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Old 01-03-2013, 04:14 AM   #1 (permalink)
Alexcantsleep
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Torque converter lockup

Hey gang! First off, want to thank everyone, you can see the list in my sig of all the mods I did to my truck, it was a breeze based on the research and info I got from this site. With the exception of cutting my hand and needing stitches, but that was operator error.

I do have a question though that I wasnt really able to answer by searching.

On the highway, around 50-60 MPH, my torque converter locks up, unlocks, locks, unlocks, every few seconds if the grade changes slightly. Once Im up at 70 or so it seems to stay locked. At a lower speed I can't seem to make it unlock with the brakes but if I hit even the slightest bit of resistance it will unlock.

With 4:10s is this normal? Temp stays nice and cool and (come to think of it, I've only noticed it since it's gotten colder out) the fluid and filter have been changed in the last 1500 miles or so and it's clean and at the proper level.

Any thoughts?

Alex
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1996 Suburban, 3/4 ton, 6.5 Turbo, 4L80E, JD7 brakes, 4:10, 14 bolt rear end, front and rear air, 50,000 original miles. New IP and rebuilt Turbo. New AC Delco Balancer and pulley, Diamond Eye 4 inch exhaust, 2.5 inch crossover, Bosch glow plugs, HO water pump, dual AC Delco 190 degree stats, Dmax fan and clutch, Glowshift gauges on pod (Boost, Tranny temp and EGT), Angelo Fished PMD relocate behind grill, Lubrication Specialists oil cooler lines, 12 inch aux fan over oil cooler.
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Old 01-03-2013, 04:49 AM   #2 (permalink)
2010flhp
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Sounds like a nice truck. I'd like a pic of your new gauges. Where'd you get them? As far as the trans, here is what mine does:

My trans locks up at 45 mph and will go out of lockup if I drop below 45 mph. Above that it stays locked unless I floor it and the trans downshifts. The TC is supposed to unlock when you tap the brake but mine doesn't, I suspect a bad brake pedal switch. You may have this problem also. When I let off the gas the TC seems to unlock and there is no engine braking. The engine drops to idle. Normal? Not sure. Below 170 degrees engine temp the TC will not lock up.

Have you verified your speedometer is reading correctly? BTW I have the 4:10 also.
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1996 Suburban 2500 2wd 6.5 TD (imported from Texas), Bumper mounted PMD, LubeSpec braided steel oil line kit, Rotator lightbar and hidden strobes (fire dept), Fluid Film undercoating, 202,050 miles, blah blah blah looks like any other white Suburban, parked for winter!
1983 4wd longbox, 6.2 NA, Automatic, 40k miles, fire dept vehicle
Ford gasser van (for winter, front wheel drive)
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Old 01-03-2013, 04:57 AM   #3 (permalink)
Alexcantsleep
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Thanks!, I like it! And oddly enough, after doing all these mods to tow with Ive hauled 36 full 16 foot trailer loads of ....wait for it.....STYROFOAM! All I've towed with this far is 16 foot long, 5 foot wide, 8 feet tall block of foam!

But I digress....

Everytime I let of the gas theres no engine braking so it's disengaging but its not staying engaged until about 70 mph or so.

I wonder if this cold weather coupled with the 190 degree stats is making the ECM think its too cold to stay locked up? My gauge shows about 190 or so (I had 195's before)

Ive never had a lock up converter vehicle before, so this is an odd thing for me. And may be perfectly normal.

Alex
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1996 Suburban, 3/4 ton, 6.5 Turbo, 4L80E, JD7 brakes, 4:10, 14 bolt rear end, front and rear air, 50,000 original miles. New IP and rebuilt Turbo. New AC Delco Balancer and pulley, Diamond Eye 4 inch exhaust, 2.5 inch crossover, Bosch glow plugs, HO water pump, dual AC Delco 190 degree stats, Dmax fan and clutch, Glowshift gauges on pod (Boost, Tranny temp and EGT), Angelo Fished PMD relocate behind grill, Lubrication Specialists oil cooler lines, 12 inch aux fan over oil cooler.
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Old 01-03-2013, 10:07 AM   #4 (permalink)
bigblazer
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Check your brake light switch. There's actually two switches in one. One for the lights and one for the trans.your converter should unlock if you tap the brakes. The switches are 12$.
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Old 01-03-2013, 12:19 PM   #5 (permalink)
Tannerjpowell
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This is exactly how mine behaves. Not sure if that's normal or not. I'd kinda like it if the RPMs kept up a bit more.

Quote:
Originally Posted by 2010flhp View Post
Sounds like a nice truck. I'd like a pic of your new gauges. Where'd you get them? As far as the trans, here is what mine does:

My trans locks up at 45 mph and will go out of lockup if I drop below 45 mph. Above that it stays locked unless I floor it and the trans downshifts. The TC is supposed to unlock when you tap the brake but mine doesn't, I suspect a bad brake pedal switch. You may have this problem also. When I let off the gas the TC seems to unlock and there is no engine braking. The engine drops to idle. Normal? Not sure. Below 170 degrees engine temp the TC will not lock up.

