Why are automatic transmissions so mysterious? No one but transmission specialists seem to have the brass to open one up and do a rebuild themselves?
Are these transmissions REALLY that difficult?

How can one guy build a transmission with a gm rebuild kit and it stand up to a 400hp/tq beating daily, while another guy who builds the same tranny with the same rebuild kit have problems 4000 miles into the rebuild, burning up clutches and what not?
Is it just a matter of having certain clearances wrong? Any tech heads on here know of common problems/causes of premature clutch failures? post it up!

 

I am not sure but I know for sure that not many tranny builders know what the hell they are doing. I constantly see people with "built" tranny's breaking them with 12 second cars. Its ridiculous. I only go with Rossler, period. I have seen many other supposedly top shelf tranny's bite the dust prematurely. My stock tranny held up to a summer of street racing and track time (11.61 at 117+ mph) and is now slipping in second gear (hence the Rossler tranny going in). Other had cars running 11.9 or slower and breaking three Speed Inc and other tranny's during the summer!

 

Good post!! I know what you mean I read about "built" trannys going out after a few 1000 miles and stock units hold up for a ton of miles with high HP and a ton of abuse. I hope mine lasts a long time cause when it goes I'm not going to know what to go with!! One person will tell you to buy x brand and someone else will tell you that they had the same tranny go out after 5000mi

 

I've said this before but it holds so true I'll say it again:

70% builder

20% parts

10% luck

I've seen stock rebuilds stand up to major abuse and "performance" rebuilds will all the goodies die in 3 months behind a 375rwhp car. Mechanicly they're not that difficult. Setting one up and attention to detail is where all the magic happens.

 

Exactly. My question is, what is it that good builders do differently than the other guys? Any tech heads out there know?

 

i guess i'm going to find out this weekend cause i'm going to try my luck at rebuilding an aod out of my cougar. i've rebuilt a TH 350 a few years ago and it's still holding up and all i did was follow the manual so hopefully i'll have the same luck with the aod.

 

What I have seen that causes problems is OVERLY hard shifting. That will break internals in no time. You want quick tight shifting, barking the tires are 2500rpms part throttle is bad no matter what you hear. It's like putting an impact hammer on your internals, they will eventually break.

Also the 3-4 clutch pack...that drum usually gets smoked due to a lack of fluid flow as torque increases. What that means is addition of line pressure can't cure it...it needs to be increased via the seperator plate (what part of the TransGo shift kit does). I do not think that a 9 piece Alto setup is great despite it's numbers. The thinner clutches/steels will heat up faster and die quicker. You'd want a thicker setup like the Raybestos Blue Plate Specials, but I think you can only get 6 in there w/o mods to the 3-4 drum. (maybe an older TH350 uses slightly thinner clutches so you could add more?)

Haven't seen too many Forward clutches die or many broken 2-4 bands. I'd just imagine on those forward clutches that they just wear down. And a broken anchor on the 2-4 band is more probable than a smoked band.

Good builders probably have just built the transmisson so many different ways that they know what works and what doesn't. If I had the time I'd try to build one up and see what works.

Clearances are VERY important so with halfassed rebuilds you get what you pay for...crap work that is just tossed together. There are different thickness backing plate for the clutch packs, bearing end play is specific, 2-4 band clearance is specific, etc. All castings are different so there is not just a "one size fits all" for a hi-po automatic, they need someone who knows what to look for go through them.

With the best internal setup you still need to correct how the factory designed the valve body...for the average joe. TransGo makes by far the best shift kit for transmissions. They have been at it for around 40 years now and I install nothing but those shift kits in my vehicles. They are not just a seperator plate, they are an indepth kit that swaps out springs in the acutal valve body, adds springs to the stock/'Vette servo, adjusts band clearance, etc. The list goes on and on...basically gives you a trans that shifts quick and tight.

My 2¢