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vibes at highway speeds! Pinion angle???

O

obijuan

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details in the sig line. i just installed mannys old axles in my truck and they have 456 gears compared to my old 308's w/ 35's. with the 35's i was sure this would be the optimum condition for highway driving. well today when i took it out on the highway, i was coming back from my destination, bill millers if its important lol. i was checking for shift operation and it didnt seem to get into OD. shifts fine on ol country roads up to about 55. i counted 3 shifts, and i topped out on rpms and my motor was popping back as i slowed down. also as i decellerated, and let off the gas, there was this awful vibration i could hear really loud bouncing off stuff around me and feel in the gas pedal and the floor. i am kinda thinkin its the torque convertor? but i really have never had a bad one before. all the ujoints seem good and tight it feels like and the rear pinion ujoint is new. heres the pinion angle:
IMG_2417.jpg

could these gears be too much for my ol 700? well not so old because it has 10k on the rebuild by PO from aamco. those 10k were with 308s though. i also installed BTO's lockup kit not too long ago and it worked and drove good with the 308 gears. what are some things i can check to figure out what i have going on here?

my problem in a nutshell, when i let off the gas at highway speeds i get a loud harsh grinding sound and vibration coming from my underside. feels like its right under me.

any help is really appreciated and i will try to help yall! thanks in advance
 
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I'm certainly no pro, but I posted about this about a year ago, and will see if I can dig it up. I had the exact same problem, and once I dropped the t-case an inch, cleared it right up. I am running 4" spring front and 4" shackle flip rear.
 
my TC is dropped!!! ok this is what i did. i took it out for a test drive and i did a few things. i had the windows up and the vent windows closed with nickels. i noticed it when i let off the gas and put it back on. at low speeds of 20- and higher above 45+. i concluded its definately coming from behind me. i wish yall could hear it dammit.

also i think i confirmed its in OD by pressing the brake pedal and hearing it slip and raise rpms. does it only lockup in OD?

i also put my hand on the floor shifter and could not feel anything when i did it. what it sounds like to me is if you have a bag full of coins in your hand and you are moving your fingers around under it and its muffled a little

could it be the rear ujoint? how can i tell if it is or if its the rear end. when i got the rear end from manny, the wear on the teeth was very nice and even and no scars on it. i doubt its the gears.
 
obijuan said:
my TC is dropped!!! ok this is what i did. i took it out for a test drive and i did a few things. i had the windows up and the vent windows closed with nickels. i noticed it when i let off the gas and put it back on. at low speeds of 20- and higher above 45+. i concluded its definately coming from behind me. i wish yall could hear it dammit.

also i think i confirmed its in OD by pressing the brake pedal and hearing it slip and raise rpms. does it only lockup in OD?

i also put my hand on the floor shifter and could not feel anything when i did it. what it sounds like to me is if you have a bag full of coins in your hand and you are moving your fingers around under it and its muffled a little

could it be the rear ujoint? how can i tell if it is or if its the rear end. when i got the rear end from manny, the wear on the teeth was very nice and even and no scars on it. i doubt its the gears.
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Matt, you did put the correct amount of gear lube in the diff's right? Don't mean to sound insulting, just checkin'. Also, I'm still wondering if the drive line is out of sync? Is it possible that the u-joints are not properly aligned? Drive shaft out of balance? Can a conversion joint do that? Sorry if that sounds moronic.

Next time you take it out, have someone sitting in the back with their ears to the floor. You can tell if its rear axle or tranny related that way. Sitting in the drivers area can be deceiving.

Manny
 
You are correct on the lockup in OD, thats a great way to see if it's working, also there is a huge diffrence in 4.56 verses 3.08, I'm going to go with a bad u -joint , just guessing, did you put the tranny in nutral and check the joints setting still?like I said just guessing from my pc, Dave
 
no i didnt set it in neutral. i do that then jiggle stuff? ill do that tomorrow and would 456 gears change my top speed for higher top speed or lower? or change shift times? isnt the 700 fluid controlled shifts? sorry for all the questions but this kinda aggrevates me cause i cant figger it out immediately. i just gotta narrow it down thanks again 1fastchevy, have you read the thread about all the texas guys getting together and going to shiloh ridge in april? you should head out.
 
