A way to check for wishbone bush wear? Not visually... [VIDEOS INCLUDED]

[mookie 0]

I've tried numerous things to eliminate my on/off throttle jerks. Different ISV, engine mounts, pipework, ECU rest, new throttle damper... nothing has worked so far.

 

However after I spent a bit of time forcing the car to do it on purpose, I have come to the conclusion I can feel weight shifting at the front of the car - like the engine is moving and isn't tightly fastened down and is knocking forward and backwards (best way I can describe it...). Trying to rock the engine by hand produces virtually no movement at all so I'm assuming my mounts are alright - the only movement is generated in the rear engine mount but it's slight and I'm unsure if it's as it should be?

 

I am also able to create a clanking sound that is hard to hear in motion, but if I say engage reverse and come on and off the clutch whilst moving slowly, is very audible. Soooooo my final area to troubleshoot seems to point to wishbone bushes.

 

I've jacked the car up and had a look. Visually the two rear wishbone bushes look fine. The don't look at all perished or crusty. Having said that, there's no evidence in the service file to say they've ever been replaced either... the front tubular bushes I couldn't see clearly enough.

 

So aside from a visual check, is there another way for me to try and decide whether I need to change them or that I might be barking up the wrong tree? Could they generate the aforementioned clanking sound?

Edited July 30, 2012 by mookie

[davidwort 0]

I'd say it's still your engine mounts, wishbone bushes usually look split if they are worn, MOT testers will pry them with a tyre lever to check for excessive movement.

[mookie 0]

I replaced the gearbox mount, the front mount is a VT mount and seems solid. The back engine mount hasn't been replaced... but like I say there is only fractional movement if you rock the engine by hand. None towards the front or gearbox, with just a tiny bit of flex in the back mount, but no knocking... movement feels more like what you'd expect as it's so so slight and more like flex than play.

[CazzaVR 0]

Worth checking the VT mount- I've had one fail before. The new GB mount and VT mount may well have caused the rear mount to wear more quickly too. Pop the handbrake on, put car in first and gently lift clutch up to biting point. With the bonnet up you should be able to see the top of the engine through the windscreen while you do this. This will show excessive movement straight away.

[mookie 0]

I hope the VT mount is OK... I actually bought a new standard mount without realising I already had a VT mount... but can't use the standard mount as it's missing the lower cup bit now on the subframe.

 

I'll try what you suggested and report back.

[Kevin Bacon 5]

Push hard down on the engine at the alternator end and see if the engine lifts up at the gearbox end. Some gearbox mounts (i.e. GSF ones) aren't worth the time of day.

 

You would know if the VT mount had failed!!

 

Get someone to observe what the engine does when you come on and off the clutch quickly with the handbrake on. Excessive movement = knackered mounts.

 

Also get the same person to check how far the front wheels move backwards under hard braking. You can do this at a few mph, just stand on the brakes very abrubtly and very hard. If they move back a fair bit, this = knackered rear wishbone bushes.

 

Also, the 4 isolating bushes in the front cross member seldom get checked, but they rarely cause problems. But they too can get soggy and perished with age.

[mookie 0]

Sorry, it's a VR6.

 

I can't get much movement out the engine at all by hand, however I have taken a video of the engine bay - handbrake on, in gear, releasing the clutch. First part is in 1st gear, from about 27seconds it's in reverse.

 

[video=youtube;AhOM-x16wIo]http://www.youtube.com/watch?v=AhOM-x16wIo

 

Direct link: http://www.youtube.com/watch?v=AhOM-x16wIo

 

Rather than the engine lifting up on it's own, you can see the whole car move and settle. Does this look alright? It doesn't look out of the ordinary to me... :bonk:

[mookie 0]

Now I've also taken a pair of videos of the two rear wishbone bushes. I used a fairly short pry bar (about 6inches) and even in the tiny clearance between the wishbones and the ground, using just a couple of fingers on the bar and levering it maybe 2inches up and down, I was able to create movement in the wishbone - this was with very very little force applied. Is that normal? I'd expected it to be much stiffer than that? In the second vid (driver side) you can hear the bush make a funny creak/squeaky sound.

 

Video 1 - passenger side - 28seconds it very obvious

 

http://www.youtube.com/watch?v=DeMQ6p9EYLc

 

Direct link: http://www.youtube.com/watch?v=DeMQ6p9EYLc

Edited July 30, 2012 by mookie

[mookie 0]

Video 2 - driver side - listen for the noise

 

http://www.youtube.com/watch?v=ad9_pfSOxgM

 

Direct link: http://www.youtube.com/watch?v=ad9_pfSOxgM

[dr_mat 0]

Well, my wishbone bush has been screwed for about 20k miles (6 years!) and passed every MOT on the way. They prise at them with pry bars repeatedly and deemed them fine..

Symptoms of dodgy wishbone bushes:

- bad tramlining

- scary heavy braking

- lots of torque steer

- uneven tyre wear

- unpredictable steering weight

 

.. much the same symptoms of a dodgy lower ball joint, or seriously messed up geometry.. but most other things are easier to check. In general, if you find that your steering feels "better" after the car has been jacked up then it's probably the wishbone bushes ..

 

---------- Post added at 12:18 AM ---------- Previous post was at 12:17 AM ----------

 

And btw the bush isn't supposed to be stiff in the face of prying in that direction, though I'd admit that doesn't look right to me. It's only really supposed to resist movement fore and aft.

[mookie 0]

- bad tramlining - occasionally but it's got skinny tyres so...?

- scary heavy braking - braking is fine

- lots of torque steer - has some torque steer but not sure what is acceptable?

- uneven tyre wear - inside edges of fronts

- unpredictable steering weight - steering feels great

.

 

I've now replaced the rear engine mount and the problem persists. 100% sure it's not the dashpot causing the off throttle jerk... so bushes then?

 

---------- Post added at 12:32 AM ---------- Previous post was at 12:20 AM ----------

 

Any suggestions for how to check for play for and aft? I tried the hard braking test and theres no obvious movement in the front wheel, although the speed used wasn't a lot.

 

Here's another video from today, I thnk it's clearer - just so you know, the amount of force required to do this was tiny, using only about the first couple of inches of the bar as a lever.

 

[video=youtube_share;0H_Ad2bhONE]http://youtu.be/0H_Ad2bhONE

[dr_mat 0]

I think you'd feel it .. with good bushes I know (now) that the Corrado feels immensely planted and stable under power and braking - you almost can't tell it's a front wheel drive car. If you find yourself fighting the steering to keep it straight instead then you have problems somewhere.

TBH I doubt you have anything fundamentally wrong with those bushes .. the OBD1 engine management system isn't totally smooth and isn't really capable of keeping the power on/power off/idle/overrun transitions very clean under all circumstances. It's quite hard to do, tbh. Particularly when you're sat in traffic and the engine is bathing in its own 90 degree air ..