th400 second gear intermitent
 

transmission guys:
last week had my th400 transmission miss second gear several times ,but it was intermitent to where i was able to get 3 full passes out of thee eight atemps(you could feel it hit and then the motor hits the chip) ,get back to the pits and put it second and the gear held (flash the converter to 4000 in second) sometimes work and sometimes not,take the trans out bring it to my builder and tear it down,the trans is perfect no clutches burned,fluid red,checked the spags (witch i thought for sure would be the problem) but they look ok
my questions:can a sprag roll over and not break the outer race,is it possable that it could just not lock up
is it possable the converters sprag is bad and note the converter has only 4-5 % slipage

full manual tci valve body

any help would be greatful gmonde

Re: th400 second gear intermitent
 

First thing to check is the shifter and cable. Any slop at all change the cable. It may be going past or not quite getting to the right spot in the valve body every time.
Cables or sloppy linkage has caused more problems to not be a real issue.
Been there done that and felt stupid afterwards after pulling a trans 3 times taking it apart 3 times then fixed by changing the cable.
My 2 Cents

Re: th400 second gear intermitent
 

after the second pass attempt thats what i did,jacked the car up and make sure the cable was adjusted and didnt go past the detent when shifting ,,,,i wish it was that gmonde

Re: th400 second gear intermitent
 

what shifter do you have? We had a Hurst pro matic in one of our cars it did the same thing...it was a ratchet style & would not catch the notch sometimes! Sent the shifter back & go a new 1 no more trouble.

Re: th400 second gear intermitent
 

hurst quarter stick,solid gate operation gmonde

Re: th400 second gear intermitent
 

Just checking the detent is OK but I did the same thing 3 times before changing the cable.
Cables cause more problems than people think. If it is several years old I would still look at it. As a cable gets older it will get loose on the compression and stretch.
Like I mentioned earlier pulling the tranny out and apart 3 times with no problems found but changing the cable made me feel pretty dumb a few years back. The cable looked good and I thought it was good but changing it sure did fix the problem.
My 2 Cents

Re: th400 second gear intermitent
 

Yes, it is possible to roll a sprag and not break an outer race.

The sprag in the converter would not just affect one gear.

Do not do stall tests, loading the converter and not allowing it to release by launching the car will kill the converter.

Is this a new transmission, a new valvebody, a fresh rebuild?

Re: th400 second gear intermitent
 

this trans has 75 pases on it and worked flawless last season,tried a couple converters in this unit this year and went back to the converter that was used last year,and lost second gear,like i said we tore this down and it looked perfect ,clutches not even burned,the steels have no signs of chatter or burning (if it was a presure issue you would think it burn clutches)upon inspection of the sprag it worked as it should but there where a few small marks on the outer race but considered normal,
but if the sprag rolled wouldnt second gear not operate at all? or will it roll back and opreate normal until the load was recreated ??? gmonde

Re: th400 second gear intermitent
 

Have you tried actually replacing the sprag and the outer race?

Re: th400 second gear intermitent
 

i will change out the sprags and race before it goes back together,you just like to see something obviously wrong with a componet before throwing parts at it and hopes of repairing the problems as we all know it cost $$$ to get up to the track,to find out it didnt solve the problem

thanks for all the replys gmonde

Re: th400 second gear intermitent
 

Greg,I'm assuming you are using the smooth race 34element sprag. ....It's very unlikely you hurt the sprag, altho I've had one or two spin the inner race on the direct drum.......? are you using an aluminum drum?,very possible to spin a race on some of them ....Hard to find since the race is pressed onto the splines on the drum. ....Other than a sheared center support bolt,which feeds second gear, Id be looking at the valve body.....Tom

Re: th400 second gear intermitent
 

its not a 34 element ,we counted 17,but the replace ment will be the 34 element one ,that could be the issue gmonde

Re: th400 second gear intermitent
 

What rings are you using for the center support? teflon or steel? I had a similar problem where a teflon ring was smashed in the ring groove. caused similar problem i think it was temp sensitive, hot would fail, cold was ok. Good idea to replace the cable regularly.

Re: th400 second gear intermitent
 

teflon rings and they looked good they where not stuck in the grooves,but if it was a presure issue i would think it would show in the clutch pack, burned or marked clutches and or steels gmonde

Re: th400 second gear intermitent
 

The sealing rings on the center support are for the direct clutches and the sprag lube circuit ....they dont affect 2nd gear. ...... .the intermediate brake clutches in the case are actuated thru the center support anchor bolt....400's have been prone to sealing ring issues at the center support for years . ....some prefer teflon tings, others hard chromed iron rings. both work well when the drum stays off the ring lands ......ATI has a modified support with a floating bearing machined between the ring lands that helps support the weight of the direct drum, and keeps it from dragging on the ring lands ,which is really important with a stock iron drum at high rpm.,altho you really should have an aluminum direct drum for your application. ......Tom

Re: th400 second gear intermitent
 

It is your sprag if it does not hold no second gear. You said you have a 17 element which is stock they do not hold up to alot of power a couple of people make the double elements I used the Hughes never had another problem had to do it on a friday night at a divisional in Seattle. The tell tale sign of this is you hit the chip. I have ran S/G and S/ST for years with this combo.

Re: th400 second gear intermitent
 

The $2.00 snap ring that holds sprag in place is broke. I just went through this 3 months ago.On the street it worked great but twice at the track no second. If you guys watch Passtime my car is the Monte from the episode of AZ Fastest street cars in which it had no second and I thought I put it into neutral from coming down from a large wheelie.Sent meatl trash throughout the whole trans.
Jeff

Re: th400 second gear intermitent
 

When the sprag rolls it does not come and go in my experience. Stock sprag is really bad about rolling the elements. Should roll one way but not the other. Good call on the snap ring/spiral ring holding the sprag. Back when we ran 400's the ring was tigged in place.

Re: th400 second gear intermitent
 

the snap ring was in place,i will upgrade the sprag to the 34 element ,and try it out ,like mentioned it all looks real good ,no metal chunks,presure testsed the clutch pack for clamping presure ,checked detent for valvebody spool operation,tom your right should have the aluminum drum, but it is not in the budget for this month,thanks for the replys ,all of the info very helpful

gmonde

Re: th400 second gear intermitent
 

If your 2nd sprag has been slipping, it probably has hurt the surface finish on both the inner and the outer races. The surface finish is critical to the ability of the sprag to hold torque. The outer race is easy to replace. The inner one is ground true after being pressed on the drum, and should not be replaced. Best practice is get a different/new drum that is in good condition. Also make sure you get a 400 drum instead of a 4L80-E drum. The balance procedure on the 4L80 part might have compromised it's ability to be able to spin at high RPM. OK for a truck, iffy for a race car.