Tight fits on Poly-Graphite bushings

[Bart de Bruijn]

Hi,

Started to work on the suspension of my completely dismantled 911T '69.
I bought a while ago the well known Poly-Graphite bushings for front A-arms and rear spring plates.
Both front and rear the fittings of these bushings are that tight that I need quit some force to mount them on the A-arms and then inside the control A-arm mounts!
Should they been machined before? (They are flexible so how should they be clamped during machining?)
If yes, how and what size / tolerance (play)?

If someone has experience, please tell me, I want to finish the suspension restoration ;-)

Thanks already!
Bart

[MotoSook]

Here's one way to install polygraphite bushings:

Front Suspension R&R with polygraphite bushings ala Souk!

[jpnovak]

Yep, Souk got it right. The lathe to fit is the way to go. I prefer to press the bushings into their collars and then make the ID round so they fit the a-arm. You can use whatever method you want to remove material but they need to be fit to the car. Otherwise its just a disaster of squeaking, popping and poor suspension articulation.

btw, if you do this by hand there are a few tricks. First, when you sand/remove material the surface will be rough. After you try to press them on and they do not fit the friction will create slight smooth spots where the bushing is proud. That is the first spot to start milling on the next round. Its a slow, messy project but not difficult and definitely cost effective.

[cgarr]

Thats what we do, but first true up the hubs too. Install then bore to fit.

[Wil Ferch]

Too many posts on this topic in the archives.

Cliffs note version.
1.) for the plastic type bushings...you need to machine the ID to fit the A-arm perfectly.
2.) Not done. If you should now install the hardware "clamp" around the bushing with no A-arm installed ( this clamp that supports the bushing OD is made up of two clamshell type pieces that hold everything together... )you will note that the "clamp" will distort the perfectly machined ID to something other than "round". You're screwed.
3.) Install the outer support "clamp" around a bushing ( on the shop bench, without the A-arm installed... not in actual fact..), then notice the ID distortion. NOW try to machine ( method ?) the ID to get to the desired diameter and round-ness.
4.) Almost there. Install regreasable zerk fittings. Oh...maybe machine some groves on the ID to smear the grease around better.
5.) Cross fingers.....

[the]

Originally Posted by jpnovak

I prefer to press the bushings into their collars and then make the ID round so they fit the a-arm.

That is a must. You have to have the bushings in their collars, THEN make the ID round.

Otherwise, you might as well make the bushings "round" by using a broomstick wrapped in sandpaper. Lathing the bushing while they are outside the collars is useless.

[MotoSook]

Originally Posted by the

Lathing the bushing while they are outside the collars is useless.

You are wrong. The bushing cold flow and fitting them with just the right amount of interference is the key.

Remember, the bushing is not suppose to rotate or twist during service! Milling the ID and boring the clamps is just extra work IMO.

[the]

Respectfully disagree.

[MotoSook]

Proof is in the result....until you can prove that one way is mechanically superior in operation, you are just guessing. I have emperial results to validate my method.

[the]

Originally Posted by Souk

Proof is in the result....until you can prove that one way is mechanically superior in operation, you are just guessing. I have emperial results to validate my method.

You have empirical proof? Let's see it.

If neither of us do, all you have to do is look at the many people here who have used your method and come away with squeaking, binding bushings. That's what happens when you put an egg shaped bushing on a precision a-arm.

Anyways, if one is going to lathe out a bushing, I can't see any reason why one would NOT simply place it in the (very irregularly shaped) retainer, THEN lathe it perfectly round. That way the bushing, as assembled to the a-arm, has a perfectly round inner diameter, to ride nicely on the precision (round) a-arm surface.

As opposed to lathing it round, then forcing it into the irregular retainer, thus causing the lathed bushing to have a very irregular inner diameter. Why do that? It is not any easier, quicker, less expensive, etc.

People can do what they want, though.

[MotoSook]

The clamps are a crude way of holding the A-arms in place, and they were never meant to perform a precise operation (e.g. act as a bearing guide for rotation or twist, nope). Even the A-arm was not meant to perform a precise movement. Making them into precision parts is unnecessary since the bushings will deform and flow in service anyhow! That is a fact.

As for others who have squeaking, binding bushings I can't speak for how they performed their installation and wouldn't dare assume how they did it.

My method has performed years of street and track duty without binding or sqeaking on my car and others. Good enough data for me...I say.

If folks want to do the extra work, good for them.

[MotoSook]

Originally Posted by the

That's what happens when you put an egg shaped bushing on a precision a-arm.

Research the material property.

Originally Posted by the

Anyways, if one is going to lathe out a bushing, I can't see any reason why one would NOT simply place it in the (very irregularly shaped) retainer, THEN lathe it perfectly round. That way the bushing, as assembled to the a-arm, has a perfectly round inner diameter, to ride nicely on the precision (round) a-arm surface.

