I found the info on the GN website.

http://www.gnttype.org/techarea/bodygauges/mounts.html

http://www.gnttype.org/techarea/bodygauges/bushings.html

Bob

Guy-

If you look up on page one of this post I have listed all of the mounts for each type of G-body. On page 2 I added the Grand Prix numbers. Compare the two lists and you will see that my list that I am using is a bit more like the Grand Prix at some positions. The second list you asked for is a MC list with suggestions in the positions where you no longer can find the originals.

Larry

Hi Folks,

Larry - got your PM. Glad to post here, if it could be of any help, although mmc427ss has really done a great job of getting additional information.

About the bushing recommendation: my opinion is that stiffer at the car ends is good, and moderately soft and lossy is good for the central portion of the car. Deleting bushings makes the coupling softer, but it also reduces lossiness. For the center of the car, I think most reading here would rather have things a bit stiffer and lossier than looser and less lossy.

What does all of this mean? As I've said before, I'd go stiff at the front of the car with Delrin at #1, and roughly as stiff at the rear of the car with PU or Delrin at #7, and OEM rubber at all intermediate locations, and fully populated (i.e., full uppers and lowers at #2,#3,#4,and #6. Remember, #5 was only an "upper" from the factory for all A/G bodies.)

About the stiffness of various bushings from the factory, I have no direct data, and am disinclined to believe what I read on the internet without taking measurements (a valve spring tester can work wonders here, N.B.). Until and unless I do that, I wouldn't comment.

HTH,
MAP

PS: about Delrin at #1 and A-pillar cracks: before swapping this bushing, take careful notes, or better, take close-up photos of the tops of the A-pillars. The chances are good that some cracking is present there already. Then, swap for the Delrin pieces. After this, test-drive the car over relatively smooth surfaces and with no more than moderate throttle for perhaps a few dozens of miles. Stop and examine A-pillars and compare with photos or records. Crack propagation? Stop and replace #1 with original bushing set. No further cracking? Repeat test process with rougher roads and more throttle. Iterate this procedure as many times as necessary until you're satisfied that you've abused the car as much as you're ever likely to do. If no more cracking appears after all this, keep the Delrin pieces for good.

So for the best cornering use the OEM body mounts on 2-6 and delrin on #1 & #7. Delrin can be purchased on Ebay in blocks. Get the correct thickness according to the mount you are replacing. This has the risk of A-pillar cracks, but follow MAP's advice to evaluate.

The two sets I have listed above are for GM rubber mounts that you can still buy. The set I am using is a mix of Grand Prix and MC and will end up a bit firmer than the original mounts. The second list are closer to MC OEM.

I do not have a durometer or spring tension tester. I am simply going by my compressing each part by hand and feeling which ones are firmer and which ones are softer.

Finally, the only place to get the true OEM package (that I can find)is from Dixie's.

There's some great info in this thread & I've been keeping track of it, but I am curious about one aspect of making these delrin bushings. From checking the #1 location on my own car & seeing that they could use replacement, I noticed that the lower bushings is a "stepped" peice. There is a smaller upper half, (all one bushing just changes size if that makes it any clearer) of the lower bushings the fits inside the mounting point on the body of the vehicle.
While reviewing the measurements provided by MAP to make these bushings in the link posted & throughout this thread, I see no mention of this change in size on the lower bushing. Am I now to assume that just due to the weight upon them & the "sandwich" effect, there is no longer any need to step the size down to fit inside the body location? If so, it seems to me like there would be the chance of excess body over bushing movement side to side. Anyone care to comment on this?

MAP will have to comment on the delrin approach.

For the GM parts, the core of the lower 348080 is a steel sleeve that flutes out at the bottom into a wide washer. The upper has a flat steel washer base. Though there is some play, when the bolt is torqued down there should not be much sideways movement.

I would imagine that there would not be sideways movement in the delrin approach if the holes drilled for the bolt were very close to the bolt diameter.

Map, what if a radiator hose was cut open and glued to the top and bottom of the delrin bushing(of course shaving the delrin to return it to proper height), would this allow enough flex to reduce the risk at the A pillar but still allow the increased rigidity?

I think that there would be a possibility of the core support sliding between the top and bottom bushings but that should be limited with proper tension on the bolt although using some of that non skid mat glued to the delrin or maybe the rubber idea I mention earlier in this most may help limit movement as well.

Hi Folks,

To the best of my knowledge, the Delrin bushings I use permit no relative motion between the bushing and the radiator support, nor the frame. The clamping works like the engagement between a rim and the hub mounting flange: any torsional or lateral force inputs are reacted-to by the friction between the mating surfaces, which, in turn, is created by the clamping force that the tightened fastener(s) exert on the fastened pieces.

