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Mustang Technical Discussion > Pre 1973 > What's a good rear suspension upgrade plan for 68 GT390? > Community Forums > Mustang Forum Australia - Mustang Tech

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What's a good rear suspension upgrade plan for 68 GT390? Reply to topic

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mungus
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So whats the best spring eye bushing material to use then? The OEM rubber kind? Nolathane? Urethane?
Seems most aftermarket suspension & steering outfits provide them for every "soft" bushed pivot point as part of their upgrade kits, and they are also sold as an upgrade in themselves.

I've got OME (ARB) nylon bushes in my 4x4 and found them good, outlasting the OEM rubber ones and tightening things up a bit, feel wise.

So whats the go?


Grumpy old git!

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mert
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Opinions will vary. This is one of those issues that brings out a lot of views (like the curved vs straight monte carlo bar debate). While there are a lots of views I've never seen anyone post a simple empirical dataset showing the same car, same driver, same track/run, same conditions and a set of times to weed out statistical errors of small datasets to actually show what difference it really makes in the end. Lots of "feels better" and "I like its" but facts and figures are in short supply...

Depends on what you want. My view is "Best" in these types of issues is a tricky term. No such thing, as driving style/ability will dictate. Some want a cruiser, some want to feel every pebble in the road.

If you buy into the race-cars-use-them-so-they-must-be-better go for the harder materials.

Obviously rubber will flex more, but is a less harsh ride.

As for durability I've never had to replace OEM rubber for wear, only due to restoration for looks (they only lasted 20+ years in street use).

You seem to keep going between a nice safe street car (the kids-in-the-car comment elsewhere) to "max Power".

I'd bet if you ran rubber, drove the streets in a legal manner, then swapped to other rear spring bushes and repeated you would not notice much difference at all... but I've never tried it. Maybe pushing as hard as possible on a track it makes a difference, but on the street... I'm not buying it as significant, if even noticeable if the rest of the suspension is solid. Good shocks will make a far more noticeable difference.

I run rubber and have never been disappointed.


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Last edited by mert on Thu Nov 26, 2015 11:29 am; edited 1 time in total

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ozbilt
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Nice reply mert ..... Like

I for one have had both rubber bushings & urethane bushings in the same car. In the front end the urethane cracked, then split after only a couple of months driving in California (it was a daily driver) & I replaced with MOOG bushes (they are still in there some 15 years later).

The rubber rear front bushings were replaced with urethane at that same time. Once the grease ran out (hot in California) it squeaked its head off. If you could grease it I would have left them in. I have always ran rubber in the rear bushings.

If you don't want the diff to move side to side, then a panhard bar or watts link is needed. For a road car, both are a waste of time, effort & money.


Kerry

It is easier to get older than it it is to get wiser

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trav68
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I personally do not agree that all urethane bushes in all applications are rubbish. Certainly, some specifications of urethane in some suspensions points are a poor substitute for rubber and for the general user rubber is probably a better option as is long lasting and basically maintenance free.

My other car (VY SS Commodore) has a few selectively chosen applications of urethane used in the suspension (including front and rear of radius rod/caster bar) and it is a significant improvement in composure under braking especially when coming down a hill on a slight grade. You can feel this difference in general road driving and even further amplified on a track or skidpan. With regards to longevity those bushes have been in the car now for maybe 8 - 10 years ( 70,000 kms or even more) and only now is one rear bush looking due for replacement. These bushes were all installed as per manufacturers instructions and have never required maintenance as a result of squeaking etc.

I think it is an application issue (i.e maybe using urethane for rotational pivots where there the suspension setup allows for a large range of movement/articulation is unwise and rubber is the preferred choice).

Also comes down to the quality and composition of the urethane some look and feel so hard they are better suited to a mine site whilst others are reasonably pliable. Rubber bushes also come in a range of qualitys - e.g OEM (and Moog, Mackay etc) bushes have a different hardness to a cheaper brands.

My Mustang runs rollerised front suspension arms with rubber everywhere except front swaybar D bushes and end links.

Just my 2c worth.


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hybrid
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I have urethane in a few places in my car.
One of them is the leaf spring bushes. My car squeaks. I greased them.

I don't know if it's those yet or the spring perches squeaking. One day I'll have a look.


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mungus
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"You seem to keep going between a nice safe street car (the kids-in-the-car comment elsewhere) to "max Power". "

Ahhhhh well, to my recollection I have never used the term "max power" as a goal at any stage on this forum.
If I wanted that I wouldn't even be building a classic Mustang, (no offence).
There are far better, faster and more powerful cars to build out there if I wanted that.
Especially in the kit car marketplace (and yes I've built kit cars before).
And yes you are correct that it will be a cruiser, but I also like things that handle and am partial to the occasional track day (done plenty on my bikes in the and pommie rubbish sports cars, albeit a few years ago), so a bit less wobble is desirable, albeit not the main aim.

I have always moved between the goals of a mildy improved and rebuilt 390 up to a fast road stroker engine, depending on my desires at the time, and have always ventured the desired figures of between a minimum of 350hp up to 400+ hp. Given that FE's making 650+hp are not uncommon these days, (or difficult to achieve if you spend the $ on easily available bits), I would hardly call 400+ hp "max power".

