E-mail your tech questions to us at carcraft@primedia.com (include the words "What's Your Problem?" in the subject line) or fax them to 323/782-2223. All correspondence must be signed with the sender's real name (not a nickname or a screen name) and include the sender's hometown and state or province. While mail cannot be answered personally, Car Craft will publish as many letters and replies as space permits. Photos are welcome, but no materials will be returned.
Shift RescheduledI have owned an '84 Camaro Z28 for a few months. The car ran well when I got it, but I thought it might pick up some power if I swapped the intake. I installed an Edelbrock Performer RPM and then reinstalled the factory computer-controlled Q-Jet. The car started right up and is running well, but now the transmission won't shift properly. I'm afraid that maybe I've confused the computer somehow, possibly by altering the vacuum signal or something like that. Is there any way I can get the computer to make the trans shift right? Do I have to have it reprogrammed or get a new chip?Adam HelmsenReno, NV
You may suspect that the computer is the culprit here, but you're giving the ECU on your '84 Camaro way too much credit. Back then, the ECU was much less involved with the rest of the car than modern automotive engine management is on typical late-model cars rolling off assembly lines today. The ECU on your car can alter air/fuel mixtures through the carburetor and ignition timing through the distributor, but the only control it has over the transmission is in the lockup function of the torque converter-shifting still occurs via mechanical means on that TH700-R4.
The problem is most likely in the adjustment of the throttle-valve (TV) cable, which links the carburetor linkage to the transmission. Many people overlook the TH700's TV cable as a source of problems because they think it's simply a down-shift linkage, as found on the super-common TH350 transmission. However, the TV cable plays a more vital role in the operation of the TH700. In a sense, it acts as a throttle-position sensor for the transmission, indicating how far open the throttle is at all times. When the cable isn't adjusted properly, shifting doesn't occur at the right times. The potential danger to the trans lies with the fact that the TV cable mechanically raises the transmission's internal fluid line pressure as the throttle opens, so if the cable isn't being pulled out far enough to raise line pressure by the appropriate amount, damage can soon follow.
When you installed the new intake, the relationship between the TV-cable bracket and the carb may have been altered-it only takes a slight movement to cause a significant difference in shifting. To readjust the cable, look for the large plastic housing surrounding the cable on the backside of the cable bracket. There should be a "button" to depress, which will unlock the cable sheath and allow adjustment. Most mechanics advise to push the button and depress the accelerator to the floor, but with older cables this can often pull the sheath too far forward. A more accurate approach would be to adjust one "click" at a time. If your car feels like it's shifting too soon, pull the sheath back towards the firewall. If shifting seems delayed, allow the sheath to more forward toward the carb a notch. It's probably a good idea to mark the sheath before unlocking it, as they will often move as soon as the button is pressed. Also, you should expect the button to be a little stubborn at first if it hasn't been touched for some time. A little spray lube may help, but don't get too rough-it's only plastic.
Goat UpdatesI want to turn my '67 GTO into a street machine using '90s technology, but I'd like to use a low-buck approach. Would it be possible to use a late-'80s F-body TPI engine and overdrive transmission without too many modifications, or should I just go with an overdrive trans swap?Brianvia e-mail
Installing a "corporate" TPI engine-which was originally installed in third-gen Camaros and Firebirds and C-4 Corvettes-in your GTO would be fairly simple and a lot less painful than dealing with the Pontiac faithful the first time you open your hood at the local cruise. TPI engines are pretty much the same as other Chevy small-blocks, with the main difference being the use of the one-piece real-main seal beginning with the '87, which only requires that a compatible flexplate be used. To drop it in, you could simply find a set of Chevelle small-block frame mounts and bolt them to your GTO's frame, which most likely already has the proper holes (most GM intermediate frames of the era were drilled with all the possible engine-mounting holes). Then, bolt a set of the proper engine mounts to the TPI small-block and swing it in. If you use the TH700-R4 automatic trans that accompanied the TPI engine, you'll find its tailshaft is even longer than that of the TH400 that the GTO probably has now. You may be able to accommodate this by sliding the transmission crossmember farther back on the frame and making new mounting holes. However, if your car has the BOP-style crossmember with the rubber isolators at the ends, you should probably find a Chevelle-style crossmember, which is tubular and bolts directly to the frame. In some cases, sliding the crossmember back on the frame won't be an option, either because of obstructions, or because it will raise the tail of the trans too high. In these cases, modifying the crossmember may be a better approach. Most swappers going this route will cut the mounting pad for the trans mount off the front of the crossmember and weld it to the back, which, when coupled with minor frame positioning adjustments, will usually do the trick. It's important, however, to maintain the proper operating angles on the driveshaft, which will have to be shortened and fitted with the proper slip-yoke for the TH700-R4. The simplest way to ensure this is to make note of the angle of the original transmission's tailshaft and maintain the same inclination with the new trans.