About the size of the Delrin pieces not matching the factory bushing: this is deliberate. The Delrin blocks are very large, so that the contact area with the radiator support is maximized. This minimizes the locally-transferred stresses to the radiator support, and permits the perimeter of the bushing to make closer contact with locally stronger areas of the radiator support.

This aspect of the design is far, far less important with the factory bushing, since it is orders of magnitude more complaint than the Delrin pieces, and thus transmits much lower stress to the radiator support for any given force input to the suspension and steering gear.

In short, don't make the Delrin blocks any smaller.

I might add that the increased transmission of stress to the radiator support with the Delrin bushings, increases the need to cross-brace the central radiator opening in the radiator support.

Hi Gruvin: you wrote, "What if a radiator hose was cut open and glued to the top and bottom of the delrin bushing(of course shaving the delrin to return it to proper height), would this allow enough flex to reduce the risk at the A pillar but still allow the increased rigidity?" First, it's next to impossible to glue anything to Delrin, because it has very low surface energy. The stuff is almost as bad as Teflon. Second, you can always make the bushing more compliant to reduce stress transmission into the body, but then you're losing the primary benefit you're after in the first place. My recommendation would be go for the maximum benefit at the very outset, and dial-back from there when and if necessary.

Best,
MAP

MAP,

Could you give the dimensions for position 1 and position 7 again, please?

Thanks,

Larry

Hi MM,

I posted a link to that many posts back, but here it is directly:

"The dimensions for the Delrin blocks are: bottom half of bushing: 1.0" x 2.5" x 4.0". For the top half, they are: 0.5" x 2.5" x 4.0". The long dimension of each bushing half gets aligned with the long dimension of the radiator support; i.e., the long dimension goes transverse to the car.

The bottom half of the bushing "sits" on a fender washer of approximately 2.0" OD, 0.5" ID, and a thickness of about 0.10" (this dimension isn't well confirmed, but it corresponds to the height required to allow the bushing to "sit flat" on the stepped frame contour at this location, which in turn corresponds to the wall thickness of the frame.) The fender washer surmounts the fastener used to clamp the bushing with the frame and radiator support.

The top half of the bushing receives another fender washer, or perhaps two, of the same dimensions under the bushing-clamping fastener head.

I didn't check, and I don't well recall, but the inside of the frame where the fastener protrudes, possibly receives a washer as well under the hex nut that goes with the machine screw that clamps the bushing assembly together. As for the machine screw itself, I seem to remember using 1/2" UNC grade 8, with a length of 3". It's absolutely imperative to use a split-ring lock washer under the hex nut, since Delrin does exhibit some creep, and we don't want that assembly to come loose over time. [N.B. 1/12/09: the use of a prevailing-torque nut in this location would also be a good idea. Again, you don't want to take any chance that this assembly will work itself loose.] Using a medium-strength threadlocker as well couldn't hurt, but never omit that lockwasher. [N.B. And/or the prevailing-torque nut.]

As for the clearance hole in each bushing half to receive the fastener, it should be located on the centerline of the long dimension of each bushing half, and about 1.0" to 1.2" (not well confirmed) from the end of the bushing which is nearest the outboard side of the frame."

HTH,
MAP

Thanks MAP

I agree with your final statement but I am also concerned as I would like the best handling characteristics but do not want to have to pay more $$ if an a pillar crack appears(just spent 6K on a complete exterior make-over) The OEM upper bushings of the core support are a joke at best(JMO) so I figured use of some rubber in one or more locations while maintaining most of the rigidity would be a good choice. Any thoughts are appreciated.

I have been reading about how to tighten up our G-bodies. There are postings that suggest an F-body 36mm swaybar plus the crossbraces to solve the problem. I read that T-Tops are especially helped.

SC&C and Kirban have triangular bracing for the front end that helps with the responsiveness.

I wonder how much of the front end responsiveness should be done with body mounts and how much with triangular braces, better sway bars, etc. Mabe we could get by with the addition of bracing. Maybe we need the hard body mounts plus the bracing!

Here is a chassis brace link.
http://www.scandc.com/chassisbraces.htm

Hi MM,

I'd say if you're using tires geared toward handling performance up front (stiff/short sidewall and a wide section width,) then you'll need all the bracing you can get, plus the stiff #1 bushings. Once upon a time, just motivated by curiosity, I swapped-out the Delrin front bushings for the OEM rubber. Now this was with the full complement of front-end braces still in place, mind you, and 255-45ZR tires. I drove the car several miles in this state over bumpy roads, and decided then and there that the experiment was an utter failure. The front end felt as loose as a bowl of wet spaghetti. So back to the Delrin it was, with no regrets (and no propagation of cracks that had pre-existed in the A-pillars, incidentally.)