Have you verified your speedometer is reading correctly? BTW I have the 4:10 also.
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1994 2500 Suburban 6.5L - 2wd Auto - 8200 lb brakes - 3.73 posi - 4" Diamond Eye System, 2.25" x-over, PMD relocate and heat sink, Custom LCD readout for EGT, Boost done, working on IAT and EOT. Heath MaxETorq, Turbomaster, Duraterms. In Progress: TransGo HD2, Updated Transmission Solenoids, 2000 model water pump, spin on fan clutch and duramax fan.

2003 ECSB 4x4 6.6L - PPE Hot - MBRP 4" - 1/4 E.T. 14.74 ------- Sold
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Old 01-03-2013, 01:27 PM   #6 (permalink)
2010flhp
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Quote:
Originally Posted by Tannerjpowell View Post
This is exactly how mine behaves. Not sure if that's normal or not. I'd kinda like it if the RPMs kept up a bit more.
What rpm do you turn at 70 mph? At 60 I'm turning about 1900. I have 4:10, not sure why they put that in a 2WD except maybe for towing?
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1996 Suburban 2500 2wd 6.5 TD (imported from Texas), Bumper mounted PMD, LubeSpec braided steel oil line kit, Rotator lightbar and hidden strobes (fire dept), Fluid Film undercoating, 202,050 miles, blah blah blah looks like any other white Suburban, parked for winter!
1983 4wd longbox, 6.2 NA, Automatic, 40k miles, fire dept vehicle
Ford gasser van (for winter, front wheel drive)
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Old 01-03-2013, 03:09 PM   #7 (permalink)
Tannerjpowell
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Alex,
On my truck I used GMTD scan tech to observe when the computer was engaging the TCC and what duty cycle it was being engaged at. I was also able to observe the calculated slip between the transmission and motor and it was very little (10-20 rpm at most). In my case, the TCC was locking up very well, although I felt it wasn't engaging because I wasn't seeing the RPM I expected. Cycling the TCC manually, I could clearly tell the difference between locked and unlocked.

If possible, I would try to observe what the computer is telling the transmission to do while it feels like its locking and unlocking. If you can monitor TCC slip and TCC lockup state while you're feeling the surging, it will greatly help you diagnose the problem.

Either the TCC is being commanded to lock and is failing to stay locked, or the ECM is cycling it because of some other fault.


2010flhp,
3.73 here. Mine sits just a hair above 2500 rpm at 70mph. At 60 mph I'm around 2250. Mine seems to run quite a bit higher RPM than it should, but I can't guarantee that my tach is reading right. Seems that having a gasser alternator can cause higher than actual RPM readings. Not sure if it also affects the RPM the computer thinks the motor is turning.
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1994 2500 Suburban 6.5L - 2wd Auto - 8200 lb brakes - 3.73 posi - 4" Diamond Eye System, 2.25" x-over, PMD relocate and heat sink, Custom LCD readout for EGT, Boost done, working on IAT and EOT. Heath MaxETorq, Turbomaster, Duraterms. In Progress: TransGo HD2, Updated Transmission Solenoids, 2000 model water pump, spin on fan clutch and duramax fan.

2003 ECSB 4x4 6.6L - PPE Hot - MBRP 4" - 1/4 E.T. 14.74 ------- Sold
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Old 01-03-2013, 04:22 PM   #8 (permalink)
bigblazer
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The ecm doesnt see alt rpm. If the brake switch is bad it could be doing exactly what your talking about.mine wouldnt engine brake at all, then when slowing with the brakes to 35/40 it would buck locking and unlocking the converter. Remember theres a big heavy pedal hanging off the brake switch, just a little vibration on an over oversensitive switch could trigger your symptoms, even vibration you cant feel. By the way my brake lights always worked fine.
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94 Chevy blazer. 929 block, hd 4l80e, pmd relocated in bumper, #9 resister, ssd "80" hp chip, gm8 with DIY boost controller now 18psi, 3 down tube 4" straight pipe 5" tip, k&n cone, optic bump, kennedy injectors, boost/egt/trans/oil pres/water temp gauges, 3 core aluminum radiator w/dual fans, 98 "h.o" w/p with restricters installed, cowl hood. 4.10s in 14b semi floater, 35 firestone m/ts 8" rough country lift 3" body lift. Dos cientos quatro whp As of 2/21/13 thats all she's gonna put out!
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Old 01-04-2013, 01:47 AM   #9 (permalink)
Alexcantsleep
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Ill check that switch next, are their literally just two side by side on the pedal assembly?
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1996 Suburban, 3/4 ton, 6.5 Turbo, 4L80E, JD7 brakes, 4:10, 14 bolt rear end, front and rear air, 50,000 original miles. New IP and rebuilt Turbo. New AC Delco Balancer and pulley, Diamond Eye 4 inch exhaust, 2.5 inch crossover, Bosch glow plugs, HO water pump, dual AC Delco 190 degree stats, Dmax fan and clutch, Glowshift gauges on pod (Boost, Tranny temp and EGT), Angelo Fished PMD relocate behind grill, Lubrication Specialists oil cooler lines, 12 inch aux fan over oil cooler.
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Old 01-04-2013, 02:42 AM   #10 (permalink)
edzzed
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I have 4.10's and my tcc lockup is at 45 mph. If I do 44-46 mph it goes in and out of lockup on level ground unloaded. At 47 mph and above it stays in lock up unless I am on a hill or give it more fuel or place any load on the engine. The higher the speed, the more I need to give it more fuel, loads or steeper hills to drop out of lockup.
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