turbo 400 causing engine front bearing failure?

Just talked to my tranny. guy and he said that there is a theory around that a turbo 400 can get so much pressure on it's torque converter that it causes it to expand and push on the engine crank shaft and cause the front bearings to fail.

Any truth to this and if so how do I prevent it.

Gary

 

not sure why...the rear bearing in a sbc is the thrust bearing

 

Gary
I've never heard of it. I got a lot of miles on an engine with a tricked out 400 behind it and the bearing seems OK. I guess I could tell you more once I pull it apart some day.

 

Only time I had engine bearing troubles when running a th400 was my own fault for downshifting way too often just to hear the tires chirp. Course I liked to let it upshift by running it up until the governor forced the 1/2 shift. The downshifting really loaded the upper half of the bearing shells. Was a long time ago...

 

We used to run the shit out of Turbo 400s in one ton trucks with big trailers, we never toasted a thrust bearing or even had a crankshaft failure cause catastrophic engine failure.

 

do they mean the fluid presure. like thrust pushing on the crank forward.?

 

Any automatic puts some forward thrust on the crankshaft, but it isn't enough to cause damage.The effective "piston" area is only the diameter of the torque converter snout, less than 2", and not a terrible amount of oil pressure acting on it. And as stated by belle, the thrust bearing is never the front one on any engine I have ever seen.
Why would a 400 be any worse than any other?

 

This was a problem on early P32 Motor home chassis. It is referred to as the torque converter disease. On the some early TH400's the torque converters would expand from the constant loaded condition of motor home service and prematurely wear out the thrust bearing on the 454 driving it. If I remember correctly some where in the early 80's they modified the torque converters to solve this problem.
Is appears a motor home is one of the most severe services a transmission sees since it is fully loaded every time it moves.

 

Not sure but I think he was talking about a turbo 400 behind a 454.

 

been running a 400 in my 55 chevy for 33 years ... no problems ...

 

You hit the nail on the head. That is what I am talking about. An '85 P chassis motor-home. Please don't delete this thread as it might be pertinent to other applications.

The motor-home has about 70,000 miles on it. It just had a heavy duty trans rebuild when the engine crank went away and a rebuilt engine was installed. It went about 500 miles and the front bearings went on it. I pulled it again and had it rebuilt but before I installed it I noticed the centering washer on the torque converter had broken off and was laying on the ground. I bought and a rebuilt torque converter and I have installed the rebuilt 454 and are wondering what to do to prevent this from happening again.

 

The cooler line should have around 40 PSI. The 400TH can exceed this sometimes a lot this causes the torque converter to want push itself out of the front pump. In doing so it applies pressure on the thrust bearing and will cause early failure. This is more common on motor homes and trucks as well as manual shift modifications and trans brakes. I have seen it on cars that were still under warranty as well but only a few.

A modification to
restrict the converter feed passage in the front pump.

Drill the existing hole to 21/64".
Tap the drilled hole with a 1/8 npt tap.
Install a 1/8 npt allen pipe plug.
Drill an orifice hole through the pipe plug. 7/64" is a good size. Do not go to small this will cause cavitation.
Draw a file across the face of the pump cover to knock down any raised metal caused by the orifice installation procedure.

 

Wow thanks. Think I might pop for this modification as soon as I can get to the tranny shop.

 

a diesel convertor has allways been the most used fix

 

Are they saying that the torque converter shell is ballooning or is it being pushed forward by the hyd pressure in the tranny ? I had a 400 sbc in the shop one time that had a destroyed thrust brg surface and it was from an auto trans car. I thought it was really weird. Fortunately I had the motor on the test stand sitting on a slight incline and when I would rev up the motor the crank would move forward and I saw it happen.

 

Just for future reference, this is commonly referred to as 'torque converter ballooning'.

 

It is not uncommon to have crankshaft failure on GM cars with THM 400
Here is what happens: the torque converter has a hub that fits the transmission pump and turns the pump gear. Since the hub is open, there is less surface area on the transmission side of the torque converter than the engine side (approximately 1.76 square inch less). When the torque converter is pressurized it wants to move towards the engine. Example: if the torque converter were pressurized to 100 psi, it would exert 176 pounds of force on the crankshaft.

