TH 350 Problem
 

Hey guys I'm a senior in high school. I have a 72 GMC C20 350/TH350. Trans was rebuilt last fall. Dropped it and reinstalled myself. It was built by AAMCO. I always babied it along as it is my baby :gmc2:. Well in March the truck decided to catch on fire when I was driving it to school for the first time this season:censored:. Well I rebuilt the truck and replaced just about everything. I got my hands on a 450HP corvette 350 motor ;). Well I decided I wasn't going to buy a new trans because it was just rebuilt so I figured I run it until it dies then get a nice built one from Monster Transmission. I also decided to stay with the stock stall converter to make it a little easier on the trans (not as hard of a launch). Consequently, I have to have the idle set at like 1500-1600 otherwise it dies when in gear (cammed engine probs). Anyhow I recall when I drove it for the first time it was pretty sketch because it was far from being finished. I didn't have a vacuum line running to the modulator so I just used L1 and L2 to go around the block. But if I remember right "D" always worked fine it just didn't shift out of first because there want a vacuum line to the modulator and I'm not going 45-50MPH around the block to make it shift. Well now it will not into D. But reverse and low 1 and 2 are fine still. When you shift into D it makes a terrible noise and it sounds like something is spinning and possibly thrashing around in the trans but there is no power to the wheel and the engine RPM's are as if there is no load. If I go from D to reverse it makes another bad noise and SLAMS into reverse. Probably because what ever is spinning is suddenly stopped and must spin the other way. IDK tho!!!!! I also recall like the second time I drove it or moved it in/out of the garage it would sometimes be fussy about going into D. But I would always be able to make it to move. However, now I'm questioning myself if I was just putting it in low. Also when you go from D to park and it making that bad noise it will continues for a few seconds even though it is in park. I did some research and someone said his grandpa told him if it pops out of gear hit the brake and giver her some gas as dirt can clog the valve body and this gets it out. and when it does it will slam into gear. Another post i saw mentioned the roller clutch not engaging. I'm not sure what I can do about that without dropping it and having it rebuilt. I called AAMCO they weren't much help. They told m my forward clutches were fried. Then I told them they built it last year and then he got defensive and thought I was mudding and blew it up. Well sir its a 2WD truck and I always babied it. Plus I'm running a big AUX cooler. He seemed to think something broke internally. Well all I know it I was cruising along fine with it before the fire at 50MPH. I don't think the fire really affected the trans at all because the plastic vent is still intact so that why I decided it was probably ok to reuse. ANY advice would be much appreciated!!!! I was hoping to get some life out of that rebuilt tranny but if not then I guess I'm going to be fessing up $1500+ for a trans from monster, and a higher stall converter haha.

Re: TH 350 Problem
 

Also if I go from low to D it will stay in gear.

Re: TH 350 Problem
 

Hook up the modulator and see what happens.

When it caught fire, did you slam the brakes and do a panic stop and throw it into park while still moving by chance?

Re: TH 350 Problem
 

No I coasted to a stop it died on me I didn't even realize that it was on fire until I stopped and smoke came up from under hood haha. My EX friend told me I had been smoking far like 1/2 a mile before it died. No idea why he didn't try and signal me or anything. Anyways I did hook up the modulator a month or so back and I double checked I had vacuum. I never put a gauge on it or anything, just used my finger. I have a gauge that I could check it with if you think I should?

Re: TH 350 Problem
 

stay away from monster transmissions they have alot of bad reveiws get a tci

Re: TH 350 Problem
 

If you go directly to L1, is there any noise?

Check the trans fluid level?

http://www.lsxtv.com/tech-stories/di...transmissions/
This site mentioned that not having the modulator could burn out the clutches. Do you have a steel modulator line?

Checked the pan extra parts?

Re: TH 350 Problem
 

Shifts fine directly into L1 or 2 for that matter. Fluid level looked good I added some more just to be sure though. Yes I have my modulator hooked up. I never had the pan off but like I said it worked fine before the fire. All I did was pull it out with the old motor and drop it back in with the new motor. I replaced the dipstick and detent cable as they were both toasted pretty good at the top.

