R.I.P.S RB30 runs 8s with 1.4 bar, street tyres, gasoline, no NOS

[ATCO]

I think you've got some wise suggestions from people Rob. It always about changing one thing at a time to narrow down the likely culprit.

Tyre shake can be the symptom from several causes, the obvious being tyres themselves, tyre pressure, temp, wheel balance, even occaisionally serious flat spots or an out of true rim. Given you have not really changed anything in that area since previous successful runs then attention possibly focuses elsewhere. The transmission would have been one of my suggestions, plus make sure there isn't any play in a bearing at the hubs or diff. If it is definitely tyre shake and not 'straight vibration' then I assume you can discount the propshaft (not put a new one on have you?).

Usual analytical/methodical step by step approach. Keep it simple and the problem eventually becomes self evident, it just can be time consuming and frustrating, especially if in the middle of a race meeting!

DaveG

[R.I.P.S NZ]

We have noticed a small amount of run out on the rims but its always been there, we havn't changed driveshafts and we have checked the UJs after ever meeting or dyno session and nothing has changed in any area.

We are on the same rims, same tyres, same shock settings, same everything.

As you know, I use to wheelstand smoothly to 1.3 60fts with ease, we started to lower the wheelie bars and up the power slightly and over about 10 runs the styre shake has just got worse and worse and about 5 runs ago I started getting an "under full power" shake or vibration towards the end of the strip.

After speaking to a 4 link guy, we took the car to him, dyno'd it to find its whp, he set the 4 link and corner weighted the car (he said it was MILES out), setup the sway bar etc and went on our way.

As I said, the last dyno run with some NOS netted a very low mph V rpm and we also had LESS boost than with the same boost controller settings and no NOS so something funny was going on at that stage (no vibrations or funny business on the dyno though)

He told me the rear was setup to leave with full power so on the first run I left with about 30psi with NOS and the bloody car felt like it was going to explode and leave me sitting on the track, no matter how much I pedaled it or tryed to smoothly apply power later in the run it kept shaking (getting less violent the further down the track I got)

We tried tyre pressure changes and it made no difference then on the 2nd pass, massive tyre shake and the trans was definatly on the way out in top, then on the next pass I had no reverse after the burnout, I rolled up for a run, no transbrake, so I rolled off, it left slowly but quite smooth, went through 1st and 2nd ok then no top gear. Game over.


Rob

[tweenierob]

NOt sure if you saw this or not Rob?

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[R.I.P.S NZ]

Yeah I had seen that thanks Tweenie.

Well the trans has been pulled apart and its absolutly worn out, not smashed to bits, just 2nd gear pressure ring is cracked in 1/2 and massive wear and distortion on all the plates and discs.

Plates that are suppose to be 0.080 thick were 0.050 and the metal discs were blue and distorted, the 2nd gear clutch pack was so thin it raised up about 3mm and allowed a big O ring to come out and get eaten up.

I'm not a trans expert by any means so I'm only relaying in laymans terms what I saw and what he told me lol.

My trans man builds drag transmissions for alot of the top V8 drag cars in NZ and he was in shock that we could run 164.5mph on the trans the way it was, he said its been on its way out for quite some time so our recent whp readings and 1/4 mile times/mph would have been seriously effected, judging by the look of some of the parts I have to agree and I'm actually quite pleased in a way.

The trans was used when we got the 240z as a roller, he checked it over way back then and said it was in OK condition and would probably be ok for a while.
At that stage none of us ever imagined we'd be making the power we are or doing what we are doing now and I never thought to strip it again after last season to see if it was still in the same condition as it seemed to be working ok, I wish I had have as we would have found it was badly worn and it would have been freshly built for the dyno and the 1st round, silly boy.

At least I know I don't have a faulty shift light, our data of huge rpm in top gear without the mph to back it up was correct and the dragstrip wasn't made of wet grass afterall, lol.


Rob

[ATCO]

Makes sense Rob. I know it isn't quite the same as the weight is considerably more, its got 4WD to go at, less power than you and its through a carbonetics triple plate and sequential box, however when the guys were prepping the Garage Bomber for the first event in 2008, apart from all the carbon dust off the clutch plates, the input shaft splines to the box were twisted out about 3mm with visible to the naked eye cracks in them. This was effectively after only one season (around 20 10sec bracket runs?) and less than 5000Km of road use. The box was sent off to the factory who replaced the shaft, one gear and all the bearings.

What it tells you though is how much hammer the transmissions get. I know your clutch set up etc. helps but in the end mechanical abuse takes its toll. Implication is you might have to schedule in 'preventative maintenance checks' after 'n' number of runs - your guide is how many previous runs you did and half it!

Best part is that at least you now 'know' and that the rest of of the set up is good (for now!).

Fix the transmission and tell Reece next time you won't need any help at the lights from him......

DaveG

[stonehac]

Rob,

I noticed in one post you said you didn't bead lock the tires.

next time out try this (if you don't already). mark the wheel and tire so that if it spins on the rim you can tell.

A buddy of mine had a set of RD on 16 inch wheels and after every run the tire spun 1/4 on the rim. that cant be too good.

Good find on the tranny sounds like you found you issue.

[R.I.P.S NZ]

We've always marked the tyres and we usually get about 20-30mm movement on the rim per run.

On the old 4wd skyline we had alot of people stumped when they'd look at our marks on the front tyres as we'd actually turn the tyres BACKWARDS on the front rims.

We have another set of rear rims which we'll put on some new slicks and locks so we can still try the old tyres with the new trans and if we still have shake we can quickly go to the slicks to see if its better or fixes it.

The ultimate goal is to run low 8s/170 on street tyres so if at all possible I'd still like to do that.

Rob