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Discussion Starter · #1 ·
I've got a lot of metal in the oil of my Rankin 4 speed dog box. It's behind a 500 hp SBC in a 3200 lb tube frame road race car. I've run it about 4 times for about 2 hours of track time each day. After each day, I've been checking the drain and fill plugs and see a lot of metal shavings. Today I got the transmission out to replace the clutch and opened it up. I don't see any wear on the gears or dogs that's different from it was when I got it.

Not sure where all this is coming from or if it is just normal to have this much metal on the magnetic drain plug after 2 hours of track time.

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Discussion Starter · #3 ·
has it bearings or thrust washers?
Good question. I'm not sure. I had the front bearing retainer off before and it had spherical roller bearings on the input shaft. So it wasn't the cone bearing type deal like on the T5 where you have to shim it to a certain preload.

On the T5, it has these flat roller bearing (that look like washers) between the gears. Maybe this is what your asking if it is bearings or washers? I'm not sure. I suppose I'd have to tear it down to find out.
 

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In the picture,it looks like the edges on the dogs are chipping away.I’m not familiar with this trans,but I’ve rebuilt a few Liberty transmissions and they wear in the same area.Common on transmissions without synchros.
 

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Discussion Starter · #8 ·
Yes the corners of the dogs are chipping. I've compared to pictures of when I got the transmission and they look pretty much the same (it was a used trans when I got it).

It just seems like the volume of metal flakes doesn't match the amount of wear that I'm seeing on the dogs... but I'm new to this type of transmission so I dunno.

I'm not the best at shifting it... maybe I have 5 or 10 missed shifts in a day where it grinds the dogs trying to get it in. So I know that's happening... it may be just metal wear from the dogs grinding. It just seems like more metal than I'd expect...
 

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What you're seeing is a fair amount of grit, but if that started life as a homogenous piece of metal, it wouldn't be very big. And to 3w's point, it may take time for the metal from a gear grind to float by the magnet. It could just be the Dog clutches doing what they do. But I understand your desire to get a handle on it. Im with Lmsport; get more supporting documentation before you go digging in.
Does this box have a supplemental oil pump? If you do, its possible that it has been damaged or contaminated from earlier damage and this is metal thats being flushed out.

Does the gearbox walk out of gear?
 

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Discussion Starter · #11 ·
What you're seeing is a fair amount of grit, but if that started life as a homogenous piece of metal, it wouldn't be very big. And to 3w's point, it may take time for the metal from a gear grind to float by the magnet. It could just be the Dog clutches doing what they do. But I understand your desire to get a handle on it. Im with Lmsport; get more supporting documentation before you go digging in.
Does this box have a supplemental oil pump? Its possible that if you do, it has been damaged or contaminated from earlier damage and this is metal thats being flushed out.

Does the gearbox walk out of gear?
I just added an external oil pump and it's been doing this since before.

I don't find that it hops out of gear on me.

What would the difference make if it were a thrust bearing transmission? More grit would be expected in that case?
 

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That is brass which points to bearing or dog clutches as the source. The trans has several types of bearings usually ball on the input shaft and either needle rollers or brass bushings on the other shafted gears. The thrust washers between gears and case are brass. All bearings and bushings take a lot of force as the desire of engaged gears is to push away from each other so the forces are being held by the case through these bearings.

The synchro in this case is sliding sleeve that is attached to the shift forks. It is splined internally so that engages the shaft while being able to move so that it engages gears thus attracting or locking them to the shaft. Inside this mechanism are hard steel dogs, sometimes called struts or keys, that have a spring load on them such that they snap out ahead of the sleeve when it is moved toward engagement. At the ends of the sleeve are the blocker rings which on your transmission are brass. These have slots for the dogs to engage and an outer row of teeth that the shift sleeve engages with its inner splines. The gears on either side of the shift sleeve are floating on the shaft until engaged then the moving sleeve locks the selected gear to the shaft. The blocker rings have a female cone which essentially functions as a clutch. The floating gear has a male cone where between the cone and its gear teeth is another row of small teeth similar to those of the blocker ring.

Engagement as you perform the shift moves the shift sleeve toward the desired gear that is currently free of its shaft. As the shift sleeve stats to move the dogs pop forward to engage the blocker ring. The blocker ring moves forward to engage the male cone of the desired gear. This clutches the gear and spins it up the shaft speed of the shaft the shift sleeve is attached to. Then the internal splines of the shift sleeve slide over the teeth of the blocker ring and those of the selected gear locking that gear to the shaft. Note the floating gears are continuously being turned by the cluster gear if per chance a failure occurs where a selected gear is engaged before the deselected gear is detached on the main shaft then there are two connected gear ratios of the main and cluster shafts which jams these shafts and something explodes usually gear teeth but sometimes the main case as well. This often happens on the front face as the input shaft is twisted busting its bearing and often cracking the case across the front.

Wear on the brass blocker rings is not only where the dogs engage their pockets but also where the sliding sleeve overruns their teeth and from the engaging face of the female cone as it spins up the gear. The larger the gear by mass the higher the load so mass being a function of not only weight of the gear but the speed it has to assume as it’s linked to the shaft. All of the forgoing paragraph as motions are concerned happen in the time it take to make the shift. A missed shift is the result of the needed coordination of these parts not occurring in the scant allotted time. This is a sign of wear on the shift parts or of bearings. Popping out of gear under load is usually shaft bearing wear. The shafts start to orbit rather than just rotate to where this walks the engaged parts out of engagement.

Bogie
 

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Discussion Starter · #18 ·
Growing up we had a lamp on the table beside the sofa and a little caddy with remotes where my dad would keep his magnifying glass. Pretty often I'd see him there on the sofa with the lamp shade tilted sideways holding something up in the air to look at with the magnifying glass. 30 years later.... I get it.

I've just confirmed two things...
1) the dogs on my gears are getting chewed up from all the missed shifts
2) I'm getting older

Upon closer inspection with a lighted magnifying glass, the edges of the dogs are clearly the source of all the metal I'm seeing in the oil. They look fine from afar... but up close is a different story. They didn't look this bad when I got the transmission and there's plenty enough volume of metal missing from the dogs to account for the amount of metal I'm seeing. Glad I've started this journey with a used transmission... better than learning on and chewing up new parts I suppose.

Well that mystery is solved! Thanks everyone for their ideas!!
 

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It's a crash box right? No syncros. If you look at the dawgs, the faces are cut so that under load the dawg and the gear are pulled together. Any chipping in that area would produce magnetic chips. Yours seem to be bronze/brass. Are the wear pads or shift forks this material?
 

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Discussion Starter · #20 ·
It's a crash box right? No syncros. If you look at the dawgs, the faces are cut so that under load the dawg and the gear are pulled together. Any chipping in that area would produce magnetic chips. Yours seem to be bronze/brass. Are the wear pads or shift forks this material?
Yes. Dog box with no synchros. My chips are all magnetic... they were picked up by the magnet on the drain plug and I found more by fishing around with the old magnet on a stick. I think the bronze/brass thing might be just a lighting affect in the picture.
 
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