starts going up exponentially over about 65. The engine would push the car with no problems even up hills maintaining about 75 (only 2100 rpm) without "lugging", but you could tell the engine was working. I wanted 3.31 gears, but they were harder to find and I settled on 3.55 gears (the same Jeep used in 4.0L/AW-4 XJ Cherokees). Gas mileage should have went DOWN by popular belief, but it went UP by 2 mpg on average. The engine was working more it its power range (2400 rpm @ 75, 2250 rpm @ 70) and the engine wasn't working as hard. As rpm goes up so does power (to a degree). It needed those few more rpm to develop the power to push the car more efficiently at higher speeds. On the low end the car needed less throttle to take off since there was more gear reduction (think of it as more leverage). I may improve another 1-2 mpg with 3.31 gears, but that's not enough for the expense. I'll put a slightly taller tire on next time (70 instead of 65 series) and that will just about be the same as dropping a little gear.  Trans/gears/tires need to be balanced for good performance and mileage.  If you change to the Jeep AW-4 (what I'd recommend as well) be prepared to change the rear axle ratio as well.

Get a new mechanic.  Any American car with a PCV system needs to have it connected.  It doesn't sap any power.   Regarding the A/C system, there are numerous shops that can repair it for you.   If it has been opened you will have to replace the dryer (near the condenser in front of the radiator) and  you will have to pump it down with a vacuum pump to get the air and moisture out of the components.  You compressor may need to be resealed and you might need new hoses, but it's all doable if you want to spend the money. 

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Edited by MN Gremlin - Oct/20/2012 at 4:36am