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#21
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Only a pawn in game of life. |
#22
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Was the engine balanced when it was rebuilt? The flexplate is counterweighted, and if they neutral balanced the engine, you will have a bad vibration when you bolt on the stock flexplate. You should check with the people who built the engine to see what was done. If they didn't balance the engine, but changed the rod or piston weight significantly, that will cause a bad vibration also. Engine out of balance is sometimes hard to notice at an idle, but the faster you run the engine, the worse it gets. I would do as Steve mentioned earlier, unbolt the torque converter, push it back, and start the engine, and slowly rev it up and see if the vibration comes back.
The other thing I've seen is if you are running steel wheels like a Rally II, or Rally I, the taper around the lug holes that centers the wheels, and becomes a seat for the lug nut, gets worn to where the lug nut actually bottoms out on the brake drum instead of the wheel. Then when you get on and off the gas, the wheels shift, and cause vibrations. Seen this on two old GTO's, the first one we discovered this on, took out the transmission, and the main bearings before he figured it out. They vibrated bad when the wheels shifted. At other times it was perfectly smooth. The second GTO, we knew what to check when it happened on it. New wheels fixed both cars.
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Paul Carter Carter Cryogenics www.cartercryo.com 520-409-7236 Koerner Racing Engines You killed it, We build it! 520-294-5758 64 GTO, under re-construction, 412 CID, also under construction. 87 S-10 Pickup, 321,000 miles 99Monte Carlo, 293,000 miles 86 Bronco, 218,000 miles |
#23
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Sounds like its skipping. Wires crossed maybe.
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Bull Nose Formula-461, 6x-4, Q-jet, HEI, TH400, 8.5 3.08, superslowjunk |
#24
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'78 Macho T/A DKM#95, 460cid, SRP pistons, KRE 310 D ports, 3" pypes, Hooker 1 3/4" headers, hydraulic roller, 10" Continental, 3.42 gears 11.5 @117.5mph 3900lbs ([_|_] ##\|/##[_|_]) |
#25
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IF it was the Flex Plate.....the engine doesn't know you put the car in neutral. Plus you could just rev it in park and make it vibrate.
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1968 Firebird 400 RAII M21, 3.31 12 bolt, Mayfair Maize. 1977 Trans Am W72 400, TH350, 3.23 T Top Everyone you will ever meet knows something you don't. Bill Nye. |
#26
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Agreed. He's probably letting the rpms drop to idle speed after going to nuetral. I brought up revving it in nuetral in the driveway in my previous post.
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'78 Macho T/A DKM#95, 460cid, SRP pistons, KRE 310 D ports, 3" pypes, Hooker 1 3/4" headers, hydraulic roller, 10" Continental, 3.42 gears 11.5 @117.5mph 3900lbs ([_|_] ##\|/##[_|_]) |
#27
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Test
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1979 Trans Am 307 RWHP 380RWTQ 13.8@103 1979 400 Block, 1970 Heads, Unknown Cam, Comp Cam Lifters, Edelbrock RPM Intake, Hedman Headers, Holley 750 Carb, WFO Drop Base SOLD 1968 GTO convertable project. 400 auto with air. west coast car . Not started in 15 ..update now running (around block spinning tires all the way. Have a lot of cosmetic work to do winter of 17/18 1969 GTO 400 4 Speed this a complete project. Rebuild will start in spring of 2017. SOLD Last edited by MD79TA; 05-04-2017 at 06:56 PM. Reason: Wrong |
#28
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The TH400 has a special 12 point 3/8" bolt that holds the center support. This can be left loose or work loose, and causes a harsh engagement going into reverse or drive. From your description, the vibration is RPM related, not road-speed related. That rules out driveshaft, u-joints, tires, etc. You need to look at the engine and transmission. The advice about unbolting the converter and running the engine up is a good one. If it vibrates with the trans out of the equation, it could be a bad harmonic balancer, fan, or flex plate.....or even internal issues. If it's smooth with the trans disconnected, you next need to look into the converter and the transmission. Good luck.
