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This has happened to me twice in a couple years. Both times at the track lifting and getting back in it. The inner gear is breaking in several pieces. CK d3 with 200psi fixed pressure.
I’ve built probably 30 units the same for customers without a single problem. No one is making similar power though.
Any ideas?
If you would like to keep your Build private, you can PM me your Phone Number. I can call you tomorrow to discuss it.
I know plenty of guys whom do not wish their Engine or Combo information to be all over the internet.
I don’t mind discussing here. I’ve learned a ton from this site and like to help others with my knowledge (when I have some lol).
Engine combo is twin turbo 390ci which makes close to 1400rwhp.
Trans has all mods for ck brake, plugged epc with 1/16” bleed hole for lower pressure at idle, and fti converter. Converter spacing is right at 3/16”.
I log line pressure and it was right at 200 when gear broke.
-midplate?
-SFI bell or stock bell
-are you softening the crescent/rounding the nose?
-pressure balancing the gear?
-converter locked or unlocked when it breaks
No mid plate
Stock bell
No softening or rounding - can you explain what needs to be done?
Are you talking about milling a bathtub similar to th400 pumps? If so, yes this was done.
converter is always unlocked when racing
you are breaking pump gears
it sounds to me like the gear is getting caught on the leading edge of the crescent and breaking.
The causes for this are multiple. They are tough to see or deal with.
Dowels not perfect
flexplate not running true
converter hub not true
wear on the gears or converter hub such that they don't have a good fit and let the gear "wander"
just a poor pump pocket that has the crescent not perfect.
You can add a radius to the leading edge of the pump crescent. I only like to do this if there are issues that aren't being remedied otherwise.
The radius will let the pump gear not get caught and break.
This will slightly alter pump performance. If done carefully, it's never enough to even be noticeable for the most part.
If you want to see what I'm talking about with the pump gear "catching" on the crescent. Take a pump half with the gears in it, spin the inner gear by hand and press it towards the crescent. You'll get it to "grab" or hang up.
Now imagine what happens when that is done with the engine running.
On/Off throttle when this happens makes some sense. The pressure and volume of the pump is changing. PR valve is VERY active when this is going on. And that pump gear may move in a way it normally doesn't.
Building a unit at this level of HP is more than just a selection of the right parts and this is just one small thing in a long list of things that needs attention to build a quality unit.
I think you nailed it. Looking at the damage, it did get caught on the crescent. This was the first race on a new converter (many street miles though). Hub might of had more clearance. I did chuck it up in the lathe and hub to pilot it true.
pump gear to converter fit is something often overlooked.
in your pictures, the side of the crescent that is broken is not the side the gear would have to catch on to break
pump gear to converter fit is something often overlooked.
in your pictures, the side of the crescent that is broken is not the side the gear would have to catch on to break
You’re right. The other side looks fine. No signs of interference
Just a fly on the wall here reading and looking, I'm well aware of those who are commenting have a metric ton of transmission experience, but just an observation/question, the leading edge of the crescent in relation to the pump turning is the blunt side (clockwise rotation and we are looking at the front pump half) and the tapered trailing side is broken, pushing into the outer gear. Is it possible that when the tooth hit the leading edge and the gear split, that it pushed the non-contacting portion of the gear into the trailing side and broke it? With that, it would seem like the original diagnosis would be spot on, and as originally recommended, smoothing down that leading edge may still work. Am I off?
Edit: Also, if you were to pull the gear and inspect the bottom-most portion of the teeth parallel to the leading edge of the crescent, near the cracks (maybe the larger of the two splits) would it be enough protrusion in the runout to leave a witness mark of where it contacted?
Last edited by 93Z2871805; Nov 2, 2021 at 07:05 PM.
I would think that is highly unlikely that the engine stopped as soon as the pump gear broke. So the gears relation to the crescent wouldn't show much. Me just thinking out loud, could be wrong.
I would think that is highly unlikely that the engine stopped as soon as the pump gear broke. So the gears relation to the crescent wouldn't show much. Me just thinking out loud, could be wrong.
When the gear broke, there was enough room for the converter to keep on spinning.
There’s no witness makes on the leading edge.
Another thing to note, is the pump bushings is completely spun which could be from gear damage or running for 30 seconds after breaking. 🤷🏻♂️
did you check gear to converter drive hub fit? ive seen some incredibly sloppy **** from some well known know-it-all type shops. a brand new hub is cheap to have installed.
Something that I keep hearing from DIY builders...
is that they do not purchase a Torque-Converter until the Transmission is ready to be installed.
They never inspect any of the Converter to Pump Components for proper fitment.
That is crazy!!!
Years ago a guy brings me his THM700-R4 and tells me that the Engine will not crank after installing the Transmission.
He beat the Converter into the Pump with a Hammer!
Converter and bushing seized.
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Broken pump gear 4l80 
