Hi MM,

I should have clarified. Use Delrin for the front radiator-support locations only. I first tried PU and then Delrin at those locations, and Delrin worked quite noticeably better in giving the front end an obviously tighter and "less jiggly" feel. At the rear corners of the car, PU is actually very satisfactory. Everywhere else, OEM rubber is my choice.

About where to buy Delrin - not sure. McMaster-Carr is always a reliable source, but usually expensive. Have you tried eBay?

Best,
MAP

Ebay looks good for the delrin.

MAP---

your post gives rectangular sizes for the front mounts.

For the back, is there a source for a single set for the pair of position seven needs? I can only find a full set of PU.

If I went with delrin, would it be essentially the same thickness as position 1?

Hi MM,

About the rear corners: no, I'm not aware of a source that will sell you that pair alone. At that point, it might be cheaper to do it with Delrin. Just measure the gaps you've got now with the car in normal trim, and duplicate those dimensions with your custom bushing. It's been so long since I've been back there, that I can't immediately recall the configuration of the bushing that's needed; i.e., whether round, square, rectangular, or what-have-you.

As a general rule, I can say that the larger the contact area of the bushing, the better, and that you want to clamp the captive part of the supported body with a roughly equal size and thickness of bushing material, above as well as below the captive part.

Best,
MAP

The thing that surprises me a bit is how there are no difficulties because of the combination of materials. I would have thought that tieing down the front and rear while letting the main section of the body move might end up with cracks in the paint in various points of the body.

Hi MM,

The main risk is possibly, and I want to repeat possibly, cracking of upper A-pillars. I haven't seen this to an extent that points to a clear cause/effect relationship, since this area often cracks from the factory.

In any case, I've written at length in many past posts about the benefits and detriments to this bushing configuration. It isn't a panacea by any means. Please do a search.

Thanks,
MAP

Mark,

I have read most of your posts on this and the GNational site. I really appreciate your insights on these matters.

Well, here is another question. I understand that the Grand Prix was the hardest OEM rubber for body mounts. Does anyone have a full set of OEM part numbers for the 7 positions, upper and lower for the Grand Prix?

Well, it has been a while, but here is the result of my research and what I plan to do:

Many G bodies had bushings left out. Some that are left out (position 5) make the rider softer. I would think that leaving out lowers and only using washers would make the rider a little harder.

As I understand it, the Grand Prix bushings were the genearlly stiffer than the MC. They are as follows:

position-----Upper----lower
--2---------330986----457915
--3---------348080----457941
--4---------348080----457917
--5---------556755----none
--6---------330942----377801
--7---------1242754---457915

I could not find all of the MC bushings. In position 1 I could not find the 1255795. It is very similar to 457915. However, 457915 is a little harder and more shallow on the first inside shoulder. I know some other people are going with 377801, which is shorter and a little softer than 457915. I think that going with a harder substance that fits tightly with 348080 may make the responsiveness of the cornering a bit better. I also put stiffer mounts on position 7. Staying away from delrin might protect my A-pillars. I have a t-tops.

I could not find MC uppers for positions 1, 2, 5, 6, and 7. The lowers from softer to harder are: 457941, 377801, 457915. I have been told that 457915 will work for position 1 upper and all lowers 2-7.

Where I could not get MC parts, I went with the Grand Prix parts. In some of the positions, I stiffened the lower part a bit since I have a little more HP and wanted it a bit firmer ride. Since GM had a pattern of having positions 3 and 6 lowers a bit softer, and since I had the parts, I went a little softer there.

Here are my choices:

position----upper----lower
---1-------457915----348080
---2-------330986----457915
---3-------330951----377801
---4-------330951----457915
---5-------556755----none
---6-------348080----377801
---7------1242754----457915

I believe all the parts I chose are all still available. GMpartsdirect.com, oepartsource.com, discountpartshub.com are all potential sources. I would note that you will quickly find Dixie's price a decent one IF you have to order in ones and twos and pay shipping from each source. Try and bunch up your order as much as possible.

