Vn ss knock then shudder when acclerating from 80 pls help

[sootty grunter]

hi guys just bought this car... when cruzing at about 80 then accelerating to about 3thou revs there is a knock then a shudder. took it to a mechanic and he put it on the computer and could not find any faults. maybe transmission? any help would be appreciated its an auto vn ss

[wortus]

It's not a miss under load? Take off your spark plug leads and check their resistance.

[sootty grunter]

hey man thanks for the reply... happens even when going down an incline though . may be torque converter after reading about an hours worth of threads last night

[db_notso]

check if driveshaft bolts are loose
check trans mount ok not sagged or loose
check engine mounts not split or loose
check diff backlash ok (would do in other gears normally but)
check auto oil level ok and clean

if none of above do an auto service before replacing the box or getting diff checked by a professional

[sootty grunter]

thanks m8 had a quick look at all bolts and mounts seems fine, oil level is fine and like new clean.how much is a service usally and i pressumed the converter is its own part/ no .........spoke to a transmission guy yesterday and he said if its the converter it should be round 900...

[db_notso]

does the knock sound like its under you or behind you or infront of you?
exactly when noise occurs
eg driving staying at 90 then flat to floor accelerator and it knocks as gear changes

a service is cheap but oil is costly this is a last resort before replacing trans though!~

[sootty grunter]

the knocks sounds like it comes from underneath

[db_notso]

then safe to assume its gearbox related
first i would check mounts VERY WELL if they are split or sagged the motor will twist the box and it hits the floor pan
often mistaken for internal gearbox fault

so

when the knock happens does the whole car shake like its affecting acceleration? or is it just a sound? EDI|T soz re-read title

a shudder means its a problem with the supply of power to the rear wheels
my gueass at that speed would be converter or low pressure of the fluid inside the box
either way i would "recomend" having the car driven by the gearbox mechanic so he can feel the fault occur
his knowledge and on hand feeling the fault happen will help him make an educated decision on wether or not its inside box or converter
he will MANUALLY go through the gears and try to make fault occur and also in DRIVE make fault occur
then he SHOULD be able to tell wether or not to rebuild the box or just put a new converter in
if it is converter when its cruising it would be in its highest gear when you accelerate there would be a longer than normal delay then it would drop down a gear
this is caused by the converter getting stuck this
is also common fault..
let us know how you go!~

basically i can give you more checks to do but without feeling the fault myself i might lead you the wrong way and we
would both end up very frustrated

[sootty grunter]

somtimes its a faint knock then a shudder other times its hard knock doesnt happen any other time going through gears even up to 100 only happens when ur cruzing at 80-100 then acclerate

[sootty grunter]

yeah.. its affecting accleration for the period of the shudder then stops once its into gear

[db_notso]

sorry i read title again see above post ^^^^^^^^^

[db_notso]

somtimes its a faint knock then a shudder other times its hard knock doesnt happen any other time going through gears even up to 100 only happens when ur cruzing at 80-100 then acclerate

this would lean me towards the converter~! or the switching of the converter (oil pressure in box)
as it would be in top gear 1 is to 1 ratio or converter locked into place providing drive directly to the wheels from the motor (basically )

[sootty grunter]

nah no point gettin frustrated! think the trans mans the best go thanks heaps for all your advice will let you know how i go not that mech minded so might get him to check mounts ect thanks again

[db_notso]

yeah too easy pm me when you know what fault is

im one of "those" mechanics that has to know the end result

[sootty grunter]

no probs ... will do.

[wortus]

The other thing you could check is the transmission cross member, not sure about a V8 but on a V6 auto they are in two parts, there's a small one bolted to the rear transmission mount then this bolts to a bigger one that then bolts to the car. I had a knocking in my VN and the rubber gearbox mount bolts to the cross member were loose, you couldn't see them from under the car without taking the larger part of the cross member off first.

[sootty grunter]

Hey guys took the car to a transmission bloke today,as always the problem did not occur as bad as it has been , but did occur slightly ,as advised buy db_not so.(your onto it) .he advised me of a service and a tube of something to prevent the converter from sticking cost roughly $180 all up booked in next tues.we'll see how that goes otherwise he'll have to pull out the box but service will not be wasted for future problem havers......will let u all know how it goes.

[db_notso]

any luck mate?

[sootty grunter]

hey guys nah spewing no luck with the service etc..must be the converter have to save some coin and sort it out... want her running sweet ... also found a matching transmission/converter whilst working is this of any use?..thanks

[Alex R]

i have a the same thing happen in my v6 auto sometimes...

[MasterOfReality]

Have you checked your plugs and leads yet?

I had this exact same problem, it honestly felt like the box was about to fall apart.

It was just a misfire - a new set of lead and problem solved.