Serious Rear End Suspension Issue

[Jensen]

Hi There

Car: MGF
Year: 1998
Engine: 1.8i
Mileage: 50,000

My car just recently is getting dangerous to drive, I can basically steer the car with the accelerator..! If I floor it, it pulls to the left if I lift off it pulls back to the right & if I apply the handbrake whilst in motion the back end veers to the right making me steer right into it, If I floor it off the mark it just feels normal but once I go over around 40mph it becomes dangerous

I have had the car up on the ramp & checked the rear track rod ends, Wheel bearings & all suspension bushings with a lever bar & it appears to be tight, I even asked the MOT guy about 3 months ago to really look out for anything during the test as I couldn't find anything wrong & he passed it & said all was ok
I have also grabbed the rear wheels with both hands & tried to pull the wheel about form its central position & all seems tight & rite
The car is steadily got worse over the last 3 months since its MOT to the point where I have stopped driving it now as I nearly killed myself in it over the weekend as the back end went rite out on a corner at slow speed, When it done this it almost felt like the D/S/ wheel moved causing the car to veer off but I was going around a left corner at the time
It is also very boaty at higher speeds like 60-70 mph
I have had 4 brand new budget tyres fitted ( Same size all round 195/50/15") & 4 wheel laser alignment done - Problem no better or worse

Just to inform everyone I have been running this car on 195/50/15" tyres for over ten years now and it hasn't caused any issues what so ever

I've read that compliance bushes can be the issue here on this

Any ideas people ??

[Rob Bell]

You've done some very sensible checks - sounds like bushes, track rod ends and wheel bearings are okay given the the lack of play.

Not entirely sure whether the replacement of your tyres with "4 new budget tyres" where before or after the handling problems? It should be noted though that the MGF (and any mid-engined sports car such as the MR2 or Lotus Elise) are very sensitive to tyres - and tyres can certainly cause unpleasant handling characteristics.

Have you had the tracking checked? I presume that the tyre pressures are all okay? Also, what ride height are you running on your car?

It may also be worth bearing in mind that the Hydragas units may need re-gassing with nitrogen...

[talkingcars]

As I was reading the description I was wondering about tyres.

Budget tyres will not help.

Also the tyre size you have won't help.
The standard tyre size on the 15" wheels 185/55/15 at the front and 205/50/15 at the back.
195 was accepted as an option when the better 185/205 were not available.

Also worth looking at the EPAS if fitted. To test this just pull the fuse.
My speedo cable snapped so was giving an intermittent incorrect speed so that the EPAS was cutting in at 50 mph giving full assistance. Steering was interesting and the rear would go floaty.


Is there anyone local who can lend you a set of tyres to absolutely rule the tyres out.

[Jensen]

Hi
Thank you for replying

The tyres like I stated have been 195/50/15" for over 10 years now (roughly 3 sets all same brand & sizes & budget range) with no previous issues before, I'm quite aware of the different sizes on the front to the back but there is something else causing this

1. The tyres are all brand new with full tread on each complimented with 4 wheel laser alignment & wheel balancing
2. The tyre pressures are all correct
3. All suspension checked over by myself (Qualified mechanic of 25 years) & by an M.O.T inspector during MOT test.
4. Ride height adjusted at each side via the valves in the front - Ride height standard & perfect.
5. Electric power steering appears fine & isn't the cause of the 'Boating effect' this is caused through acceleration & cornering.

What ever has happened to this car has drastically went down hill in the last 4 months & started before the new tyres were even fitted, It has got really bad this last 1000 miles so the car is now off the road because its so dangerous

My next step is to start stripping out suspension arms & visually & physically checking them off one by one as it has to be a suspension issue due to the nature of the issue

Will update with my findings

[Barbour]

What tyres did you have fitted?

[Crash Dummy]

Maybe a silly question, but have you checked for a dragging brake or siezed wheel bearing?

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[Charless]

Tyres.

[Chris Tideswell]

Are the engine mounts OK?

