Should I or shouldn't I, to bush or not Options

[iankarr]

Hi Guys,

I've disassembled the rear of the bumblebee and the control arm pivots and bushings look to be in good shape.

My plan was to blast and powdercoat the control arms, which would require removing the pivots/bushings (due to the heat)...but I hear re-installing these can be a beeotch. And I generally prefer keeping as much OEM as possible.

So...do you think it's worth leaving the bushings and pivots alone and just painitng the arms? I'm aiming for this bumblebee to be a solid #2 car when done.

Thoughts? Thanks!

[76-914]

Too bad we're 2000 miles apart. We could do a video that would simplify this process for others. (IMG:style_emoticons/default/beerchug.gif)

[914_7T3]

Yes, 100%

[Zaffer]

I once did the bushings on my ‘75 years ago and it was a PITA. I had access to a good shop press, but it was getting everything lined up and stable enough to press everything in/out.

I was contemplating the same thing on my current control arms and decided to paint them instead due to the bushings being in good condition. Personally, a good paint job will be almost as good as powder coating and won’t require as much effort, IMO.

[914Sixer]

914Rubber has the kit now.

[Superhawk996]

Unless bushings are showing signs of dry rot, cracking, or having become delaminated from the trailing arm, I'd leave them OEM for a street car. Photos of your parts look pretty good. I wish I had a set like that! Mine are chunked and cracked. I'd really like to find a decent set of arms rather than rebush mine. We'll see what turns up before I need mine done.

The OEM bushings are vulcanized into the trailing arm and will have a torsional, lateral, and longitudinal spring rate to them. Replacment bushings will never be quite the same and cannot duplicate that rate.

Nothing against aftermarket bushings since in some cases, it simply can't be avoided. Same for track use - there are advantages to changing them.

Once you veer away from OEM, you end up in all the other debates:

Rubber vs. Urethane vs. Delron vs. metal bushings (like self oiling Bronze) vs. needle bearings and/or spherical heim joint solutions all of which have their Pro's and Con's both for ride & handling and NVH.

[iankarr]

Too bad we're 2000 miles apart. We could do a video that would simplify this process for others. (IMG:style_emoticons/default/beerchug.gif)

I think you just tipped the scales, Kent. Part of why I got this BB was to do videos documenting every step of restoration. Thanks for reminding me why I shouldn't skip this. I'm happy to take your reccos, though!

I remember @eric_shea talking about how the bushings need to be jb welded in to the arm. Any other tips?

@Superhawk996 you make valid points. Do you think that the modern replacements are inferior...or just different?

Thanks, everyone for chiming in. And Jeffrrey
@914_7T3 ...wow!

[mepstein]

I thought jb weld was for polybronze bushings, not rubber?

[JamesM]

Even if they are 100% intact that rubber is still 46+ years old. Rubber ages faster than probably any other material a car. While they may be original bushings guaranteed they do not ride like "OEM" anymore.

I installed the Rebel Racing solid ceramic bushings in the front of one of my cars and despite having a stiffer than stock swaybar and SOLID bushing its still the most comfortable riding 914 i have. 46 year old rubber is trash.

Yes, removing them is a royal PITA and installing (if you stick with rubber) is probably even worse, but if you want your car to be right you have to do it.

[Superhawk996]

Do you think that the modern replacements are inferior...or just different?

I'll start with the fact that I'm biased toward OEM both because I work in the industry and because I used to be involved in chassis tuning. I know how much work goes into engineering bushings and it's not as simple as most think it would be.

Short answer. Because they will be different.

Long answer. Porsche engineers knew what they were doing when it engineered the bushings as vulcanized parts. What might seem like minor differences in bushing design (press fit vs. canned vs. vulcanized to inner/outer cans) can make a huge difference in ride, handling, and NVH.

I'd be a whole lot more inclinded to replace the bushings had they been designed to be replaced. If they were a canned bushing that could simply be pressed in/out of the trailing arm, I think I'd certainly do it. But . . . that is not what they are.

