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Tech Questions Answered in CC's What's Your Problem?

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Track Time
Steven Patillo, California City, CA: I have an '85 Monte Carlo SS with a 350 and want better traction. I was on a road course this year and I kept spinning the right wheel while coming out of tight right turns. I checked out the Powertrax and other posi and limited-slip diffs, but the Powertrax causes an understeer and I can't tell if the other units do the same.

I want to be able to run the car on a road course, so would the Powertrax be a poor choice, or is the understeer just a small problem that can be handled with proper corner setup? By the way, after the road course, I installed disc brakes all around.

Terry Mcgean: You're right about the tendency of vehicles equipped with locker-type differentials to understeer or "push" in turns. The Powertrax is a sort of semi-locker, but the effects in turns are essentially the same. Many road racers dislike locking diffs because of their unpredictability in turns; a driver may enter a turn with the differential unlocked and then inadvertently lock the axles by applying power, upsetting the car in the process in mid-turn. Plenty of road-race dedicated vehicles used fully locked axles, either through the use of a spool or by using the old-school practice of welding the spider gears together. In these instances, understeer is obviously still there, but it becomes far more predictable, allowing the chassis tuner to set the car up accordingly, and the driver to use the locked axle to generate throttle-induced oversteer on command, rather than being a victim of understeer.

For many years, street/track cars have used factory-style limited-slip differentials for the track, though the problem, as you found with your stocker, is that these units usually aren't set up tight enough for track use, allowing the inside wheel to spin up in corners as it's unloaded. Common practice was to shim the clutch packs and tweak the preload springs to reduce the slippage, though the success of these methods is hit or miss.

A better alternative for you would probably be a torque-sensing-type differential, as offered by Torsen and Tractech. These use a series of gears to feed torque to the wheel that needs it the most, but without using slipping clutches or an in-or-out locker arrangement. This makes for smoother applications of power to the wheels and greatly helps in negotiating turns under power.

David Freiburger:
While I agree with Terry that average guys can freak out with a locker, I'd like to point out that NASCAR road racers all use Detroit Lockers. In my experience, a locker is ideal for open-track use, and if you're throttling back and forth in turning conditions where the locker might react negatively, then you need to learn to drive. A locker's push tendencies are, however, a problem for tighter parking-lot racing.

The Black Art Of Brakes Explained
Tom Kinney, Eagle Rock, MS: I have a '72 Chevelle and I recently performed a disc-brake swap using used parts from a '71 Monte Carlo. I reused the rotors but installed new wheel bearings and also used the Monte's calipers with a fresh set of parts-store pads. I transferred the Monte Carlo's power-brake booster and master cylinder along with the factory proportioning valve, and I plumbed everything accordingly. I know that I probably should have installed a new master, but the Monte was running and driving until a month prior to my taking the brakes, which worked just fine. I figured I'd get the system functioning and then replace stuff as needed. But now I have a couple problems.

First, I can't get the system to bleed to the rear. The Chevelle has new hard lines to the axle and new axle lines as well, so the fluid has a long way to go, but I still can't get fluid back to the wheel cylinders even if I depress the pedal with the bleeder screws open.

Also, a couple friends are telling me I'm dumb to put new pads on old, uncut rotors, but the rotors looked great, and as I said, the brakes on car they came from functioned perfectly up until several weeks prior to the swap. Should I have them turned again? If I get new rotors, do I have to have them turned? Will I need to perform some special break-in procedure for the new pads?

Jay Buckley, Bendix Friction Materials division, Honeywell Corp.: Your questions touch on fairly common trouble areas that cause even professional brake technicians to call our tech line regularly. All can probably be dealt with quickly.

First, the trouble you're having bleeding the rear brake circuit is probably due to the proportioning valve. Two kinds of proportioning valves can cause this situation, sometimes both in the same vehicle. The combination/metering/proportioning valve shifts when it detects a leak in the rear so brake fluid won't be continuously sent to a wide-open path of escape. Once this has happened, the valve must be re-centered until brake fluid pressure in the rear again reaches a normal level. You can usually use a spring-clip to re-center the free-floating valve.

Note that some newer vehicles (though not your Chevelle) use some form of load-sensing proportioning valve. Any time the rear wheels are hanging-as they usually do on a lift-this device (if present) will block brake fluid flow to the rear. Most of these valves have an override function for bleeding (described in the appropriate manual), but in some cases you may need to jack up a suspension member.

Your friends' comments about combining new pads with old rotors aren't necessarily correct. Some of the best rotors you can install are used ones, as is. When everything is working as it should, with quality pads and rotors, as the pads wear they condition the rotors, smoothing their working surfaces and embedding them with a microscopic layer of friction material. Using rotors like these (if they meet specs for minimum thickness and thickness variation, and if they're not badly scored) usually delivers superior initial stopping performance than using rotors with new surfaces. Obviously, as-is rotors must be used in pairs to avoid the tugging of the steering wheel one way or the other under braking.