[Jensen]

Hi All

Thanks for all the replies

The brake calipers, sliders & brake pads are all grand, The wheel bearings are all ok to

The tyres as I have stated before are all new & full tread - The brand is a budget tyre called HIFLY 195/50R15 86V HF805 XL which is a V rated tyre capable of up to 149 mph which is more than adequate for that wee car - I No for sure the tyres aren't the issue here people as I have been running this car on budget tyres for over 10 years now and the wee car never flinched & sat to the road well until now

I am going to check engine mounts along with the suspension arms when I start tearing it down here but my gut feeling is the mounts are fine as when I apply the handbrake at about 40mph it dangerously veers of the left as well & when I let the handbrake go it veers back to the right , Exactly the same as when I accelerate

The car is also very wobbly at the rear end when cornering without acceleration or braking so it has to be suspension - Just weird how I can find anything when the car is on my 2 poster ramp with a crow bar wedged in every part of the suspension

Just to mention I bought a PG1 gearbox & a Torsen Type B LSD Differential from a Rover 220 Turbo & amalgamated the two so she has a LSD box fitted for about the last 2 years but again this problem wasn't there when I did that so cant really blame the LSD for this

This we car only does about 1000 - 3000 miles a year & with only just turning 50,000 miles last month I'm shocked at TBH

Anyway I Will know soon enough when I start to strip her down & find the culprit(s)

thanks for all the replies to date

[Crash Dummy]

Interesting. When I suggested binding brake or siezed wheel bearing, I was trying to identify possible sources of what they call in aviation "asymmetric thrust". Since I don't know the mechanism, I can't comment on your LSD, but is there a chance a fault has developed?

Just something to consider. Cheers.

[Jensen]

Being from the Aviation background these days myself (Aircraft Engineer) I had thought of that but different ball game

[Deepfat]

Sorry to bring it up again but tyres, you say they are the same size and brand you have used for years but are they the same? has the manufacturer changed the compound or the sidewall rating which these cars seem to be sensitive to. I presume like most of us when they were changed the tyre fitters disposed of them so checking will be difficult, perhaps you could email the manufacturer to find out if changes have been made since your previous set.
I also think the suggestion to beg or borrow another set of tyres for comparison is a very good idea, you would be best discounting the tyres once and for all before stripping all the suspension looking for something that may not be there.

[Bigfootmgf]

The only time I have experienced fishtailiñg was when a front droplink was cracked. My mechanic, mot man didn't find it first time! Worth a look!

[Rob Bell]

Not keen on the tyre choice, but as the problem started before changing the tyres (and all four tyres were changed at the same time) I agree with Jensen that the tyres may not be the route cause of this problem.

The LSD ought not be causing this problem - it's a torsen not a plate-type, but to be honest, I don't really have enough experience with failure modes on these (I have a torsen-A in a close-ratio PG1 to go in the car soon!)

The asymetric thrust idea is a good one: there is a thrust axis on cars that is dependent on the tracking. Jensen mentions that the car has been through a 4-wheel laser alignment. Of course, these are only as good as the person doing it- but if you're prepared to spend a bit of time, I'd do a manual measurement, which is fairly straightforward to do given some flat ground, some string and a ruler

Is the suspension moving as it should (i.e. not seezing) and are the dampers in good condition?

[Crash Dummy]

Another possible diagnostic, if you've got a GoPro, set it up to record one rear wheel at a time to see if there is any fore-aft movement when you accelerate and brake.

[Rob Bell]

On this thought line - is the subframe solidly mounted? A 1998 model year should have rubber subframe mounts - but the rubber could have degraded or the mounts themselves can rot - although the latter is more of a problem on the later MGF 160 and the TF models where the rubber is deleted and water sits in the void formerly occupied by the rubber bush...

[Jensen]

Hi All

Thank you for all the replies

I drove the car yesterday again & carried out some simple tests whilst in motion - Its definitely a suspension issue & I reckon its the drivers side rear corner as when I put it into a left turn & all the weight of the car leans on to the right hand side and as soon as that happens I can feel the drivers rear wheel coming inboard which throws the car into a slide so I has to be either of the following:

Rear tie bar inner bush or interface bush with lower arm
Lower suspension arm inner/outer bush
Upper suspension arm inner or outer

What ever of the three arms 1 of these or more is the issue

Will hopefully get a look at it this weekend or possibly next week - No rush as its only my spare/track/fun car

Regards Glenn

[Jensen]

Hi Rob

Well check the subframe mounts as well as that is a very good point - It definitely feels like something is giving way allowing the car to float & go out of control

Thanks Will check that out

Regards Glenn

[Rob Bell]

Good luck finding the problem Glenn - this must be really spoiling the car for you at the moment. Do let us know what you find!

[Crash Dummy]

Have you resolved the problem yet? I'd love to learn how you fixed this.

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