I think there are lots of good reasons to replace a set of obviously worn and/or damaged trailing arm bushings, but, personally, I'd never do it just for the sake of doing it. Though rubber does age, it's a matter of degree and in this case, most of the rubber is vulcanized within the trailing arm and isn't exposed and won't age out as fast as a fully exposed bushing. Yes, the rate will definately be different than it was in 1973 (my car's age). Without data on the installed rate of the OEM bushings vs. new aftermarket bushings of a different design, we are all guessing.

To be completely transparent, it's a hard question to answer the question without data acquisition and some objective evaluation metrics to compare against.

You'd be surprised how evaluation bias (knowing a set of bushings has changed) can over ride subjective comparisons. There have been times when I drove cars blind (not knowing what was changed) and I thought I knew what was changed, made a subjective assessment, only then to find that the objective data didn't match the subjective assessment, and that the parts which were changed were not those that I thought. I.e. I was completely wrong!

Driving parts blind is something that good development engineers do from time to time to keep evaluation skills sharpened and to keep themselves honest. Most of us working in garages on our hobby cars can't do this (we know what was changed) and are inclined to think that we've improved things even if we haven't. Sometimes the metrics change (like wanting improved handling vs. OEM ride or OEM NVH) and that justifies the improvment. Other times, it's just wishful thinking. Been there done that.

[bbrock]

@Superhawk996 I like asking dumb question so here is another. Do you think there would be any benefit in coating replacement rubber bushings with cold vulcanizing cement before pressing them in? I know you can't really answer without having data to know what specs we are shooting for but curious if that would help bond the bushings to the tube which seems to be what vulcanizing does. (IMG:style_emoticons/default/popcorn[1].gif)

[Superhawk996]

@Superhawk996 I like asking dumb question so here is another. Do you think there would be any benefit in coating replacement rubber bushings with cold vulcanizing cement before pressing them in? I know you can't really answer without having data to know what specs we are shooting for but curious if that would help bond the bushings to the tube which seems to be what vulcanizing does. (IMG:style_emoticons/default/popcorn[1].gif)

I don't think I would.

I should be careful with the term vulcanizing before I get eveyone wound up. Vulcanizing isn't really a bonding process.

Vulcanizing is the process of modifying the rubber itself for durability and elasticity.

I belive that the OEM bushings are probably bonded (probably with chemicals & heat - thus the term vulcanized bond) to the trailing arm and the pivot shaft. The other option is that they are press fit so tightly that for all practical purposes, they are mechanically gripping the shaft and trailing arm to the point that they cannot move relative to one another.

So why not bond them with the cold vulcanizing cement?

My reasons would be:
1) Not sure the cement is compatible with the aftermarket rubber and/or could cause degradation to the rubber.

2) If or when the cement bonding gives up and breaks free, it might actually then work against you by allowing easier movement of the parts realtive to one another. Relative movement will lead to rapid wear and won't have bushing rates anywhere near OEM intent rates.

3) From everything I've read (remember my trailing arm bushings are shot), the amount of press work and swearing associated with installation is pretty intense. Having to deal with the possibility of having the cold vulcanizing cement partially curing before I get everything seated home and then inhibiting installation seems like a risk I wouldn't want to take.

Having said all that, I haven't done this job yet myself but the pitfalls are almost enough to make me consider poly-bronze bushings and I know I'd hate those for a street car based on prior experience with them.

I don't wan't to promote myself as some sort of expert on 914 trailing arm bushings. I'm just sharing my rationale on why I'm not inclined to change out a set of trailing arm bushings that aren't otherwise damaged based on my professional experience with the nuances of bushings. There is more to them than meets the eye.

Ask yourself this question, how many vintage cars, trucks, vans, etc. are out there on the road that haven't had all the bushings, trans mounts, and/or engine mounts replaced wholesale? Quite a few, and they still get around just fine. Could they be better? Yup, I'm sure of it in some cases. Could they be worse, yup, lots of cars out there with all sorts of aftermarket bushings & mounts that actually made them worse.

