Impoving handling of Fiat 128 / Yugo / Ritmo

Non-engine, eg: aerodynamics, gearboxes, brakes, suspension
NickRP
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Post by NickRP »

Update:
Unforunatelly, the 128 PU bushes do not fit Yugo suspension arms.

I am taking three weeks of holiday for Chrismas, and I plan to perform the mods during that time. Unforunately, (due to incompatibility with 128) lot of custom fabrication has to be done, so I spent most of the (spare) time taking measurements, making drawings and purchasing material.

I still struggle to find any information about recommended interference fit on front sway bar carrier polyamid bushes. Preload is very important, but this appears to be kept top secret. Help still needed on this!

Up to now, I purchased:
1) Front shock absorbers (Monroe GasTec)
2) Longer front suspension arms (resulting in wider track, negative camber, more castor)
3) New steering arms
4) Aluminum bar for machining the front sway bar carriers
5) Polyamid bar for machining front sway bar carrier inserts
6) Front strut tower brace
7) "Magic camber" strut upper bolts

Yet unknown is whether the longer suspension arms are going to cause problems with drive shafts. Yugo has (just like 128) tripod joints on gearbox side of drive shafts. I will "dry-build" the suspension first and check the position of the tripod joints inside the diff. I can always put spacers behind the CV joints, to compensate for a few millimeters, but if this is not enough, I'll be in major trouble (i.e. I'd have to find longer drive shafts and machine them to fit).

I will post details and pics afterwards... in about a month, I hope.

All the best,
Nikola Radenkovic
NickRP
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Post by NickRP »

Well, holidays are all gone and I am back with most of my car's front suspension being rebuilt.

Unfortunatelly, it took lot of trial and error to make it right, mostly due to my inexpirience with suspension mods, wrong information that I was getting from various "reliable" sources, inadequate or non-existing uprated aftermarket parts etc. It proved very useful to have machine shop at my disposal for free, otherwise, machining labor price would be very high.

First of all, Monroe 'Original' gas shock absorbers (although doing wonderful job on sunmodified suspension) were inadequate for lowered car. They are a bit longer than the stock items, and they bottom out very easily (however, bottoming can occur almost as easy on stock shocks). Many people use them on lowered Yugos, and on all the cars I've seen so far, the problem existed (unfortunatelly, only after I found out the problem the hard way, I started examining the other cars) . Alternative is to use Fiat 127 front shocks (they are shorter and fit Yugo), but I could not find them within the tight time constraints I had (New Year's and Xmas holidays didn't help, either). So I had to shorten and rebuild the original shocks. Shortened by 40mm, they were safe with my 30mm lowered front end. I did not want to upset the ride quality, so I left their stock settings intact and I used oil of equal viscosity as the original one.

As for the front sway bar carriers, initially I made ones according to the dimensions I got from other Yugo owners. After the paint had been stripped from the bar, the diameter was 20.99-21.01mm, however, the surface finish was not so good. After lot of discussion I decided to go to 20.98mm polyamid bushing ID. Too much of a tight fit makes terrible sound while sway bar is moving, while loose fit results in play that also sounds bad and creates impact wear (all of those I was said). With all the parts ready, it became apparent that the axial play of the sway bar (totally undesirable on F-128 type suspension) would be limitied only by a contact point between sway bar and plastic bushes. So I had to re-engineer the sway bar carriers, so that additional axial carriers take care of axial positioning. A few modifications were neccessary to allow use of longitudal reinforcements between front suspension arms mouting points and sway bar carriers. Lot of "come and go" to machine shop indeed.

Finally, strut tower brace was about to be installed. I was concerned if it is going to clear the carburetor air inlet housing suficiently to avoid any contact while the engine is running. Luckily it did. However, it did not clear a spare wheel (located in engine bay) and hood reinforcements. I reworked the spare wheel carriers to move it 5mm downwards, which proved sufficient... hood reinforcements had been bent slightly, to clear the brace, but there is still some occasional contact waiting to be sorted out.

