SBC 350 vibration cause?

I got the front end alignment done today. My home done toe in and camber were actually pretty close but the caster was way off. It’s good now. I left the shop and got about 1/2 mile down the road and the car quit. It was raining hard. I assumed it was wet ignition. I phoned the shop back and they came and towed it back to their shop. The mechanic diagnosed the problem as a bad coil. Who new. It’s running good now with a new coil in it. Unfortunately that didn’t solve the vibration issues.😄
 
If your running a a 200 r4 behind your sbc . I,m thinking more then likely your running the flex plate that would go with the transmission . I,m not that big on sbc stuff but I think the flex plates that go with the 700 an 200,s have balalnce weights on them and a bunch of big round holes in them
How hard would it be for you to slip the trans back and put on a flex plate that is for the year of the block / engine ??
One of the best things about g m motor design is it can start and run with out having a transmission bolted to it
Somebody can correct me if I,m wrong but I think the earlier sbc is a neutral balance flex plate and the newer sbc runs a flexplate with a balance weight on it , and unless the motor build needs a lot of balance work , usually on a neutral balance motor , they keep all the balance work on the inside .
Or if flex plate on it now , has the balance weights , just for giggles and sh*ts what about picking up another one taking the weights off and trying it on the motor and see what happens ????
 
Hi 77. I decided tonight that am going to change the flex plate. I need a 168 tooth internally balanced or neutral balanced one. Some are rated as SFI for racing. I don’t think I need that. The flex plates aren’t too expensive. I think I’ll pull the transmission while I’m at it and I’ll get the torque converter checked and balanced.
 
Ken47 said:
Hi 77. I decided tonight that am going to change the flex plate. I need a 168 tooth internally balanced or neutral balanced one. Some are rated as SFI for racing. I don’t think I need that. The flex plates aren’t too expensive. I think I’ll pull the transmission while I’m at it and I’ll get the torque converter checked and balanced.
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Pulling the transmission to change the flex plate is optional??. I didn't think you could pull the torque converter back far enough to get the flex plate bolts out/in.
 
I have read and been told that you can remove the drive shaft, unbolt the transmission mount and bell housing bolts etc and slide it back a few inches on some long bell housing bolts installed to allow access the flex plate bolts. That’s what I was referring to although rereading my post it wasn’t clear at all. I guess my thinking is that to move the transmission back a few inches is 90% of the effort to remove it altogether which will make the flex plate job a lot easier.
Yesterday I rev’ed the engine with the torque converter connected. The vibrations start at around 1300 rpm. When we disconnected the torque converter the vibration is less but still there. I’m wondering if the flex plate is out of balance a bit would the mass of the torque converter accentuate the vibration even though the TC is in balance.
My fear is that when the engine was built there was a vibration in the internally balance engine and someone tried to fix it by trying to externally balance the flex plate to solve the balance issue. I hope im wrong.
Any thoughts?
 
Hi I don’t think it’s a warped flex plate. One thing I did on the weekend was to replace the exhaust donuts between the rams horn manifolds and the exhaust pipes. I noticed exhaust substantially leaking there. When I took it apart I realized the shop that built the exhaust put 2” donut gaskets in where it needed 2 1/2”. They had completely fallen apart as well. I replaced them. It’s frustrating that you pay good money to a shop and end up with crap workmanship.
I also reclocked the torque converter by 120 deg. The vibrations seem a lot less now. I’m not sure if I’m expecting too much in the way of vibration with this engine/cam set up. I checked the compression and all cylinders are 145 psi. The saga continues. 😄😄
 
Hi 77. There are no weights on the flex plate so I’m pretty sure it’s a neutral balanced plate - or supposed to be.
Just for fun and to eliminate other potential problems I took the drive shaft in to be checked (different shop). Turns out my “new” drive shaft with only 500 Kim’s on it was bent and out of balance. There was 18 thou run out in the middle of the shaft and it needed more weight in a different location on the tube to balance it. Another case of paying good money for substandard work.
I know this doesn’t solve the engine/TC vibration but it’s good to know the drive shaft should not be an issue once I get it driveable again.
 
