Making a gearbox track-ready with crack checking a...

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[Editor’s note: This article originally appeared in the June 2020 issue of Grassroots Motorsports.]

What when you might stave off a transmission failure lengthy earlier than it occurs? That’s the place crack checking comes in.

Each the fixed and instantaneous load stresses utilized to a transmission’s shafts and gears can result in cracks. “These usually are not points that may ever get any higher, and even cease getting worse,” explains Jeff Horton of GearFX Driveline. “As soon as cracks begin to develop in a pressured half, it’s principally the start of the tip. The one query is when.”

However wait, it will get worse: A component failure inside a transmission is never remoted to simply that element. Image all of these spinning, meshing and sliding bits inside a transmission. What do you suppose goes to occur when tiny, razor-sharp shards of hardened metallic are launched to that blend? Nothing good.

The easiest way to stop these disasters is to preemptively substitute elements which can be on their strategy to failure. And to determine these cracked elements, we turned to GearFX Driveline.

The Magic of Crack Checking

Scattered (truly, neatly organized and cataloged) all through the GearFX Driveline facility are transmissions, rear ends and drivetrain elements from NASCAR and IMSA racers, classic racers, street racers—any automobile that locations a number of stress on rotating and meshing elements. GearFX specializes in prepping these elements to carry out at their optimum and—this half is essential—to not explode.

Not exploding was definitely a trait we wished within the transmission of our C5 Corvette Z06 project, so whereas the gearbox was out of the automotive, we took it to the parents at GearFX to obtain their magic. After disassembly, the inspection course of is pretty easy.

“First we simply take a look at the whole lot,” Horton explains. “Should you can see defects with the bare eye, you recognize proper off that the half isn’t any good and must be changed.” The kind of injury can point out a necessity for additional inspection in associated areas, too: “Worn engagement rings is usually a signal of worn synchros; broken gear faces will warrant a detailed take a look at the shafts and bearings holding them; and so forth.”

After the visible test, it’s time to get slightly extra high-tech with a moist magnetic particle inspection. This technique of crack checking is included in the price of a transmission rebuild from GearFX. (Should you simply have some free elements you want checked, the service is offered à la carte for $95 an hour—assuming the elements are clear and able to go.)

The method is usually known as Magnafluxing, a time period derived from a selected model identify of magnetic particle inspection gear that’s grow to be ubiquitous in use, even within the business. (The Kleenex and Band-Support individuals really feel their ache.) Regardless of the sci-fi identify, Magnafluxing is simple and excels at revealing cracks that aren’t seen to the bare eye.

1. Some cracks are straightforward to identify. The cracks on the root of those gear tooth could be seen by the bare eye, so the repair is simple: Simply toss the faulty half.

2. Different cracks are much less seen however can result in failures simply as devastating. That’s the place magnetic particle inspection is available in (aka Magnafluxing, because the Magnaflux model has grow to be genericized). Handled with magnetic dye, this in any other case invisible crack turns into obvious beneath UV mild.

3. Crack checking is simple sufficient that no half ought to be excluded. This gear was hiding cracks not solely on the perimeters of the tooth, however on the faces as properly. It’s a failure ready to occur.

First, the inspector magnetizes the half by passing a magnetic area by it. Then, the half is drenched in a fluid that suspends microscopic magnetic particles, that are pulled into the cracks and fluoresce dramatically when hit with UV mild. The method takes just a few minutes however can forestall a world of damage on the worst potential time. For elements product of non-magnetic supplies, like aluminum or magnesium, the inspector applies a fluorescent, penetrating dye that sinks into cracks by way of capillary motion.

“We Magnaflux virtually the whole lot that comes by the door,” says Horton, “clearly any elements which can be coming off an present meeting that we’re going to reuse, however new stuff as properly. It’s simply too straightforward to test the whole lot to verify one thing wasn’t broken in delivery or has the uncommon manufacturing defect that might imply catastrophic failure down the street.”

How properly did our transmission maintain as much as inspection? “There have been a number of burrs right here and there that we might cope with on a case-by-case foundation,” Horton explains, “however nothing confirmed up throughout Magnafluxing that nervous us from a crack perspective.” He notes that common fluid modifications and correct method—not placing any extra stress on the transmission throughout upshifts and downshifts than it was designed to face up to—truly go a great distance towards stopping longterm injury.

Shining These Inside Transmission Elements

Whereas our transmission was aside, we figured that the whole lot deserved a correct shining. The method we used right here is REM sprucing: a really mildly abrasive course of that imparts a silky, nearly impossibly clean floor to mechanical bits. In our case, these mechanical bits had been the rotating, sliding and meshing elements of our transmission and differential.