Longer suspension arms, luckily, did not require longer drive shafts. I will have to check where the tripod joints are sitting after the front suspension geometry was adjusted, but initially it looked like there is going to be more than enough place for their safe movement.

Wheel camber was set to -0.5‚°, with other settings left stock (toe-in and castor).

I did about 2000km after the mods. The impovement can be felt, there is no doubt on this. Torque steer is virtually gone, understeer is much reduced. However, suspension is a bit noisier and still expiriences bump steer (in about the same extent it used to).

Pics will be available soon.

All the best,
Nikola
Guy Croft
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Post by Guy Croft »

Model Post


widely read and so informative, well done.

GC

By the way, Nikola watch out with that bump steer effect and importantly check behaviour or suspension when going over a rise or hump, where the car 'lifts off' (or goes totally airborne), it must come down nice and straight. If the wheels are all over the place (camber, caster) on landing it's awfully dangerous.
unoracer
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shorter struts for 128/yugo

Post by unoracer »

Re 'shorter' front struts for yugo/128: I have been told by a couple of sources over the years that x1/9 REAR struts will fit on 128/yugo front. I believe that the top mounts of course need to be changed over, and that some variants/ages of x1/9 rear struts may not be suitable for some reason! Sorry for third hand advice, but you never know, it may help someone!
NickRP
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Post by NickRP »

Sorry for not posting any photos yet. When I come from work, it is too dark to take them, and I was absent during weekend.

As for the X1/9 rear struts, yes, the early ones ('74-'79) fit Yugo. But it is virtually impossible to find those over here...

I am a bit short of ideas how to fight bump steer. I am even unsure whether it is inherent to the suspension type present in Yugo. I didn't go so far in testing (it takes time to gain confidence in car, and it is being used on public roads, so I have to be careful).

Hopefully I'll manage to take some photos during daylight soon.

Regards,
Nikola
Guy Croft
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Post by Guy Croft »

have a good read of this Nick

http://www.racerpartswholesale.com/longtech3.htm

GC
NickRP
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Post by NickRP »

Thanks Guy, I went through it... I am starting to understand what is going on now on my front suspension (too bad those rules of thumb were not given for MacPherson struts).

The problem is that there are very limited adjustments possible. I had some discussion with guys that drive X1/9 in SCCA racing. X1/9 has very similar front suspension to 128/Yugo one. They all report significant bump steer when the car has been lowered (the lower it is, the worse it gets). The cure is to stiffen the front end suspension dramatically, so there is minimal change of wheel to chasis relative position. And I can't do that on a street car.

If I weren't so tight with time, I would have constructed mathematical model of my front end suspension linkage, so that I could easily visualise what is happening when the wheel goes up and down. This is definetely an area where my car hadling needs improvement.

Regards,
Nikola
sumplug
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Post by sumplug »

Nikola.
You must have your car so low, that the suspension is lower then the centre of gravity. X1/9's at the rear have a similar problem if set to low. This will cause Bump Steer. You need to raise the front slightly.

Andy.
NickRP
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Post by NickRP »

Front end has been lowered by 30mm. Before this winter, it used to be even 10mm lower than that. Suspension arms are now siting slightly below horizontal (i.e. outer ends are lower than the inner ends), so this should give (at least initial) correct camber change with wheel vertical movement. The photos will show that the car does not look too low. I hate using words like 'look' here, but still it is some indicator (at least in comparison to some other lowered Yugos).

But I have no idea what is happening with toe in on wheel vertical movement. I do blame myself for jumping into modifying something without clearly understanding how it worked (e.g. which arcs steering and suspension arms exactly were making, how critically was the position of roll centre upset when the car was lowered etc). I was blindly believing that everything was coming from the suspension bushes being either to soft or detorated with age.

One part surely came from the bushes, but not the bump steer. I am now only wondering if I made it worse somehow by installing longer suspension arms. Shouldn't be though, as the angular movement of the longer suspension arm and longer tie rod is actually reduced as their length is increased... but then again, due to the lack of knowledge (math. model, expirience), I can only guess (another word I hate in this context).