Hope this helps.

Larry

Hey MAP,do you have any comment on this selection of body bushings ??
As you know,I want to do some work on mine,I'm not looking for the ultimate in autocross handling,but I would like an improvement in handling without sacrificing all the ride quality,a bit of a compromise,if possible.The delrin scares me off a bit because of the possibilty of cracks developing in the A pillars.
Looking forward to your opinion as always.
Guy

Map,

I would love to have your input as well.

Larry

Larry,I can see that you have put a lot of thought into this,are you going this route with your Monte ?? I checked GMParts direct,and all of these bushings are available,at an average price of $ 10 a piece.Would your list above need to be doubled to provide an entire set ?
Guy

Exactly.

You end up with a total of 26 body mounts. Don't forget shipping. With GMpartsdircect the first part is $12 for shipping and each part thereafter is $2 - $3. Assume you pay $13 per part, you end up with a bit over $300. Now if you have to search and find them by ones and twos (like I did when I was casting about for MC parts) you might end up with some costing you a bunch.

Not totally what I have for position 1 is good or not. The original 1255795 part has a little more cushion since
1) it is softer and since
2) the 348080 sits on the outside lip, not the inside shoulder of 1255795.

348080 sits on both the outside lip AND the inside shoulder of 457915 at the same time.

Dixie is the only place for a full set of originals--and you only pay one shipping cost.

Larry

This sentence in the last post should be changed.

Not totally SURE what I have for position 1 is good or not.

So are you saying these are comparable to a set of original bushings ?
Guy

probably stiffer than original.

I will look forward to MAP's reaction. I think I will PM him to encourage his post.

I have a few 457941 and 377801 left over after I decided to stiffen up the ride a bit more.

I was going to use 377801 in position 1 and 7 and 457941 in position 2.

Some interesting reading for you. Thanks Larry for doing the leg work on the G bushings. Years ago I talked to Scott Mueller after reading his tech writeup on the Impala SS forum. I never finished the research needed to know exactly which part # would be the best for a G-body. Here's his writeup.

http://www.indipalass.com/ARCHIVE/TechCorner/ARTICLES/Enhanced%20Body%20Mounts.htm

Also a recent thread on there about bushings.

http://www.impalassforum.com/vBulletin/showthread.php?t=212778

There was good info on the GN websites about bushings and the procedure to change them out, just can't find it right now.
Bob

So would you mind making up a revised list ?
I wonder if these bushings are available from my favorite GM dealer ?
To get these parts shipped to Canada would probably be close to double the price in the US
Guy

I think these would be closer to OEM.
Position 1 is a tossup. 377801 is what TMOS87 is going with. Softness is around what the 1255795 is, but the structure is a little different (shorter, softer). I am going with 457915. I think you would need a couple of extra washers to get the ride height right if you use 377801.

position----upper----lower
---1-------377801----348080
--------or-457915----348080
---2-------330986----457941
---3-------330951----377801
---4-------330951----457915
---5-------556755----none
---6-------348080----377801
---7------1242754----377801

By the way, Kirbanperformance.com...Pt# 6740 is an exact replace for 556755 if that part becomes scarce. It is an aftermarket buick part. The 556755 may be a bit softer than our original. 14032559 was the original position 6 - now replaced by GM by 348080. Some people are using 348080 in position 7. These three thoughts thanks to TMOS87 and Juangomez22.

I would bet your GM dealer could get them. Depends on the parts guy. Sometimes they get burnt by people looking for older parts when they spend time ordering and the guy never picks them up and pays. They don't want to mess with the possibility of being stuck with a bunch of parts they can't get rid of. If you've got a good relationship, maybe so.

Again, I will have a few 457941 and 377801 left over if anyone is interested (I will post later on for sale page).

Bob (mmc427ss)

Thanks for the links to the impala site. Good stuff there. Helps me understand a lot better.

Larry

Would these ones be an acceptable substitute,or are they the same as the stock MCSS ones ??
Guy