lucas1979

So i just finished installing my th350 after a rebuild in my 79 t/a and i'm having problems with 1st and 2nd. When i come to a stop and let off the brake i can tell it's in first as for about half a second when i press the throttle it will lunge forward like it always has since i've owned it. Then it instantly shifts to 3rd gear and stays there. When i manually shift to 1st (Low on the shifter) it will do the same thing except instead of going to third, it seems to go to neutral or somehow engage? the clutches so that it will not actually move the car My question is this: could it be anything besides the vacuum modulator on a th350? does the detent cable really not matter on these 3 speed autos like it does on a 700r4 or another overdrive auto? right now my detent cable does not want to move at all unless i have the sleeve out of the detent slot. e.g. i can pull on the connecting rod that goes into the valve body assembly if the sleeve is off, but once attached, the rod will not move up into the sleeve. perhaps my understanding of how a detent cable is supposed to pull this rod is wrong. please help me, my car will move but i don't want to hurt the transmission as it's always been reliable for me

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sgt473

The detent cable is just for passing gear. the modulator is the torque sensing element to tell the trans how much load is on the engine so the proper pressure is obtained. Was a shift kit with a dual feed installed? If the detent is not fully closed the trans will stay in first gear for a longer time. How was the clearance on the intermediate clutch pack? was the pump replaced? Was the intermediate over running roller clutch installed and tested prior to assemble. If the mechanical parts are correct, you should have manual low and it should shift into second manually but at a higher speed, if the modulator, governor, and detent are adjusted some where close. Thats all I can think of now, hope it helps

lucas1979

no shift kit, it's all stock parts, the clearance on the clutch pack seemed fine to me, and it was the same amount of steels as in the original assembly, stock pump as well

i'm not sure about the over running roller clutch, i didn't have any tools to test anything while i was putting it together

a combination of the governor, modulator and detent were my first thoughts, you are saying that it won't manually shift into second unless i'm at a certain speed?

sgt473

If the trans is assembled correctly a manual upshift from first to second will varrify this. If the governor is working properly and the modulator has vacuum it should still shift manually, even if the detent is way out of adjustment. Did you replace the valve body gaskets if so did they match up with the original ones. Did you install the pump gasket correctly? Did you check the bolts on the steel plate in front of the valve body? Hope this helps

lucas1979

i am 100% sure the gasket was correct and the bolts were torqued properly, i checked and triple checked them

the vacuum modulator might not have vacuum as i think i have it hooked up to a thermal vacuum switch on the intake right now, and i read it is supposed to be hooked into the same vacuum as the brake booster?

i'm not sure i stated this in my OP, but when i manually shift into first, after i give it any throttle it feels as if the clutches engage (relating to a manual here, so it's like being in neutral) and i no longer have forward motion when i press on the throttle, it just rolls

i am going to try it with the vacuum modulator unhooked, then with it hooked into the brake same hookup as the brake booster and see how that goes, if i can get 1st gear to work that way, i will also try a manual from first to second

or should second work regardless of this little 1st to neutral problem?

lucas1979

i just tested manual first second and drive, in first it's not as i thought, it's more i push on the throttle then it feels as if the brake is on when i give it more throttle

when i shift into second it feels like second gear, takes a lot of work to move from stop, but it does work

i changed the vacuum modulator line to a different intake vacuum outlet with no change, but i didn't adjust it either (it is indeed an aftermarket brass can small style)

reverse works just fine as well, partial throttle or full, it will move it and spin the tires as it should

sgt473

How many intermediate clutch plates did you install? Was the trans from a 5.7 or a 5.0? Most 5.0's and six cyls have 2 usually the 5.7 have 3.
If it dad 2 fiber clutch plates and you added one this could be the problem. The intermediate clutch pack for a 5.7 should have 1 thick pressure plate 3 fiber driven plates,3 thin steel plates and one wave plate. The modulator should have manifold vacuum not ported. I you remove the pan you should be able to see the intermediate clutch pack from a small hole in the bottom of the case near the pump. You can check the clearence with a feeler gague. should have at least .060 clearence. Look for burned fluid and any signs of debris in the pan. By any chance did the modulator valve fall out when you had the trans apart?

lucas1979

it's from a 6.6 olds 403

in the intermediate clutch pack i have the cushion spring, 4 steels and fiber plates then the pressure plate on top of them

the modulator i never took out until i finished all the internal clutches' assembly, then i took it out to clean before putting it back and putting together the valve body

before i took the transmission out to repair, i had a blown front main seal and sometimes i would have very hard shifting when in D from a stop, it would rev as if in neutral and then hard shift into first at around 1000......i don't know if this information helps at all

thank you for all your help so far sgt473

sgt473

The 4 steel plates may be a problem. the only time I use 4 steels is when I remove the cushion spring for a firmer 1-2 shift.and add one steel. On most 350's there isn't enough room for an extra steel and a wave. If the original problem is usually caused by a pressure loss. some time the screen bolts loosen and some time you get an air leak in the suction side of the pump low fluid causes the harsh engagement when revving the engine. For first gear in drive range the forward clutch is applied. Second in drive range the intermediate clutch applies and locks the over running roller clutch. third gear the direct clutch comes on and the intermediate clutch is in effective. Unless check balls were miss installed and the clutched were assembled incorrectly the problem reverts back to the intermediate clutch pack. The trans does have a 1-2 accumulator but the original problem of not going into gear would not cause a problem in second. The part I don't understand is when you say it feel like the brake is on, that can only happen if two elements are applied at once. Meaning the direct clutch and the intermediate clutch, at that time the clutch with the most surface area destroys the other and it does feel much like the breaks are applied. That's pretty much how a trans brake works.It locks the trans in two gears at the same time . Also the trans may feel sluggish when starting from a dead stop, like a second gear start. Hang in there.

