Brasil 10 Report post Posted March 3, 2011 Hello folks.... i have a new problem with my 69 Mach1..... when I am cruising at 55 - 55 mph there are some minor vibrations I had alle there wheels /tires balanced, also the driveshaft.. the flexplate is new ( 28 ounces ).. and the engine ( shortblock from promar engines ) is balanced within 1 gramm.. But the worst thing is, that if I am going faster than 70 - 80 mph....and the stay off the gaspedal and / or brake the car down...then vibs are worse ... ( the brakediscs are also new... and the run smooth ..) could it be a problem of the aligment from engine /transmission / driveshaft / rear axle ?? And if so, how can I check that ? My combo ist a 351 W / C 6 Tranny / 9 inch rear.... the car has stock heigh.. Thank you for your help Juergen Quote Share this post Link to post Share on other sites
rwcstang 201 Report post Posted March 3, 2011 could be a number of things could be worn transmission/Engine mounts? are you sure its not balanced as a 28oz not a 50oz? Im assuming 28oz. is the Harmonic balancer new? do you get any stuttering or any kind of engine problems? like when the transmission down shifts? Quote Share this post Link to post Share on other sites
Brasil 10 Report post Posted March 3, 2011 hello rwcstang... I am sure the the imbalance is 28 oz... the trans /motormounts are new.. The balancer is new ( from Summit also with 28 oz ) but I changed to the "old one " and it is the same... By the way .. a member here told me , that in the pic that I posted from my shortblock he saw a difference in the direction of the pistons.. Could that cause the problem...??? Greetings Juergen Quote Share this post Link to post Share on other sites
Brasil 10 Report post Posted March 3, 2011 Here is a pic of the engine.. Quote Share this post Link to post Share on other sites
rwcstang 201 Report post Posted March 4, 2011 hello rwcstang... I am sure the the imbalance is 28 oz... the trans /motormounts are new.. The balancer is new ( from Summit also with 28 oz ) but I changed to the "old one " and it is the same... By the way .. a member here told me , that in the pic that I posted from my shortblock he saw a difference in the direction of the pistons.. Could that cause the problem...??? Greetings Juergen hey brasil.. I would look under your car and make sure all vacuum lines and drive train linkages are properly working. Has your transmission ever been rebuilt or replaced? Im in another forum and someone I know was experiencing the same symptoms u have. they changed everything and finally aftering looking at the transmission found out the drive shaft was a little loose inside the tailshaft extension housing. he changed the seal and rear bushing along with changing out the transmission oil/filter and repairing a broken kick down linkage and problem was solved. Im Assuming maybe the Rear seal in the transmission tailhousing may be the problem..but unsure. as for the for the piston placement i would expect some type noise or binding with the valves since the piston has the valve reliefs but the reliefs look indectical so idk maybe a balance problem?..doing some research ppl reverse the piston to get more hp but unsure if it would cause any problems. im sure someone can chime in but i wouldn't rule it out though. Quote Share this post Link to post Share on other sites
BuckeyeDemon 211 Report post Posted March 4, 2011 can you put the car in neutral when going 55 mph to let the engine RPM's drop to see if the vibration still exists? i assume your u-joints are in good shape since you had it balanced. Quote Share this post Link to post Share on other sites
purple69 10 Report post Posted March 4, 2011 If the vibration get worse when braking it most likely wheel balance. Have the wheel balance rechecked also check that all your lug nuts are thight. Some time on new wheels lug nut will loosen. To check engine vibration put car in park and rev the engine slowly to almost red line note RPMs when/if vibration starts. Good Luck. Quote Share this post Link to post Share on other sites
LindenBruce 27 Report post Posted March 4, 2011 Sounds like you could have an out of round rear brake drum. Do you feel the vibration more in the seat of the pants or through the brake pedal. Bruce Quote Share this post Link to post Share on other sites
LoneWolf2U 136 Report post Posted March 4, 2011 First try and isolate the problem, get it up to 75mph and kick it in neutral and let it coast along at an idle. Is the vib still there? Yes... then the driveline may be your problem. No.. then look into wheel alinement specs. You describe the vib is worse when braking from high speed. This leads me to think that the front wheel alinement may be off some. As the down force when braking is tossed to the front tires and they may be skipping on the pavement. Quote Share this post Link to post Share on other sites
Brasil 10 Report post Posted March 4, 2011 Hello... today I started a new try and error session... first I had my wheels balanced again, in an other tire shop....Now the vibrations are less than before... that´s the good news. The rear drums could be out of round... because when I turn the rear wheels there is a point, where the wheels stick... so I have to bring them to a machine shop to have them machined. But the funny thing is, that I can´t feel a pulsing in the brake pedal... the U-Joints are new... I bought them at MU last year, and now the are approx. 500 mls old... The transmission was rebuilt 3000 mls ago... in the USA.. ( that´s what the former owner told me... he upgraded to a B& M shift Kit also... the shifts are fast and hard.. so the tranny works fine.. but to be honest I didn´t check the output shaft till now... ( if there is any play...) the front end aleignment is like this.. Camber 0`20 Deg Neg Caster 1 Deg Pos. toe in 0´05 so this should be o.k.... Greetings from Germany Juergen Quote Share this post Link to post Share on other sites
