911

On my hill climb Sti v3, when I do a very hard start, ie 5000 rpm and dump the Ap Organic clutch the rear subframe/diff crashes and bangs like a Moggie Minor's axle tramp!

I have nylon bushes in the diff mounts and poly bushes in the front rear diff carrier arm ends.

Anyone tried to fix a similar problem?

All the suspension is fitted with Poly bushes, no rubber anywhere.(which might be the problem)

Graham.

Tim W

iTrader: (1)

Graham, I beleive that Whiteline offer some solid links for securing the diff more firmly, have a look on their website or in Demon Tweeks

I think the part your looking for is the 'Rear Subframe Lock Kit, Part No KSB751'

911

Got it on already!
Apart from welding it on solid not sure what else to do.
The banging is the nose of the rear diff hitting the frame I think.

Graham.

Tim W

iTrader: (1)

Hmm...odd

I used to have problems with my diff carrier bushes clonking under hard acceleration but then I fitted the full Powerflex chassis kit (every bush except the rear subframe to body mounts) and it stopped...and my launch technique was possibly even more brutal

I'm told you can make your own bushes for the subframe to body mounts by cutting them out of a sheet of the hard rubber that is normally used to make the 'rally style' mudflaps

Other possibilities that spring to mind:
Have you got solid anti rollbar drop links?
Have you thought about making some rose jointed rear links?
Have you got uprated engine and gearbox mounts?

Although I never had problems at Elvington with full bore launches at Santa Pod (where I seem to have less traction) I got terrible axle tramp at the front, violent enough to twist the engine and gearbox back on they're mounts to press the gear stick against the body and knock the car out of gear I'm going to look at up rating the top engine stabiliser either with an aftermarket Sti one (with stronger bushes) or even a rose jointed brace just for doing staright line drag runs...if I get the same problems with the Group N engine mounts (gearbox mount already fitted)

Sorry, rambling, but hopefully there'll be something useful coming out of them

911

Front end is ok, but will make some special mounts for the engine/box using polyurethane bushes in the summer.
The front wheels spin to a short degree on launch.

The whole rear frame is tied down to the shell using poly bushes. Carman tried the rally rubber spacer thing and he too suffered still.
This happened with Toyo and Kumho (sticky) tyres.

Maybe it is just the front/rear distribution ratio on my non dccd box?

Thinking caps on when I get under there again soon!

Graham.

Tim W

iTrader: (1)

Graham, just a thought I got from flicking through Demon Tweeks last night, it seems there are two Whiteline diff locking parts, one for the subframe and one for the front of the diff, have you got both?

Pavlo

Could this be related more to the movement you get at the engine/box setting up a resonance? I would try the group N uprated engine and gearbox mounts first and see what happens. I only get this sort of effect when the clutch judders badly (4 paddle jobbie).

paul

911

Tim, I've got all the Whiteline stuff on this car!

The noise (and feel) is the front of the diff casting hitting the subframe violently (you think something has broken)
If I get it just right on the startline, then the car launched smooth and true with a bit of front wheelspin, I can get this issue in the dry and the wet too!

The diff rear studs (where it bolts into the two rubber biscuit mountings are also polybushes from Powerflex.)

Paul, do you know where to get stiffer mounts for the box/engine from?
David Wallis said Prodrive.

I'm thinking of making some from old mounts and Powerflex 'general purpose' bushes.
I am sure I've seen some on a USA web site but can't recall the Company.

Graham.

StickyMicky

this wont help you much but a mate of mine says he has heard his rear diff bang off the floor when he was at a 0-60mph even at croft

i have the launch on video, you can hear no noise from outside, but his first launch was at high revs with a grippy clutch and resulted in what looks like 4wheel spins

the second, after he heard the horrible noises was a bit more laid back and kangarooish

Tim W

iTrader: (1)

Graham, by the sounds of things it's more than likely that your gearbox and engine mounts need replacing like Paul says.

I bought my Group N Gearbox and engine mounts from Mark of Lateral Performance fame for less money than the other usual suspects (GGR, RCM etc)

911

What exactly are Group N mounts?
Are they just stiffer construction/rubber compound over and above Sti?

How much roughly?

