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#1 |
Senior Member
![]() Join Date: Jun 2014
Location: Bushwood, MD
Posts: 510
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RPM Drop When Torque Converter Locks
Hi all - I have searched for hours on the board here trying to figure out how much of a RPM drop I should expect when my 700R4 with a locking converter locks up.
Background - 350 SB, 700R4, 4:10 rear. The mech that put the trans in says it will only be around 200 RPM. I think it should be more. I'm not seeing/feeling it... Bottom line - I don't think the TQ is locking... Thoughts? TIA, Randy |
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#2 |
Registered User
Join Date: Jan 2012
Location: Henderson,TX
Posts: 336
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Re: RPM Drop When Torque Converter Locks
mine seems to be 200-300 rpm maybe 400
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#3 |
Registered User
Join Date: Apr 2011
Location: Klein Texas
Posts: 3,852
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Re: RPM Drop When Torque Converter Locks
Roughly 10% depending on load.
So if you're running 2500 rpm in fourth under light cruise the rpm drop should be 250 rpm with the converter locked
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My Classics: '72 K20 Suburban + '65 Dodge Town Wagon '72 Corvette Roadster +'67 Corvette Roadster '73 Z-28 Camaro '63 Ford SWB Uni Pickup '50 Ford Coupe |
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#4 |
Registered User
Join Date: Feb 2012
Location: Ruskin Florida
Posts: 4,559
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Re: RPM Drop When Torque Converter Locks
You should feel it. It is slight and correct for about 2-300 rpms. Mine is loud and rumbly so I can hear in the exhaust. I also have a switch so I can turn it off for testing and carrying heavy loads. You really shouldn't use fourth gear for towing or loads anyway.
I just got all the parts for my tach dash to confirm this just haven't had time to put it together and install it. What system are you using for the lockup?
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#5 |
Senior Member
![]() Join Date: Jun 2014
Location: Bushwood, MD
Posts: 510
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Re: RPM Drop When Torque Converter Locks
From what I can tell he only hooked it up for vacuum control. With the old inaccurate tachs we have (well me anyway) it's hard to see a small drop like that...
So if you guys are only seeing a small drop in RPMs then apparently he isn't blowing smoke... My best guess is I'm running around 2000/2100 RPM at 60 with the 4:10 and 29" tall tires. Does that sound close to what y'all are seeing? Again - thanks to all! Randy |
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#6 | |
Hittin E-Z Street on Mud Tires
![]() Join Date: Nov 2004
Location: Greenville, SC
Posts: 23,090
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Re: RPM Drop When Torque Converter Locks
Quote:
http://www.bowtieoverdrives.com/cata...php?ITEMID=332 A simple lock up test is to get up to cruising speed where you think it's locked up, and blip the throttle just a little bit, if the rpms move a good bit it's not locked up, if the tach barely moves, it's locked. A couple hundred rpm drop is about right. I have a 3.73 rear and I think mine only turns 2300 @ 70 mph so those numbers sound about right.
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Jesse James 1967 C10 SWB Stepside: 350/700R4/3.73 1965 Ford Mustang: 289/T5-5spd/3.25 Trac-Loc 1968 Pontiac Firebird: Project Fire Chicken! 2015 Silverado Double Cab 5.3L Z71 2001 Jeep Wrangler Sport 4.0L 5spd 2020 Chevrolet Equinox Premium 2.0L Turbo 2011 Mustang V6 ~ Wife's ride ![]() American Born, Country by the Grace of God ![]() 1967 CST Shop Truck Rebuild! My 1967 C-10 Build Thread My Vintage Air A/C Install Project "On a Dime" Trying my hand at Home Renovation! 1965 Mustang Modifications! |
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#7 | |
Registered User
Join Date: Jan 2012
Location: Henderson,TX
Posts: 336
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Re: RPM Drop When Torque Converter Locks
Quote:
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#8 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,594
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Re: RPM Drop When Torque Converter Locks
Punch in your numbers and check it out.
http://www.advanced-ev.com/Calculators/TireSize/ |
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#9 |
Registered User
![]() Join Date: Feb 2014
Location: West Iowa
Posts: 1,106
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Re: RPM Drop When Torque Converter Locks
Best way I have found to tell if the converter is locked is to lightly tap the brakes at cruising speed. If it is wired properly and working properly, when you tap the brakes the converter will unlock, the engine will speed up slightly. As soon as you return to cruising the converter will lock and the engine RPMs will drop again. Bruce
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#10 |
Hittin E-Z Street on Mud Tires
![]() Join Date: Nov 2004
Location: Greenville, SC
Posts: 23,090
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Re: RPM Drop When Torque Converter Locks
Did a little googling... didn't know about the vacuum switch kit. I'd still recommend using one in conjunction with a brake kit. Nothing like slamming on the brakes and having the motor stall with power brakes...
__________________
Jesse James 1967 C10 SWB Stepside: 350/700R4/3.73 1965 Ford Mustang: 289/T5-5spd/3.25 Trac-Loc 1968 Pontiac Firebird: Project Fire Chicken! 2015 Silverado Double Cab 5.3L Z71 2001 Jeep Wrangler Sport 4.0L 5spd 2020 Chevrolet Equinox Premium 2.0L Turbo 2011 Mustang V6 ~ Wife's ride ![]() American Born, Country by the Grace of God ![]() 1967 CST Shop Truck Rebuild! My 1967 C-10 Build Thread My Vintage Air A/C Install Project "On a Dime" Trying my hand at Home Renovation! 1965 Mustang Modifications! |
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