Torque Converter

[Tjbucket]

Gents,
Now that I got it fired up and carbs adjusted, a new problem has come up. I have a 350 SBC, with a powerglide and 3.38 gears. Just sitting as you rev the engine in park not bad, in neutral the car almost learches (maybe learch is strong....but you can tell it wants to move) forward. Secondly, when I shift into gear RPMs drop to the point of stalling the engine. I did replace the trans pan and found nothing wrong with the fluid and no material in the pan. My assumption after doing some reading is the torque converter is bad or locked up when it shouldn't be. So, now I am looking to replace the torque converter but, am unsure of what type to get. When I assembled it I did not see any markings or numbers on my current converter so, not sure what it has. I don't need something with a high stall, but, wondering what others maybe running. Or if the problem that I described may lead to some other problem??

 

[choppedtop]

This is what I am running with powerglide in roadster. APE34000 purchased from Summit. Pretty much for stock engines.

 

[PotvinGuy]

I run a B&M Holeshot 2400 converter with my crate 350 and TH400.

 

[Tjbucket]

This is what I am running with powerglide in roadster. APE34000 purchased from Summit. Pretty much for stock engines.

Thanks.....am I missing something or does it sound like that is the root of my problem?

 

[PotvinGuy]

Thanks.....am I missing something or does it sound like that is the root of my problem?

Oops. wait...you say it lurches when you shift into neutral? I'm not a 'glide guy, but that sounds like a tranny problem. There shouldn't be any movement in P or N no matter what the TC is doing.

 

[Tjbucket]

Oops. wait...you say it lurches when you shift into neutral? I'm not a 'glide guy, but that sounds like a tranny problem. There shouldn't be any movement in P or N no matter what the TC is doing.

Yeah, lurch forward is probably not the correct description.....but, you can tell and feel forward movement. I read on another site when setting my carbs, that idle drop a couple hundred RPM or greater to a stall indicated a bad TC? Just, don't know if there is even a way to rule it out or confirm that is the problem.

 

[PotvinGuy]

Yeah, lurch forward is probably not the correct description.....but, you can tell and feel forward movement. I read on another site when setting my carbs, that idle drop a couple hundred RPM or greater to a stall indicated a bad TC? Just, don't know if there is even a way to rule it out or confirm that is the problem.

Boy, I'd think any movement in P or N is tranny related. Any 'glide experts out there? When I shift into Drive the revs drop a bit, but not P or N.

 

[tdkkart]

The first thing I'd check would be the shifter adjustment, sounds like it may be partially in gear when the shifter says N.
What is your idle rpm?? Past experience is that with a stock converter the idle has to be down pretty low to keep it from
trying to pull forward, the higher the rpm, the harder it pulls.

 

[choppedtop]

I know that my p/g tries to make a little lurch forward in park when I first start the engine. After initial start up, it don't do it any more. I beefed up the clutch pack in the rear a little also. Don't know if that has anything to do with it or not. Seems fine as soon as everything warms up. Neutral is fine hot or cold.

 

[Tjbucket]

The first thing I'd check would be the shifter adjustment, sounds like it may be partially in gear when the shifter says N.
What is your idle rpm?? Past experience is that with a stock converter the idle has to be down pretty low to keep it from
trying to pull forward, the higher the rpm, the harder it pulls.

I will re-check all the detents and pin movement at each, thanks for the suggestion.

 

[PotvinGuy]

Tj, do you have a stock converter? What diameter? The dummies that built my first hot motor used a stock (about 12" diameter) TC and I had to stand on the brakes at a stop sign. The car would do 20 mph at idle!

 

[Gerry]

Standard converters are build to 'slip' at a stand still for heavy cars. Once a standard TC is in a light rod like a T it will try and pull it forward. I have a 350 350 and had the TC stalled by 400 rpm to stop this. The TC is dragging the engine revs down when you put it into gear, but you may have to up the idle speeda little. what idle speed do you have in P and is the cam a standard grind???
Also had a rod in last year (built in the 80s with a standard TC) and the guys said he had to lever on the brake pedal at lights to stop it moving forward. Had the TC stalled by 4-500 rpm and it solved th problem after years of him putting up with it.
You need a higher stall Converter but not by a lot. 4-600 rpm should do it. Any good trans shop could get it done on your original unit.

