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Author Topic: Rear end feels unstable after coming off the power over 100mph  (Read 5484 times)
Stefan Rossi
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« on: April 11, 2011, 11:49:34 am »

Hi

Whenever I drive my beetle on the motorway and I go over 100mph, when I come off the power and all the weight is lifted off the back wheels, it feels horrible like the car is going to roll or flip!

So last night I welded some stops under the spring plates to stop the weight lifting off under power.

I've heard a lot of people doing this, I also tried home made limit straps but they were a joke to fit.

I am going to the rolling road again this afternoon and last time the car got upto 120mph and when he let off the power the whole rear end bounced around.

Hopefully the stops under the spring plates will stop this. I guess ill find out later today.

If not, has anyone else had this problem and how have they solved it?

I don't know any suppliers for limit straps over here in the UK?

I want it ready for the cal look drag day this weekend and I don't want to hit the wall at 120mph!

Thanks

Stefan
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Torben Alstrup
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« Reply #1 on: April 11, 2011, 12:45:00 pm »

Alignment is not correct,
Your rear sits at too high a stance,
shocks too soft,
shitty tyres.

Since it does it on the rolling road too I doubt it is lack of caster angle, but how much does it have ?

T
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Stefan Rossi
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« Reply #2 on: April 11, 2011, 12:49:09 pm »

It isn't shocks, they are gaz adjust ones on the stiffest setting. The tires are a cheap make and they feel quite soft but this is my second pair now and they still do the same, the previous tires were good and made no difference. Alignment is my worry?

What do you mean by stance too high? It is about half a spline each side but I have adjustable spring plates.

What is an easy way to check my alignment without lasers ect ect?

Stef
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kepajake
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« Reply #3 on: April 11, 2011, 12:56:35 pm »

I think you should never use motor brake in speeds over 100mph, allways press the clutch first. Especially in swingaxlemodels motor brake lifts the rear and narrows wheel gauge. When I aligned my rear wheels to 2mm toe in that helped a lot also.
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BeetleBug
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Snabba grabben...


« Reply #4 on: April 11, 2011, 12:57:35 pm »

I second what Torben wrote above here:

Alignment and height plays a MAJOR role in how the car feels. Do this as a starter to check if you notice any difference:

Mark the current placing of the axles on your spring plates. Then loose up the 3 bolts holding it all together (no need to unscrew them) and move the axle all the way forward as far as possible. Please repeat on the other side. Take the car for a ride because you have now as much toe in as possible. Any difference? If not then you can put them back to the original position and focus on your height instead.

Of course a pro alignment would be the best and this is just ment as a check.

Drive carefully and DO NOT take your car up to 120 mph before it behaves better!

BB


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Stefan Rossi
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« Reply #5 on: April 11, 2011, 13:02:56 pm »

Thankyou everyone for your help Smiley I will do this within the next hour but ill let the rolling road take it to 120mph to see if it still does it or not. If it does then iv got a serious problem somewhere :s
Thanks again

Stef
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Torben Alstrup
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« Reply #6 on: April 11, 2011, 17:33:13 pm »


Drive carefully and DO NOT take your car up to 120 mph before it behaves better!

BB


TS!  Roll Eyes 

No, Im with ya ! just couldnt resist pulling your leg a bit.  Grin
T
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dannyboy
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« Reply #7 on: April 11, 2011, 19:29:28 pm »

how did it go steff??? Smiley
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Stefan Rossi
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« Reply #8 on: April 11, 2011, 20:51:11 pm »

Danny its a nightmare!

Sorted my fuel leaking problem FINALY and now it idles. The problem is the transition from idle to full throttle, when you give it large its awesome but street driving is horrible! He said the IDA's are designed for race only and my fk89 cam doesn't help! He is making some sleeves to go down the air collector pipes and he said this will speed my airflow up between 1000 and 3000rpm which is where I need it and he said for racing I can just take them out.

I drove it home so ill limp it to santa pod on sunday for the drag day Smiley

How are you anyway danny? I asked after you at the vworld show but you wernt there aha
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dannyboy
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« Reply #9 on: April 11, 2011, 20:56:56 pm »

ill see you at dragday m8 get a sub 15 and come get your sticker  Grin
reckon efi is calling you m8 Wink
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H67bug
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« Reply #10 on: April 13, 2011, 16:59:17 pm »

Swing axle car...you asked what others do...

Bump stops
Uprated spring plates to stop flexing
Bus snubbers stops to prevent dropping on launch
Adjustable avos
Rear wheel alignment
Solid mounted engine and usual stuff


All nice and stable now.

IDAS with fk89 should still be streetable although lumpy. Maybe worth asking someone to have a look at them at the track- those with experience can cure most ill running.
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Bernard Newbury
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« Reply #11 on: April 13, 2011, 21:01:05 pm »

Danny its a nightmare!

Sorted my fuel leaking problem FINALY and now it idles. The problem is the transition from idle to full throttle, when you give it large its awesome but street driving is horrible! He said the IDA's are designed for race only and my fk89 cam doesn't help! He is making some sleeves to go down the air collector pipes and he said this will speed my airflow up between 1000 and 3000rpm which is where I need it and he said for racing I can just take them out.

