New Diff - axle tramp and engine/exhaust labouring ... can someone explain to me why?

[FrangaFry]

Hi folks, on my never ending quest to actually learn something (or just sound like an idiot); As the title suggests, I have recently had a complete diff change.

I drive a VYSSII wagon with a Harrop HTV1900, the suspension has been upgraded (Koni adjustable all round and Whiteline Sway bars front and rear, with the Diff cradle bush and few others being changed as well). My old Diff had 3.73 gears in it and the new Diff (complete Diff swap, not just gears) has 3.45 gears in it.

Previously I had not experienced any axle tramp when 'accidentally' turning the tyres (it's easy to do with the blower.....); I have noticed since getting the new Diff that (especially in the wet) when the wheels are turning (by accident of course - seriously), the car sounds like there is a jack hammer going off (it seems MUCH louder on the driver side than passenger.. but this just may be b/c that is where I am sitting...) and I have to back RIGHT off really quickly (the noise is SOOOOO loud that it scared the crap out of me when it happened, as I just wasn't expecting it ... my daughter was in the car the other day and taking off a little quickly the tyres turned and the noise freaked her right out - it's REALLY loud). With the old DIff I NEVER experienced axle tramp even with the blower (it was as smmmmmoooooooth as a babies bum even when the wheels were spinning,wet or dry, not that I do it intentionally, HONESTLY!!).

Added to the above I have also noticed considerably more 'drone' and vibration through the car and the engine seems to labour a bit on acceleration (say cruising at 80 and put the foot down slowly to accelerate smoothly to 100 it moves due to the blower but the engine seems to labour... there seems to be a completely different sound and vibration out the back than there was prior to the Diff replacement?)

Does anyone have an explanation for this (tweaking was made to the EFI live setup to cater for the gear ratio change)? I love the new Diff and ratio (as the old was seriously noisy) but the axle tramp issue is seriously p1ssing me off and the drone in the exhaust and extra vibration in the car is getting to me as well (it just seems so much different and the only ting that was changed was the Diff and gear ratio).

I am reluctant to hassle the tuner/mechanic at this stage, as he has been great in the past and I have had to go back and hassle him more times than I would have liked over the previous Diff and I just don't want to sound like a complete whinger and piss him off until I know that this issue is actually normal?

If it is normal, and the issue is just due to the new ratio (tyres not turning as quickly with the new ratio???) then I might have to seriously consider going back to the 3.73 gears as the axle tram is just TOOOOO much (and with the blower the tyres tend to turn way more than you intend).

Any advice?

Thanks in advance,

[JezzaB]

To get axel tramp you need some grip. Now you have a different ratio you arnt spinning the tyres as quickly with no traction at all. Droning because it is loading it up more and labouring as you suggested. Its a side effect but you will get more out of each gear and more grip and then pushed back in the seat more. You want more wheel spin and faster changes, put the old diff ratio back in or cheaper tyres or look at the suspension setup

Turbos love that loading, it makes them work harder. Blowers dont gain the boost from the loading but they gain the traction and pushing back in the seat.

[FrangaFry]

To get axel tramp you need some grip. Now you have a different ratio you arnt spinning the tyres as quickly with no traction at all. Droning because it is loading it up more and labouring as you suggested. Its a side effect but you will get more out of each gear and more grip and then pushed back in the seat more. You want more wheel spin and faster changes, put the old diff ratio back in

Ok, so this is normal then. I really do like the new ratio, as you say, it seems allot stronger and I seem to have more mid range and top end (with the 'push in the seat' feeling still very much there from a start) and the wheels don't spin as much in the dry. So, this is all part and parcel of the setup I have... is there anything that can be done to reduce the axle tramp (it's really only a problem in the wet but god damn it's loud and when it does happen every head within 100 meters turns to look at the ...... maybe I just need to pull my head in when its raining).

And the drone and vibration is normal as well?

I did like the 3.73 (quick as of the line) but the wheels did turn too much and I noticed the mid range and top end power loss. The 3.45 gears seems to suit the blower so much better. So the advice is live with it and change my driving style or put the old gears back in? Hmmmmm...........

Edit, maybe a blower cam will help.......

[VY-SV8]

hi mate,

i had issues with axle tramp too when i hit the strip and what helped out for me was swapping over the rear bushes to polyurethane item. i swapped all of mine over to superpro items and you'd be surprised how much it helped. good luck getting the dreaded tramp sorted, it is a real pain when it rears its ugly head.

[FrangaFry]

hi mate,

i had issues with axle tramp too when i hit the strip and what helped out for me was swapping over the rear bushes to polyurethane item. i swapped all of mine over to superpro items and you'd be surprised how much it helped. good luck getting the dreaded tramp sorted, it is a real pain when it rears its ugly head.

Thanks for the feedback guys, I am feeling a little better about the issue. Given that I have recently installed Konis on the rear and a whiteline sway bay (with supplied bushes) + the diff cradle, can you let me know which bushes you would recommend changing (with the Super Pros I assume?)

Cheers,

[VY-SV8]

when i did my bushes, i did pretty much all of them, front and back. however for your situation i'd guess you only need to do the rear ones. I'd suggest the following, although i'd be happily corrected from someone more in the know.