So here’s a geometry question. When I put my digital angle gauge on the diff pinion u joint bearing caps I get different angles between the top and bottom. I put my angle gauge on a 17 mm socket (it’s fits on the bearing cap the best) to get above the yoke and u joint strap so I’m pretty sure I’m measuring just the pinion angle albeit on the bearing cap. I would have thought the angles would be the same. To get pinion angles I’m now measuring the top or bottom but not mixing the position I’m taking the angle readings Could the paint on the yoke cause this sort of problem?
 
So the latest: I took the 47 to a performance shop today and they ran the car on a hoist with the wheels up and they concluded the vibration is coming from the transmission itself. I didn’t think that was possible but that’s their conclusion. The vibrations start at around 2000 rpm and get very bad at about 3500 rpm. Maybe there is something wrong inside it. So I’m on the hunt again for a 2004R transmission. Any leads on one would be greatly appreciated.
 
More laterst😄. I was reading about muffler system vibration etc. So today I took the 47 into the muffler shop and asked the owner there if, in his opinion, the muffler system as installed is too rigid and vibrations may be transmitted to the car. He said he believed it was too rigid. It is on hangers but the way the first installer did the installation it can not move at all. I was thinking that any vibrations in the muffler/piping would translate to the frame of the car. It has Flowmaster 50 mufflers. They installed flexible joints in each muffler pipe ahead of the mufflers. The vibrations in the car are greatly reduced. They aren’t gone yet but it’s way better. I might change the motor mounts too. They are “new” but 15 years old 😄. The hazards of a multi year build. 😄
 
The latest😄. I took the transmission out yesterday. I changed the flex plate. I did find loose engine mount bolts (the 7/16” through bolt). I also found loose bolts on the transmission bell housing. I guess I’ll use lock washers this time 😄. I did find my oil leak which is on the rear intake manifold China wall gasket. So I’m fixing that today. This week I’m going to replace the transmission extension shaft bushing while the transmission is out. I’m also going to see if I can get the torque converter balanced. I’m told this can’t be done once fluid has been in it but I’ll find out😄. I’m also going to put a new slip yoke on the driveshaft since I’m putting a new bushing in the transmission. If all this fails to solve the vibration then I know for sure it’s the engine. Then I have two choices; live with it or fix it😄. If I decide to fix it I think I’ll get a long block crate engine👍
 
Wow..your going to end up redoing the whole car by the time your done...I use a silicone for the front and rear intake gaskets. Put on too much then wipe off the excess after tightening. Those gaskets that you get in the kit squish and get deformed when you tighten down the bolts and never fit right...
 
Thanks Johnny. Yeah I feel that way too. I approached the transmission shop here and asked about balancing the TC. They said that it can’t be done after oil was in it. They’d have to cut it apart, wash it out, reweld it and then balance it. That was going to be half the cost of a new converter so I opted for a new non lockup converter. I also got one with a lower stall speed which I’m told better suits the car’s weight, power and the way I intend to drive it. It seems when you call it a hot rod people think you’re going to be launching it off the line and spinning the tires off of it😄. I suppose some do😄😄. I took the transmission to a fellow here who changed the extension housing bushing (the one the slip yoke runs in). There was lots of slack (I’m guessing 10 thou) between the old busing and an old yoke he had. It was a turbo 350 bushing not a 2004R but I think they are very similar. When the bushing was replaced there is almost no slack between it an the old yoke. I haven’t put the new driveshaft yoke in it yet.
I used a felpro intake gasket for the intake manifold with ultra grey around the water passages and ultra black for the China wall end gaskets. I didn’t use the rubber ones supplied. I was almost black and blue trying to find a consensus on the internet whether to use ultra black, blue, grey or bronze. There is so much conflicting info out there😆
 
Latest update. I think it's fixed👍 Here all that I did:
Changed harmonic balancer
Changed flex plate
Changed torque converter (put in 1600 rpm stall)
Replaced tailshaft bushing
Replaced driveshaft yoke
Straightened and balanced to drive shaft
New u joints
Corrected drive shaft angles
Fixed the oil leak At the back of the intake manifold
Leaned out the carb 8%
Put in better spark plugs
Tightened motor mount through bolts
Tightened the transmission bell housing bolts
So it was the shotgun approach to solving the issues. At least it doesn't vibrate any more. Not sure which of the above was the culprit. Maybe a combination of a few things.
 
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