Average Th400 Rebuild Cost

every time I have built one for anyone the parts alone are what Jim said about 400 bucks now a days. and that's assuming your trans is old enough to use the upgraded spray. if not its wise to source a direct drum that will allow you to install a 34 element intermediate spray. this is a must in my mind, plus dual feeding the direct circuit which almost a 0 cost upgrade. just whatever an 11mm freeze plug cost.........but if whoever you take it to doesn't at least know what these 2 things are dont let them touch your transmission.

wow Jim, you can burn through one in 10 hrs..........shows what experiences gets you in time saving. I have only built 15 or 20 but cant do it anywhere near 10 hrs.

 

Hey Ben up to what year trans does the drum accept the new 34 element sprag? My trans should be a 69 th400 but may be a 72. Also excuse my ignorance but I've never built a trans before and what's is the dual feeding the direct circuit?? Can you elaborate a bit and what parts do I need for this?

 

I think to 71 for the drum. i also believe then 4l80e us the same drum with the smooth inner race allowing the use of 34 element sprag over the 16. this provided more than twice as much holding in 2nd gear.

dual feeding direct involve simple removing 1 of the sealing rings on the center support and or removing the inner seal on the inside of direct apply piston. once done you now need to plug the leak by install a freeze plug in the case on the correct side of the center support bolt.

this mod now basiclly allows the direct clutch to be filled by 2 circuits instead of 1, the piston will apply faster and you have a more even clamping pressures across the piston. the only cost is the 11mm freeze plug

 

Ok that makes sense now! By doing this simple mod essentially makes the trans stronger, correct?

 

yep. in 3rd gear your really only applying half the piston, this mod now uses the entire piston= more clamping force. the sealing ring to leave off the center support is the 2nd on down from the top. and passage in the case that plug cup goes into is the reverse feed passage........its the passage directly to the right of the center support bolt with the output shaft part of the case facing down. I use an 11mm plug cup but a think a 3/8 fits too just slighter deeper in the hole.

I also like to eliminate the 2-3 accumulator when I do this,. remove the spring under the piston in the valve body, take a c clamp or vice. crank it in remove the e clip, toss the spring. You also need to block the 2-3 accumulator feed hole in the valve body. This requires a 5/16" set screw and proper tap.

Tap the hole that feed the backside, or spring side, of the accumulator piston. Install the set screw. Re-install the accumulator piston.

What this does is eliminates accumulator function on the 2-3 shift. This results in a very positive 2-3 shift. You could leave 2-3 accumulator function in place and go slightly bigger on the feed hole. but with it gone about .110-.125 feed hole for 3rd feels nice to me on the street......in my race trans I use .140. remember the bigger the feed hole the harsher the shift, you can go too hard. the 3rd feed is also used for reverse so too big will make reverse harsh engaging too. I normally do the 2nd feed hole slightly under the 3rd, and try to not go more .125.......my race trans has this also at .140. I only did this after putting in my forward shifting trans brake valve body.......my 1-2 shift seemed a little slower.

I remove the big inner spring in the rear servo, make sure the clutch packs and end clearances are in spec, new bushing, make sure the valve body isnt sticking or worn bores, you should should have s nice shifting trans, just daily in the governor to taste afterwards and enjoy

 

I appreciate your tips Ben. I'm going to have to read over your last post a few times to fully understand how to do that part LOL

 

I'm sure if you Google it someone has a video out there or pictures

 

Not trying to butt in, but the only issue with using the 4L80 drum is for some reason Hydromatic decided to eliminate one of the feed holes that was present in the old 400 smooth race drums. On a standard manual or auto shift valve body the lack of the extra feed hole is no big deal. The issue is on transbrake installs. The reduction in fluid release with only one feed hole slows transbrake release ever so slightly. It’s a small change, one that so far everyone I have talked with has been able to compensate by changeing delay box settings. My “butt-O-meter” can’t feel the difference, but it does show up on a time slip.

 

I always drill a tiny 1/16th hole in the direct drum. under the piston, running at an angle out. 2 reasons helps that drum release on the brake, and helps with centrifical apply. fluid trapped in there can actually start to apply that clutch in the higher rpms.

I have never used a 4l80 drum but heard they can be used

 

I do the same, and for the same reason I install all 16 return springs. I save the direct clutch springs from transbrake builds to add the 2 springs that hydromatic omitted.

 

Hey Chris any progress on the trans rebuild?

 

I still haven't gotten to it. I just did my rear disc brake conversion and about to rebuild the front end with all new steering and tubular control arms and 2in drop springs and new shocks. So a lot to do. But I could see the rebuild happening in about 3 months or so. When it does I'll update my progress.

 

I hear ya, always something else to do! I will be starting my rebuild hopefully beginning of April and I will start a thread with my progress. I just ordered a borgs&warner 34 element sprag yesterday

 

That's awesome, I look forward to seeing your progress!

 

If you are having the transmission rebuilt by a reputable shop,$1,000.00 or less is going to get you an OEM to mild rebuild. Nothing crazy,but dependable and reliable. $1200.00-1500.00 will get you some upgraded parts for your higher HP/torque street/strip applications. If you have a core that is 72 or older,it will have the better drum/sprag in it already,so make sure you aren’t paying for something you already have. Most places only mention the red clutches,as if that is the only thing that exists,and for what you are doing,those will be fine,but there are also blue,green,and black,which are different levels of aggressiveness. However,you can have the case machined to accept an additional clutch,like some of the Olds W30’s and Stage 1’s did from the factory. It can only help. A Trans-GO or TCI stage 2 shift kit are both the same. They come from the same plant,but they just color the parts different for TCI vs Trans-Go. Get a deeper pan and matching pickup to hold more fluid,and run a good transmission cooler. I like to run a separate one without the radiator. Let the radiator cool the engine. And do NOT run one of those remove oil filters for the transmission. They work fine for an engine,but they are too restrictive for a transmission. The fluid can’t get back to the transmission quick enough,and you will do harm to the transmission.

 

$500 bucks???

yea 30 years ago ,even cheaper at any local trans shop and usually only what was wrong with it was rebuilt .
3 month warranty

 

hey chris, how did the th400 come out at the end? may be needing a rebuild soon.

 

I haven’t opened it up unfortunately, just haven’t had the money and now I’m getting married so really no money to throw at my car. I’ll update it when I do it though

 

I have used Larry a couple of times and had excellent results here in Sarasota

 

Hey Doc,
I reread my post 3 times and can’t see where I said it was Larry? But it definitely was. He’s a great guy and a wealth of knowledge. He rebuilt the tranny and installed one of Jim’s 9.5” converters and my ET went from 13.3 to 12.5.
Cliff