I think i can do a diy job for about £60 (and a bit of fun doing it).
Wish Mark would get his website done!

Graham.

Pavlo

the group N parts are stiffer engine mounts, and a different gearbox mount with more rubber moulded in. The prodrive modified gearbox mount also adds some extra polyurethane set into the other voids in the gearbox mount stiffening it further. I have found the standard STI uprated box mount to be fine.

Paul

StickyMicky

this is a technique that the nova boys use when fitting larger engines to there cars

not sure if you can apply this to the scoob as i havent seen the rubber mounts up close, but the nova boys fill in any gaps in the rubber mount with that black windscreen sealent stuff which stiffens them up a treat.

Tim W

iTrader: (1)

The only problem with that windscreen bonding stuff is that it doesn't like any UV (not a problem under the car really) or oil (ah...)

911

Nova's leak, Impreza's don't.
Unless 407/340 spec motor shreads the gearbox (sorry I'm boasting )

I found a picture of the Cusco mounts this lunchtime, ver simple, so I will get some old mounts off API, cut out the rubber and weld-in some poly bushes as substitute.

Still can't see how weak engine mounts could contribute to the rear frame moving so much.

Graham.

APIDavid

iTrader: (4)

Graham, I reckon we may be able to get you sorted on this problem. We have a few tweaks we've developed that seem to work. Perhaps you could pop in with the car sometime and we'll stick it up on the ramp and see whats what.


David APi Engines / APi Impreza

jim litten

TAS do some solid ally engine and gearbox mounts.

911

Thanks David, will do when the weather a bit better, tired of washing/cleaning my suspenders! (suspension sorry). I'll bring you some money too...

Who/where are TAS?
Solid mounts kill the chassis and with chassis flex will kill the block too. 911's tried this and fooked the trans/motors.

There needs to be a bit of give in the system or it all gets too buzzy when the excitment wears off. (just like an RA gearbox on the motorway...)

David, seen the revised numbers on the engine? Glad you fitted the head bolts.

Graham.

APIDavid

iTrader: (4)

Studs, my dear fellow: STUDS !! See, we always [ partially ] build engines that are up to it........... Good power figures - why the revision did I miss something?

Solid mounts indeed?? Whatever next?

David APi Engines / APi Impreza

911

Seems the 5 power runs taken were not averaged as I assumed, but I just got the print-out of the last one @ 373bhp.

The 3rd run gave 407 bhp and 340 lbft (not too sure of the torque).

Sorry, studs. Started work at 6.30am.....

Care to let-on what you have to offer in the mounts dept?

Graham.

jim litten

TAS: TransAutoSport Ltd in Leyland Lancs ( www.tas.uk.com ). May not be completely solid but very chunky looking at the photo in the catalogue.

vulnax999

iTrader: (7)

The STi Engine and gearbox mounts, ( compared to WRX parts ) are more substantial - harder rubber and more of it, more metal to support it, worthwhile mod ( got mine off Xtreme and RCM ) but as 911 has an STi already, probably not much use unless his are shot!.

For a competition car, Rose Jointing is the way to go!

Pavlo

the sti mounts are not standard fitment on most STIs.

Paul

APIDavid

iTrader: (4)

Pavlo - I think you mean that STi SPORTPART mounts are not standard fitment on STi's - there is a difference. Horrible on a road car but in Grahams case worthwhile. Start saving G they're not cheap.

Regarding your horsepower - anywhere over 350 horsepower is very definitely Steel con rods territory. did you fit any? If not be careful. You may be lucky and a have a 'Monday set' but if you have Friday ones.............

Good Luck David API

PS No I won't post on here for the rear axle tweak, l'll pm you. That stuff takes a while to figure and giving info away to the masses free doesn't do anything for the bottom line.

Tim W

iTrader: (1)

IIRC the 'Sportpart' gearbox (or rear engine mount) cost about 75 quid, and the engine mounts about 80 quid for the pair...not exactly stupid money?

vulnax999

iTrader: (7)

Seems about what I paid Tim, unless those were the std STi parts and not the STiSportsparts?

Ditto STi suspension top mounts all round.

Tim W

iTrader: (1)

Well mine came out of the Prodrive Group N parts catalogue, and they don't look like the stock Sti mounts that I've seen