Howdy all. I’ve screened the forum threads for some issues that I have been having but none really fit the bill that I have seen. So to start this is my Silverado 4.8 on boost. I smoked my trans a while back and decided at my power level (~600) I would just stick with the 60. I wish I could go back and slap younger me and force an 80 down my throat but I digress. Sent my old trans out to be completely built by a very reputable tranny builder in Florida by the name of Transbuilderguy. He has been exceptionally helpful but can’t help me with my issues as of late. At the same time I opted for a precision torque converter 10” with 3400 stall. Trans is fully built aside from billet input and output shafts. I also did the 4l79 billet 3/4 clutch pack which is supposed to make these damn things last. I drove it about 250 miles and from the jump the tranny had a steady rpm fluctuation at about 2500 rpm and ~60mph on highway cruising. I am sure the converter was unlocking and locking erratically. I noticed but decided it might be as a result of converter restall instead and wound up filling the pan with gold glitter. I removed the trans. Sent it to get looked at and cleaned as well as had precision cut and clean my converter which they noted had a broken fin on the pump impeller as well as a glazed clutch friction. So yesterday I finally got her all buttoned up and driving after about a year of life getting in the way. I have out about 150 miles on it regularly checking and topping off fluid. I still notice the converter unlocking and locking quickly and then completely not locking at all after some time of steady cruising. If you mat the pedal rpms run up and the truck builds boost but doesn't actually accelerate with the rise in rpm as if the clutches were slipping. Here are the symptoms in a more digestible list...

-At first truck drives totally normal from light to light and on highway
-5minutes into steady driving at ~2500rpm a steady rpm fluctuation begins. Vehicle speed doesn't Change with rpm increase/decrease however I do see my wideband fluctuation up and down in harmony with the rpm
-converter begins to lock and unlock until is just stops locking all together.
-after initial burnt trans I installed derale’s largest cooler with built in fan (no trans temp gauge however)
-truck pulls hard in first but will hang the rpm and bang off the limiter and won’t shift until I get off the throttle a bit. This happens through every gear it seems. with no clean shifts in WOT conditions
-after getting up to temp truck no longer creeps at idle as well as needing more throttle input to actually get going (new stall? idk this is my first higher stall vehicle) and will actually knock from a stand still to moving.

Had Jeremy formato (my tuner) turn up line pressure all the way and verify vehicle speed to shift points to make sure full converter pressure was happening and proper WOT commands but no change. I read on a few threads that tps or brake switch might cause this problem so I swapped both from a known good donor truck but to no avail. The trans and the converter are new. I really don’t want to continue to drive the truck this way while trying to diagnose the issues and risk burning the box down again. I neither have a hp tuner or local trans guy to lend a hand so I’m turning to you folks. I know it’s a lot to read but I’ve tried to include the entire picture as best I can so that y’all can help me as best you can. I appreciate any help at all and if there is any more I can include please ask away..

 

Did you have James' father's transmission business do the trans? Or even look at it, if they did not build it?

 

hey buddy thanks for the response. Not sure who James is it his father maybe you could elaborate?

 

James works in the same shop as Jeremy Formato...

He works for Garrett Mitchell (Cleetus Mcfarland) who shares that shop with Jeremy.

James' father has a transmission business in that area... That's why I asked.

 

oh gotchya! I’m actually about 4 hours away from Jeremy and his shop. It was a guy in Gainesville that built the trans for me. I’m just trying to see if there is anything I can do on my lift at home before having to set myself up time and money wise for a shop to take my truck and start throwing parts at it.

 

Did you have the transmission cooler and lines all cleaned out? Not doing so is a quick way to ruin a new unit.
The Brass you found when the trans. crapped out before can and will recirculate through the new unit.

Alright... First things to do are:

-Inspect the data stream for out of range metrics and/ or diagnostic trouble codes.
-I would borrow a scan tool if you do not have one... or try one of the mobile-app solutions for cell phone use.
-This way you can manually command lock-up, or a lock-up percentage... monitor temp and flow at the same time.
-Transmission fluid temp can be observed this way... or install a temp. gauge.
-Inspect ATF level with the engine running and the gear selector in Park with everything warmed up.
-Inspect line pressure in all gear ranges both at an idle and while driving. You may have an intermittent pressure issue. You want a gauge and hose long enough to tape to the windshield for driving.
-Inspect cooler circuit flow. You may have an intermittent pressure issue.
-Inspect the internal and external transmission wiring harnesses for visual damage as well as circuit continuity.
-Inspect solenoids and internal electrical components for proper resistance... manually turn on and off as well.

 

Also... How much does your truck weigh?

6,500 pounds and 600-650 HP measured at the crankshaft is where the 4L80E becomes the better investment.

In lighter vehicles (let say 4,000 Lbs or less) 750 HP at the crank is still good.

These transmissions can be built for over 1,000 HP at the crank... But they cost too much/ are a bad investment when a 4L80E will handle the power much better and for less money.

My best example for building something other than a 4L80E for 1,000 HP... is for the guy who has a Buick Grand National and refuses to use anything other than a THM200-4R transmission. Which works out great... but cost far too much.

 

this is perfect info for me thank you so much. I have a buddy with a pretty decent scan tool so I’ll see what kind of functions that thing has. I cleaned the cooler out and redid the hoses anyways so no real concern about contamination there. I don’t have a pressure tool to monitor line pressure maybe you can suggest a decent one? When I get to checking solenoids I will have to ask y’all what the resistance should be so might as well ask now lmao. The truck weights ~4600lbs. It’s a swb truck so not as heavy as you might think. If I get this figured out I would love to have one of the fastest 4l60 trucks in the country it’s just getting things ironed out lol. I appreciate the info I’ll let ya know what I come up with