Rebuild th400 or 4l80e?

bucket said:

I installed a temp gauge in my Suburban, back when it was my tow rig and had a 700r4 in it. I ran a fairly large cooler and it was not plumbed through the radiator cooler. The idea being that I wanted to cool the fluid, not put it through a 190* radiator. I often thought about running it through the radiator, because in cold weather, the trans ran at around 100* during normal driving. Working the trans hard in the summer, if the temp got up around 220*, I'd always back off the throttle for a bit until it got down to 190* or so.

Are y'all suggesting that if I ran it through the radiator cooler, it would have ran warmer in the winter and cooler in the summer?

Also, at some point years ago, I saw some chart about trans temps in relation to the life expectancy of the trans. According to it, the life expectancy dropped WAY off with temps over 200* or so. Is there no factual truth to that?

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Ricko1966 said:

Factory gm used radiator cooler and auxiliary cooler plumbed in series. I think was a 2018. It's how I've done them for decades. Maybe I'm right maybe I'm wrong just how I was taught at work.

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NickTransmissions said:

Yes - never reuse one way assemblies in any transmission unless you like doing the job twice...While the ones in the TH400s/4L80Es are fairly resilient, if your luck is like mine, they will fail on you if you reuse them. Not worth the gamble to save a few lousy dollars, IMO.

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txaggie said:

It will screw down onto the shaft but it seems too tight.

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NickTransmissions said:

Your new aluminum 2-3 acc piston is threaded? I've never encountered that before.

It should have a smooth bore. You can use a press or vice to compress the spring to install the retainer clip. Test fit the piston without the spring then put a little assy lube on the shaft if it's a bit snug before installing it for the final time.

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txaggie said:

Not threaded but it won’t slide up and down on the shaft. Almost like the center hole of the piston is too small?

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NickTransmissions said:

Your new aluminum 2-3 acc piston is threaded? I've never encountered that before.

It should have a smooth bore. You can use a press or vice to compress the spring to install the retainer clip. Test fit the piston without the spring then put a little assy lube on the shaft if it's a bit snug before installing it for the final time.

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txaggie said:

Nick,

I am thinking of running this as an external cooler for the trans in addition to the cold case radiator internal trans cooler. Have you had any experience with these?

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NickTransmissions said:

I personally have not had experience with those particular coolers but if you do buy one, I'd blow shop air through it to see if there's any manufacturing debris...If so, send it back...Had a customer once that bought a cooler from either Summit or Jegs and hooked it up to a 700R4 I had built for his Silverado...It would not hold line pressure (needle was moving all over the place)...Brought the transmission back to me thinking it was a valve body issue but everything was fine...I told him to flush his lines/cooler out of an abundance of caution and he reported having a ton of metal shavings come out of the brand new cooler...I cleaned out and reassembled the trans...He sent the cooler back and got another one, which he flushed as soon as he got it...All was well after that.

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Bennyt said:

I'd rebuild the 400 and add a Gear Vendor.

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