All new brake pads require breaking in before they are fully effective-something now acknowledged in many newer vehicles' owner's manuals. Fresh rotor surfaces also need breaking in, so the combination of new pads and resurfaced rotors means the driver will definitely notice a (temporary) need for more pedal pressure as well.

The brakes will break in after only 100 to 200 miles of average driving. But hard braking that excessively heats the friction material, like panic stops, can slow the process or halt it entirely. If you want to accelerate the process, use the simple 30/30/30 break-in procedure: With moderate pedal pressure, bring the car to a gradual stop from 30 mph, 30 times, with at least 30 seconds between stops to let the brakes cool. It can be done in under a half hour.

Here's one other tip that may come in handy next time you're swapping brake components: Whenever removing or replacing a brake hydraulic component, use a pedal depressor (or suitable substitute) to slightly depress the brake pedal. This will close the ports in the master cylinder, preventing brake fluid from draining out. It will also greatly speed up the bleeding process.

Backward Holley
Brian Rock, via e-mail: I think it's great to have a decent carb article in the mag ("Holley Rehab," Apr. '05). I have been a hands-on carb guy for a long time, so I'm scratching my head at why Tim Moore has the main body installed backward on this Holley. What am I missing here?

Jeff Smith:
Ever had one of those days when you're moving just a little too quickly? We can't blame Tim for this one-I put the carb back together and later realized I had the main body reversed. Several sharp-eyed readers caught this error and brought it to our attention.

Mystery Oil
Matt O'Brien, Tallahassee, FL: I recently bought a '69 Camaro with a 327 and a Powerglide. I'll admit the car isn't in great shape, but I hope to be able to drop in a Ram Jet 502 and a 4L80E later. For now I want to keep it in at least running condition, and being a college student makes that a little tough money-wise, depending on the work. Recently I have discovered a mysterious oil leak coming from a bundle of wires tucked near the firewall right around the wiper motor. I'm 99 percent sure this car doesn't have an oil cooler. Does this problem sound like something I should junk the motor for? If so, should I save any of the components? It has a Weiand manifold, a Holley 750, and a set of street headers. I had thought about a 383 stroker instead of the big-block and I'm not sure if the manifold, carb, and headers on the 327 would fit a 350 block. If you guys can help out a broke beginner I would really appreciate it.

Terry McGean:
Your oil leak hardly sounds like a reason to junk your engine. It's almost certainly one of two things: Either your oil-pressure sending unit is leaking, either from its housing or from the port in the block, or your intake gasket is leaking at the back of the block. Both are fairly common and both are simple to correct.

If you look at the back of your engine, along the back of the intake manifold to the left (driver side) of the distributor, you should find either a pressure sending unit with a wire connected to it, which would be the stock oil warning-light sensor, or a tube of either transparent white plastic or copper, which would be a feed line for a mechanical oil-pressure gauge. These are common for aftermarket gauges, and in fact, the stock oil-pressure gauge on '69 Camaros, located in the console with four other gauges, used a copper feed tube. Some gauges use an electrical sender as well, though these usually have a larger cylindrical housing than the sender for an idiot light. The plastic feed lines frequently break, either from being tugged or from kinking, and copper lines are also susceptible to damage. Stock senders have crimped-in plastic guts that can also leak or break. If you find you need to replace something that requires installing a new fitting or sender, make sure to use a sealer on the threads-we like Permatex Liquid Thread Sealant with Teflon. Since you're dealing with pipe threads, the fittings won't necessarily seal when tightened and shouldn't be overtightened anyway.

If you find that the leak is at the back of the intake (you did say you had an aftermarket manifold, so someone has been in there at some point), remove the manifold, clean the mating surfaces on the intake, heads, and the ends of the block. Then, after placing your new gaskets on the heads (it's usually best to use a thin film of gasket sealer around the water passages), discard the end seals that come with the gaskets and lay a bead of gasket sealer on the ends of the block instead. The bead should probably be a little more than 11/44 inch high; you may want to set the intake in place with the gaskets and no sealer first to get an idea of how much of a gap there is at the ends-too little and it won't seal, too much and you'll make a mess. Once the manifold is set in place, snug the bolts following the factory-recommended pattern (start with the middle bolts and go around in an expanding circle pattern) and let it sit to cure; we usually give it about 10 minutes when thrashing on the dyno, but an hour would be better. Then come back and tighten the bolts in the pattern to finish it off.

By the way, all of your parts for the 327 should bolt right up to a 350, as they would with most pre-'86 small-blocks.

