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MG MGF Technical - Diagnosing suspension problems

I'm still worriting away at this from time to time and here's my latest request for advice. Sorry for the long-ish post, but the background info is necessary and the questions at the end should be interesting.

Description: My 1995 MPi, 66,000 miles is much loved and driven fairly hard. I now find that the back end skips on corners at speed (though the road to work has some poor surfaces) and the car feels floaty at times. I would also describe the ride over poor surfaces, manhole covers and the like to be harsh. The degree of contact with the road bothers me most - I certainly cannot corner as well or with as much confidence as I did a year ago. I know that what is harsh to me may be OK to you or normal for the car, but I think the ride is worse now than a year ago and I think that this is not the Hydragas-smooth ride for which the MGF is famous.

Background: I've had a recent 4-wheel alignment and tyre pressures are spot on recommended levels with good condition Avon Z1s (?) on front (car came with these) and Bridgestone RE270s on the back. I was concerned that the trim levels were high or markedly different from one side to the other (see unequal camber thread from months ago). My own checks of the ride height have concluded that it is at the 368mm level.

Questions:

1) Silly, I know but how fast do people expect to be able to corner without sliding the back end or scaring themselves? What corner you say? Well, how about a neat 90 degree left hand turn as a standard.

2) I assume that the hydragas system is working fine as the ride height and pressure checked out OK. Is this a reasonable assumption?

3) Would lowering the ride height to the bottom end of the approved range instead of the middle have an appreciable effect on the handling? Does anyone know what the relationship is between lowering by X mm and changes in camber settings by Y degrees?

4) That leads me to the shock absorbers or dampers, which as far as I know perform as secondary role, helping the Hydragas return to neutral faster than it would on its own. How long should shocks last? How do you tell if they are in need of replacing (no signs of weeping)?

5) Clearly the bushes at the bottom of the shocks are knackered. Could this alone be responsible for the lack of connection between me and the road?

6) If replacing the bushes and therefore removing the shocks, should I replace the shocks and if so with what and at what cost (without going down the full Techspeed route)?

7) Is there anything else I should check out before trying the above in order to diagnose and treat the problems I think I have? I am assuming that the fall off in cornering performance, ride quality and general feel is a suspension issue, but tell if I am barking up the wrong tree (or simply barking)?

8) Other than my regular and OK Rover dealer is there anyone else in the SE or in London who you would recommend to check out these issues?

Cheers all

Chaz
C Golvala

Having done 66k your dampers will definitely shot. I can only recommend that you go to Tech-speed and get your suspension sorted. This is what I have done and cannot recommend them highly enough.
Blue Pocket Rocket

"Having done 66k your dampers will definitely shot."

Why?
Isn't it more age related?

Some other answers:
"1) Silly, I know but how fast do people expect to be able to corner without sliding the back end or scaring themselves? What corner you say? Well, how about a neat 90 degree left hand turn as a standard."

No easy answer. Sorry.
A comparative test is always better I'd suggest.

"2) I assume that the hydragas system is working fine as the ride height and pressure checked out OK. Is this a reasonable assumption?"

I'd say so, yes.

"3) Would lowering the ride height to the bottom end of the approved range instead of the middle have an appreciable effect on the handling?"

Yes. Without knuckles the car will have less suspension travel going over bumps. Ride will be more harsh.

"Does anyone know what the relationship is between lowering by X mm and changes in camber settings by Y degrees?"

Errmm.... Rob? ;-)

"4) That leads me to the shock absorbers or dampers, which as far as I know perform as secondary role, helping the Hydragas return to neutral faster than it would on its own. How long should shocks last? How do you tell if they are in need of replacing (no signs of weeping)?"

As you can tell above - I have no idea!

"5) Clearly the bushes at the bottom of the shocks are knackered. Could this alone be responsible for the lack of connection between me and the road?"

Why clearly? Can you see that?
If that's the case, then it will have big (negative!)effects on the handling.

"6) If replacing the bushes and therefore removing the shocks, should I replace the shocks and if so with what and at what cost (without going down the full Techspeed route)?"

It will do no harm for sure !! :-)
Note that the Techspeed suipplied shocks are of their own spec!

"7) Is there anything else I should check out before trying the above in order to diagnose and treat the problems I think I have? I am assuming that the fall off in cornering performance, ride quality and general feel is a suspension issue, but tell if I am barking up the wrong tree (or simply barking)?"

If you're sure about tracking, height and tyres... it is likely that the suspension bushes and the like could do with an overhaul. Older cars *can* be made to feel new again - in the handling department at least.

"8) Other than my regular and OK Rover dealer is there anyone else in the SE or in London who you would recommend to check out these issues?"

Ug. No idea. Soz.

Hope this helps.
P.
Paul Nothard

At a car in that age I would swap to PU-Bushes at the lower arms, and mainly at the rear tie bar (Wheel hub to subframe).
Or just add compliance washers there.

>"Having done 66k your dampers will definitely shot."

>Why?
>Isn't it more age related?

Nope, dampers wear from moving. I've a diagram anywere of an MGF been measured on a damper test stand. (German ADAC does FOC)
It shows clearly the dampers at that car with about 50k miles had only 50% damping behavior.

HTH
Dieter
Dieter K.

Dieter, don't you mean 5k miles;-)
Mike
mike

One of the reasons could be tyre in balance.

