ACECO

As a follow up to my recent post asking about overdrive filter changes, and the resultant search for info on the needed grommet, here's what I've learned so far after getting some grommets from an industrial supplier.

The grommets I purchased are Military Specification Buna-N Rubber. They are manufactured to meet military specifications MIL-G-3036 and MS 35489 and are AN (Army-Navy) approved. They offer vibration dampening and abrasion control and are resistant to oil, gasoline, and aromatic hydrocarbons. Hardness is Shore A50 (slightly softer than a tire tread). They are black in color and their temperature range is -45° to +250° F.

Now as there seemed to be some debate as to the proper size needed for the 4+3 filter application, I purchased 2 different sizes. The first one is a 1/2" ID x 1-1/16" OD which based upon forum input seems to match the size of what some "corvette stores" supply with their filter kits. However the ones in these kits purportedly are a electrical grade version. Also if you purchase a filter over the counter at a parts store, there is usually no grommet supplied and commonly a electrical grade grommet is then purchased in an "assortment multi pack" and used. I was advised not to use an electrical grade grommet as they do not hold up to the temperature and trans fluid in this application. They swell, turn to "goo" and/or disintegrate. If the grommet fails, the overdrive unit will suck air and cease to function.

The second size grommet is a 5/8" ID x 1-1/8" OD and is the size provided by another forum member. This grommets ID and OD match the size of the pickup tube (which I'm told is 5/8") and filter hole more closely than the first. However I have noted that the grommet ID is a somewhat loose "slip fit" on a 5/8" dowel I used for testing. Because of this looseness, and w/o yet having actually installed one of these grommets on the overdrive pickup tube, I have some question in my mind as to if the seal around the pickup tube will be tight enough to prevent any air from being drawn past it.

The smaller 1/2" ID by 1-1/16" OD appears to fit the filter opening/hole slightly loose and the grommets center hole is also somewhat smaller than the 5/8" needed. However when installed next to the 5/8" ID grommet on the 5/8" dowel, these 1/2" versions seem to stretch over the dowel fine and by doing so also opens up the OD to be basically the same as the 5/8" grommet. So based upon this and again w/o having installed either on the actual OD pickup tube, I'd say that the 1/2" ID size would be the safer bet to assure a good seal on both the inner and outer diameters.

Below are some pics to better show what I have observed so far.

The first pic is a side by side of both the 1/2" & 5/8" ID grommets:



The next shows the 1/2" ID centered in the filter:



Next the 1/2" ID pushed to one side illustrating its slightly smaller OD vs the filter hole:



The 5/8" ID grommet mounted in the filter:



Both pushed onto a 5/8" dowel, showing the similar OD after installation:



Another view of the 2 grommets on the dowel: (sorry this pics a little blurry):



So all that said I hope this helps someone with this "size" issue. After I do the filter change (hopefully this weekend) I will report back with any updates to this info. And as I now have a multiple lifetime supply of fifty 1/2" ID grommets, () I'd be glad to share if someone needs a couple. If so please PM me.

rws.1

check out this link and my two posts in that link for a source for the grommet

http://forums.corvetteforum.com/show...hlight=grommet

The source is in the archives with a title of 4+3 OD filter Grommet Source posted by 88redvert
(my wife's CF ID)

c4cruiser

PM sent.

Thanks a bunch for researching the grommet issue! Looks like it wil be a tremendous help for us 4+3 owners

When I originally started the thread about the Ford filter being the same as the one for the 4+3, I think it helped save money for those who had been buying the expensive accessory catalog filters. Your grommet thread carries this just that much further!!

Thanks for all your effort

rws.1

It gets harder and harder to find parts... at any price
Any sharing, like the thread you started helps us all keep Vettes going strong.

CentralCoaster

Damn and I was hoping there'd be a clear cut answer.


The sides of the gap tend to seal to the filter, not necessarily the OD of the grommet.


The grommet sold by ecklers has a 1/8" gap which is way too big and makes for a sloppy fit (and more likely to get cut).

ACECO

And to think it's still not over yet. However what I will do is measure the old grommet when removed and see if this can help determine what GM used originally. It will likely be somewhat "worn" and out of shape from what I believe is 85K miles in the car, but perhaps it still might be able to put this size issue to rest.