Brake Basics
Mark Miller, via CarCraft.com: I have a '70 Camaro and I am looking for a brake upgrade, specifically calipers using factory stock or junkyard parts. I already read the 12-inch article and I don't want to change my spindles. I've looked at aftermarket rotors and will probably use them, but aftermarket calipers seem very expensive. Are there any factory-caliper upgrades that will bolt to my stock spindles? Any help will be appreciated for a small budget. Thanks

Jeff Smith:
Since you're on a budget, Mark, then let's keep this simple, easy, and low-buck. My recommendation would be to retain the stock calipers and 11-inch rotors. These pieces are sufficient to adequately stop a 3,600-pound Camaro given the right components. The single-piston floating caliper is not ideal (pistons on both sides of the caliper are a better, but more expensive, solution). The first key is a quality pair of rotors. Raybestos offers not only a stock replacement rotor, but also a Brute Stop drilled rotor that we found for under $100 each on a Web site called rockauto.com. Or, Summit Racing offers a pair of slotted Stainless Steel Brakes rotors and pads for $189.95 (PN A2350001). Keep in mind that high-performance rotors tend to use a harder iron and are more durable than replacement rotors. The plan is to use the stock calipers but upgrade the pads. There are a bazillion pads (the industry standard reference for this pad is D52) for your Camaro from Performance Friction (PN 0052.20), Hawk (Stainless Steel Brakes' choice), Wilwood Polymatrix "D" (15D-4334KK) or "A" (15A-5737K) pads, SBS Pro Touring pads from Baer, or any one of dozens of other pad manufacturers. Porterfield (porterfield-brakes.com) is a source for most of these pads and can offer guidance in choosing the best kind.

Next, invest in all three braided-steel brake lines from either Russell (PN 692080, $71.88 at summitracing.com) or Earl's HyperFirm lines (PN 28A210ERL, $69.95 at summitracing.com) to firm up your brake pedal by reducing hose expansion. Buy a quart of quality brake fluid and completely purge your old fluid when replacing the lines. You should also update the rear drum brakes as well. We recommend eliminating the factory brake bias valve and installing an adjustable brake proportioning valve to allow you to custom tune the pressure to the rear brakes. Wilwood offers a great valve (PN 260-8419, $39.99, summitracing.com). Be sure to spend time "bedding-in" the brakes by following the manufacturer's recommendation and then enjoy your newfound brake performance.

One crucial point we've learned through hundreds of 60-to-0 and 100-to-0 brake tests is that high-quality front tires will make a huge improvement in stopping distance. It's all about footprint and traction, just like with drag slicks for acceleration. You can upgrade to monster Trans-Am-style brakes, but if your front tires are junk, the brake torque you can put to the ground will be minimal.

Shift Fix
James Feeley, Bend, OR: I'm in the process of installing a late-model overdrive automatic trans in an older Chevy pickup. The trans is a 4L80-E from a late '90s Suburban, and the truck it's going into is a '71 C10 pickup. I have the aftermarket controller for the trans and the harness, and I had the driveshaft modified appropriately, but I can't seem to get the shift linkage to work. I want to retain the stock column shifter even though it wasn't designed to control four forward gears. I know the indicator won't be accurate, but what can I do with the linkage to get it to smoothly shift the 4L80? Currently it's really hard to shift and feels like it's binding-do I need to visit a fabricator?

Terry Mcgean:
You should be able to reuse the column shifter, and you may not have to compromise as much as you think. First of all, there is a better way than trying to force uncooperative factory shifter parts to work together. Lokar offers a trick little column-shift kit that was probably originally intended for street rods but works great even on cars that have the stock column and trans. The kit includes a solid-steel rod with two small Heim joints along with a billet-aluminum shift arm. Instead of using a bell-crank arrangement like a lot of older GM cars, the Lokar setup connects the stock shift tab on the steering column directly to the shift arm on the side of the trans. The billet shift arm is splined so that it can be clocked in any position, and the steel rod is shipped extra long to accommodate a wide variety of applications. We've used this on two or three different vehicles with great success. Not only does it work, but the shift action is very positive, and as a bonus, the new linkage often cures header/shift linkage conflicts.

As for your indicator, try finding one from an '80s Chevy or GMC van with overdrive, as these used steering columns that were similar to the earlier GM trucks, though many left the factory with overdrive. It may not bolt directly in place (we haven't tried this one yet), but it should be fairly easy to adapt. Of course, the shift gate in the column won't be exactly right for OD, but altering that will take a little more effort.

