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SmalltownSS

Broken input shafts built 4l65e

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I have been having a hell of a time with my rebuilt trans. The stock transmission was slipping at 121,000 miles so i sent it to a local performance shop in Manitoba to be rebuilt before it got worse. They did a performance rebuild with what appeared to be all the right parts (alto red band, kolene clutch plates etc) and said it would be good to 550 RWHP which would be more than good enough for my worn out stock silverado motor with headers, custom tune and a cat back. I put 165 miles on the truck and heard a bang when it downshifted from 4th to 3rd during a pass on the highway...... no power to any of the gears. Got the transmission sent in again to be fixed on warranty, it was the input shaft that broke apparently (i have the shaft and drum they sent it to me, it busted the collar where the splined shaft is inserted . I was just driving it around again yesterday and it made it to 70 miles when yet again, passing a mini van at 45 mph it downshifted to 3rd from 4th and went "bang" no power in any gear and making the same "zinging" noise as the first time, so im going to guess its another broken input shaft!! Has anyone else had trouble with this with a N/A stock motor and a 4l60? what is causing this problem? It must be something wrong and I cant afford to have this truck off the road for this much time!! Any advice would be good.

 

Thanks

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Input shaft failure is common specially at the spline of the input drum and shaft. Think about it, ur splining steel to aluminum which obviously isnt a strong point. Three options, one you can install a billet collar where the spline is. Two you can install a billet input shaft with a billet collar. Or three you can drop big coin and upgrade to the billet input drum from Sonnax with a billet input shaft

 

I love when independant shops tell their customers a horsepower rating for 60's.

Edited by 2BFAST

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LOL I agree as above. The downshift is especially hard on the input shaft however with your modifications, the input shaft shouldn't snap 2x like that. Other than what was stated above, I would question your tranny builder, parts used and also look into your tune for some possible issues on the downshift commands.

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Input shaft failure is common specially at the spline of the input drum and shaft. Think about it, ur splining steel to aluminum which obviously isnt a strong point. Three options, one you can install a billet collar where the spline is. Two you can install a billet input shaft with a billet collar. Or three you can drop big coin and upgrade to the billet input drum from Sonnax with a billet input shaft

 

I love when independant shops tell their customers a horsepower rating for 60's.

 

x3

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Input shaft failure is common specially at the spline of the input drum and shaft. Think about it, ur splining steel to aluminum which obviously isnt a strong point. Three options, one you can install a billet collar where the spline is. Two you can install a billet input shaft with a billet collar. Or three you can drop big coin and upgrade to the billet input drum from Sonnax with a billet input shaft

 

I love when independant shops tell their customers a horsepower rating for 60's.

 

Is it a common failure with N/A stock motors? How come it never broke in 121,000 miles with the stock transmission? I agree the shops transmission horsepower ratings are probably bogus! I think its strange that a truck that makes 300-315 rwhp (if its lucky) would be able to break an input shaft unless there was an internal problem in the tranny.

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So you are saying the shaft and the collar for the input drum both broke? Or just the drum?

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So you are saying the shaft and the collar for the input drum both broke? Or just the drum?

It looks like the spline where the input shaft slides in is broke on the drum side. Here is a picture post-20102-0-42559200-1357613440_thumb.jpg

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I have never had or heard of that happening twice in a row, especially on a stock motor. My old truck had 142K on the trans I never had that issue. Sounds like someone isnt putting together something right.

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That isnt a shaft failure but an input drum failure.

 

Hard to say what happened

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They took it apart and it broke the input drum where it connects to the collar and input shaft, which is a very thick piece of metal. Probably because it had a reinforced collar this time, something else had to break! They had the test gauges on it driving down the road and all of a sudden the line pressure went to 200psi and stayed there, it also flipped a "ratio code"? They cleared the code and it has been on 3 test drives since with no high pressure or codes.

 

Anyone heard of this, or have any thoughts?

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Custom tune by zippy, but tuned to be a reliable daily driver, no change to shift pressures or force motor amperage, only changed shift points to match sonnax shift improver Kit. I don't thin it is the tune, the tranission shop was blaming the tune originally but has not mentioned it since they took the truck for a test drive.

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My SS is still at the transmission shop, they still aren't sure what is causing the input shafts to break, there has been some progress though. A sonnax super hold billet 2nd gear servo was used instead of the common "vette servo" From what I have been told by another builder is that the super hold servo is alot more aggressive than the vette servo and that could be what is breaking the shafts while shifting into 3rd gear. Lots of guys run the super hold, but generally with high stall converters, and or high horsepower with billet input and output shafts/ drums. The shop has used super hold 2nd gear servos in builds for 2 wheel drive trucks before and have not had any problems but they say "it just chirps the tires when shifting" has anyone else run a super hold 2nd gear servo w/stock input shaft and stock converter with all wheel drive?

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