Th400 freewheeling in second

[75Monza]

Okay, since I noticed a th400 issue topic, thought I would bring mine up, this is on my 86 K20, 383, th400, 4.10's, 37's. About a month or two ago, I noticed that when I'm going down a hill going to work, I put it in second gear to keep the speed down since it's a 25mph zone that I typically reach 55 by the bottom if I don't lay on the brakes constant. While being held in second, as I start to go faster, motor is freewheeling so it drops to idle, can slowly step on the throttle and bring the rpm up till rpm catches up to the speed. I've ran across this before in a 76 K20 400/400 combo I had years ago, never figured out why this happens. Any Ideas on what might be happening?

 

[Honky Kong jr]

Okay, since I noticed a th400 issue topic, thought I would bring mine up, this is on my 86 K20, 383, th400, 4.10's, 37's. About a month or two ago, I noticed that when I'm going down a hill going to work, I put it in second gear to keep the speed down since it's a 25mph zone that I typically reach 55 by the bottom if I don't lay on the brakes constant. While being held in second, as I start to go faster, motor is freewheeling so it drops to idle, can slowly step on the throttle and bring the rpm up till rpm catches up to the speed. I've ran across this before in a 76 K20 400/400 combo I had years ago, never figured out why this happens. Any Ideas on what might be happening?

How steep was the hill and how was your fluid level. Was the pick up tube where it was supposed to be and was it cracked? Stupid plastic tube. Lol

 

[75Monza]

Probably around 7% grade. I have a deep fined pan on it with the filter adapter to get it to bottom of pan. Fluid level is fine, this happens on flat ground too. Get it up to say 35 mph and let of the throttle, RPM's drop to idle. Almost wonder if it is something to do with the Hayes XTM converter I put in. Another note of interest is that with the 8" lift, there is a good 2" drop kit on the crossmember to try and get less angle on the drive shafts, so on level ground, trans tilts to the rear slightly. This only happens when I keep it in 2nd instead of just putting it in Drive.

 

[HotRodPC]

Without looking at a Th400 diagnostic flow chart, IIRC sounds like the Intermediate roller clutch has let loose or the outter race has broke. All works good in Drive including 2nd gear? If it was first gear you had this problem, it would be a worn band or the defective servo sealing ring that operates that band. Hell, it might even be the front band for your issue and 2nd gear. I'd just have to look at the diagnostic flow chart to be 100% certain. Nonetheless, the transmission will need to be pulled and taken apart to fix it.

 

[75Monza]

Well, put it in drive, goes up through the gears just fine no slipping. From a dead stop can floor it and lay rubber till the start of second gear about 35 mph before full tire grab. At 55, can mash it and have downshift...not at 60 though. I know the tranny was gone through before I bought it, but don't know if they monkeyed with anything. What it acts like is a reverse valve body with no engine braking.

 

[74 Shortbed]

If it freewheels it's a band issue...

 

[HotRodPC]

If it freewheels it's a band issue...

I believe you're right and why I 2nd guessed myself when I recalled the 1st gear with no engine braking. Band or Servo issue. The intermediate clutch failure would be no 2nd gear propulsion.

 

[74 Shortbed]

I believe you're right and why I 2nd guessed myself when I recalled the 1st gear with no engine braking. Band or Servo issue. The intermediate clutch failure would be no 2nd gear propulsion.

That's what the band is for, build a drag race tranny with a manual valve body and the band is always left out don't need it.

 

[HotRodPC]

That's what the band is for, build a drag race tranny with a manual valve body and the band is always left out don't need it.

Right, neither one. Though I'll take that back too, isn't it the rear heavy band and servo needed for Reverse? I'd have to cheat and look at my chart.

 

[74 Shortbed]

Right, neither one. Though I'll take that back too, isn't it the rear heavy band and servo needed for Reverse? I'd have to cheat and look at my chart.

Yes, the rear one is needed, guess I should have mentioned that, lol..

 

[HotRodPC]

I'm not real familiar with some of the diagnostics without looking at the chart. Why? Because MOST of time, it really don't make a ****. I can waste time splitting hairs diagnosing a ruptured forward clutch drum seal or worn pump gears but does it really matter? NOPE it don't, because bottom line the transmission has to come out and be tore down and while you're in it, you may as well freshen it up with at least new clutches and seals, then bushings and steels as needed.

 

[74 Shortbed]

I'm not real familiar with some of the diagnostics without looking at the chart. Why? Because MOST of time, it really don't make a ****. I can waste time splitting hairs diagnosing a ruptured forward clutch drum seal or worn pump gears but does it really matter? NOPE it don't, because bottom line the transmission has to come out and be tore down and while you're in it, you may as well freshen it up with at least new clutches and seals, then bushings and steels as needed.

Very true...

 

[75Monza]

Thanks guys. Not exactly what I wanted to hear, but will work with my future plans in a way since I want more power, my plan was in a year yank the 383 and put a healthy big block in it, can just have a trans ready to go and swap everything at once. Probably should just leave it as it is, put I can't help myself, lol.

 

[HotRodPC]

Thanks guys. Not exactly what I wanted to hear, but will work with my future plans in a way since I want more power, my plan was in a year yank the 383 and put a healthy big block in it, can just have a trans ready to go and swap everything at once. Probably should just leave it as it is, put I can't help myself, lol.

Yep, I'd just drive it. It won't leave you stranded with a bad band. Just no engine braking in 2nd gear since the front band is toast or the servo is non op.