I guess when I said OD I did imply the very outer diameter. However in my mind I was thinking about the OD if the gap where it meets up with the sides of the filter hole. As can be seen on the pic of the two grommets on the dowel, the 1/2" one because it's stretched actually has a larger outer "gap" diameter so it should fit tightly into the filter hole. However I suppose this does raise the question that if the particular filter you are using has sharp inner edges of the hole then this additional pressure on the holes inner diameter could cause the grommet to be cut. The filter I have has a nice smooth edge so I believe this won't be an issue. However this certainly would be a good thing to check for and correct if found, before one were to install the filter.

The 1/2" ID grommets I have are a 1/16" gap so they seem to fit snugly and as they should. For that matter so are the 5/8" ID versions. However I'm still concerned about the loose inner fit of the 5/8" version. The 1/2" ID have a 13/16" gap diameter which is a 1/16" smaller than the filter hole ID. However stretching it over the 5/8" dowel increases this size to fit snugly within the 7/8" hole.

The 5/8" ID grommet has a 7/8" gap OD which seems to fit the hole nicely. However with the loose inner fit providing no pressure to help with the seal, I'm still not convinced it is the right way to go.

I guess the only way I'm going to know for sure is to get under the car and actually install one of them in the trans. Again this weekend I hope to if the weather cooperates. It's pouring out right now with some rain forecast for the weekend so we shall see. I will keep everyone posted.

ACECO

In reviewing my post above, I realized that I never provided the source for the grommets. Here's the info for future use:

Grommets were purchased from McMaster Carr. Website address:

http://www.mcmastercarr.com

The 1/2" ID version was part number 9307K26 and they come 50 to a bag.

The 5/8" ID grommet was part number 9307K53 and these are available 10 pieces to a bag.

And if someone wants to get adventurous, they also sell a 1/2" ID silicone grommet to in 5 piece quantities. Part #1061T18. I would think these would also work fine but I did read somewhere that silicone is not oil/solvent resistant. I thought silicone was, but that's what I read. FWIW.

I hope this helps someone going forward.

Repzard

PM Sent about garmmet

Thanks ACECO for info and your help.

Chatman

May I ask about the source of the statement:

"However the ones in these kits purportedly are a electrical grade version."

I'm wondering whether to redo mine.

Thanks

ACECO

Greetings,

Well, as my point of reference was being told by a few people who have experienced the grommet failing that what is supplied is a electrical grade version, this was my "weasel worded" way of saying "This is what I was told but don't really know for sure first hand".

What I do know is that a electrical grade grommet will likely not hold up to heat and trans fluid for long. I've seen them turn to goo before in other industrial applications. And while I'm confident that what I was told to me is accurate, this particular point was somewhat moot for me as I purchased a filter locally and it didn't come with a grommet. I just wanted to find something that would work and also relate what I had learned for anyone else's future use.

Now all that said, I THINK the worse case scenario for you would be that the grommet would fail and the OD would suck air and stop working. At that point change the grommet and all should be well again. However I hope CentralCoaster or someone more knowledgeable on this subject will jump in here and correct me if I'm wrong about if the grommet failing will adversely affect the OD unit mechanically.

And if you do elect to change the grommet now as a precaution, it would be interesting to know what condition it is in and how long it's been in the trans.

Hope this helps. Good Luck!

CentralCoaster

I am the source of that opinion.

Electrical grade ones are cheapest as they don't require any special chemistry for withstanding fluids or temperatures. I don't have any faith in Ecklers or their supplier to go the extra expense and step to find a suitable material that would cost more. I mean, they're also putting a pan gasket in the set that GM never used from the factory. Do they really know better than GM in this case? Everyone's experiences on here would say otherwise. I could be wrong about the terminology "electrical grade" but regardless, I don't think it's the right material.

With that said, the grommet I removed from the car originally was rock hard. (not sure if it's original or not, I think the overdrive was rebuilt at some point in the 50K miles previous to my ownership.) The Ecklers one I used turned very very soft, and was cut easily by the filter. I bought a small pack of generic grommets off the Napa shelf and it turned to butter also. Some of the filters I've bought had a sharp edge too, so the grommet is especially important.

