TF, over flashes, spragless converter

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VOETOM
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TF, over flashes, spragless converter

#1 Post by VOETOM » Sun Oct 04, 2009 9:37 am

Have a pal with a 3400 pound E-body car, 3.55 gear, large BB engine, runs 9.90s as driven on street. It was time to freshen trans and engine. I took the 727 and redid it as I normally do with the right components for the application. It went together with the right clearances, engine the same. Now, when it hits the converter on the line, it "over flashes" or, the converter builder suggested slip in the transmission. I have the TF 727 back apart in the shop, it is 100% perfect, no sign of any slippage, low-roller clutch is fine, all clutches are fine. All parts look like they always do when I build them. No sign of slippage or rear roller clutch roll over. Nothing odd or out of the ordinary.

Has anyone ever had a spragless converter "over flash" on the line, yet act normal all the way down the track. It is normal on the street when traction is not perfect. Only when this is loaded and with ultimate traction does it flash 1000 to 1500 rpm too high. It seems to me as it may be ballooning the converter, causing the clearance between the converter turbine and pump to expand and thereby lose the coupling efficiency.

It is not a Trans Specialties converter. I think it is a recognized brand but not 100% sure right now. Anyone with similar experience or ideas to share?

Thank you for any suggestion or comments.
Tom

Marty Chance
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Re: TF, over flashes, spragless converter

#2 Post by Marty Chance » Mon Oct 05, 2009 11:57 am

OK we have several things to address.
First converter ballooning will not cause this as the vortec flow inside the converter will pull the turbine tight to the pump impeller on stall (trans brake)
Second things that will increase flash stall:
*an increase in low rpm power (advanced cam, higher compression,ect was there any changes to the motor?
*converter itself may have fins pulling out on it or if it has been freshened lately was any parts changed or updated such as stator or bearing styles.
*transmission- controls all fluid going in and out of converter , this is a delicate balance that creates "converter charge" , which is the only way a converter can become effecient. was anything changed in the trans that may cause a low converter feed pressure or an increased exhaust flow?
Neal Chance Racing Converters
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VOETOM
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Joined: Sun Oct 04, 2009 9:03 am

Re: TF, over flashes, spragless converter

#3 Post by VOETOM » Mon Oct 05, 2009 4:17 pm

Same converter, engine put back as it was before, fresh yes but no massive increase in power.

He described it as almost instantaneous flashing up. If the trans had any sign of slippage in the frictions in the rear clutch retainer or the overrunning (roller) clutch, i could believe the trans is at fault but it does not.

It also sounds like a hydraulic issue to me but the pump was perfect before and it went back the same. The valve body was not taken apart. There were no signs of residue in the trans so I left it as is. I wonder if the converter control (pressure) valve has a bind but if so, it would have issues down the track and at random times.

When the engine is running at speed, the trans does not know any differently since line pressure is set by the pressure control spring, not controlled by throttle pressure. This takes out about any argument for low fluid apply pressure at start and on the contrary, when stalling at 4500 to 6500, the pump is being run faster than when the car is actually accelerating after a shift. So why does it not act odd under load while accelerating down the track?

Mr. Chance, thank you. I'll look more closely at the valve body after while.

Update, valve body is fine, all pressure control valves are free and basically fall out (after fluid drains out). Over running clutch assembly is perfect, rear clutch retainer, just like hundreds I have done before. No trans errors noted.

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Re: TF, over flashes, spragless converter

#4 Post by John_Heard » Mon Oct 05, 2009 5:47 pm

May or may not apply, but how about looking at the shifter adjustment?

VOETOM
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Re: TF, over flashes, spragless converter

#5 Post by VOETOM » Mon Oct 05, 2009 6:01 pm

Thank you but it is right on. TFs are pretty easy to get exactly correct.
Tom

Marty Chance
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Re: TF, over flashes, spragless converter

#6 Post by Marty Chance » Tue Oct 06, 2009 8:44 am

it sounds like you are covering all the bases, somewhere we are all missing something. I wish i could be of more help. with the converter flashing too high could you use a msd digital 7 and make a timing retard curve to control the flash so the car is raceable until you find the problem? I have seen changing pistons on a freshened motor change the power curve, even when the overall compression ratio stayed the same. Were the pistons replace? cam replaced or installed advanced? The reason i keep coming back to this is if the low rpm power (from idle to launch rpm) gained , that will increase the flash stall.
Marty Chance
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VOETOM
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Re: TF, over flashes, spragless converter

#7 Post by VOETOM » Tue Oct 06, 2009 7:49 pm

After more chats today, I am leaning towards your choice #3 Marty, the converter flashes due to temporary oil starvation. Maybe the extended pickup O-ring sucks air or the acceleration shoves the oil back in the deep pan and it is slightly low and uncovers part of the filter?

Will reassemble it after looking over the pressure valve in the valve body.

Thank you for your time and suggestions. I will share what we discover.
Tom

VOETOM
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Re: TF, over flashes, spragless converter

#8 Post by VOETOM » Sat Oct 24, 2009 9:34 pm

After one more going through of the 727 and checking EVERYTHING, car does same thing. Overfilling changed nothing.
Converter place was shooting for 4500 flash but it hit 5500 except now, it buzzes to 6500 then drops back as car moves the first few feet. WEIRD!!!
Tom

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Re: TF, over flashes, spragless converter

#9 Post by Marty Chance » Mon Oct 26, 2009 5:43 am

do you have a data log you could send me?
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VOETOM
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Re: TF, over flashes, spragless converter

#10 Post by VOETOM » Mon Oct 26, 2009 9:11 pm

Marty,
The car has no data logging capability, wish it did, we would have made some determination by now.

Converter shop says it is not the converter but I was told they are having issues getting a converter to work at the customer-prescribed 4800 rpm stall. They let him know they could get 4500 or 5500 but nothing in between with this core.

Still not sure how anything inside the trans could let it flash to exactly 6500 each and every time. If it had internal slippage, it would vary with oil temp and it should get worse and the rear clutches should show signs of slippage, but they show nothing but new markings.

I am like them, how in the heck can this thing over flash and then settle back in to act normal? But from the trans-builder point of view, nothing is internally slipping. And, if it was a pressure issue, it should manifest itself down the track too. The first few feet past the start line should be as violent as the first hit and it should not settle back down to normal rpm. With a constant pressure valve body, it should not vary with rpm, technically. And with the converter spinning at 4500, the pump for sure is putting out oil off line and while running down the track.

They are building a new converter and so with its installation, we will know if it is the trans or not. If it is the 727, I am out of tricks as three times I have seen it and all three times it is fine and air checks fine and measures fine.

Thank you for hanging with me.
Tom

VOETOM
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Re: TF, over flashes, spragless converter

#11 Post by VOETOM » Mon Nov 02, 2009 8:15 pm

Marty, got it fixed. Email me or call me at the number from the other day and I can let you know some details.
thand@kc.rr.com

Tom Hand

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