7 replies to this topic

[FTodaro]

I am rebuilding a transmission for a friend of mine. I have done several now, but I have never come across one that detonated like this one did. It looks like third gear came apart and then took out the idler gear and a metal fragment got the 4th gear too, (gear on left).



Not sure what would cause this to happen but it sure looks violent.

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[FTodaro]

Not sure why I got a double post, can someone delete the one with not attachments?

another point about transmissions. i rebuilt mine after 22 races. it started out with all new shift forks. after 22 races the shift forks were pretty well warn. I have been using MTL in the tranny thinking thin is fast, and it may be but you are going to pay a small price in durability too. MTL is thin but it does not protect all that well either. i have actually went to a blend of mtl and synthetic 75/90 for a little more protection.

When you do change the transmission fluid, " you do change your transmission fluid right" if you find a little square chunk of metal on the magnet that is a bad thing. that means that you broke a Hub spring. its about the size of a pencil led and its a sq shape. Time to pull out the tranny its in failure mode.

this is what happens when you have time on your hands because the wife made me stay home this weekend to go to a wedding. which I have to go get ready for. ...................

[Keith Andrews]

I've gone through 2 transmissions in 11/2 years. Both went like this one did. Third gears shredded and I'm pretty sure the shrapnel does the additional damage. I've been using Redline MTL. After both the transmissions went they were scrapped. The guys around here feel it isn't cost efficient to repair. I've thought about trying the Gibbs MTL but I think I could break any transmission regardless of the type of fluid I used.

[Alberto]

I have been using MTL in the tranny thinking thin is fast, and it may be but you are going to pay a small price in durability too. MTL is thin but it does not protect all that well either. i have actually went to a blend of mtl and synthetic 75/90 for a little more protection.

I don't use MTL anymore on any track or race cars. It is too thin. I had been using MTL in my RX7 track car for years. Changed it once a year. Had it rebuilt b/c it was worn and had a tired 5th synchro (common issue on the RX7). Every single bearing was toast. Builder asks "You were using MTL right?". He's seen this sort of wear from other transmissions running MTL.

At 75/80, MTL is too thin to be used in a race car w/o frequent changes. The trans builder had suggested using an 80/90 weight oil. I started using a 75/90 weight oil after than. First NEO 75/90 for 3-4 races (didn't shift as well as Redline - esp 2-3 upshift) and now Redline MT90 rest of last season (much better at 2-3 upshift). I have a sample of the MT90 ready to go to Blackstone Labs for analysis. I have thought of trying Swepco but will wait until I see the results from Blackstone.

[davew]

That issue has nothing to do with the oil. It is totally a driver issue. The driver is downshifting too early into 3rd gear.

Trans gears are helical gears, they are cut straight on the drive side and angled on the back side, Kinda like this : /l

When you push on the straight side, all the force is pushed against the flat edge. On down shift the force is put against the angle, which acts as a ramp. The 2 gears try to seperate. The force is applied towards the tip of the tooth rather than at the root of the tooth. Obviously, the tip is the week point. Once one tooth breaks, it wedges in between the other teeth and off they come.

Learn to downshift properly and you will save transmissions.

That box is financially not worth rebuilding. The cost of a cluster shaft, 3rd gear, and all the bearings will exceed the price of a donor box.

In all the cars we maintain, and all the transmissions we rebuild, I have never seen a lubrication failure. I use MTL exclusively. If the fluid is not burnt, it is not a fluid failure.

[FTodaro]

That issue has nothing to do with the oil. It is totally a driver issue. The driver is downshifting too early into 3rd gear.

Trans gears are helical gears, they are cut straight on the drive side and angled on the back side, Kinda like this : /l

When you push on the straight side, all the force is pushed against the flat edge. On down shift the force is put against the angle, which acts as a ramp. The 2 gears try to seperate. The force is applied towards the tip of the tooth rather than at the root of the tooth. Obviously, the tip is the week point. Once one tooth breaks, it wedges in between the other teeth and off they come.

Learn to downshift properly and you will save transmissions.

That box is financially not worth rebuilding. The cost of a cluster shaft, 3rd gear, and all the bearings will exceed the price of a donor box.

In all the cars we maintain, and all the transmissions we rebuild, I have never seen a lubrication failure. I use MTL exclusively. If the fluid is not burnt, it is not a fluid failure.

I Agree Dave the box above not a fluid failure, my point about fluids was that in my box with 22 races on new shift forks the forks were about done. My point about fluids is that the MTL does not provide as much protection as a good 75/90.

[Sphinx]

Help me understand this: I was missing shifts this weekend, going from 2nd to 5th repeatedly (though by accident). Too long away from the car and the track. Each time, I would get a nasty grind. When I finally started getting it together and shifting into the third, the grinding went away.

Why would it grind under those circumstances? I've never experienced that before. Using MTL

[FTodaro]

I have missed a few second to third shifts myself, the grinding you hear is the that the transmission is not able to mesh the gears well from 2nd to 5th.

The secret to this shift, one that blew twice myself last weekend on separate starts, is that you need to left the shifter find the 3/4 gate on its own without you putting in input to find the gate. The 3/4 gate is spring loaded to push the shifter into this gate so when you go from 2nd to 3rd, or 3rd to 4th or 5th to 4th you only need to put pressure on the shifter with an open palm. It will find the gate.

easier said than done in the heat f the moment.