No way to know with certainty without objective data.

Based purely on reported outcomes with the various aftermarket rubber bushings from our usual vendors I think they will be just fine for our hobby cars and I don't want to come off as snubbing them. I'm glad the parts are availble. It's really just the question of effort vs. reward. Each of us will have a different sweet spot.

[bbrock]

Ask yourself this question, how many vintage cars, trucks, vans, etc. are out there on the road that haven't had all the bushings, trans mounts, and/or engine mounts replaced wholesale? Quite a few, and they still get around just fine. Could they be better? Yup, I'm sure of it in some cases. Could they be worse, yup, lots of cars out there with all sorts of aftermarket bushings & mounts that actually made them worse.

Thank you sir! As you know, I'm always looking for that extra inch to match OE quality but your answer is pretty much what I expected.

OTOH, I've had a vehicle rendered unsafe to drive due to deteriorating bushings. Old Pathfinders are kind of notorious for it. Wholesale bushing replacement brought the car back to like new.

Unfortunately, the bushings on my 914 were shot and dry rotted so no choice but to replace. I have a set of 914Rubber rubber bushings ready to go in so will be watching for Ian's video (IMG:style_emoticons/default/beerchug.gif)

[Superhawk996]

Unfortunately, the bushings on my 914 were shot and dry rotted so no choice but to replace. I have a set of 914Rubber rubber bushings ready to go in so will be watching for Ian's video (IMG:style_emoticons/default/beerchug.gif)

Me too (IMG:style_emoticons/default/headbang.gif)

Will be replacing with rubber and I look forward to Ian's video too!

[Superhawk996]

OTOH, I've had a vehicle rendered unsafe to drive due to deteriorating bushings. Old Pathfinders are kind of notorious for it. Wholesale bushing replacement brought the car back to like new.

Yup, me too. Michigan potholed and frost heaved roads destroy bushings fast.

Not sure of Pathfinder bushing design but most modern bushings have way more rubber and voids than a 914 trailing arm bushing which is sort of an apples to oranges comparison.

Modern bushings usually allow for a whole lot more travel (kinematic recession), isolation, and they are used to influence steering behaviors via compliance. All that travel and flexing will lead to them wearing out in different ways vs. 914 trailing arms. Luckily, more often than not, modern bushings are designed to be replaced unlike 914 trailing arms.

I've had cars where the bushings weren't able to be replaced and had to replace the whole control arm. (IMG:style_emoticons/default/barf.gif)

[bdstone914]

@914Sixer

I have yet to find the rubber bushing on their site. I ordered the only bushibg they had and they were poly which i will not use.

[yellowporky]

When i restored my 73 1.7 i went with the rebel racing front and rear set up and i love the way the car feels on the road. Of course it was more money but so easy to install it was so worth it.
And we have some pretty crappy roads here is in northern california too.

[Mark Henry]

How should the rear trailing arm hang?

Without shocks or the axles hooked up my trailing arms fairly quickly fall till they point close to straight down.
My front A-arms stayed relativity fixed with the old rubber bushings, but now I have McMarks full motion (bearings) bushings they also will hang straight down like the rears.

I'm debating whether to rebuild the trailing arms or not, but I'm thinking seriously about bracing the console as I have 250+hp.
If I let her rip up to 7K rpm I can feel the ass end getting a little squirrelly, mostly from the right rear.

[mlindner]

If you decide to paint use Imron. Used on truck frames and trailers, pretty bullet proof.

[Montreal914]

@bdstone914 ; There you go (IMG:style_emoticons/default/smile.gif)

I have a set that will go in your rebuilt trailing arms. Not sure yet how I will proceed. Hoping to see a video from Ian (IMG:style_emoticons/default/popcorn[1].gif)

https://914rubber.com/rear-trailing-arm-bus...for-porsche-914