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Discussion Starter · #1 ·
What happens when a convertor with a mechanical diode goes bad? I have a Transmission Specialties 8" that has a mechanical diode in it, and 3 weeks ago, something went sour and I'm starting to think it's the convertor. I thought it was the barrel valve or pump, so I sent them back to Ron's and had them rebuilt, but it didn't fix the issue. When I put it in gear, the rpm drops about 500 rpm (it never used to do that), and when I set the transbrake and try to put it on the 2 step, it goes to 1800 and stops (4800 chip, convertor used to stall 6000.) When it went "bad", it was during elims, so I went ahead and ran it, and it wouldnt make any rpm for about 100 feet or so, then it came out of it and ran 'decent', but not fantastic. It normally goes 1.41-1.42 sixty foot and upper 6.40's @ 107 mph (1/8 mile), but that one pass it went 2.35 sixty foot, and 8.09 @ 98 mph. I have checked everything in the motor, and I cant find anything wrong.
 

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Discussion Starter · #3 ·
Thanks. I was afraid of that. I really don't want to pull the trans, but it's looking like that's the next thing on my "to do" list.

It's my father's car, and I am trying to sell it for him. The upside is, I get to race it while I try to sell it. The downside is, I have to fix whatever breaks.

And about the mechanical diode, I know nothing about them or how they work. The convertor in my car is a steel stator, spragless convertor.
 

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A mechanel diode is a type of sprague.

Converters can be equipted whith steel stators with a sprag or mechanical diode, but if its spragless, there is no sprag to break. The trouble is more than likely is somewhere else.
 

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Discussion Starter · #5 ·
The convertor in my dad's car is the one with the diode, and the one with the issues. I was just using the convertor in my car as a comparison to show how little I know about diodes.

Thanks for the info.
Looks like I'm pulling a trans tomorrow.
 

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Not a lot of power to be killing a mechanical diode.. They are suppose to be much stronger than a sprag.. But your problem sure does sound like the converter sprag...
 

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its the ignition or two step, i just had it happen to me, sent the 7al3 back to msd & fixed the problem. same thing went bad from one round to the next. it revs fine not on the t-brake, it will not rev to launch rpm on the t-brake? launch control! i would have never believed it, from one round to the next.
 

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If you knew what was in a diode it would scare you. They usually don't break, just slip. Put a sprag in it. Or have it converted to spragless.



 

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Discussion Starter · #9 ·
Thanks again to everyone. Before I pull the trans out, I'll plug a different 2 step in and check it. And after that, I will unhook the 7AL2 box and hook up a new 6A box I have sitting on the shelf just to see if it makes any difference.

When it went bad (whatever crapped out on me), was during the first round of elims. The car hit the tires, moved 10' under power hard, then fell flat on it's face. The guy I was racing never looked back and broke out even though I was idling down the track. I was .001, and got the bye for the second round. I pulled the injectors and cleaned them, thinking that was the issue; it wasn't, so once again I just idled down track. So for the third round I dialed 7.99 (as slow as I can dail in Top), and was hoping it would move enough off the starting line to at least cut a light; it didn't.

I talked with my father yesterday, and he thinks it's been at least 6 or 7 yrs since that convertor has been gone thru, and quite possibly as long as 10 yrs.
 

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Stator support tube...

I had the exact same thing happen on my Outlaw 10.5 car twice. It was the stator support tube both times. I bet it has twisted/turned, not allowing the fluid to pass correctly
 

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Does the car launch hard THEN fall on its face everytime?

I had the same issue that chevette posted. Mine was a two-step that went bad. The car would not launch hard but at about 60-80 ft out it came alive and ran w/o issue. Chased fuel, conv stall check in pits was ok. Tried another low-side chip - no help. Then someone suggested pulling out the low-side chip and just leaving off the conv. Right back to running 5.60s

Good luck.
 

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Discussion Starter · #15 ·
No, it wont leave at all now. The pass it messed up on, it left hard, moved about 10 feet then fell flat on it's face. Now it wont stall over 1800 rpm. I unplugged the 2 step and it didnt change anything. It will drive around the pits fairly normal, except for the fact it wants to idle about 500 rpm lower when in gear now than it used too.

Thanks again guys. Now I just need to get off my lazy ass and pull the trans out.
 

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Just some info to pass on here. Dura sprags and element sprags are among the most common sprags that come into Trans Specialties with failure. Thats why we use the Mech diode exclusively in our race converters, ONLY, if the application is to be driven on the street. (meaning we HAVE to put something in there.)

We still believe that mechanical diodes will fail. especially after 2+ years of racing against it. As in the pictures shown above it's a very primitive design that lacks thought and quality.

If you get it pulled out and want to get it back to Trans Specialties to be made spragless (my reccomendation) or replace the diode, send me a PM and I can accomidate you through the process.

Thanks
 

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No, it wont leave at all now. The pass it messed up on, it left hard, moved about 10 feet then fell flat on it's face. Now it wont stall over 1800 rpm. I unplugged the 2 step and it didnt change anything. It will drive around the pits fairly normal, except for the fact it wants to idle about 500 rpm lower when in gear now than it used too.

Thanks again guys. Now I just need to get off my lazy ass and pull the trans out.

Sounds like conv...........
 

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X-LESS said:
Dura sprags and element sprags are among the most common sprags that come into Trans Specialties with failure. Thats why we use the Mech diode exclusively in our race converters, ONLY, if the application is to be driven on the street. (meaning we HAVE to put something in there.)...
Thanks
Okay...so you'd rather see the MD in a street/strip application then? What would you use if it was not driven on street? Spragless altogether?

On street driven MD's...where does the wear typically occur? What fails?
 

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If the car is a low horsepower street car it probably doesn't matter what sprag goes in. If it is your race car that see's tons of track time but sometimes hits the streets for an extended cruise, I would say the Diode is the best option. If the car comes off the trailer and hits the track only it's a real benifit to discard the extra moving part to strengthen the overall design and durability of the converter.

Take a look at the picture posted on page 1. The little flapper doors brake off and the springs are so tiny that they can fail or wear out. The actual case with the grooves also wears down and creates problems as well.
 
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