Dont forget a Gilde is a 2 speed....

 

[fletcherson]

It shouldn't lunge or lurch or load the engine or anything in n or p ever. That doesn't sound like a converter issue in itself. As for the converter selection, no offense to anyone, but you owe it to yourself to get all of the info together and call a reputable converter manufacturer to match it to your car and driving habits or you will likely be disappointed. You need to figure tire diameter, gear ratio, cam, etc. to get a good match so the converter engages at the correct rpm. Vehicle weight is a big consideration too. I think from your description, that you have something else going on. Did the trans work before? Make sure the linkage is adjusted and that the valve body is installed correctly with no leaks between the case and valve body. It could have some debris in a valve or any number of things. Even if the converter is locked up, the forward clutches shouldn't be applied in n or p, so that issue should be addressed before the converter, in my opinion, from my understanding of your description. Look at b&m, Tci, and other sites for some information about converters. They have trained techs that can help also.

 

[Tjbucket]

It shouldn't lunge or lurch or load the engine or anything in n or p ever. That doesn't sound like a converter issue in itself. As for the converter selection, no offense to anyone, but you owe it to yourself to get all of the info together and call a reputable converter manufacturer to match it to your car and driving habits or you will likely be disappointed. You need to figure tire diameter, gear ratio, cam, etc. to get a good match so the converter engages at the correct rpm. Vehicle weight is a big consideration too. I think from your description, that you have something else going on. Did the trans work before? Make sure the linkage is adjusted and that the valve body is installed correctly with no leaks between the case and valve body. It could have some debris in a valve or any number of things. Even if the converter is locked up, the forward clutches shouldn't be applied in n or p, so that issue should be addressed before the converter, in my opinion, from my understanding of your description. Look at b&m, Tci, and other sites for some information about converters. They have trained techs that can help also.

Fletch, my description maybe a bit on the exaggerated side.....what Gerry described above is more along the line of what is happening, which makes sense to me. I have no idea what cam I have as I did not take the engine apart and the previous owner had little to no information on it. The trans worked previously, well, I should say what little I actually drove it. I did nothing except replace the pan, did nothing to the valve body and the pan was clean and fluid was also. I need to get a hand held tach and actually see what my idle RPMs are.....it sounds right, but, that is a guess. I do have a bit more checking to do on the detents etc.

 

[Tjbucket]

Tj, do you have a stock converter? What diameter? The dummies that built my first hot motor used a stock (about 12" diameter) TC and I had to stand on the brakes at a stop sign. The car would do 20 mph at idle!

My guess is that it is stock and 12" sounds about right. I looked for numbers when I had it out and found nothing part number, name etc...Are you using a 10"?

 

[PotvinGuy]

Are you using a 10"?

That sounds about right. It was definitely smaller than the stock unit.

 

[fletcherson]

Fletch, my description maybe a bit on the exaggerated side.....what Gerry described above is more along the line of what is happening, which makes sense to me. I have no idea what cam I have as I did not take the engine apart and the previous owner had little to no information on it. The trans worked previously, well, I should say what little I actually drove it. I did nothing except replace the pan, did nothing to the valve body and the pan was clean and fluid was also. I need to get a hand held tach and actually see what my idle RPMs are.....it sounds right, but, that is a guess. I do have a bit more checking to do on the detents etc.