Re: TH 350 Problem
 

Idle is way too high in my opinion - need to do whatever it takes to fix that first.. Stock idle is more like 580 to 650 for my TH350 in a 290 HP 350 Cubic Inch V8 with a stock Corvette HP cam (but sounds like you have even more HP than that) - But at least your extreme high idle is affecting your vacuum levels which is then affecting your trans valve body logic. 1500 RPM is well into the jets and the butterflies are completely out of the idle circuit, so vaccum is lower than it should be at idle.

Then if those steps don't fix things I would worry about how the converter was bolted up to your new flexplate.. That install is kind of tricky for me anyway...As in which bolt goes in first and assuming you get the right one in first did you torque that one all the way to spec before putting the other bolts in or did you install all bolts finger tight first and then tighten the rest sequentially? (some bolt holes are slotted and one is meant to be dead on). Did you use a torque wrench to cinch the converter to the flex plate?

Why did it catch on fire anyway?

Next (or even first) I would worry about the trans fluid level - It needs to be checked with the engine warmed up, engine running, select each dear position for 15 seconds, then finally in Drive, Parking brake on and idle speed at spec of course.. and you need to have the correct dipstick - then you can't have any extra fluid in the trans.. that will just foam it all up.. The fluid level needs to be just right and it is only one pint between low and high on the dipstick - not a quart as many people assume.. If it is above full get a $6 drain plug kit and drill the 1/2" hole in your pan in the flat spot provided..

Actually I wouldn't spin that motor up again until I pulled the transmission pan to check for any extra parts as one previous poster so wisely pointed out..

Finally do the checks for the modulator as in the books.. money well spent for the Cliff Ruggles TH350 book - less than $20 - No transmission shop is going to be interested in making $20 so start with the book and a little patience..

https://books.google.com/books/about...d=Fj9bCQAAQBAJ

Re: TH 350 Problem
 

Forgot to mention - was there a pilot bushing in that Corvette motor? If so you would have needed to either remove it or driven it in so it would clear or not interfere with the fit of the torque converter..

Re: TH 350 Problem
 

Member clinebarger is the resident trans expert, send him a PM

Re: TH 350 Problem
 

[QUOTE=Gromit;7450387]Idle is way too high in my opinion - need to do whatever it takes to fix that first.. Stock idle is more like 580 to 650 for my TH350 in a 290 HP 350 Cubic Inch V8 with a stock Corvette HP cam (but sounds like you have even more HP than that) - But at least your extreme high idle is affecting your vacuum levels which is then affecting your trans valve body logic. 1500 RPM is well into the jets and the butterflies are completely out of the idle circuit, so vaccum is lower than it should be at idle.

Then if those steps don't fix things I would worry about how the converter was bolted up to your new flexplate.. That install is kind of tricky for me anyway...As in which bolt goes in first and assuming you get the right one in first did you torque that one all the way to spec before putting the other bolts in or did you install all bolts finger tight first and then tighten the rest sequentially? (some bolt holes are slotted and one is meant to be dead on). Did you use a torque wrench to cinch the converter to the flex plate?

Why did it catch on fire anyway?

Next (or even first) I would worry about the trans fluid level - It needs to be checked with the engine warmed up, engine running, select each dear position for 15 seconds, then finally in Drive, Parking brake on and idle speed at spec of course.. and you need to have the correct dipstick - then you can't have any extra fluid in the trans.. that will just foam it all up.. The fluid level needs to be just right and it is only one pint between low and high on the dipstick - not a quart as many people assume.. If it is above full get a $6 drain plug kit and drill the 1/2" hole in your pan in the flat spot provided..

Actually I wouldn't spin that motor up again until I pulled the transmission pan to check for any extra parts as one previous poster so wisely pointed out..

Why would the idle speed matter? My vacuum is going to be lower anyways because of my cam. I thought the modulator just affects when it upshift not going into gear period. My plan was to adjust it to shift earlier to compensate for the lower vacuum. Now I did replace the dipstick because the old one was burnt and the rubber seal at the top was burnt so every time you messed with it little bits of burnt rubber would go down the dipstick. I think I checked to be sure that the levels were the same. I ordered it from AZ and they said it would fit my tuck. If the fluid was low I don't know why it would only affect drive. and it would have to be REALLY low for it not to go into gear. I had a blazer with a 700R4 that they guy only put a quart of fluid into it consequently, one minute reverse worked the next it didn't. He thought it had a broken drive shell. Added, fluid it worked fine. point is it would need to be really low. I added additional fluid, but it made no difference. As to why it caught on fire I think the culprit was a brake line connector that was rubbing on the header. it wore all the way through so I think brake fluid caught on fire and it went down hill from there.

