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Heavy vibration under accelleration


rkneeshaw

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Background:

 

Replaced transmission with a MTX-75 with Quaife that was rebuilt by TH. During the installation, we replaced the front and rear motor mounts with SVT units and installed the ES inserts. Also, I had a torn boot on both drive shafts, so we replaced both drive shafts with new units from Autozone.

 

First 60 minutes or so of driving from the garage was fine, no vibrations at all, smooth as silk. Everything seemed great! And my 3rd gear synchros where fixed!!! weeeeee! But then.....

 

Symptoms:

 

Vibration only under accelleration. If I coast while in gear, no vibration. The only time I have the vibration, and its heavy at times (usually ~35MPH), is when I'm applying throttle and the wheels are being given pressure to move the car.

 

 

 

I'm wondering if we didnt tighted the nuts on the end of the drive shafts tight enough? Shoot, I'm really stumped to be honest. Anyone have any ideas or insights? TH?

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I'll double check motor mounts again although both are brand new.

 

Only the trans was pulled, not the engine.

 

If it was a motor mount, wouldn't I notice the vibration even when I rev the engine without the trans engaged?

 

I fitted a new RAM clutch with the install which is breaking in nicely

 

One detail I forgot to mention was/is a missing subframe bolt :wacko: When we went to bolt the front subframe back up, the last bolt, passenger side, rear bolt, de-threaded. The bolt is fine, but the threads in the frame it bolts to are toast. I have the car at a shop right now to heli-coil (sp?) it and try to get something in there to hold it. But anyway, I drove the car home (4 hour drive) with just the three bolts holding up the subframe :/ it was thought that wouldnt' cause these symptoms though, but I guess thats why I'm posting, to get more opinions. The other three bolts on the subframe bolted up good and tight.

 

Our airgun wasnt' the strongest though, so thats why I was wondering if not tightening up the driveshaft bolts would've caused one of hte new shafts to not sit quite right?

 

Oh, and the vibration is independant of engine RPM. It's only relative to the speed I'm moving. I tried this: shift to 4th at about 40 MPH, got the vibration, shifted to 3rd at 40MPH, had the vibration at the exact same intensity level. She smooths out a bit around 80MPH+ but I didnt have the guts to go faster than 95 :sick

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NEVER EVER DRIVE WITH MISSING SUBFRAME BOLTS...NEVER!....you don't need to helocoil a thing on the rear front frame mounts...pull back the carpets...to the black sound pad...feel for a 'ribbed' surface...cut away the sound pad.....see the slotted secction in the flooor pan....cut the slots...pull them back and look in the frame channel...see the 'nut' head...that is where the bolt screws into....!Now you can fix the thread/replace the nut!..PS..NEVER use an air-gun to tighten drive shafts...they MUST be torqued 'by the book'...an air gun will damage the hub bearing upon re assembly...sounds like the build up was a bit out of wack here!

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Oh cool, so it's just a bit of carpet to pull back, and cut through some sound deadening material and you can get at it?

 

Phew, that makes me feel better

 

Any idea what ft-lbs those drive shafts should be tightened to? I can't locate my Haines manual...

 

The buildup went pretty smooth except for the subframe bolt threading out. The airgun wasn't that strong, we ended up tightening the drive shaft bolts by hand, but didnt torque them down, I think we overlooked that.

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...this is directed to ALL who may take out the front subframe in the future...on the rear mounts you will see holes in the frame near the bolt..spray with PB Blaster well before the 'drop date' of the subframe...DO NOT use an air gun to shock off the mount bolts...more chance of spinning the captive nut that way....use a long bar & socket and easssssse it before you reach for the air gun...and even if you don't think you will be pulling the frame...take one bolt out at a time and apply copper or nickle 'Anti-sieze' to the threads and torque it back in....can save you a lot of problems in the future!!!!

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Got the subframe bolted back up, had a local shop help out. They got to the nut in there and it had just spun loose, just like you said Terry.

 

My problem with the vibration is a little better, but definately still there, especially around 40MPH.

 

It would be hard to beleive a drive shaft has gone bad already, but I guess it is possible. Any other thoughts?

 

I mean jeez, the only thing I can think of is it's either motor mounts, something inside the trans, or the driveshafts. Those seem like the ONLY components that could cause these symptoms, right?

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.....if it was the trans it would be at all speeds...suggest you re check shafts,mounts etc.Part of the problem of not taking out the whole engine/trans/subframe is that the clutch can be damaged when the trans is forced in...I never do clutch or trans work that way,it saves little time as the whole lot can be dropped out in under 3 hrs....I cant tell you how many 'shops' have F'd up an install of my transmissions this way....damaged clutches,loose steering racks,damaged oil seals etc etc....Re check it all as,from what I can see, the install was not 100% correct...

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....start with the inner cv joint and be sure there is no play when you try to rotate the shaft with the cv fixed.The inner CV can pop out of the tripod within the boot and one of the 3 bearings can lay in the boot...did you zip tie the inner cv halves together before you pulled it out the trans ....?...was it held together with zip ties when it was refitted or just 'free' on the end of the shaft?....

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I am having the EXACT same symptoms you are having. I have been having this vibration for quite a while. I replaced both CV joints and that fixed it, but the problem came back pretty quickly. Terry, could you explain your last post in a little more detail, or a different way, I am not sure I understand what you are saying to check? I am going to have to get my car on the lift to change these CV joints out, so I want to be able to find the problem before I pay to have them changed again. Also, could you explain the zip tie thing you were talking about again? I didnt do anything like that when I replaced my CV's the last time. Also, how is the reinstallation supposed to go? I think the guy thats helping me knows too much about working on old pick-ups than he does modern, european inspired cars (IE. if something doesnt work right, hitting it with a BFH will help the problem) Thanks... -Nick

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I'm going to be swapping out these drive shafts again this weekend. They were new rebuilt shafts from Autozone that we installed when swapping out the trans. I drove the car for about an hour or two before the vibration started. A couple guys I talked to have said its not too uncommon for rebuilt driveshafts/CV joints to go pretty quickly, and sometimes you have to try a few before you get a good set!!

 

So, this weekend, we'll see if I can luck out and get a good set :wacko:

 

I'll know more this Saturday night

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.....re-man shafts can be an issue....re-balance etc ,use genuine Ford parts here...OK so its $$$ but the only time I've had zero probs with shafts is 1) Use Ford shafts or 2) I REBUILD the CV's myself!!!...I'll pen the 'zip tie' thing later today (In prep for a trip to the PRI Expo in Indy!)...

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Good news! its fixed!

 

Passenger side drive shaft's inner CV joint seems to have grenaded itself and shot something through the boot, spitting grease everywhere down there. Swapped out the shaft, and the car drives GREAT!!! wooot!

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