Okay so I've got a 78 f100 ranger, with a 351m borred and stroked to a 406, a c6 trans with 4.10 spool Adrian racing gears. It's always 4wheel drive no taking it out. I've replaced 3 flexplates by now and this time I need to replace my flex plate and harmonic balancer cause the rubber on it slipped and ripped. My dad who's been working on trucks all his life is telling me it's putting out too much torque and I need to downgrade to a 2wheel drive. I don't want to there has to be a way to fix my issue. I've tried racing flexplates and no luck.... I guess I should stated this earlier but it's cracked the flexplates that have been replaced. Does anyone know potential fixes? Would a rock climber type custom flexplates and harmonic balancer work or anything I can do to fix this. I don't see how spinning force(torque) is cracking a flexplate and not doing anything to the trans. The trans and engine build has 7-8k miles on it. (I can't supply pictures as it is a southern truck and I'm up north right now not with it. Just what I say is all I got)

 

Are you running the spacer plate or block alignment plate or whatever it is, between the block and the transmission? Not sure if a missing spacer plate is enough to strain the flex plate, but theoretically the torque converter could be pushing forward on the outer portion of the flex plate, while the center of the flex plate cannot go forward because of the crankshaft.

 

I'm not 100% would have to ask the guy that did it. I did it the first time and put it all back together the same way it came out just with a new plate. Second time paid someone now she's kinda sitting waiting for the third.
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Also check if the 2 a linemen dowels at in place.

Don't know how the do this but the crank & trany center lines have to be lined up.
One of them is off and why the cracked flex plates.
Dave - - - -

 

what torque converter? What stall? What is you oil pressure? Does this "high performance engine" have any measurable cap walk? Do you know how to check for cap walk? do you know what cap walk is? Is the converter "balooning" on stall and thrusting the crank? is the pilot bearing properly configured tothe torque converter nose? there are more than one pilot size in a hi top c6. What diameter converter are we running? conventional or spragless? Do you know? How many of these combonations did the "guy" build? one? yours? Pretty hard for even a pro to get it right the first time. Engine mount condition? Is this setup running stock ford mounts? With the one little stud? If so you better chain it. I know from experience. About 8 first place trophies from pump gas sled pulls in a 1978 f250 4x4 sno fighter. How many rpmis this fire breathing dragon turning?

 

Can you explain some of this stuff? I would like to know what it is
thanks Fert

 

A high performance engine and/or high rpm operation causes a condition in our rotating assemblies called deflection. What deflection is caused by is the crank shaft actually "bending" or "deflecting" and what that does is basically puts linear strain or excessive "thrust" against the block. The main bearing thrust is capable of handling this for all normal purposes, however at some point in time at 6000rpm and further north for that matter, deflection of the rotating assembly begins to overcome the available stability of the 2 bolts and the main cap as well as the block webbing.

A 460 has larger mains and more robust construction coupled with a shorter stroke, fundamentally making those engines less susceptible to crank shaft deflection, a 400 has a 4" stroke coupled with rather small mains,coupled with a 2 bolt block, making crank deflection much more attainable. A stressed 40+ year oldcrank, made of cast iron or whatever it's conventional construction is, is by laws of attrition not much able to withstand 6000+ rpm for any appreciable duty cycle whatsoever, especially hefting around a 5000 lb 4x4.

Cap walk is what happens between the cap and the block webbing when the crank deflects and exerts excessive pressure into the thrusts of the main bearing, this causes the main cap to actually shift around atop the mating surface of the block webbing. Refered to more commonly as "walking" and then developed into "cap walk"

 

torque converter ballooning.

 

What You Need To Know When Choosing A High Performance Torque Converter
explanation of torque converter anatomy. The one thing with today's technology over yesterdays (technology from the 1960s) is that we are able to measure gains of different modifications electronically, thus alleviating the guessing game of cam profiles, piston clearances, timing curves, ignition energy, and o2 sensors, so we no can sit in our garage, order a set of pistons, a pairof cylinder heads, and a split pattern cam, some gaskets and with the help of you trusty matco tool guy you can feasibly bolt together a very radical pump gas v8, I know, I have done it. no problem other than now we don't really have a good lower end to handle the abuse nor does a 50 year old transmission with some DIY mods like the punishment, the power is there, but how do we get it to the ground? Rubber compounds of modern radial tires are way more capable, roads are smoother and stickier so when we punch it, the old 700-15 bias tires that were installed in 1980 don't blow off anymore, now the lt metric 235/75 radial hooks and goes, WOW!! All I can say is WOW!! now all that excessive torque goes somewhere else since it can't roll smoke from the bias tires. U joints? Torque converter? Crank shaft?

 

bah just install a thrust bearing like we have on the main generator here at the plant, we make 1200+ MW at 1800 rpm... might be heavy but it will work ..

SERIOUSLY!! thank you for the info. knowing is half the battle

Fert

 

What do you use the truck for? You said it's always in 4x4 so if you drive it on the street like that when you go around corners it will bind up the drive train and that could cause several things to wear out prematurely.

 

That's alot of stuff I'm not too sure about. I'll see what I can do to look into it. And the truck is purely a toy that can go alot faster then what most people think it does. Also 4w burnouts are great on 35's

 

Well, you have your homework.