struggling with vibes up me rear

[Tonk]

i have a vibe from the back end (feels like a uj gone or prop out of balance) but the rear prop is perfect and was fine before i started mucking around with things, is it possible for a lt230 to give out the same sort of rumble? if i take the rear prop off the and engage difflock and drive on the front prop then all the rumble goes away.

any thoughts or comments much appreciated

Mark.

[dollythelw]

anything changed from "pre-rumble" days Tonk?

[Tonk]

only thing i've done is fit a lt230 onto the back of the lt77 rather than the series transfer box, transmission length grew by 17mm but have moved things around so its now only 7mm longer than it was, have also dropped the rear output by 5mm now and tilted the diff nose up by 20mm to try and mend it.

last night moved rear axle back by 20mm but ran out of time to test drive last night, will do that tonight, just thought i'd ask on here incase i haven't fixed it still.

[Tonk]

just to add, this is in a 88 inch wheelbase, so my rear prop is quite short and have to run at a fairly steep angle, hence why i'm looking at having as much room between g/box and rear axle as i can

[dollythelw]

we share wheelbases - quick test would be lower the back end as far as you can and see if that shuts it up, Im thinking its a combo of increased operating angle and the change in drive flange operating angle "relative" to each other shifting the harmonics about, any idea what prop/flange angles you've got now? Ive got a groovey digi inclinometer if you need a borrow?

[Tonk]

i could stick some lowering blocks and lower the rear of the truck easy enough.

i've no idea wot the angle was before i strarted but am running the same prop, its got a 4.5" slip to take up any difference easy enough, transmission to axle length in theory now is actually longer than it was before so fingers crossed it is fixed, will know more tonight.

i was just asking about rumbles in the transfewr box as a possibilty really as another option, although i drove the vehicle it came out of before it was scrapped and all was fine.

angleometer thingy might be useful, will let u know

ta

Mark.

[dollythelw]

no worries, if you need it then its here word of warning about the inclinometer though - I thought it would be a one trick pony but its addictive and speeds all kinds of processes up, you'll want your own

for what its worth I'll put money on it being a prop geometry issue though

[Hybrid_From_Hell]

I had this with the old hybrid.

The greater the prop angle the harder the U/J has to work, at certain angles it can set up a "Pulse" as it rotates.

Check for wear in splines, UJs, and than it is 100% "In Phase"

Have you room for a double cardon ?, if not then a wide angle may help

Moving the axle back 20mm will as you have prob sussed reduce the severity of the angle a tad...

Nige

[Tonk]

its got a wide angle yoked prop in there

no room for a double cardan wotsit cos total length is about 430mm.

i might change uj's anyway although they feel absolutely fine. its perfectly in phase cos propshaft clinic made it for me, but will check anyway.

ta

[Astro_Al]

Tonk, if you've no room for a double cardan jointed shaft, your only option (and, no doubt the source of the vibrations) is to ensure your transfer output flange and diff nose flange angles are either the same (in parallel planes) or offset the correct angle to match the way the shaft was built (i.e. they can be made to cater for a known difference in flange planes, but this must have been done at the construction stage, and won't change).

So, if you didn't order your shaft with a known difference in planes, you must make sure the two flanges are parallel.

Cheers, Al.

[Astro_Al]

Just re-read your post:

only thing i've done is ... have also ... tilted the diff nose up by 20mm to try and mend it.

Bingo.

I can't attach pics, but go here, down at the bottom see diagram 1a - 'Z-deflection'. you want your 'beta 1' and 'beta 2' angles to be equal for zero vibration:

http://www.gwb-essen.de/fahrzeugbau/english/seite_20.html

By rotating the diff you've made the two 'beta' angles different. This technique (as far as I know) only works with a double cardan, which can take care of the odd angular rates internally, not like a pair of 'normal' UJs on a shaft.

Hope it helps, Al.

[Tonk]

it had the vibes when both flanges were in same plain, but obviously running a steeper prop angle, if i'm still in trouble with this set up i have now i'll leve the axle 20mm back but correct the diff nose angle back to normal.

keep the ideas coming

[bill van snorkle]

There are 2 ways of getting equal universal joint angles. The usual way is to set the t/case and diff flanges parrallel(equal and opposite angles), but this tends to give severe UJ angles on swb trucks. The other way is to tilt the diff up above centre(equal angles on same plane). This reduces the operating angle of the UJs yet still cancels out vibrations. This is how I set it up when I used to run a 110 Salisbury in my swb. However due to the 3 1/2'' greater right hand offset of the 110 diff compared to the leaf sprung Rover diff I had to place the UJ's out of phase by indexing the slip joint one spline at a time ,trial and error until I found the sweet spot that gave smooth vibration free operation on both drive and coast over the full range of speeds.

Bill.