Not sure of what you mean on the top end, in some cases yes you can go faster with lower(4.56) gears becuse you can rev the motor up more to a better power range, if you have tall gears (3.08)and 44" tires a stock truck sometimes cant move over 80-90mph even with the truck hitting passing gear,yes neutral and make sure you block a tire, Dave thanks for 411 on shilo
 
and on the shifts, my buddy runs 4.10's in one of his trucks, I have the 3.42's in the same truck both totaly stock and he hits 3rd when mine will still be in 1st, so the trans is just shifting when it thinks it needs to, if you have 4.56 's you should, I;m guessing with 700 be able to run 38's and be hitting some nice RPMS without killing your gas mileage, ( some light 38's not boggers) and your doing a great job, truck looks great and it's a chevy, Dave
 
Not to sound stupid, but if it does it when you let off the gas, then your pinion would be tilting down because of axle wrap. Double check your u-bolts since you just put the axles in. I guess a u joint also, but I always say check the easy most overlooked stuff first.
 
will do! them ubolts are tight but are due for a good retorquing. ive done it 3 times since monday and will do a few more times till i am positive theyll stay that way. how do i infact check that the ujoint is to blame and isolate that area? just want to be sure.
 
you will know, it should not move at all, no slack, from driveshaft and joint, wiggle the rear pinon at the rearend and drive shaft also, just to check the pinon bearing, I have replaced at least 20 u joints in my 4x's and only 1 in my 2002 chevy and it has 180,000 k on it and i replaced it becuse I was worried about it, Dave
 
Helpo McHelperson

I just installed a 4" lift on my 87 K5. Springs up front, blocks in rear. Although i bought the lift from a friend who took it off his K5, I had troubles that he didn't. Under braking, the entire vehicle would shudder and feel as though it were going to fall apart. I completely searched every option on the brakes and finally found that it wasn't the brakes, but rather than under deceleration or braking, the weight tranfer caused a bind in the pinion angle, even though it appeared to be at a correct angle. I did a transfer case drop of 1 inch, and it helped. I had to take my blocks and have them remilled to a better angle (which i perfected with test blocks of wood.) Now all is well.
Our best guess is that my old springs were sagging (and still are) so bad in the back, it allowed for a different pinion angle than normal springs.
 
I'm actually having the same problem in my 85. Between 25-45, it vibrates pretty good. I think some of it is from the tires flat spotting from sitting but I think its a Ujoint, which I'm replacing all of them this weekend. Hopefully that will fix it. I have a 3" lift and the rear doesn't seem to be sagging much so I'm not sure if its pinon angle related.
 
Your pinion angle should be the same as the angle from the transfer case unless you have a cv joint at the transfer then your pinion should be pretty close to strait maybe down 2 degees. I had the same problem with mine when I went to 4.56s. I ended up adding a cv joint to the transfercase and moving the spring perches to raise the pinion. The other option to raise the pinion is to get rid of the blocks and do a shackle flip then add the cv joint to the transfercase. The 4 inch shackle flip should position the pinion just about right.
 
bdozeraz said:
Your pinion angle should be the same as the angle from the transfer case unless you have a cv joint at the transfer then your pinion should be pretty close to strait maybe down 2 degees. I had the same problem with mine when I went to 4.56s. I ended up adding a cv joint to the transfercase and moving the spring perches to raise the pinion. The other option to raise the pinion is to get rid of the blocks and do a shackle flip then add the cv joint to the transfercase. The 4 inch shackle flip should position the pinion just about right.
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I second this . My CV made all the difference . I just have old truck noise , and tire noise , and tailgate noise :D

And the 4.56 with 35's are great with OD . I still turn real low rpm cruising , didn't go up as much as it should of on paper .
 
ok ok. so if yall are saying i get a cv shaft at the TC end of the driveshaft that eliminates this problem? yall are saying the couble cardan style ball deal on that right? then do i still have to adjust the perches? i am definately going to reweld my perches. but is this cv a must with a straight pinion angle? my driveshaft is still good and all so id like to keep it. shackle flips are great but thats later.
basically will my rewelding the perches fix this vibration? thats what i need to know.
also what kind of play should be in teh rear pinion yoke itself if any? again thank yall so much.
 
ok i can get a 1350 cv driveshaft made up for $495. or i could reweld my perches to near level but would this be too harsh of an angle? i got a 6 inch lift with tapered blocks to point the pinion upwards. this is how i got it before the swap and i ran it for a long time like that. you can kinda tell here maybe....
DSC04312small.jpg

pinion angle is alighted with the shaft. whats the rule on running like that? there were like no vibes at all when i had it before. i am just looking at an inexpensive alternative obviously.
 
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