I'm hoping for some insight on the two blown pumps in my 4l70e. Over the summer I swapped a crate LS3 and installed a 2800 stall converter at the same time. The pump in my 122k mile trans didn't survive the initial tuning, so I had the trans completely rebuilt. My trans rebuilder thinks the converter needed shims and backed out of the pump causing the first failure. We compared the stock and aftermarket converter and every measurement was within .010.

Fast forward about 2k miles on the new trans and now a second failure. This time the slider and rotor broke but the new pump survived thankfully. There was minor damage to the converter hub which I’m having repaired. There was evidence of the rotor chattering across the slider causing the failure. My trans guy blames the second failure on excess line pressure in the tune. He says it’s the only thing he’s known to cause the rotor to chatter across the slider like that. I don't see how this is possible, as I've been running the same line pressure for over 100k miles, and the regulator should be protecting the pump anyway.

Prior to the slider failure, I was getting some pretty bad chatter on the 1-2 shift which got moderately better with some Lubeguard anti-shudder additive. On disassembly however, the band and drum look brand new. Not sure if this issue is possibly related or not.

I ordered and SFI flexplate while its apart to eliminate that as a possible issue. So now while I’m waiting on the converter repair I thought I’d throw this out there to see if anyone’s got an explanation other than a line pressure issue. I really want to get this right this time.

 

Got a copy of your tune you can post?

 

Unfortunately I do not, and my tuner hasn't gotten back to me about the issue. My understanding is that the stock line pressure is 90 percent of the max pressure the PCM will allow, and my tuner increased that 5%. He's running a 4l60e in his truck with the same converter and identical transmission programming for what its worth.

 

Look at the converter pilot where it goes into the crank. Make sure the converter is able to move back forth in it. It's way too long to explain but I have had that wipe out a pump, thrust beaRing, crank, etc. It's very hard to check , but miss matching factory parts sometimes creates the problems, and we over look the stupid simple things.

 

Changing the flywheel is the first thing i would of done...also id look into a circle d 3000-3200 budget converter..and if you want extra insurance get a good almost new pump with a billet rotor..FLT sells the billet pump rotor for 150 bucks

 

I've got a Circle D 278mm in there now and a Circle D flywheel on the way. The pump I've got is basically brand new and thankfully it survived the rotor/slider implosion unharmed (unlike the original pump). I'll talk to FLT about the billet rotor, thanks,

 

Just found out that FLT doesn't sell the billet pump rotor separately anymore. Did a google search and found a few vendors selling billet 13-vane rotors for $165 and up. Does anyone have any experience with anyone else's billet pump rotor? For that kind of coin I don't want a piece of overseas junk.