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Jeff |
#29
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So heres an update:
Took the car for an extended test drive today for about 20 minutes and some of our previous observation were not so accurate. First, the burning smell is from the front passenger brake. Based on the heat of the wheel after driving and pull while braking the caliper is likely frozen and dragging. The transmission fluid is at proper level, looks brand new, and smells brand new. The car definitely shifts hard in to D and R, but the idle is also likely way too high, we are going to adjust it down, but we really need to hook up a tach. The car is definitely not down on power, I take that back. It will absolutely melt the tire if you lay into it. The engine has no vibration at all in park. You can rev it up and hold it at a sustained RPM and it is completely smooth. Maybe a little lumpy at idle, but I attribute that to the cam. The car shifts through the gears perfectly fine while cruising and at WOT. The vibration is actually still present even in neutral. I thought it was going away last time but today at 40mph I put it in neutral and could still feel it. Perhaps it's not as bad, but still there. Never got to get over 45mph today, but the vibration seems to be at its worst from 30-40mph. Transmission tail shaft shows no signs of leaking, someone asked about that earlier I think. Based on this our next course of action is: fix the brakes to make the caliper stop dragging. Probably unrelated to the vibration, but should be fixed regardless. Pull driveshaft and take it to have the U-joint checked out and to check to see if it is in balance. Front end alignment and wheel balancing. These are all possible culprits that need to be addressed anyways so that's where we will go next. Thank you everyone for your input, we will keep you all updated! |
#30
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I had a bad vibration and it ended up that the crank was not balanced Correctly....it was a process of elimination last resort pulled the engine had the crank checked and rebalanced/repaired vibration was gone ....this was felt in Park slowly revving the engine and
the short drive and I mean short drive down the street, I thought I had a flat tire/tires the vibration was so bad... I had replaced exchanged everything I could think of that could be changed out, carb,,removed belts, diff flex plate, diff balancer,,spark plugs, wires, dist, checked and rechecked valve adjustment, compression test, etc Just another thing to check once u have exhausted everything else...... Good luck ..hope u don't end up tearing it down....
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1973 Firebird Navajo Orange w/shaker,1973 400/461,1972 Intake SD CNC'd,1977 Q-Jet 800 CFM w/ Cliffs Kit,Tanks Inc PA4 255 Walbro intank pump ,-8an feed/return,RobbMc Regulator,RobbMc 40 micron filter,253 CFM 6x-8's w/H.S 1:5 Roller Rockers,SD Stump Puller H/R Cam 230/236 @.050 112 lobe separation 565/.570 lift,Crower Solid Rollers,28150 Hedman Headers,3" exhaust,full tailpipes,350 Turbo,9.5" 3200 Converter,3:42 gear,8.5 posi,C/E slide-alinks,Koni adj frt shocks,Best 12.18@110.55 Lookin for 11's Last edited by cnc; 05-04-2017 at 09:48 PM. |
#31
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Put the rear axle up on jack stands and spin it up. Report back.
BTW, do you feel the vibration in the steering wheel, the seat, or just so bad it's everywhere? You would be well served to get someone to take it for a ride with a trained azz ( seasoned veteran mechanic), shouldn't be hard to find a taker! Last edited by STEELCITYFIREBIRD; 05-04-2017 at 09:55 PM. |
#32
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We will keep it in mind if we continue to strike out. I really don't want to pull the engine or trans, it took us 4 years to get to where we are now. |
#33
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You do not need a Tack to adjust the idle, for now just get the motor fully warmed up, check that the choke is open and set the idle as low as you can with a soid stable idle with the car in gear .
Then check that you get no off idle stumble and your good for now. With the Cam it sounds like you have a 750 rpm idle speed should be had in gear no sweat as long as the Carb if functioning normal. Also if your running a Holley Carb any readjustment of the idle speed will call for a readjustment of the pump arm, and this assumes it was adjusted right in the first place of course! My money's on a shot U joint in regards to your vibration issue.
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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! Last edited by steve25; 05-05-2017 at 06:32 AM. |
#34
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Yup, sounds like U-joint.
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#35
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"First, the burning smell is from the front passenger brake. Based on the heat of the wheel after driving and pull while braking the caliper is likely frozen and dragging"
Check the rubber brake line going to the caliper too, These can delaminate internally and create a check valve effect such that the caliper doesn't release after braking. Had this happen to me. Good luck with the vibration problem, hope you get it figured out.
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65 Tempest, 400, TH400 86 Fiero SE 2.8 |
#36
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#37
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#38
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I had pretty much the same problem and it was the U-joints. My vibration was around 60-70 mph and worse when decelerating. $100 for new U-Joints and balanced.
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I don't always cross thread the bolt - but when I do I run that bitch in with an impact until it's tight! |
#39
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As for the caliper. Get wheel off. Get someone to pump up the brake pedal, then release pedal. Now try to turn rotor, rotor is stiff? loosen bleeder, if rotor spins, hose is bad, if rotor is still stiff, caliper is dragging.
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1968 Firebird 400 RAII M21, 3.31 12 bolt, Mayfair Maize. 1977 Trans Am W72 400, TH350, 3.23 T Top Everyone you will ever meet knows something you don't. Bill Nye. |
#40
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This vibration, could you be feeling something "grounding out" as in a exhaust pipe hitting the floor boards while under a load? Trans case hitting in the tunnel. Like asked before where do you feel it Steering wheel,seat or whole car feels like a big vibration? Also check the rubber insulators on each end of the trans cross member where it bolts to the frame.
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'68 GTO '69 Corvette '75 Cadillac Coupe Deville TOM |
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