Th400 Slipping in 1st gear... and whining... - The 1947 - Present Chevrolet & GMC Truck Message Board Network

73CheyenneSuper20 · 01-11-2009, 12:20 AM

Background: It's a '73 C20 454 with a TH400 trans, not a daily driver, more of a weekend driver/ project.

What it's doing: It has started slipping in 1st gear, and has gotten worse every time I'm driving it. I drove it tonight and it really doesn't want to go in 1st, but once it shifts, it seemed to be ok in 2nd and 3rd. It also has a highpitched whine that goes with it, it whines regardless of being in a gear, neutral or park. I haven't noticed if it whines in reverse. Because it whines in park or gear, I think it's torque converter related. The whine has been there before the slipping, and was barely noticeable and then has just gotten louder.

Whats been done: Fluid level seems good, doesn't smell burnt and isn't black. I added a can of TransX and nothing happened. I added a quart of trans fluid and it got worse and started leaking. (The dipstick is chrome and kinda funky, it might not be accurate) I've been looking at other threads on here, but haven't found anything like whats happening to me. Have found a lot of other interesting info though.

What do you guys think? What is it? If/ can a torque converter go bad, what happens? Should I rebuild the trans? If I do, should I get a new converter? (Low budget)

Thanks in advance!

willett · 01-11-2009, 01:00 AM

tranny rebuild my friend.
i had the same problem not 6 months ago

James McClure · 01-11-2009, 03:23 AM

73. It's not the converter. The whine is the front pump failing. Only fix is an overhaul. jim

73CheyenneSuper20 · 01-11-2009, 10:49 PM

Crud. I used to hope the whine was a cam that the PO put in...
Thanks for the info.

1984 swb chevy · 01-11-2009, 10:54 PM

if your trans is going then you will want to replace your converter also. There may be metal in the fluid and it will be inside the converter too.

01-11-2009, 12:20 AM	#1
73CheyenneSuper20 Registered User Join Date: Nov 2008 Location: San Bernardino, CA Posts: 92	Th400 Slipping in 1st gear... and whining... Background: It's a '73 C20 454 with a TH400 trans, not a daily driver, more of a weekend driver/ project. What it's doing: It has started slipping in 1st gear, and has gotten worse every time I'm driving it. I drove it tonight and it really doesn't want to go in 1st, but once it shifts, it seemed to be ok in 2nd and 3rd. It also has a highpitched whine that goes with it, it whines regardless of being in a gear, neutral or park. I haven't noticed if it whines in reverse. Because it whines in park or gear, I think it's torque converter related. The whine has been there before the slipping, and was barely noticeable and then has just gotten louder. Whats been done: Fluid level seems good, doesn't smell burnt and isn't black. I added a can of TransX and nothing happened. I added a quart of trans fluid and it got worse and started leaking. (The dipstick is chrome and kinda funky, it might not be accurate) I've been looking at other threads on here, but haven't found anything like whats happening to me. Have found a lot of other interesting info though. What do you guys think? What is it? If/ can a torque converter go bad, what happens? Should I rebuild the trans? If I do, should I get a new converter? (Low budget) Thanks in advance! __________________ '71 C25 Camper Special, 402, TH400, Longbed, Power Loc axle, Figuring out the rest of the details.... '10 Dodge Charger SXT - DD '91 Kasel M101A2 3/4 ton trailer (It has Chevy rims!)

01-11-2009, 01:00 AM	#2
willett Another Day, Another Dollar Join Date: Nov 2008 Location: North Vancouver, BC Posts: 1,316	Re: Th400 Slipping in 1st gear... and whining... tranny rebuild my friend. i had the same problem not 6 months ago __________________ -78 K20 Cheyenne 454 long box, 4" lift, 35" MT's, '84 cab, '80 box "its hip to be square"

01-11-2009, 03:23 AM	#3
James McClure One shot, one kill. Join Date: Dec 2007 Location: Saratoga Springs NY Posts: 859	Re: Th400 Slipping in 1st gear... and whining... 73. It's not the converter. The whine is the front pump failing. Only fix is an overhaul. jim __________________ 1984 K20 350M engine with 465,000 miles. Well, it's finally done!! Almost 2 years of work, but it was really worth the effort. Little stuff left to do is mount winch, wet sand & buff out and build belly pan\running boards. Body work takes lots and LOTS of beer!!!! God, Guts and Guns made America and God, Guts and Guns will preserve it! The worst thing you could do is get into my sights, but that don't matter, you'll never know it, cause you'll never hear the shotJim or Paladin whichever you choose.

01-11-2009, 10:49 PM	#4
73CheyenneSuper20 Registered User Join Date: Nov 2008 Location: San Bernardino, CA Posts: 92	Re: Th400 Slipping in 1st gear... and whining... Crud. I used to hope the whine was a cam that the PO put in... Thanks for the info. __________________ '71 C25 Camper Special, 402, TH400, Longbed, Power Loc axle, Figuring out the rest of the details.... '10 Dodge Charger SXT - DD '91 Kasel M101A2 3/4 ton trailer (It has Chevy rims!)

01-11-2009, 10:54 PM	#5
1984 swb chevy Registered User Join Date: Nov 2007 Location: New Jersey Posts: 466	Re: Th400 Slipping in 1st gear... and whining... if your trans is going then you will want to replace your converter also. There may be metal in the fluid and it will be inside the converter too.



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