Ok, I never really understood how the torque converter worked, but now that I have had mine off and had the engine out and had a chance to look inside it, i have a better idea. (up until now, I wondered why the trans fluid didn't pour out of the bellhousing where those thin aluminum shields were, without any gaskets, etc....) BUT!!! Am I correct to think that the engine is tied to the tranny with only those four bolts, small ones at that, like 3/8 or 7/16"? It seems to me that the first time I nailed it those four bolts would shear right off. Am I missing something? What is keeping the engine and tranny tied together and not just shearing those bolts off and spinning freely?
Yep, that's all there is--- Four 3/8" NF thread studs. They're so short though, it takes more torque than you'd guess to shear them. The converter slips though and you'll never apply the torque needed to shear them.
Just seems kinda eerie that those four small bolts handle all the power that goes from the engine to the wheels... I got to looking around to see if I was missing something. Just doesn't seem right...
Might be a different story if the tranny wasn't also being held to the motor by 6 more bolts. You should really hear the motor if you leave the convertor bolts out like you can in a chevy motor. No resistance at all.
So, is the bellhousing bolted to the engine block also pulling the converter against the rear of the engine kind of like a rim bolted to a hub? So the friction of the crank hub also grabs the converter... does that make sense...hard to put into words. There is a "nipple" that slips from the converter into an indention in the rear of the crank. Is it all being pulled together in a way that part of the force is transferred through the two pieces of metal being pulled together, and not just those 4 bolts?
It's also a big factor that those are typically grade 8 bolts. If you just grabbed some random stuff from the hardware store they probably would sheer.
Scott, let me try..the flexplate is connected to the crankshaft...the converter is connected to the flexplate...the converter is driving the front pump in the transmission.(that's why it is important to seat the converter in the pump before bolting it to the flexplate).i didn't once and it took out the front pump this is why there is so much power loss with an auto tranmission...you are pumping the power to the rear wheels... ...Frank...:Handshake maybe Paul will get in here and get us all straight...
All the torque from the engine goes through those four 3/8 inch bolts to turn the rear wheels. the shear trength of those four bolts is well above any amount that your engine will produce. It may be hard to believe but a 3/8 inch bolt can lift 8835 lbs in a straight pull with no shock loads. (That is about 10 big block Fords) 80000 psi of tensile strength times .11 square inches. With an automatic the greatest losses are due to the hp to drive the pump and the inertial and frictional losses in the transmission. When you use a bolt to clamp a drive plate to the driven plate the clamping force adds to the shear strength of the bolt. If the bolt worked loose then it wouldn't last long because of the impacts that it would recieve with each power stroke of the crank. The losses in a C4 in a quarter mile are only about 35HP a four speed manual is close to 20HP and a three speed is about 18HP. If you add all the losses in the drive train you lose about 10 to 15% of the engine HP at the differential input flange. The differential loses HP at the rate of its gear ratio but it increases torque in the multiple of the gear ratio. So your rear wheel hp is always less than the engine HP as measured at the flywheel.
The "shear" strength of any bolt is far greater than the "separation" strength, so Paul's use of the 8835 lbs. is useless here. The shear limit of those four studs is many, many times greater than that 8835 lbs.
Okay guys. I can see in the near future this thread turning into another of those "I will not be proven wrong" threads, so before it does, let's just take a breath. By the way, I sheared my converter studs this past summer, but I think it was because I was a dummy and over-torqued them.
From my "Pocket reference" book: grade 5 bolt 3/8" 16 tpi Proof strength 85000 psi (tensile strength) Clamping force 4941 pounds at maximum torque (shear strength is less) shear strength not listed but I can find it if need be If you over-torque or under-torque the bolts its clamping strength is less. If you over-torque the bolts the tensile strength is less.
Your converter has play between the hub an tranny. Very important to check an verify that with it unbolted an all in place that the converter will slide app 1/8 in. I'm sure someone will chime in actual measurement. Manual trannys hit hard an only have 6-8 bolts holding pressure plate, and if you've seen a clutch look how thin they are where engageing the shaft. Put some play in them bolt holes an watch how fast you can shear them
No one was doing anything of the sort. I only pointed out that Paul used the wrong factor in trying to illustrate what Scooper was wanting to know.