GearFX’s Jeff Horton explains that the outcomes of REM sprucing are removed from simply beauty, nonetheless. “Don’t consider it a lot as an influence adder,” he says, “however extra as an influence loss reducer.” In the end, the arrow factors in the identical course irrespective of the way you describe it.

So how does this all work? How does shining up a transmission’s innards lead to measurable good points in output? In accordance with the SAE-published analysis paper “Horsepower Retention by ISF (Isotropic Superfinishing) of Automotive Racing Parts,” the reply lies in lowering inner frictions. Give it some thought this fashion: Lowering friction by smoothing these mating and sliding surfaces means much less power transformed into warmth, which means extra power despatched to the wheels.

4. Friction results in warmth, and warmth results in failure. We polished lots of our transmission’s interfacing elements to cut back friction and put on.

5. Sharpening with the right media is essential to the perfect end. tech chooses media that matches the job necessities.

6. Our transmission’s guts, prepared to return collectively, appeared shiny and slick.

A minimum of that’s the speculation. However the writers of the SAE paper confirmed that principle by precise dyno testing with an engine hooked to a NASCAR-style T101 transmission. Within the exams, the baseline, unmodified transmission persistently produced about 5 horsepower fewer than one with REM-polished internals—from 383 horsepower inventory to 388 with the shiny guts. We’d be comfortable to see these good points from an even bigger {hardware} change, like a cold-air consumption or cat-back exhaust system.

The sprucing course of advantages the transmission in a number of different methods, too. The decreased thermal load is best for bearings, and the decreased sliding friction of interfacing surfaces makes for smoother shifts and decreased likelihood of fatigue-related failures in these elements.

Not like Magnafluxing, this course of requires some specialised gear. Elements are loaded into a large vibratory tumbler with the REM media and given a superb spin. After some time, the elements come out shiny and clean as glass. The entire sprucing course of for a five- or six-speed transmission prices round $500.

Whereas it sounds easy, there’s an artwork to the science. “Figuring out what exact media to make use of and for the way lengthy to get the outcomes you’re searching for, that’s the place the expertise is available in,” Horton says. “I’ve totally different blends of sizes and shapes of the ceramic-based media that we will use and mix for various durations and at totally different speeds to get preferrred outcomes. It’s a comparatively easy operation, however it takes some ‘really feel’ as properly. You may throw the stuff in and flip the change and it’ll shine up good, however an skilled operator can actually produce some wonderful outcomes.”

A Little Transmission R&R

In fact, having the technicians at GearFX polish the whole lot and test for cracks could be pointless in the event that they didn’t additionally substitute all of the worn bits. Our transmission truly appeared higher than most, however there was nonetheless seen proof of damage on some vital synchros and kit engagement rings, like third gear. We had undoubtedly skilled poor engagement on quite a lot of events in third, and a fast visible inspection confirmed that it wasn’t solely due to our driving.

7. The 1st step to opening up a T-56 transmission: Hit with hammer. GearFX’s knowledgeable hammer techs did a much better job than we ever might.

8. Our transmission internals appeared good however not nice, displaying largely typical put on—just like the burrs on the tooth of this cog.

9. As soon as all the transmission was disassembled, it was time for cleansing and crack checking.

10. These previous synchro rings confirmed warmth injury and extreme put on on the inside floor of the blocker rings.

11. These heavy-duty replacements function extra sturdy carbon pads on the within of the blocker rings for longer put on.

12. Changing the inventory shift fork pads with bronze fork pads is a beneficial improve for any Tremec that may see harsher shifting than regular day by day road driving. These examples present a typical put on sample. The decrease two pads are severely worn and cracked. This may be brought on by localized warmth from worn blocker rings or compelled shifting. For the reason that pads push the synchronizer, as soon as they begin to put on, it takes extra fork journey to interact the synchro meeting. This turns into a compounding situation. The bronze fork pad improve helps guard towards this and in addition supplies a extra exact shifter really feel, particularly in high-performance purposes.

So all the transmission was handled to an upgraded rebuild package which dropped proper into our present case with none modification or machining. The $1599 bundle contains bearings, bushings, seals, synchros and upgraded carbon blocker rings. The package additionally replaces the inventory shift fork pads, that are liable to degradation from age and laborious use, with bronze items.

Due to the entire sprucing and rebuilding, the refreshed transmission additionally requires no devoted break-in interval as soon as it’s again within the automotive. Simply fill it up with the manufacturer-recommended Dexron 3 or a superb high quality artificial transmission fluid and let the joy start.

We didn’t simply rebuild and shine our T-56 transmission, we threw some upgrades on the rear finish as properly. A Wavetrac diff and polished gears now reside contained in the rear finish housing, able to put energy to the bottom. We’ll be discussing the loopy physics of torque-biasing differentials in a future installment.