The clamps are imperfect in shape and how they mount. Why spend the extra effort to only install them on an imperfect mount? The extra machining will not previde concentric bushing and A-arm in operation. The mounting also won't provide a perfect A-arm axis (parallel to vehicle axis). The material will also flow to fill and if you don't leave enough material, the bushing will soon go loose, and there goes any concentricity or parallel axis that might have been found with all the extra work.

Originally Posted by the

As opposed to lathing it round, then forcing it into the irregular retainer, thus causing the lathed bushing to have a very irregular inner diameter. Why do that? It is not any easier, quicker, less expensive, etc.

I'm a great believer in doing things right, but when getting something right in 3 steps, why go another 3 steps when they provide no advantage?

[the]

Originally Posted by Souk

The clamps are a crude way of holding the A-arms in place, and they were never meant to perform a precise operation (e.g. act as a bearing guide for rotation or twist, nope). Even the A-arm was not meant to perform a precise movement. Making them into precision parts is unnecessary since the bushings will deform and flow in service anyhow! That is a fact.

As for others who have squeaking, binding bushings I can't speak for how they performed their installation and wouldn't dare assume how they did it.

My method has performed years of street and track duty without binding or sqeaking on my car and others. Good enough data for me...I say.

If folks want to do the extra work, good for them.

True, the clamps were a crude way of holding the a-arms in place, and were never meant to perform a precise operation. That's why they are so terribly out of round.

But they were designed to be used with highly compliant, RUBBER bushings. They weren't designed to be used with hard plastic bushings

Big difference.

As to others who have had problems with your method, you don't have to assume how they have done it. They've posted it here. They either lathe out the inside or the outside, with the bushing out of the retainer, put it in the retainer and assemble on the car, like you did. And they have had problems.

As far as these rock hard plastic bushings "cold flowing" to conform to the precision A-arm surface, how long do you think/propose that takes? Instantly, upon installation? 1 month? 6 months?

[the]

Originally Posted by Souk

I'm a great believe in doing things right, but when getting something right in 3 steps, why go another 3 steps when they provide no advantage?

What is the extra step?

You have to install the PG bushing into the retainer. Where's the extra step in lathing it after installing in the retainer, as opposed to before? Exact same number of steps, just a slightly different order of operation.

[MotoSook]

Originally Posted by the

True, the clamps were a crude way of holding the a-arms in place, and were never meant to perform a precise operation. That's why they are so terribly out of round.

But they were designed to be used with highly compliant, RUBBER bushings. They weren't designed to be used with hard plastic bushings

Big difference.

As to others who have had problems with your method, you don't have to assume how they have done it. They've posted it here. They either lathe out the inside or the outside, with the bushing out of the retainer, put it in the retainer and assemble on the car, like you did. And they have had problems.

As far as these rock hard plastic bushings "cold flowing" to conform to the precision A-arm surface, how long do you think/propose that takes? Instantly, upon installation? 1 month? 6 months?

The bushings are not rock hard. If you worked with these enough you would know that. I can deform the material with my hand. You're making a lot of assumptions and making a broad stroke of the brush to lump my installation in with failed installations.

[MotoSook]

Originally Posted by the

What is the extra step?

You have to install the PG bushing into the retainer. Where's the extra step in lathing it after installing in the retainer, as opposed to before? Exact same number of steps, just a slightly different order of operation.

Read above why I think it's not necessary.

[the]

That's not my question.

[MotoSook]

You don't have to like my method, but you should understand how everything works together before you judge.

For the record, I never said that the extra steps would harm anything (if done right..even if you do the extra work, a poor interference fit will also have the bushings squeeking and binding...if too loose, then you'll be putting in new bushings sooner than later!), but I don't find that they provide adequate advantage in operation.

[the]

Originally Posted by Souk

You don't have to like my method, but you should understand how everything works together before judge.

For the record, I never said that the extra steps would harm anything

One more time, WHAT "extra" steps?!?

I do know how everything works. For no extra work, no extra steps, and no extra costs, all other things being equal (which they are), one will have a better chance of success by installing a perfectly round PG bushing assembly on the perfectly round a-arm, as opposed to installing a bushing assembly with an egg-shaped inner diameter.

(If you ever try my method, you'll see by the amount of the material removed during the lathing process how significantly egg shaped the bushing ID is when installed in the retainer. It is a lot).

Lots here have done your method and immediately ended up with squeaky bushings (or binding bushings, or worse. If these bushings are soft enough to "cold flow," how could they ever bind? The ends are unsealed, why don't they cold flow out the ends to get a perfect fit?). None have ended up with squeaks with my method.

[Won]

Fit bushing in the hub.

Flapper wheel on Dremel.

Zerk fittings with grease channels.

Jamie raises a good point - you can see where you need to remove the material when you test fit them as you go.

The bushing is rubber; You don't need thousandths-of-an-inch precision to make them work.