Re: TH 350 Problem
 

Are you putting 450 horse to stock rebuilt turbo 350?

Re: TH 350 Problem
 

Yes haha, I know it sounds dumb but I don't want to let the $1100 I spent on a rebuild go to waste. As long as I don't beat on it I'm sure it'll last a while.

Re: TH 350 Problem
 

[QUOTE=Gromit;7450387]Idle is way too high in my opinion - need to do whatever it takes to fix that first.. Stock idle is more like 580 to 650 for my TH350 in a 290 HP 350 Cubic Inch V8 with a stock Corvette HP cam (but sounds like you have even more HP than that) - But at least your extreme high idle is affecting your vacuum levels which is then affecting your trans valve body logic. 1500 RPM is well into the jets and the butterflies are completely out of the idle circuit, so vaccum is lower than it should be at idle. =QUOTE]

Then what happens when you started it on a cold morning with the choke and high idle activated and put it in gear without hitting the gas a little to take high idle off? High idle is like 1500rpm

Re: TH 350 Problem
 

I fear you may have voided your warranty.

Re: TH 350 Problem
 

Why? because of the fire?

Re: TH 350 Problem
 

Ok I am no transmission expert but I was looking into a book I have on the th350. In there is a chart showing the mechanical power flow. In D1 it says it uses the forward clutches and the low roller clutch. In L1 it uses forward clutches the low roller clutch AND the low/reverse clutch. Here's where my lack of expertise may be showing. But I'm guessing normally in low, power is distributed between the low roller clutch and the low/reverse clutch. Assuming my roller clutch is the problem all the power goes to the low/reverse clutch. But since D1 doesn't utilize the low/reverse clutch I have no power to the wheels and it makes a whining noise. Is that perhaps the issue????????

Re: TH 350 Problem
 

PM Clinebarger, he'll have a good idea of whats going on with it...I dont know the specifics of the warranty AAMCO gave you but if it's still in effect then I would show up and talk to the man in charge and let him drive it? Whats the chance of burnt rubber debris getting down that filler tube and clogging the valves? That fire (whatever the cause?) at the back of the motor getting hot enough to burn the dip stick seal would have burnt the kick down cable as well? Whats the story on the kick down (Detent) cable? was it properly hooked up and set? Nothing wrong with running a THM350 behind a 450HP motor as long as it's been built with aftermarket components like a hardened intermediate sprag race and a wider low roller clutch & support. I've been running a "Monster Transmission" stage-2 HD 350THM in my 400+ HP big block C-10 and so far, so good, it's held up for 6 months so far. I wish I had known then what I know now in that the only bad rap I can put on Monster Transmission is they are WAY overpriced! You need to either get your existing 350THM rebuilt to handle 450HP or cut your losses and buy one from a reputable builder that stand behind their work, they are out there...One more thing, if your motor aint right, your tranny cant be right especially with radical cams and stock vacuum modulated shift tranny's! That idle issue is reaping havoc (or reaped) on that tranny? AAMCO first, if the warranty is voided, then it's time to match a transmission to the motor...Then you'll snap u-joints and tear up rear ends, 450HP aint no punk. "just sayin"

Re: TH 350 Problem
 

^^^ What Ironangle said ^^^. You need a lot of updated components on a th350 to handle that many ponies. And that idle is really high.
Best of luck.

Re: TH 350 Problem
 

If this trans is blown I'm not getting it rebuilt. I know it wont handle this much power but I didn't want to just throw this trans away. I saw a stage 1 350 on JEGS for less than $1000. Stage 1 means up to 450 HP perfect! ! I'm not sure about a warranty I didn't see one mentioned but ill look into it should the need arise. Detent cable was replaced. fire was caused by a brake line that was rubbing on the header and wore through. I purposely set my idle high because I kept the stock converter and it would kill the motor when put in gear because it is cammed and makers like no HP at idle. and I did PM Clinebarger