Ok, it threw me thinking it was pulling in n or p.... That infers the forward clutched are engaged, and that shouldn't happen. If you have a relatively smooth idle at low rpm, 600, 650, and good even vacuum, it's likely a stock or very mild street grind cam, which infers that the rpm power band is at a low enough rpm that a stock stall converter would work. The issue then becomes the weight of the car. Then what Gerry said is right on about raising the stall speed enough to allow it to idle and not pull. Look at some service tune up data for the type engine you have, and there will be vacuum numbers that will allow you to determine more closely about the cam. The reason that a " bigger" cam requires a higher stall speed is that with a bigger cam, the lift and duration are higher numbers and that basically moves the power band to a higher rpm, so with a stock type converter and a big cam, it's like letting the clutch out at idle and bogs the engine... Over simplified, but just a basic idea for anyone who doesn't understand the idea. I have heard of guys cutting open converters and modifying the turbine fins to adjust the stall speed, and re welding them, which is what I think Jerry was talking about, but I don't know of any commercial transmission shops that provide that service. There are professional transmission supply companies that sell re manufactured converters for a fraction of the cost of aftermarket, but you would need to know the stall speed for a specific converter for a specific application to end up with the right one, from my experience. I'm sure someone knows how to figure out the stall speed, but it's not advertised, or wasn't when I done this regularly... GM was good about parts intergangeability and you used to be able to take a converter out of a smaller, lighter car and put in a car with a bigger cam to get a higher stall speed. Typically a smaller diameter converter is a higher stall. You also gain mechanical advantage as far as leaving the line with a smaller converter as long as the car is light enough. The trick used to be a converter from a vega, 8" or 10"... A bigger diameter converter from a full sized car or truck will likely be too much for a bucket. Do your homework, pulling trannys is not my idea of fun anymore!

 

[Tjbucket]

Standard converters are build to 'slip' at a stand still for heavy cars. Once a standard TC is in a light rod like a T it will try and pull it forward. I have a 350 350 and had the TC stalled by 400 rpm to stop this. The TC is dragging the engine revs down when you put it into gear, but you may have to up the idle speeda little. what idle speed do you have in P and is the cam a standard grind???
Also had a rod in last year (built in the 80s with a standard TC) and the guys said he had to lever on the brake pedal at lights to stop it moving forward. Had the TC stalled by 4-500 rpm and it solved th problem after years of him putting up with it.
You need a higher stall Converter but not by a lot. 4-600 rpm should do it. Any good trans shop could get it done on your original unit.

Dont forget a Gilde is a 2 speed....

Just curious, what TC are you running? You say you had it stalled by 400 rpm?

Ok, it threw me thinking it was pulling in n or p.... That infers the forward clutched are engaged, and that shouldn't happen. If you have a relatively smooth idle at low rpm, 600, 650, and good even vacuum, it's likely a stock or very mild street grind cam, which infers that the rpm power band is at a low enough rpm that a stock stall converter would work. The issue then becomes the weight of the car. Then what Gerry said is right on about raising the stall speed enough to allow it to idle and not pull. Look at some service tune up data for the type engine you have, and there will be vacuum numbers that will allow you to determine more closely about the cam. The reason that a " bigger" cam requires a higher stall speed is that with a bigger cam, the lift and duration are higher numbers and that basically moves the power band to a higher rpm, so with a stock type converter and a big cam, it's like letting the clutch out at idle and bogs the engine... Over simplified, but just a basic idea for anyone who doesn't understand the idea. I have heard of guys cutting open converters and modifying the turbine fins to adjust the stall speed, and re welding them, which is what I think Jerry was talking about, but I don't know of any commercial transmission shops that provide that service. There are professional transmission supply companies that sell re manufactured converters for a fraction of the cost of aftermarket, but you would need to know the stall speed for a specific converter for a specific application to end up with the right one, from my experience. I'm sure someone knows how to figure out the stall speed, but it's not advertised, or wasn't when I done this regularly... GM was good about parts intergangeability and you used to be able to take a converter out of a smaller, lighter car and put in a car with a bigger cam to get a higher stall speed. Typically a smaller diameter converter is a higher stall. You also gain mechanical advantage as far as leaving the line with a smaller converter as long as the car is light enough. The trick used to be a converter from a vega, 8" or 10"... A bigger diameter converter from a full sized car or truck will likely be too much for a bucket. Do your homework, pulling trannys is not my idea of fun anymore!

Fletch,
Thanks for the information and yes, I am still looking into it but, everything is point in the direction of the TC. Really don't want to pull it If I don't have to, especially since I just put it together not long ago......grrrrrrr!

 

[SRM1952]

their has been a lot of talk on this forum about torque converters ---this one has a lot of talk of what others have run

www.tbucketeer.com/threads/torque-converter-selection.16206/#p

 

[fletcherson]

Just curious, what TC are you running? You say you had it stalled by 400 rpm?


Fletch,
Thanks for the information and yes, I am still looking into it but, everything is point in the direction of the TC. Really don't want to pull it If I don't have to, especially since I just put it together not long ago......grrrrrrr!

At least the bolts are clean! Lol...