lucas1979

you are exactly right, if in D it will do a .5 second lunge in low/1st gear then shift directly into second and stay there no matter my speed (i can't get into 3rd at this time)

if i shift into manual Low/1st it will feel like that braking action i described after the same .5 second lunge

it sounds like it's definitely going to be a pull and disassemble job at this point, which is what i was hoping to avoid

as for the amount of steels i was mistaken and talking about the forward and direct clutches, i'm not sure about the intermediate and i will have to take a look at that

the checkballs i know are right as i had the holes marked previously and doubled checked with the metal plate layed atop of the valve body

sorry for running back and forth and all around on the symptoms of this

the braking that seems to be going on in manual 1st guarantees a clutch pack problem am i right? or could that still be a problem with perhaps shift valves not being where they are supposed to and allowing fluid to bypass?

sgt473

When you take it apart again, look at the governor bore, double check the clutch packs. If it's an 8 cylinder trans you should have 5 forward 4 direct and 3 intermediate driven clutched( fiber plates). Look for any signs of hot spots on the steel plates, look at the hub on the torque converter, check for excessive ware. Look real close at the pump bushing, you said it blow the seal, if in doubt replace the bushing and check the fit on the converter hub.If the valve body wasn't taken apart there shouldn't be a problem. varify that none of the valves are stuck. check the sealing rings on the back of the pump, sometimes a broken ring can cause a cross leak especially on the direct drum. Make sure the governor valve moves freely. Let us know how you progress?

lucas1979

when i replaced the seals on the pump it's possible i missed one, i know i had gotten steel rings (i think) and not the standard teflon, i put 2 of the teflon back on as they were skinnier and i didn't have replacements, would it be better to just go buy some teflon or replacement steel ones so i have them all for sure?

sgt473

The rings are different sizes if i remember correctly. there are two for the forward drum and there for the direct drum. I like the older rings. The teflon some times pose a problem in very cold weather. Before you reassemble the trans you can stack the drums on the pump upside down and air check to make sure all is well I usually do this to every trans, Some one here may have a blow up of the pump to identify the oil feed holes where you blow the air 90 pis will do the clutches should apply with very little air leakage.

lucas1979

sorry for taking so long to get back here and post again, i was in the middle of a move when this happened, probably part of the reason it did as the rebuild was sort of rushed

anyway, after moving the car to the new house, i did a manual drive in second and it drove normally, then shifted to D and it kicked into direct drive (third) so now all that's missing is first gear, sorry again for the mis-diagnosis, but am i still looking at clutch packs with only the first gear shifting far too early, and when in manual seemingly shifting out or losing fluid?

my thought is that it might be a mis-aligned valve or something in the valvebody not moving freely or properly, and directing fluid where it shouldn't go

sgt473

If you start in manual 1st and shift to 2nd then go to third. Will it hold 1 st gear until you shift? If every thing works ok manually and doesn't slip in any gear including reverse you may have a governor or valve body problem. happy hunting

lucas1979

well in manual first it has what feels like a braking action, at first throttle it will move, then change to the braking, as if it's being held back, when in drive, it does the same delayed action, but instead of the braking, it just shifts into second gear

i agree that it's likely the valve body or the governor, but i'm just not sure which to check, would it be one of the valves that's not directly connected to the linkage? most of these i didn't touch when rebuilding the transmission so perhaps one got bumped or moved during the removal/installation

sgt473

It sounds like your in to gears at once. If I remember correctly there were a few different valve body gaskets. uppers and lowers. The easiest thing to do is pull the valve body and go over the location of the gasket in reference to the spacer plate. Make sure that no holes are blocked and that the surface is flat and no miss aligned. If the fluid isn't burned you have a good chance of a repair.

lucas1979

i hope it's that easy

i used the smaller of the two gaskets i was given as i seem to remember the gasket being the same as the smaller one when i took it out, i didn't use any hi-tack to hold it in place, not even a dowel or bolt like i did with the pump, hindsight being 20/20 i probably should have

sgt473

Do I understand that you only replaced 1 gasket. Never use hi-tack if you need to hold it in place use petroleum jelly.it's one of a few things that will not clog the filter. make some dowel pins from a longer 5/16 bolt to align the vb and spacer plate. make sure the governor screen is in the right place. and check all the valves for proper movement. don't use anything but compressed air to clean the vb. while you have the pan down check the clearance on the intermediate clutch pack, you will be able to see the clutches at the bottom of the case right behind the pump thru a round hole. you must have at least .060 use a drill bit to check for clearance.

lucas1979

there was only 1 gasket to replace i thought :S when i was reading through my th-350 book it said i would have 2 but would only need the one that fit....or so i thought

i should have .060 between the clutch pack and the pump right? will have to wait until i can afford another 8 quarts of ATF though

sgt473

That's right. I've never had any luck with just using one gasket . Make sure you torque the valve body. they can warp and cause problems . If you take it down use a straight edge and make sure it's flat. Try a local trans shop they usually have the gaskets seperate so you don't have to buy a new kit. I'm sure you'll find the problem. good luck

lucas1979

yeah that would save me about 80$ on a kit

thanks for all your help sgt473, i will definitely post back when i get started and hopefully fix it