This is not unique to the THM 400. All transmissions do this. The difference is: most transmissions have a limiting system that will not allow torque converter pressure to exceed 90 psi. The THM 400 does not have a pressure limit system for the torque converter. Because of this the THM 400 puts a lot of force on the crankshaft during high-pressure conditions

If the torque converter ballooned it would stay that way it is not made of flexible material. It would take little ballooning for it to split open.

 

Interesting thread! So, if I am following this correctly, a 400 trans produces this effect when it is in a high pressure mode and not all the time, unless it is under a constant high pressure situation like the P chassis motor home example. So, if it is used in a lighter duty application, like a 3000 to 4000 pound vehicle in normal street use, this condition is not encountered except when temporarily pushed hard ?

However, is the restrictor mod illustrated here recommended for any 400 as a "can't hurt, may help" situation?

Ray

 

Yup my buddy had that happen on a small blk chev with a 400 and an aftermarket convertor. It was so bad that the thrust surface was gone on the crank enough that the crank throw wore into the bearing saddle about an 1/8 of on inch!.........''.I dunno seems likes its gots no power''

 

Installing shift kits that raise the line pressure will sometimes cause the torque converter to balloon. You can order aftermarket converters that have anti-ballooning plated welded on them.

 

Billet/ re-enforced converter should take care of issue.

 

Ive eaten a lot of thrusts ,but we're drag racing a door car with 1600 hp and a trans brake. As someone said, theres two pressure reading in a 400, internal to the converter, and line pressure read at the cooler fitting. We limited internal, but the real trick was the converter hub where it indexes into the crank. Has to be a sliding fit, not tight. Put high pressure grease on the hub before you slide the converter in. We did have this problem with a powerglide in the past, same cure.

 

If I understand the explanation offered in prior posts, it isn't the converter "ballooning" that is doing damage to the engine thrust bearing, but rather the converter in it's entirety being pushed forward by high internal oil pressure. There is no retainer to hold the converter in place on the stator shaft or front pump. The converter is free to move axially, only being held in place by the flex plate.

So, if high internal pressure does exert a 'pushing' force on the converter, the flex plate/crankshaft take the load. Perhaps there is a circumstance in which the converter housing does expand or "balloon", but even if that is so, and countered with heavier/stronger converter case materials, the forward motion would still exist and overload the engine thrust bearing. That is what I gleaned from the explanation in posts above.

Ray

 

my friend had a balooning torque converter in a th350 that was causing problems.

 

YOU ARE 100% CORRECT. This is not a ballooning issue at all.

 

Oddly enough, I bought a 350 from and 70's big truck, it doesn't have a pilot bushing in it, nor doesnt look like it ever has, but has around .100 Crankshaft endplay, someone rebuilt it i.e. .040 over decked etc and the timing chain is a replacement also but the cam gear teeth are worn so badly you could cut youself on them. I was blaming it on China parts, don't know what to think now. I'm currently using as a set up motor and will complete the tear down when I'm finished with the mock up. This might be the reason?
Thanks for the thread!

 

Thanks guys you came through again. My transmission guy agrees completely and said he has done the fix before and will do it for me.

Probably saved me $5,000 that should pay for my Alliance membership for a while.

Oh and thanks Kevin and Ryan for not shutting down this thread.

Gary

 

Ok guys, here is the deal. ANY converter can (under pressure) balloon and cause pressure on the REAR main (Chevy) bearing. The cure is an aftermarket converter with a heavy plate welded between the converter and the hub. This has been a standard procedure forever. In most cases, unless you are making a ton of power and a heavy car, there is no problem.

 

You seem to totally ignore, or miss, the point that the converter is free to move toward the engine whether or not the converter case 'balloons'.

Considering the range of movement of a converter when one is installing a transmission, requiring the converter to be pulled forward to mate with the flexplate, it would appear that a converter would have to 'balloon' at least that amount (maybe 1/4" to 5/16" or so) before it would apply any pressure to the thrust bearing. That much swelling may very well be possible.

However, if the converter is being pushed forward by high internal pressure, even with no ballooning, it could and would apply excess pressure to the thrust bearing.

So, it is fair to say the excess thrust bearing pressure is not necessarily the result of ballooning, though it could be. Stated another way, there is more than one possible cause of the thrust bearing wear.

That is the deal........

Ray

 

x2 w/ us marshall anti ballon good quality conv.have killed a mess with a mud truck.