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Car is a lsx 427 with a billet 106 with Fast XFI as management system. Recently had some trans issues and finally got everything back together and decided to do some trans brake testing and tuning with the new Griner 1-2 leave option valve body. This past sunday I went out and fired the car up in the shop and let it warm up and then proceeded to test the car on the brake. First started in 1st gear, normal routine..... Foot brake the car to about 3200 then grab the brake and let it climb to the 2 step set point which was 4000. Everything worked great so moved the limiter on up to 4200 where it normally is. Again everything worked flawless. Continued to do this 5 more times in first and then did the second gear testing and same result. No issues and it build rpm and boost as it should. Move ahead four days to last night (thur) and the car hadnt been touched at all( I mean nothing) all i did was add a quart of trans fluid and then started testing the brake for final tuning adjustments for the track tonight but the car will not come up on the brake at all. Same routine, foot brake til 3-3200 and then grab the brake and the rpms start to come up by then act sluggish and never reaches the two step limit no matter what. Ive lowered it all the way down to 3200 and it will reach it then but also does what Im about to tell you next. As Im on the brake and building boost and rpm the car reaches about 3550-3700 and then falls flat on its face no matter what we do. Every log is the same, I will be at 100% throttle and rpms will start falling while im still wide open and will be for another .5-1.0 then I will lift off the gas. In this time frame rpms drop about 3-400 every time. Car has never done anything like this and nothing has changed. Not one thing!
 

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Sounds simple but make sure the gas tank is full enough, fuel filters clean, fuel tank vent clear.,crank trigger tight, did the turbo swallow a rag, V-bands tight,etc? seen all of this simple stuff happen more than once over the years,, Are you sure it not dropping a cylinder under load do to any number of reasons? Are you watching AFR and timing while building boost? The O2 correction should be set to become active well above your boost building and 2 step rpms..
 

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Discussion Starter #5
Yes we are logging every test and watching afr and timing very close. The o2 correction isnt set until further up in rpm, 5200.
 

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What coolant temp is this happening at? I know my car is very sensitive to spooling when the temp is too low... Double check the coolant/vs /enrichment sections and see if it could have any effect on it?
 

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Any chance your trans didn't have enough fluid in it so the pump was cavitating and causing the converter to be looser? Now with full fluid the converter is operating normally. A 10.5 is tight for a small block so it should be fairly tight. Another possibility is the sprag or diode in the converter has broken or it has broken the stator support tube.
 

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My car did the same this earlier this year while at Holly Springs spring race, I thought the convertor was the culprit, took tranny out at the racetrack, nothing. Took pan off, nothing, then said hell I'm there, so I started to take the front pump out and I was like I'll be damned, the stator tube in the pump had turned and would spin in the pump with ease. Also, burnt up clutches, so replaced clutches, band, and front pump and made next qualifier next day.

I may be wrong, but I believe, what it's doing is filling the conv up with tranny fluid when the transbrake is applied, therefore pulling the rpm back down. I'll bet that if u drive it around or free revved it, it would act normal, right?? Btw, mine is a TH400 2spd


Thanks,
John
 

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Any chance your trans didn't have enough fluid in it so the pump was cavitating and causing the converter to be looser? Now with full fluid the converter is operating normally. A 10.5 is tight for a small block so it should be fairly tight. Another possibility is the sprag or diode in the converter has broken or it has broken the stator support tube.
That's what I'm thinking. My 400, while nowhere near as serious as this one is is very sensitive to fluid level. BTE 10" converter and a hipsters brake.
 

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Any chance your trans didn't have enough fluid in it so the pump was cavitating and causing the converter to be looser? Now with full fluid the converter is operating normally. A 10.5 is tight for a small block so it should be fairly tight. Another possibility is the sprag or diode in the converter has broken or it has broken the stator support tube.
Dusty.... Try this one? :smt110

 

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I got your pm
 
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