Nevertheless the comments on rubber bushings vs. urethane are all appreciated. As always I'll take the view of the whole package. e.g if my car already has 4.5 leaf springs I'd probably stay rubber. If it has the OEM 4 leafs and the bushes are shot then maybe a nice set of black urethane bushes wouldn't go astray. (ride height dependent of course as I don't want a low rider, I'll swap the springs if they are inverted eyes etc).

Add that to the existing plan of traction bars and some nice Koni or Bilstein shocks all around, and I think it'll do nicely.
One things for sure though, I wont be fitting any bright coloured bushes in there, that might look "trick" on an MX bike or comp 4x4 but on a classic car - no thanks.

All comments appreciated BTW.


Grumpy old git!

Last edited by mungus on Thu Nov 26, 2015 10:43 am; edited 2 times in total

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mert
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No offense taken at all.

The comment was general in nature around the the "improved performance, power, handling" themes that keep coming up, juxtaposed to some comments concerning keeping it more original. A dichotomy..

I'd agree trying to make the best car for the money in a performance area means you would be better off not starting with a Mustang. A brick can be made into a similar handling car for about the same price! šŸ˜€

For consideration (colors aside, maybe you can paint them) the Del-Alum are noted by some to be a good alternative to Urethane and an upgrade over rubber... and are grease-able by zerk.... never tried them.

www.globalwest.net/196...nsion.html


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Last edited by mert on Thu Nov 26, 2015 11:29 am; edited 1 time in total

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lukep6470
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hybrid wrote
I have urethane in a few places in my car.
One of them is the leaf spring bushes. My car squeaks. I greased them.

I don't know if it's those yet or the spring perches squeaking. One day I'll have a look.


My completely original setup squeaks like a 1970s British military vehicle now with rubber bushings.

I have a tub if silicon grease left over from rebuilding a Kitehenaid mixer of all things. Would it be worth covering polyurethane bushings in that before installing them?

I only use my car on the street and I've found the lateral movement of the rear axle very disconcerting and my wife even notices it as a passenger.


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hybrid
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Urethane bushes normally come with a grease, but I'm not sure if it's a special type or not.
As long as the grease doesn't affect the urethane, it should be fine.

I think Urethane in the rear should be fine. There is nowhere near as much movement there as there is in the front end.


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hybrid
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What is the grease supplied and where do I put it?
The Nolathane lubricant supplied is designed to optimise bush durability and performance. Nolathane grease is a molybdenum disulphide (LM) based grease and has excellent stability & extreme pressure qualities for extended life and high melting point. Grease supplied in the kits where required should only be used and applied to the bush surfaces designed to pivot (eg flange faces and internal bores) DO NOT grease pressed fit surfaces (eg outer shell) or outside surface of shackle bushings. DO NOT use rubber grease as this can affect urethane bushings.


Some interesting "facts" in that FAQ also.

www.nolathane.com.au/faq.php#q5


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boofhead
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I would not use Nolathane. In my experience it can permanently deform just as many other the other non rubber bushes can. Good rubber bushes are best. Then is needed a Watts link or other facilities.


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mungus
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mert wrote
No offense taken at all.

The comment was general in nature around the the "improved performance, power, handling" themes that keep coming up, juxtaposed to some comments concerning keeping it more original. A dichotomy..

I'd agree trying to make the best car for the money in a performance area means you would be better off not starting with a Mustang. A brick can be made into a similar handling car for about the same price! šŸ˜€

For consideration (colors aside, maybe you can paint them) the Del-Alum are noted by some to be a good alternative to Urethane and an upgrade over rubber... and are grease-able by zerk.... never tried them.

www.globalwest.net/196...nsion.html


Those Del-Alum bushings look the go, I've even read some articles saying they definitely reduce sideways movement without the need for a watts linkage etc. no doubt that side of their performance is limited but nevertheless the idea seems good. Only downside is that bright white colour for the outer bush plates.

So I'm tentatively adding them to the list. Along with a set of Konis.
Not sure if I'll go standard or adjustable yet. Any views on how good the standard ones are with standard rate springs? Or even slightly harder (4.5 leaf) springs? Happy to pay extra for adjustable if they are really like chalk and cheese, albeit they seem a bit of a pain to adjust, (I'm well used to fiddling with adjustable shocks from my past years of bike racing), but if the standard Konis are pretty good for cruising and the odd squirt, then why bother...

Once again all views appreciated!

BTW the old girl is finally here in VIC. Still awaiting AQIS but not far away I hope! Smile


Grumpy old git!

Last edited by mungus on Tue Dec 08, 2015 2:30 pm; edited 3 times in total

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Shaunp
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You defiantly want the adjustable koni classics that used to be called special D. I've used them for 25 years in all types of cars jags, mgs toranas etc . These are the orange ones though you could order them in black for a stock look for a while


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mert
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Bilstein street valved....


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trav68
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+1 for Koni adjustables.

Matched to Lovells 550 lbs/in springs on approximately half setting for street and up full on the track and the front end works harmoniously with some slicks.

Bilstein streets provide a nice compliant ride with 400 - 450 lbs/in springs but provide significantly less rebound control in my experience.


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