1. Rear subframe bush mounts
2. control arm bush
3. camber adjust kit

i assume you have already done the sway bar mounts when new sway bars went in. this is pretty much all i did, but i'd be starting at the top of that list, the rear subframe bushes would be the most beneficial to swap out to help you in your situation, however the control arm bushes are easy to do while you are already there. The camber kit i did as with a lowered commodore IRS set-up you end up wearing out the inside of your tyres with the typical "commo squat" i call it, so it was easier and cheaper to get the camber fixed than wear out my $400 tyres. The rear end grip is better too now i have more tyre on the road.

hope my ramblings help a bit, i'm no expert but i tend to listen when someone who knows their shit is talkin. So i have picked up a bit over the years.

[Wonky]

Chev often does complete bush swaps through the whole car with (I think) Pedders and in fact I'm surprised if your bushes were anything but in good condition he wouldn't have suggested swapping. On the other hand I know Ron SS has done a lot of research into VE axle tramp and suggests that replacing ALL bushes with the solid ones actually contributes to axle tramp!! See http://www.g8board.com/forums/showth...142#post856142

[VY-SV8]

Chev often does complete bush swaps through the whole car with (I think) Pedders and in fact I'm surprised if your bushes were anything but in good condition he wouldn't have suggested swapping. On the other hand I know Ron SS has done a lot of research into VE axle tramp and suggests that replacing ALL bushes with the solid ones actually contributes to axle tramp!! See http://www.g8board.com/forums/showth...142#post856142

He says in the first post he has a VY SS wagon brother, so the VE dealio doesn't apply. hence why i responded with how i fixed my VY axle tramp issues.

[Wonky]

Yes I know he has a VY because I've met him quite a few times, but what I'm saying is that Ron's research doesn't just apply to VE. What he has found applies at least to some degree on pre VE also. If you remove all flex by installing solid bushes at every possible point you potentially increase axle tramp.

[VY-SV8]

wonly i am not too sure that you linked the correct thread, i read through all of that thread posted but nothing came up that would show using poly bushes would increase axle tramp. Infact in every instance i have used poly bushes it has helped to eliminate wheel hop.

[1BEAST2NV]

cant really do much about the drone in the car,

with the 3.7's the revs would have been in that spot where it was past the drone point.

Now with 3.45's its at the point in the rev range that the drone is noticeable.

[Wonky]

That single post and the thread it's in probably don't explain why poly bushes increase axle tramp, but I have a whole DVD Ron made showing axle tramp, suspension geometry etc etc and the one thing he is adamant about, as illustrated in the DVD, is that replacing all rear bushes with poly will actually increase tramp. A few key phrases from that post he did are "This MUST result in the rubbers/poly bushes at the cradle end to squish up to allow for this geometry change." and "If you use stiffer material than the standard rubber, and use poly for example, then the control arm and trailing arm will soon wear out the material simply because the geometry is forcing it to squish up to make up for the misalignment. Rubber does this very well, poly does not. Eventually the poly "hole" becomes oval, as indeed this thread has shown. Poly mounts work by having the ferrule rotate with the poly, as it is NOT bonded to the ferrule like the std rubber joint."

He has cured his axle tramp in the dry 100% but hasn't yet solved it perfectly in the wet.

[Wonky]

Forgot one important paragraph from that post of Ron's that I guess VY-SV8 missed too:

"suppliers of poly bushes, and you know who they are, simply do not understand this geometric misalignment issue. My advice is to stay with the standard rubber bushes, or use rod ends, but only at the inner mounts. The joints at the knuckle end MUST squish up to allow for the toe arm to do its job and change the wheel angle to end up with (close to) zero toe change. Hard bushes or rods ends at the knuckle will not allow toe correction and will probably end up binding the wheel. The thing that amazes me is that it has taken some two years for these issues to finally show up ... a simple, look at the geometry is all it takes. "

That applies to VE/G8 specifically but I'm pretty sure from my interactions with Ron that it also applies to pre VE, at least to some extent.

[VY-SV8]

the rear cradle is completely different in the VE to the VY, so i am failing to see the correlation between the VE rear suspension design flaws and those of the previous models.

I did read that post and yet i can't seem to comprehend why he would think that a "misalignment" in the front LCA bush would cause wheel hop, that bush is only there to aloow the LCA to pivot up and down, in most instances you will find that front pivot is even welded to the frame i have found. So using a rubber mount bush in that particular instance baffles me as using stiffer components or bushes has been the solve for that issue even from manufacturers.

I digress, but i would be interested to learn more as i may be on a different a page to what you were referring to. I can only really comment on what i have heard when talking to my suspension guy and from people i believe to really know their shit when it comes to going fast and in every instance i have come across using stiffer poly bushes in certain areas in the rear end my axle tramp is now gone. Miracle cure... maybe, but it worked for me and many of my friends in their VY's so i can only recommend doing similar.

shoot me a PM and i'll search out that DVD you speak of so we don't clog up the OP's thread.

[Wonky]

shoot me a PM and i'll search out that DVD you speak of so we don't clog up the OP's thread.

Yes, agreed - I'll stop clogging up this thread. Apologies to the OP.