Torque Convertor Going Bad?

1982 SS

Frequent Racer
Jan 19, 2007
382
0
0
Clearfield, Utah
In my El Camino drag car I have a B&M holeshot convertor rated to stall at 36-3800 rpm. Its pretty much always flashed at 4400 in my car. A few years ago I lost the transmission and had it rebuilt. I sent the Convertor to a "highly recommended" local guy who I don't really feel like he was worth money for his convertor rebuild in hindsight. He wanted to change everything about it, but i digress. Been running it for another 3 years with no real change in power output and any minor improvements in ET have been found in chassis tuning and weight relocation (Battery to the back this last winter) and I noticed at the track last time that it seems to be flashing a lot closer to 5000 rpm on launch than it used to. I can't gve you an exact rpm, was kinda busy driving but I do know that needle was almost to 5000. Am I correct in thinking that i have something starting to go wrong with the convertor? Perhaps theres some consistency to be picked up with a fresh more application appropriate convertor.
 

bracketchev1221

Dragway Regular
Apr 22, 2009
1,111
1
0
Mountville Pa
Do you notice the 60' falling off, or is the rpm at the finish higher?
 

1982 SS

Frequent Racer
Thread starter
Jan 19, 2007
382
0
0
Clearfield, Utah
60' seem to be normal and I don't notice the finish line rpm being higher. Maybe I'm just seeing things? I made sure to watch it as closely as I could a second time and had the same higher rpm when flashed. Everything else seems to be normal, could just be the way the car is pushing the convertor after I put the battery in the back and the double adjustables on the front this last winter, maybe?
 
There are six basic reasons that you would observe a significant increase in torque converter flash stall speed.

1.) There's been a change in the overall combination that has significantly increased the load on the torque converter such as an increase in low-speed or mid-range torque production, an increase in overall weight, a reduction in gear ratio, or an increase in overall tire height.

2.) The inner portion of some (or all) of the impeller fins inside the torque converter have folded over.

3.) There's a bearing (or bearings) starting to go away in the converter which have allowed the clearances between the impeller and stator and/or stator and turbine to increase.

4.) The converter has ballooned in which case there would also be an increase in internal clearances.

5.) The transmission has developed a problem with the torque converter feed circuit and is no longer keeping the converter completely full of fluid.

6.) The transmission is low on fluid.

Normally I'd probably lean towards reason #2 or #4 based on the information you've provided, but if this were the case you would normally notice some variation in the reaction time and/or 60-foot time (although that's not always the case 100% of the time).

All that being said, there may be some performance to be gained in your combination with a purpose-built torque converter. I'd be happy to take a look at your combination and performance data to see if there's anywhere we may be able to help with some improvements.
 

1982 SS

Frequent Racer
Thread starter
Jan 19, 2007
382
0
0
Clearfield, Utah
A long overdue update to the thread.

The trans let go on me in the middle of august at a race. It went from normal the first pass to subsequent passes feeling like I blew the tires off it over the next two passes, then to grinding first with a soft second gear, and finally to losing all three gears.

I took my trans to a local guy who is the guy that a lot of the Super Comp guys take theirs too and had him go through it. When He go it apart aside from a lot of clutch material, he told me that there wer chuncks of the converter through out the transmission. Well a call so summit and I had a Hughes 4000 stall headed my way and a thrash to get the car ready for the next big race. I struggled through that race and didn't do well due to other issues with the car. Bad weekend for broken parts.

One thing noticed is that the Hughes convertor was not quite as aggressive/quick reacting as the B&M holeshot that was in there but my 60's were a little more consistent when it hooked normally. The B&M was a little violent on launch, probably contirbuting to 60' inconsistency, where the less aggressive Hughes helped it out with a more tame but still quick launch. My tires are three years old and over the next two races I struggled getting them to hook conistently. At first I wondered if heat was causing my fresh trans to act funny as It ran fast, slow, and slower in the last three runs of the year, but my 60's were also getting slower too. ATF looked clean and not sparkly or full of junk. Not enough data to form a good conclusion. Tires are first to change and try to eliminate one variable then I can begin to evaluate everything else. The speedo cable, gear and stuff fell out and I lost some fluid so I'm hoping all it is is that I'm a hair low on fluid contributing to slower times too. We will see come spring time with some fresh tires and other updates.
 
Just as FYI, our GM40 torque converter features a real negative impeller fin angle which will soften the hit at the initial launch and will help improve flash characteristics. This converter is a great choice for footbrake bracket and index racing as it will generally help contribute to good consistency.
 

1982 SS

Frequent Racer
Thread starter
Jan 19, 2007
382
0
0
Clearfield, Utah
That's cool. I figured the softer hit would help my consistency out, and it looks like it will and it helps me hit the tree in a more natural place for me mentally. It does flash at 4500 rpm behind my 383 and 3800ish pound race weight car. Is there anything I should be aware of to help get the most consistency out of this converter or anything that will help with a th350? Also, I've been doing my burnout starting in second and catching third and holding for a count and rolling off the brake followed by rolling out of the throttle before it catches hard. Am I on track there or is there a better way for the transmission?
 

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