Nose Art
Robert Atteberry, via e-mail: I am building a '94 350 (383 now) and have run into trouble with the timing chain and cam retainer. Every timing gearset I have tried does not fit the camshaft. Cloyes recommended its PN C-3056, but the bolt patterns don't match. I have tried several different gears with no luck. Either the bolt pattern does not match or the gear hits the block.

Furthermore, I am trying to locate the camshaft retaining plate. The engine has the mounts for it, and without one the cam walks 11/44 inch back and forth. To the point, I need the proper timing-gear/chain kit, along with the right part number for the retaining plate. There are two plates: One has a bolt-spread distance of 3.60 inch and the other is 3.294 inch.

Specifics:
'94 Chevrolet 350, block No. 10243880; Comp Cams kit PN CL12-211-2. All else is stock, except for the Eagle 383 kit (rods, pistons, crank, machine work). Any help would be greatly appreciated

Jeff Smith:
It used to be that interchanging parts in small-block Chevys was simple-almost everything bolted right on. Those days are unfortunately long gone. Your '94 Chevy truck engine is still basically a Gen I small-block, but in the early '90s GM converted all its small-blocks to accept a roller camshaft even if the engine didn't come with a roller cam. The truck engines fell into this category. The block is set up for a roller cam, which means it also would require the thrust plate you mentioned. The thrust plate holds the cam in place and requires a smaller-diameter cam-nose bolt pattern to squeeze through it. Regarding your question about the retainer plate, Nickey Fowler at Scoggin-Dickey says the wider first-design retainer plate is PN 10088128, while the narrower-bolt-spread second design is PN 10168501. Word is that GM created this narrower bolt spread because of retainer-plate and cam-gear interference problems.

The Comp Cams camshaft you bought has the old-style mount, which is why the Cloyes gear you mentioned won't work-it's designed for the later-model roller cam with the stepped snout and smaller bolt pattern. All you have to do is convert to an early style timing-chain setup. You mentioned that the gear you tried hits the block. This happens from time to time and may occur because you're using an aftermarket dual-roller timing set that is slightly wider. Often, the cam gear will hit a non-machined portion of the block, such as around the oil galleries where they protrude through the block. All you have to do is trim this area with a die grinder and you're home free. The correct Cloyes timing set for the early style cam is PN C-3023. This will bolt up to the early style camshaft. Be sure to use the matching crank gear in the timing set. Never mix and match cam and crank gears, especially used crank gears with a new chain. The thrust plate is not required with the old-style cam.

As a quick aside, many car crafters may want to go the opposite direction by using a later-style hydraulic-roller cam with its stepped nose in an early non-roller block. The trick there is to trim the bolt holes off the factory roller cam's retainer plate and use it as a spacer to correctly position the late-model-style cam sprocket relative to the crank gear. This is a slick little move that will allow you to run, for example, a GM Performance Parts Hot cam in an earlier non-roller cam block.

Learn to Be FlexibleChris Murphy, Dayton, OH: In your April '05 article about the 383 LT1, you stated that the "combo also required internal balancing because we were running the stock front damper." I was wondering where you found an internal balance flexplate that fits a one-piece rear-main-seal crankshaft, and if it was an SFI-approved unit.

Jeff Smith: We caused some confusion here, Chris, so it's up to us to straighten it out. In the original, '55-'85 two-piece rear-main-seal small-block Chevy cranks, GM internally balanced these engines by placing a small offset weight on the flywheel end of the crankshaft while leaving the harmonic dampener "zero" balanced. This also meant that the flexplate/flywheel on these early engines were also zero balanced.

Starting with the '86-and-later small-block Chevys, which includes the LT1 and LT4 engines, GM switched to a one-piece rear-main seal. This one-piece seal left no room for that "external" balance weight on the crank flange, so GM moved that weight to the outer rim of the flywheel/flexplate. This made these one-piece rear-main-seal flywheels/flexplates externally balanced components even though the damper is still zero balanced. On the LT1 383ci small-block buildup we followed, the Scat crank assembly is officially an internally balanced system just like the factory crank. Where we messed up was referring to the flexplate as an internally balanced flexplate. In reality, it is an externally balanced piece with the stock weight in the OE location. The flexplate used in the buildup was a B&M SFI-spec, 168-tooth, one-piece rear-main-seal unit (PN 20239, $89.99, summitracing .com). We don't know of any SFI-spec, one-piece, zero-balanced flexplates. If necessary, the weights could be removed, but this would require more weight to be added internally to the crankshaft to make up the difference.

You Got Problems?We've Got Answers!CarCraft@primedia.comCarCraft.comCar Craft Mag6420 Wilshire Blvd.Los Angeles, CA 90048

SOURCES
Scoggin-Dickey Parts Center
Lubbock
TX
N/A
www.sdparts.com
Lokar
865-966-2269
www.lokar.com
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