Gruvin, I can certainly understand your wanting to be cautious about this. The problem is, as soon as you engineer that bushing to allow relative motion between the radiator support and the frame (as the OEM bushing certainly does,) then you need to find a way to keep the clamping fastener from interfering with the freedom of that motion, while keeping the bushing set nominally and permamently centered in the frame and support mounting holes. And there's the rub (no pun intended.)

I think if I had to make a compromise, I'd try a PU bushing set up front from a company such as PST. Having tried this myself before moving up to Delrin, I can tell you that the PU gives up much in stiffness, but it should reduce stress imparted to the rest of the body as well, which could very understably be the overriding concern. HTH.

Best,
MAP

MAP,this is very interesting reading.Did you do a comparison between the OEM bushings & PU bushings,particularly in the front ??
Guy

Lots of good reading here and a very nice list of part numbers.

I went thru the core support bushing thing over the summer. That's when I found the difference in part numbers 86 prior and 87/88 and then confirmed it when Tmos87 ran into the same thing.

OK, but I beleive delrin is similar to teflon, as in a slippery product. The core support bushing opening on our cars is approx. 1 1/2" wide. If when we were to make these delrin bushing & just sandwich them on the core support eliminating the upper part of the lower bushing that fit inside the core support opening, would it not just be wishful thinking to beleive we would not get side to side core suport movement during spirited cornering due to the fact that the opening once occupied by the original bushing now only has a bolt of about 1/4 the size in that place?

Hi Monte,

That's a valid point. I've had no indication of relative movement for the five years or so I drove it with those bushings, but since the car is still accessible, let me do some close-up inspection with disassembly to gain a better understanding. I'll report back here.

On edit: until I get to that disassembly, I did some checking on the web for coefficients of static and kinetic friction for Teflon and Delrin against steel. I found a wide range of numbers, but very generally - and this confirmed my recollection - mu for Delrin is about four times that of Teflon. But concerning Delrin, Du Pont (the parent company and inventor of the product about 50 years ago,) makes dozens of variants. One caution: many Delrin variants, such as Delrin AF (AF = "Aromatic Fluoropolymer," which is how Du Pont classifies Teflon,) are designed for low friction. Avoid these! Furthermore, these are more expensive than the base 100-series Acetal polymers sold under the Delrin name. Generally, the best kind of Delrin for a body bushing will be the cheapest available.

Best,
MAP

I would think that you want some movement to be allowed. Some of the materials we are dealing with can begin to bend and crack if they have to absorb all of the stresses of the road. The question is what part of the car is going to absorb the forces.

Hi MM,

Not necessarily. Think of the frame in isolation. It would surprise most people here, I'm sure, to know how much the frame bends and twists in response to normal driving over a typical road surface.

Consider the #1 bushing location. I believe the frame can move up and down as much as about 3/4" p-p relative to the radiator support, with the car traversing a severe pothole (I actually saw a slow-motion film of this response once, so I'm not just guessing here.)

My point is that despite the stresses the frame has to experience, it still doesn't crack or bend inelastically. It boils down to the generated stress within the material, versus the stress-strain behavior of the material. Is the stress high enough to deform the part plastically? Do we exceed the yield strength of the material?

In the case of rigid coupling at the #1 bushing location, there's still plenty of compliance left in the fender and frame, so that soft bushings at the #2 location and rearward "work" without the fender nor the frame deforming inelastically.

Maybe this will help: for those who aren't engineers, the tendency is to think that anything designed to be rigid should be - well - infinitely rigid. It's rather like terra firma - we expect it to should stay put, period. (Unless if you live here or in California!) But the engineering aspect is this: let's make the part as light and as cheap as possible, while meeting minimum rigidity and strength targets.

Best,
MAP

Adding bolt information to this post

The bolts are:
Position 3 = M10x1.5x55 - grade 10.9 GM part unknown
Positions 2, 4-7 M10x1.5x80 - grade 10.9 - GM part 12337833

Not sure about position 1 (core) The head of the bolt says 8 6, so I imagine they are 8.6 hardness grade. Same 15mm bolt head as the rest of the bushing bolts. Distance from shoulder of bolt to tip is 95mm, length of entire bolt is 105mm, so I am guessing they are 10X1.5X95 - grade 8.6.

Dealership, NAPA or hardware store can get you the right bolts. Make sure they are the right hardness.

From looking at the chart I think the washers are .515X1.56X.19. Had to squint and my shop manual does not show the sizes like the chart from above.

Now the GMpartsdirect show 12337833 can be had for 1.20 each plus shipping.

Dixies has full set of bolts and washers for $70. Kirban has the bolts only for $28.

Lots of good info here - made it a sticky

Glad it is of help.

im gonna give NAPA a call or check the local "bolt n screw" he has alot i just ordered the complete set of bushings and washers for 150 CAD energery suspension, so i need to get the bolts now and this weekend going to install the, YES!