TH400 "break in" procedure.
 

I'm about to put a bow on a completely rebuilt transmission and brand new torque convertor installation. I'd appreciate advice for my first drive. My trans shop wants 500 miles before any frisky driving.

67 goat with a 428.

I jack up the rear end, fire it up and run it through the gears a few times. Check the fluid level, rinse and repeat. I also run Type F fluid.

No idea why you'd need to wait 500 miles to get "frisky".

It's not like GM gave new-car buyers restrictions like that.

I was told no heavy trailer towing for 200 miles after my 4L60 was rebuilt. But otherwise no restrictions

No break in period. Just fill it and go.

300 miles of driving, including some hard pulls. Then change the fabric filter to a screen filter.

Had to rebuild the TH400 and install a new convertor after a nitrous pass "ballooned" and internally grenaded the previous convertor. Flushed the lines and installed a new cooler, Installed it, topped it off with fluid, drove it around the block a few times to make sure everything was hunky dory, then loaded it on the trailer and went drag racing with it the next day.

Put the bird together from scratch drove it a mile down the road and back put it on the trailer took to track warmed it up and been pounding it the last 8 years no problems.

i bought a brand new th400 from TCI & it didnt say anything about break in. also just had a th350 rebuilt from an old timer thats been rebuilding trans for 50+ years & he didnt say anything about break in either. both trans are running great after 3-5 years & lots of low 11sec drag strip runs on the th400.

Start up, warm up, go thru gears without moving, and change the fluid. Do it again at about 300 miles with a filter, and I do another around 1000 miles for good measure.

You would be surprised what comes out on the 1st dump. Not many rebuild shops have clean rooms for transmission assembly.

Converters too, crap I've seen in them just pulling out of the box is insane.

Lockup converters do have a minor break-in period.

Always run a converter with an anti-balloon plate, even if you don't think you need it.

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Certain clutch plates do have a minor break-in period too....


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Make sure nothing leaks and send it!

I broke mine in one the engine test stand. Ran it through the gears, let it settle down, into reverse, back to a stop, through the gears etc. Then changed the fluid and filter.

Actually I was just seeing it worked ... seems to :)

I built my race TH400 trans ran it down the track 6 times one night and changed the fluid and filter. It's been flawless since with over 60 runs.

Thank you everyone.

This.... there's a "break-in procedure" for a TH400? :bounce:

I believe its a good idea to circulate the fluid prior to pounding on it.

You prime an engine prior to firing it up don't you?

Seems like an enormous waste of gallons of practically-new fluid to me.

IF (big IF) I were going to dump fluid and filter one or more times shortly after installing a new transmission, I'd be very tempted to pour the "old" fluid through a coffee filter and re-use it. A plain ol' ordinary paper drip coffee filter makes a pretty good ~60 micron filter element.

Alternatively, if you wanted a finer filter than that, pour the warm fluid through an aftermarket "bypass" filter as sold by Frantz or Amsoil. You wouldn't have to permanently install it--just figure out a funnel leading into the inlet hose, and a clean drain-pan or gallon jug on the outlet.

Or cram an inline trans filter on the trans cooler tube leading to the cooler. Change the inline filter, keep the fluid.

I can't see discarding fluid that's nearly new.

Absolutely no need to change the fluid or filter if it was built correctly. No break in period is required. Been building them for 40 years.

+2

No special procedures but it is imperative that the installer make sure the trans is filled correctly prior to the test drive.

I like to run them in for a few minutes on the lift with the rear tires elevated to check for fwd, reverse, and correct upshifts. Then top off if/as needed before putting the vehicle on the road.

If it works correctly during the test drive re-check the fluid once fully warmed up, top off if/as needed, and turn it loose.........