Once the engine is in, you'll have to tackle the task of adapting the engine's electronics to your car. For this, you can adapt and modify a stock Camaro/Firebird engine harness, or you can use a swap harness, as offered from sources like Street & Performance (which also offers videos on TPI swaps) or Painless Performance.
If you decide to stay with your existing engine, you can still swap in an overdrive automatic. Unfortunately, if you're running a traditional Pontiac V-8, the TH700-R4 will not bolt directly up, as it is only offered with a Chevy-style bellhousing bolt pattern. There are adapters available (Advanced Adapters), or you could use a GM TH200-4R overdrive trans. The TH200-4R was used in many Olds V-8-powered models during the '80s, though it was also used behind the Chevy V-8 in certain applications. For this reason, most 200s have a multi-case arrangement, with both Chevy and B-O-P bellhousing bolt patterns. The TH200-4R also benefited from its use behind Turbo Buick V-6 engines, as the factory strengthened the design to handle the extra output. The aftermarket took over from there, so it is possible for the TH200-4R to handle the power of your Poncho. Dimensionally, the TH200-4R is the same length as a short-tail TH350 or a Powerglide, and the rear mount is in the same location as a TH400. It also uses the same driveshaft slip-yoke as a TH350 or Powerglide, so the physical part of the swap shouldn't be difficult.
Fox StopThe brakes on my '85 Mustang GT have never been very good at slowing the car down from speeds above 50 mph, but I lack the funding to go with a good aftermarket brake upgrade. I was recently told by a friend that later Mustangs had bigger front brakes that would bolt on to my car, but I'm not sure what would be involved. If this is a junkyard deal, I can probably handle it, but I'm not sure what to look for, or how much actual parts swapping will be required. How simple is this?Brian JamesonAtlanta, GA
Your friend is right, and the swap is fairly simple. Starting with the '87 model year, all 5.0L-equipped Mustangs got bigger front brakes-about 11 inches in diameter-to replace the puny 10-inch discs they previously shared with lowly four-cylinder 'Stangs. The new brakes required new spindles, which will bolt right up to your existing lower ball-joints, but for some reason, the new spindles necessitate a different strut, as the strut-mounting flange is narrower on the newer spindles. Some aftermarket damper manufacturers include shims to make up for this variation, allowing them to offer one strut for all Fox Mustangs, but the shims are not generally offered separately. Of course, you could take the opportunity to replace or even upgrade your struts while you're at it, or you could go dirt-ball and take the used struts from the donor car.
Big LungsI have been searching for a 3-inch exhaust kit for a '74 Camaro for some time but have had no luck locating a company that actually makes a kit for my car.Silas Adamsvia e-mail
The system you seek is offered by Torque Tech, which specializes in large-by-huge exhaust kits for a variety of vehicles. For Camaros, Torque Tech covers everything from the first two generations ('67-'81), and also offers 211/42- and 311/42-inch systems. All kits use mandrel-bent aluminized tubing and Dynomax or Flowmaster mufflers are available as options. For certain 211/42-inch applications, Torque Tech even offers non-header systems.
How Best To Lock?Please settle an argument for us: How many times can you use a poly lock in valve adjustments, and is the presumed protection offered by this setup significantly better than the standard locknut? My son and I hear various arguments about the benefit of a non-scarring device, but we noticed that the manufacturers of most roller-rocker arms send some sort of locknut with their kits.Robert M. Adams MDFall River Mills, CA
You seem to be possibly confused as to which does what in terms of rocker-arm adjusting nuts. While adjustability is the primary reason for using poly locks in applications where the factory has provided no means of adjusting valve lash, in many instances, the real benefit is their ability to be used over and over with no detrimental side effects to the rocker studs or the locks themselves. Factory-style locknuts, as used on small-block Chevy engines and others, are peened at the ends so that they actually gall themselves to the threads of the rocker stud to maintain position. Since they were not intended to be removed and replaced multiple times, or even loosened and tightened repeatedly, this setup worked fine for stock vehicles. However, when the stock-type locknuts are run up and down over the studs again and again, they can actually wear the threads of the stud, eventually losing some of their ability to stay put.