Best regards,
Nikola
sumplug
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Post by sumplug »

The Macpherson strut is notorious for altering the castor on cornering, and maybe the longer arms are increasing this to bring on the Bump Steer.

So what you have to look at is increasing inset on the wheel to bring the centre of the wheel inwards. Your offset is too much and needs decreasing.

Andy.
NickRP
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Post by NickRP »

Finally some photos... a few more yet to come. Sorry for quality being suboptimal.

Nikola
Attachments
Detail of longitudal reinforcement fixing to front sway bar carrier.
Detail of longitudal reinforcement fixing to front sway bar carrier.
IMG_0314_small.jpg (50.54 KiB) Viewed 12762 times
Monroe "Magic Camber" excentric screw in upper mounting hole.
Monroe "Magic Camber" excentric screw in upper mounting hole.
IMG_0312_small.jpg (41.16 KiB) Viewed 12761 times
Section of the suspension arm 15mm longer than stock. Sway bar mounting point location unchanged.
Section of the suspension arm 15mm longer than stock. Sway bar mounting point location unchanged.
IMG_0311_small.jpg (39.28 KiB) Viewed 12766 times
Strut tower brace. p.s. now that engine bay needs some cleaning.
Strut tower brace. p.s. now that engine bay needs some cleaning.
IMG_0310_small.jpg (79.98 KiB) Viewed 12769 times
Longitudal reinforcement clearly visible.
Longitudal reinforcement clearly visible.
IMG_0309_small.jpg (49.57 KiB) Viewed 12766 times
Front sway bar carrier together with axial carrier (one per side). Longitudal reinforcement also visible (connects swaybar carrier and suspension arm mounting point).
Front sway bar carrier together with axial carrier (one per side). Longitudal reinforcement also visible (connects swaybar carrier and suspension arm mounting point).
IMG_0308_small.jpg (39.71 KiB) Viewed 12768 times
Custom built front sway bar carrier. Note that there is very short straight section of the bar
Custom built front sway bar carrier. Note that there is very short straight section of the bar
IMG_0307_small.jpg (32.12 KiB) Viewed 12771 times
My Yugo, 30mm lowered all round
My Yugo, 30mm lowered all round
IMG_0306_small.jpg (30.88 KiB) Viewed 12774 times
Guy Croft
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Post by Guy Croft »

Good photos Nick, well done.

I'd like to know more about this bump steer. What exactly is happening and under what conditions? Is the damper bottoming out before full spring compression or is something hitting a bump stop on full compression? Or is the spring fully compressing (binding) without any bump stop preventing it from doing that?

GC
sumplug
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Post by sumplug »

If the bottom arm is going past the roll cente position, then this will create bump steer. Your wheels look like they have little offset, so it must be something on the suspension. You may have to use an adjustable top mount.

Andy.
NickRP
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Post by NickRP »

Guy,

as the struts have been shortened quite a bit and the spring carrying plates on struts have been relocated to lower position, so neither the damper can bottom out nor the coil can bind. Also, the bump stop positions have been adjusted apropriately.

So under normal driving conditions, nothing will botom out. The wheel has to go up about 100mm to hit the bump stop now, which I consider safe.

What happens when I expirience bump steer... for example, I am doing some 120km/h on highway and one wheel catches the lower track on the road (made by heavy loaded trucks, sorry that I do not know the English word for that). Next moment the car is 50cm from where it used to be, and I have to correct steering wheel position to return it to original line...

Regards,
Nikola
Guy Croft
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Post by Guy Croft »

OK, thanks. I am familiar with that tendency for the wheels to follow ruts in the road, it happened on my 124CSA. I put it down to using low profile tyres, but that said, the wheels shoud self-align quite readily and on a flat road the vehicle should drive quite happily in a straight line without any steering input. It's the castor on the wheels (like on a trolley castor wheel) that gives that. Maybe you have a lack-of-castor issue?

GC
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