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dont know squat bout automatics

chevyCowboy

chevyCowboy

I might be crazy but i ain't dumb
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im not sure what trnny it is but the automatic in my back up gasser truck 88 chevy 1500 350sbis acting really wired i think its a 3speed with OD its got 1 2 d and od dont knwo much bout automatics it dosent shift at the right times. It seems to not shift untill its is at really high rpms then it shifts hard and it dosent seem to down shift. i check the fluid and its is full iv never had a automatic before some one please help could it be the torque converter going out??
 
chevyCowboy said:
It seems to not shift untill its is at really high rpms then it shifts hard and it dosent seem to down shift.
Click to expand...

Converter is probably ok. TH700R4's have a 'Throttle Valve Cable' (TV cable) which controls the throttle valve inside the trans valve body. High mileage and neglected units wear the throttle valve (TV) bore out over time causing the TV to stick inward.-(that and dirt) This valve affects everything about the way the trans acts while driving.

It's a long shot but you could try disconnecting the TV at the throttle body linkage (or carb) and tug the cable several times quickly to try and dislodge the stuck valve.

The way to know for sure if it is stuck is to hook a 0-300psi gauge to the main pressure tap about 4" up from the shifter linkage and watch the gauge while pulling on the TV cable. The farther the cable is pulled, the more pressure. You can then get a good idea on the overall health of the trans by checking the pressures in all ranges (PRND321). Compare the pressures with known pressures in trouble shooting guides available.

...or take it to your local independent trans shop.:D
 
was that year vacuum or ecm controlled. bad vacuum connection will cause very erratic behavior. As well as stuck downshift.
 
Yes, 1991, a totally new trans when the 4L80E hit the market.

The 4L60E shares the 'spinning parts' and overall dimensions of the earliest TH700R4. (1982) That's where the similarities end.

Of course the 4L60E was in the lighter duty stuff.
 
And, if may add, the newest 4L65E that is behind the very powerful Vortec 6.0L gasser is basically a seriously upgraded 4L60E, from which, you can use the 'spinning parts' (5-pinion planetaries, beefier sun shell, all roller thrusts) and retro them into your old used up TH700R4 for your hot rod. All it takes is money. :thumbsup:
 
well i did a fluid and filter change over the weekend and didnt help so i took it to certified transmision and they tell me that 4th is gone and there is very little line pressure so the tranny is done:sad:

they want 960 for a rebuilt one :eek:

i called a local used auto parts store and they want 300 for one that they say came off a truck with 85000ish miles

and i found on that i guy is selling on craigs list put of a 4.3 v6 S10 that had 112000 and he bought for the motor said it drove great before he yanked the motor
i was thinking that the one outa the Sdime would prolly be a good bet sence it more than likly never got towed with and if it did nothing heavy
 
I know money doesn't grow on trees- well at least mine doesn't- but $960 for a rebuild isn't too far out of line. Is that with or without torque converter?

If you go getting another used unit you could be back in the same boat. Money NOT well spent.

I forgot to ask the mileage of the trans you are having trouble with. So is it over 100k?

Unfortunately the stock TH700R4's are configured from GM to have a 'comfortable' shift for a daily driver. This mentality is what limits these transmissions from a better lifespan.

On a typical 1/2 ton with a TH700R4 that sees towing service, DO NOT use OD (4th) Keep it in 3rd (D). I think that's even printed in the owners manual and even on a label in the door jamb. Not giving you hell here, just saying that GM kinda knew the TH700R4's were a little weak in the knees.

Best of luck.
 
i never even towed with the truck iv only owned it for bout 6 months and i want to get rid of it so i can buy another of our favorit trucks an 86 k30 6.2 na

al most forgot my truck has 186K
 
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