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Sprag failure... Is it a GO/NO GO thing

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Rowdy

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Discussion starter · #1 ·
When a sprag fails, is it absolute. Without any catestrophic incident, my tranny just went whack. I have a detailed thread going in the tranny forum. After a vague reply by Jakeshoe, I thought a little elaboration might be found over here in performance.

This is NOT a manual valvebody TH400. My question is, can a sprag be "failing"? Or, is it either good or no good. First gear seems fine in manual 1st or drive. Shift to second is reluctant or nonexistent in manual 2nd or drive (I can't for sure say I remember. It F'd up leaving for work, so I returned home and parked it). Wouldn't manual second engage the band, overriding a failed sprag? Is the band simply not capable of disabling the drums rotation without the sprag? If so, should something resembling second gear be evident, but easily overpowered? Can the sprag be bad without tell tale debris in the pan? I have no irregular sounds coming from the tranny.

I guess this is more of a procrastination to getting out there and pulling the trans than anything. Grasping to the possibility that something might be hanging up in the valvebody. Since reverse, low and third (if I can get a 2-3 shift, which I can, just not consistently) still engage, that means that the forward clutch pack, the direct clutch pack and the low/rev clutch pack are all still functional. Which brings me back to the band and sprag. Oddly enough, in all my previous tranny issues, second was never an issue.
 
#2 ·
check the plastic gear in the govner I had one that stopped shifting and it turned out the plastic gear had stripped . there where no signs trans just wouldnt shift. is a th400 all stock. got a used gear from local trans shop for $4.00. he told me they go all the time and ppl rebuild or replace trans and all that is wrong it a lil plastic gear. so I would start there before you pull the trans.
 
Discussion starter · #3 ·
I have to remove the gov all to regularly because it sticks. The gear is good. I know that there is a lot of friction material contaminating the fluid. I'm deliberating whether to change/flush the fluid again or bite the bullet and pull the tranny again. Definitely not a stock TH400 (see sig).

I was hoping for something along the lines of, "definitely tha sprag", "sounds like the 1-2 shift valve", or "?", because........
 
#6 ·
You said you have to clean the governor regularly. That indicates metal is being constantly generated from somewhere. So, take it out and tear it down to find out where it's coming from. I have seen sprags fail intermittently.
 
#7 ·
So you dont have second gear?

Your Direct clutch drum turns twice engine rpm in LOW then when you shift to SECOND your direct drum goes to stopped, then you shift to HIGH gear and your drum goes to engine RPM

If your transmission still has the front band make sure it is good and make sure it is applying
 
#9 ·
the sprag is gone man!!!! i build a lot of th 400 transmissions. when you go back with the trans make sure you get an early stlyle high gear drum that will accept the aftermarket 32 element sprag, not the later roller clutch stlyle. i might have some of those drums laying around.....
 
#10 ·
SAJOMATIC said:
the sprag is gone man!!!! i build a lot of th 400 transmissions. when you go back with the trans make sure you get an early stlyle high gear drum that will accept the aftermarket 32 element sprag, not the later roller clutch stlyle. i might have some of those drums laying around.....
Click to expand...
Thats what i run but if memory serves you can get a 34 element sprag from Fairbanks {years ago} or ATI
 
#12 ·
The penalties of massive street power hope you get it sorted out:yes:
 
#13 ·
With an auto VB the intermediate band will hold the drum under light throttle. With a full manual VB with no engine braking there is nothing to hold the drum so NO 2nd gear.

A sprag can fail and still create some drag and hold at light throttle, and then roll over under heavy throttle and slip, but in a heavy car like a Chevelle, it will usually just slip all the time once it fails.

You have a failed sprag and a sick transmission, might as well do the inevitable.
 
Discussion starter · #14 ·
I kinda knew it. My reluctance to accept it was because it happened without any fanfare. I'm sure that anybody that has ever been in, near or within earshot of my car for more than 60 consecutive seconds would find this hard to believe. BUT, I pulled the car into the garage with 1st and 2nd functioning normally, an occasionally delayed shift to third and irratic downshift to 1st with complete stops in drive. Manually dropping into 1st was never a problem.

I changed the spin on filter, cleaned/feed the governor valve, installed a tranny cooler. and added a quart of fluid (was still one quart low). After casually backing out into the street, I slowly proceeded for three houses and turned onto a 25 mph street that had another stop sign within a couple of hundred yards. Something was felt different right away. At the stop sign, I don't remember if I had to put it in low, but I know that it wouldn't go into second. Trying all positions something began to shudder and actually started pulling me to a stop. I pulled to the right and stopped. Shifted between all positions, then turned back towards the house. The shudder nor the braking repeated itself. i never went fast enough to require shifting to higher gears.

After got a couple more quarts of fluid and topped it off, but didn't drive it for a day or two. Before I did, I again cleaned/freed the governor. No shudder or braking, but also no second to speak of. First was fine and I could get 3rd. It would hold through full grunt and as far as I wanted to push it. Second gear would free rev until it hit a certain rpm then act as though it had kicked down into 1st, which pulled normally.

I told you it's haunted.

What's a QUALITY 34 element going to set me back?
 
#16 ·
Sprag's dead for sure. Maybe other probs also judging by the debris in the pan.

I've rolled several 34 element sprags over the years in 10 second cars. Manual VB+rolled sprag=NO second gear.

I ran 2 points races shifting first to third, until I had time to fix the trans. Only lost a couple tenths but it was still consistent.

Jakeshoe built my new 400 with the 36 element sprag package for behind my 540. The trans works KILLER!:D

Thanks, Jake!:thumbsup:


Randy
 
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