Since poly locks thread onto the studs without any resistance, no wear is imposed on the studs, so in theory, they can be used indefinitely. This is why they are considered a "non-scarring device." The locking function is performed by the internal set-screw, which tightens down on the top of the stud, clamping the threads of the nut in place. Since you've pointed out that most aftermarket roller-rockers include a locknut, I suspect that you may be confusing terms, since just about all of the roller rockers we've ever used have a poly lock-style nut. As for the "protection," most racers have more faith in poly locks for holding their adjustments, while most garage mechanics would probably tell you the opposite. However, when in good condition and used properly, neither should loosen.
Pressure DifferentialI installed a GM Performance ZZ4 (Chevy small-block) short-block in my '78 Trans Am. It has cast-iron cylinder heads and a TCI automatic transmission with a 3,500-stall converter and 4.10 gears. The car is driven only about 1,000 miles a year. This past weekend, I took the car out and on the trip home I decided to open it up. With the converter I'm using, when I step on the gas the rpm really jump up fast. When I looked down at the oil pressure, it was reading 20 psi. When I let off, it returned to 60 psi. I stepped on it again and the oil pressure dropped back to 20 psi. I can't do anything to this engine with it in the car, but I would like to have a good idea what's wrong before I tear into it. Can you help? I am using a "live" oil pressure gauge in this car-not the factory electric one.Joe MinardBiggsville, IL
We tossed your question around a bit, pondering what could cause such a broad, yet consistent, swing in oil pressure. Some suggestions involved issues of windage-oil being whipped up in the oil pan by the crank, which in extreme instances can nearly empty the pan temporarily. We've witnessed this on the dyno with small-block Chevys, but only when the pan was overfilled. The extra oil was keeping the crank partially submerged, so when rpm got high, the whipping of the crank throws was splashing most of the oil up onto the cylinder walls. When this would happen, the oil-pressure gauge would falter, followed by a drop-off in power output, which was attributed to the hydraulic lifters collapsing as oil pressure went away. But your situation doesn't sound like that. Nor does it sound like a matter of oil slosh inside the oil pan. You'd have to be way low on oil to experience that kind of drop in pressure from slosh.
Kevin McClelland of Flowmaster suggested that you might have lost the pickup from your oil pump. Kevin has spent untold hours dyno-testing Chevy engines and has raced them for years. He suspects the oil level in the pan is sufficient to maintain a feed to the pump when the car is stationary, and maybe even as you drive normally. However, hard acceleration may be uncovering the feed hole in the pump cover if the pickup has, in fact, fallen out. Since that's a crate engine, the pump is probably a production piece, so the pickup tube may not have been welded to the housing, as is commonly done during performance rebuilds. Kevin also suggests that you might be able to peer through the oil drain-plug hole using a pen light or a flexible fiber-optic flashlight to see if the pickup is lying in the bottom of the pan before pulling the engine out.
Curing Thermo-BogI have a '73 Plymouth Duster with the original 340 and a TorqueFlite automatic trans. The car is a mostly original nice-weather driver, but since it sits for the winter, I often have to tend to tuning issues in the spring. My most recent trouble is with the carburetor. The original carb is a Carter ThermoQuad, and it seems to be the cause of the hesitation I've been experiencing lately when I step hard into the throttle. I was going to have it rebuilt, but a lot of people are telling me that the ThermoQuad was trash, and not to invest any money in it. Since my car is fairly unmolested, and not a racer, I'd like to avoid major changes. What's your recommendation?Jim StanfordYonkers, NY
The ThermoQuad has gained a bad reputation among motorheads mostly because it is generally considered to be a "smog-era" carb. However, as you've found, the ThermoQuad was actually in use prior to the heavy onset of emissions-control equipment. When functioning properly, the T-Quad is actually a great street carb, offering the same basic advantages of the General Motors Rochester Quadra-Jet: small primary bores for improved cruising economy and brisk throttle response coupled with large secondary bores for big-cfm power under full throttle. Often referred to as Thermo-bog, the T-Quad is also known for full-throttle hesitation. This is usually the result of a ruptured choke pull-off diaphragm, which may sound odd, but the same diaphragm that opens the choke slightly after the engine initially fires also serves as a damper for the secondaries. These are commonly damaged, particularly now that nearly all of them are a couple of decades old. When the diaphragm is bad, the secondaries basically flop wide open under hard throttle, rather than gradually opening. If your pull-off diaphragm is bad, you're probably also experiencing driveability issues during cold starts; in fact, the car may not be driveable.
A thorough rebuild of your current carb followed by the proper tuning should have you back on the road, running smooth and strong, but the key to success here is finding someone knowledgeable in ThermoQuads and the proper adjustment procedures. As an alternative, Edelbrock offers a GM-style Quadra-Jet carburetor as a direct replacement for Chrysler ThermoQuad applications (PN 1905).
