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Old 08-20-2007, 01:49 PM
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TH350 - What happened?

Pulled the pan on my TH350 today. The plan was to install a TransGo shift reprogrammer kit, a B&M 2400 stall converter, a new flexplate and a new transmission filter.

The transmission lives in a '79 1/2 ton pickup 2wd behind a warmed up 400ci small block. Stock rotating assembly with the exception of hyper flat tops, Edelbrock RPM heads, approx 10.25:1 compression, Comp 270H, Performer RPM intake, headers, and a Holley 750 Street HP. Probably a little less than 400hp, probably a little more than 400ft/lbs.

I understand the shavings in the transmission pan are well beyond normal wear, but I dont understand what came apart? The transmission shifted perfectly when cruising. At full throttle it slipped some from 1-2 but typically Id back off of the throttle and have no trouble. The 2-3 shift was excellent even under full throttle. The truck, and transmission have 63,xxx miles. The motor has 3,000.

Im afraid to install the fresh stall converter with all the foreign material that is bound to be lodged in the internals of the tranny. Im just curious as to what broke internally and why?
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Old 08-20-2007, 03:36 PM
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well cant really tell from the pics what its off of but if it was slipping in second i would have to guess it is probably pices of the intermediate roller clutch regardless the unit needs to be disasmbled and fixed there is a major failure in it that hasnt completley showed its rear yet
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Old 08-21-2007, 06:40 AM
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I wrote that incorrectly.
The transmission slipped some on the 1-2 shift. It held both first and second just fine.
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Old 08-21-2007, 12:05 PM
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350

JohnyR17, I have some advice for you, hopefully it won't tweak you out.

Do not install a shift kit into a transmission that has a problem, your words, "The transmission slipped some on the 1-2 shift". This practice will only frustrate you when you have to go back and actually fix the 'problem'.

You were right in stopping to get advice before going any further.

At about 400 horsepower the intermidiate sprag race, if it is factory, is in serious danger of breaking into a bunch of little pieces, sometimes damaging the direct drum [ high gear drum ] and the pump as well.

Although the pictures are a little blurry, I agree with performabuilt2, it looks like your intermeidate roller clutch failed.

The THM350, when properly built can withstand a bunch of horsepower and torque.
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Old 08-21-2007, 01:55 PM
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Quote:
Originally Posted by briscoe
JohnyR17, I have some advice for you, hopefully it won't tweak you out.

Do not install a shift kit into a transmission that has a problem, your words, "The transmission slipped some on the 1-2 shift". This practice will only frustrate you when you have to go back and actually fix the 'problem'.

You were right in stopping to get advice before going any further.

At about 400 horsepower the intermidiate sprag race, if it is factory, is in serious danger of breaking into a bunch of little pieces, sometimes damaging the direct drum [ high gear drum ] and the pump as well.

Although the pictures are a little blurry, I agree with performabuilt2, it looks like your intermeidate roller clutch failed.

The THM350, when properly built can withstand a bunch of horsepower and torque.
Agreed.

I use the 36 element sprag and drums in my higher HP TH350's. Even then I keep the 1-2 shift calibration reasonable.

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Old 08-21-2007, 03:04 PM
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Thm350

Jakeshoe, thats a good picture, clearly illustrates what we are talking about.

Maybe 5 years ago, I built a 350 for a pickup, big block w/ nitrous.

Held my breath on that one, but it hung in there!
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Old 08-21-2007, 03:16 PM
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I did a TH350 for a 383 (later 421) SBC in a full weight 1975 Camaro. I just used a 4 clutch direct with Alto reds, stock but new roller clutch, and hardened outer race. Modified TransGo 1-2 kit, and it made 660 ft lbs to the rear wheels with the juice flowing.
It was drag raced almost weekly for 2 yrs.
The only failure was the input ring gear. It was the two piece design. It broke when the car had a rear diff failure. Broke outwards from the 3 grooves that catch the thrust washer tangs. Bound up the forward clutches.
Wasn't the trans or builders fault, just normal stuff when a rear diff fails on a hard launch.
I use 5 BW tan frictions in the direct nowadays (cheaper and seems to be effective so far) and the drum setup shown. Other than that nothing fancy. Doubled up sun gear bushings, heavier PR spring, internally dual fed and block the 2-3 accumulator. 1-2 feed at .125-.135" and 2-3 at .140".

They work great. Almost 800 flywheel HP through a TH350 using an automatic VB.

I'm going to build one soon (to replace a TH400) using all the rollerized stuff from a late model unit, rollerize the sun shell to low inner race, probably only use 2 reverse frictions, and we're going to see how much ET we can cut off a mid 10 second car with the lighter internals, rollerized, and less clutch drag.
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Old 08-22-2007, 06:28 AM
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th350

Jakeshoe keep us posted on that one.

It is amazing how much a properly built 350 can take.

We've got one in a mud rail now, 800 hp, so far so good, but it is still early in the game.
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