I drove it home so ill limp it to santa pod on sunday for the drag day Smiley

How are you anyway danny? I asked after you at the vworld show but you wernt there aha
The most important thing to do on a swingaxle for high speeds is to get the rear end tracking correct (Toe in, camber, etc) and don't brake until your speed has dropped.  The rest (Shocks, torsion bars , snubbers) are for the launch.  To sort properly in one operation would be to convert to IRS.
« Last Edit: April 13, 2011, 21:08:12 pm by Bernard Newbury » Logged

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Stefan Rossi
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« Reply #12 on: April 13, 2011, 21:13:05 pm »



if someone at the track can look at the car on sunday that would be awesome, the old guy at Hi Tech Motorsport where i took it had no experience with IDA's on beetles but had plenty of experience of IDA's on race cars. I had my douts when he said to me 'YOU CANT USE THESE CARBS ON SUCH A SMALL ENGINE'   Cry

my rear end setup is
traction bar
adjustable spring plates (thicker so stop twisting also?)
and gaz adjust shocks on the stiffest setting
iv got some bus bump stops to fit but the rest is stock,

i havnt fitted a mid mount or rhino mounts yet because i havnt finished my gearbox yet and i dont want to snap the stock one in it now altho i probably will sunday!

stef
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Stefan Rossi
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« Reply #13 on: April 13, 2011, 21:18:18 pm »

The most important thing to do on a swingaxle for high speeds is to get the rear end tracking correct (Toe in, camber, etc) and don't brake until your speed has dropped.  The rest (Shocks, torsion bars , snubbers) are for the launch.  To sort properly in one operation would be to convert to IRS.
[/quote]

i will go and get my rear end tracking done on saturday then, i guess quickfit or somewhere similar will do it? Gutted we havnt got the stuff at my work to do it anymore!

how much toe in ect do i need on the back?

it felt alot more stable last night but i only got upto about 80mph on a dual carrageway

another thing, on the rolling road, the ercos wobble ALOT, both of them. im sure they are buckled! so i may fit my brms back for the weekend. i think the guy i brought them off sold me some race weight ones but had them advertised at street weight  Undecided

stef
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H67bug
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« Reply #14 on: April 14, 2011, 06:48:15 am »

Someone may pipe up with better info but my rear wheels are set ever so slightly with the top of the wheel out (positive camber?). With me in the car and under power they are full square to the road. 

Not a racer so hopefully someone might provide you exact specs to help you more.

I used to run Ercos on the street and it felt wobbly. Others say theirs have been fine. A balancer will be able to tell you if they are out.

Good luck.

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Martin
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« Reply #15 on: April 14, 2011, 07:11:50 am »

The most important thing to do on a swingaxle for high speeds is to get the rear end tracking correct (Toe in, camber, etc) and don't brake until your speed has dropped.  The rest (Shocks, torsion bars , snubbers) are for the launch.  To sort properly in one operation would be to convert to IRS.

i will go and get my rear end tracking done on saturday then, i guess quickfit or somewhere similar will do it? Gutted we havnt got the stuff at my work to do it anymore!

how much toe in ect do i need on the back?




it felt alot more stable last night but i only got upto about 80mph on a dual carrageway

another thing, on the rolling road, the ercos wobble ALOT, both of them. im sure they are buckled! so i may fit my brms back for the weekend. i think the guy i brought them off sold me some race weight ones but had them advertised at street weight  Undecided

stef
[/quote]



I run with 1/8 toe in on the rear car runs up to 150 no problem, and i never clutch it at them speeds. to slow down i role out the throttle even on the M62 Wink




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Martin

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Langburger
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« Reply #16 on: April 14, 2011, 12:06:54 pm »

Stef
I'll be there on Sat & Sunday...come over and a have a chat..

as all the others have said ...rear toe and limiting postive camber on decelleration is the key.
I made up some limit stops for the rear springplate travel.

re the IDA's ..no one seems to mention this but changing (increasing) the pump exhaust valve/jet improved the transition from idle circuit on mine.

Nick
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Stefan Rossi
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« Reply #17 on: April 15, 2011, 10:27:59 am »

Hi nick
Yes that would be good if we could have a chat about it. Tonight I am going to increase the wedges under my spring plates to try and stop the positive cambe when off the power at speed. Should be okay I hope.

Ref the ida's, hopefully someone at the track will have an answer. I have lots of spare jets so maybe I will bring them if someone with experience on IDA's on a vw engine doesn't mind looking at it quickly. It seems to be overfueling a lot on the power. Constant white smoke out the back when I floor it. Def fuel and not oil smoke tho.

Stef
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jamiep_jamiep
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« Reply #18 on: April 15, 2011, 14:12:37 pm »

Stef,

The read end on my Oval was setup so that even jacked up the cars wheels remained pretty much camber less) and that felt planted right up to 120mph and backing off. I had a 13mm (m8) bolt threaded into the cast section of the floorpan so there was adjustment for the stops. Its very effective!
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Stefan Rossi
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« Reply #19 on: April 15, 2011, 16:52:03 pm »

That is an awesome idea! I feel sorry for the m8 bolts that are gonna get used for this with the stress they will be under! Currently I have 2 m14 nuts welded underneath but think I'm gonna cut them off and go your way, or make them bigger cus the wheels still drop a tiny bit when jacked up

Stef
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Aircooled Engineering. Birmingham, England

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