When I had new rear tyres put on, the car got quite scary with the backend feeling like it wanted to overtake the front. I had Goodyear F1 old type and put goodyear F1 new type so different tread pattern.
I knew my car was perfectly sound as I was up at Techspeed a couple of days latter for its MOT and did get them to check everything.

The car has got better with use but still does not feel the same as before so shortly will be changing the fronts which will hopefully cure the problem.

Tom
Tom Randell @ work

Hi Chaz,I remember that camber thread...

>>Background: ... good condition Avon Z1s (?) on front (car came with these) and Bridgestone RE270s on the back.<<

I think that this line may hold the answer to your car's handling woes. I have to agree with Tom, there could be a tyre imbalance problem: Avon, and especially the ZR-1, has a reputation of mixing VERY badly with other tyre types. Have a browse through the archives, and you'll see what I mean.

Therefore before any genuine handling diagnosis can be performed, I think that you need to get your car on a decent set of rubber. Changing to RE720s all round will be fine. :o)

To your specific questions...

>>1) ... how fast [can you corner around a] neat 90 degree left hand turn<<

About 90-95 mph, depending on conditions, driving technique, and how much space there is on exit. This means that any answer to this question is, unfortunately, unlikely to help as there are too many confounding factors.

>>2) I assume that the hydragas system is working fine as the ride height and pressure checked out OK. Is this a reasonable assumption?<<

I'd say so, yes.

>>3) Would lowering the ride height to the bottom end of the approved range instead of the middle have an appreciable effect on the handling?<<

Setting the ride height to 340-350mm should have minimal impact on handling. Lower ride heights cause the spring and damper rates to soften too much, and as a result, the suspension spends all its time crashing off the bump stops. Not ideal!!!

>> Does anyone know what the relationship is between lowering by X mm and changes in camber settings by Y degrees?<<

Dieter has worked this data out, but for all practical purposes, this is not a primary concern. Just so long as the camber does not significantly exceed 1deg30min you'll be fine.

>>4) ... How long should shocks last? How do you tell if they are in need of replacing (no signs of weeping)?
5) Clearly the bushes at the bottom of the shocks are knackered. Could this alone be responsible for the lack of connection between me and the road?<<

The shock absorbers really don't perform all that much work; as you noted, Hydragas performs most of the damping function. However, whilst the dampers may be in OK condition, the damper bushes, by 60k miles, will be shot. These are readily replaced with PU items available from Mike Satur. Tim has written up some instructions for this process (http://www.mgf.ultimatemg.com/chassis_and_handling/shock_bush_replacement.htm) - or you could consider replacements from Techspeed, B&G or Mike Satur. These knackered bushes could indeed be partially responsible for the odd sensation you feel whilst cornering...

>>6) If replacing the bushes and therefore removing the shocks, should I replace the shocks and if so with what and at what cost (without going down the full Techspeed route)?<<

You might as well consider the full Techspeed route Chaz - it is one of those conversions that really is worth all the money spent on it. Dampers and lowering knuckles can be fitted for under 600 quid. It'll be the best 600 quid you'll ever spend on a car :o)

>>7) Is there anything else I should check out before trying the above in order to diagnose and treat the problems I think I have?<<

See tyre remarks above.

>>8) Other than my regular and OK Rover dealer is there anyone else in the SE or in London who you would recommend to check out these issues?<<

See Paul's Dotcomoff site for dealer recommendations. Motobuild are the closest to your area (SW London), and sorted out Duncan's F for him. But personally, I'd still travel the 100 mile trip up to Warwickshire...

Hope this helps
Rob Bell

>Dieter, don't you mean 5k miles;-)
LOL, would be only 5% less then ? and just a piece of pipe and pure shaft at 100k miles. Is 0%?
Nope, far to easy. :oP
Dieter K.

Most excellent F'ers, your advice is noted, with gratitude, as I emerge from deal-closing hell. Brief replies:

Surely the Avons can't be responsible for the floaty feel. Bite on turn-in or scrubbing when going hard round a bend I could understand. RE720s on the front is on the wish list, but hard to justify unless I slash my own tyres...(now there's a thought!)

1) Impressive speeds, Rob. I'm not sure I could do half that on an open field! What about a 90 deg LH turn from an ordinary B-road into another?

3) The reasons for asking about the relationship is that I am right on the edge of the camber range, but on one side only.

4/5) I've been reading Tim's instructions on Rob's site for a few weeks now. I think that what you guys are saying confirms my suspicions - the worn bushes are not holding the dampers firmly enough to allow them to work properly.

What happens when an MGF goes over a bump? The wheel is pushed into the wheel-arch, the damper gets compressed (and hydragas?), the body gets pushed away from the wheel (higher off the road). Then as you get past the bump (or if your wheel went into a dip/hole), the wheel and body move further apart restricted by the hydragas (as alternative for springs) and damper (?) and the suspension acts to settle the body and wheel into normal alignment.

If this is even roughly correct and the H'gas is OK, then the floating feeling is more likely to be the dampers not adsorbing the movement/restricting the movement than it is a worn bushes question. The worn bushes presumably allow more lateral movement of the dampers than is good for cornering.

6) An email to Techspeed won't hurt, but I'll have to try cheaper solutions first.

7) After reading the tyre change thread, the first thing I will do this weekend is get one of those accurate to a degree digital tyre pressure jobbies and check whether my foot pump's gauge is accurate.

Cheers folks. If anyone can explain the workings of the F's suspension any better (and I've read Rob's pages) I'd appreciate it.

Chaz
C Golvala

This thread was discussed between 25/03/2003 and 28/03/2003

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