Perhaps the other cars using this filter use the same grommet and actually have a p/n for it that is available. I'll have to check on this.



I would not worry about it enough to do an unplanned OD oil change, but please consider it for the next time around, or if your overdrive cuts out. The overdrive will protect itself in the event of low fluid pressure. The only harm done would be to your gas mileage on the way back home.

Great White North

Thanks for the info!!!Now can you come up with a new button for my shifter?

CentralCoaster

I have a late 85 shifter for sale with OD switch on top. What do you need exactly? The switch is a radioshack item. Scorp posted the source somewhere.

ACECO

Hey CC, I may be interested in your 85 shifter. Would love to have the button on the shifter vs on the console. That and my shifter has been a bit balky lately too. I was going to try adjusting it sometime soon but that would be a great time to just do a swap if I had the parts.

Let me know.

CentralCoaster

It's probably not that easy. It uses a momentary switch, which *I think* means it'd require at least a latching relay to work on your early 85. I could be wrong about this, I'll check.

Great White North

My button on my 88 shifter has broken mounting clips where it hinges.I would take it whole or part.

ACECO

I wasn't aware that the 85 up was a momentary switch. However if so and my 84 is a rocker you are likely correct about needing some kind of a latching relay or the like. However as I have an EE background, setting up a little circuit with a flip-flop or similar to latch a relay wouldn't be an issue.

Let me know about the shifter if GWN doesn't want/need yours.

Great White North

I don't want to separate a good shifter only for the button, if you can use the whole assembly.Eventualy some one must be able to make some new buttons.

ACECO

Greetings All,

Finally got around to changing my trans and OD fluids this past weekend. Here are my updated observations on the OD filter grommet and related OD items.

First here are two pics of the removed grommet along with the two I previously purchased:





The removed grommet was in very good condition and not gummy at all. It was still very flexible and I see no reason why this one couldn't have been reused. Now I can't say if the grommet is original to my 85K mile, 1984 vette (unlikely), but at first glance it appears to be a 5/8" ID grommet. The overall OD is approx 1/16" larger than the 5/8" grommet I purchased, but this dimension is somewhat irrelevant IMO. The important dimension is the OD of the gap where it fits into the filter hole, and this is the same as the 5/8" one purchased. Also the gap width is approx 3/32" which is a little bit wider than the purchased one at 1/16". Beyond the fact that it wasn't gummy and falling apart, I suppose this could have been a 1/2" grommet that is supplied by many catalog houses that has just taken on the "new" size after being stretched over the 5/8" tube. However I suspect not as it seems to be "as molded" without any distortion, etc.

I tried using both the 1/2" and 5/8" grommets I had purchased to reinstall the filter. I started with the 1/2" version and it worked OK but it was a bit harder to get over the tube due to the fingers on the tube and the fact that the grommet was now "contained" within the size of the filter hole which made stretching the inner diameter a bit harder. My original "dowel" test above didn't factor this in and it was easy to stretch the 1/2" grommet over the 5/8" dowel w/o the gap diameter being constrained. However once the 1/2" grommet was in the filter, with a little trans fluid as lube it could be carefully worked over the filter pickup tube and up into place. Using the 1/2" part the seal between both the tube and the grommet, and the grommet and the filter hole were tight and I'd have no concerns at all about it sucking air, etc. My only concern, as stated in a previous post, is that due to it being compressed tightly you would want to make sure there are no sharp edges on your filter that could cut the compressed grommet at the gap.

I then tried the 5/8" grommet. It fit snugly in the filter and went on the tube much easier. However it seemed as snug and fit about the same as the removed grommet. At that moment I wondered about why it was snug on the filter pickup tube but was a bit loose on my previous "dowel" test. Quickly broke out the calipers and found another discrepancy in my first set of tests. The 5/8" dowel only measured .610", which explains why the 5/8" grommet originally seemed kinda loose on it. :o So because the 5/8" grommet seemed to fit just fine and it was already "on there", I just left it in this configuration and reinstalled the pan.

So I have concluded that in my driveway, using my filter, my grommets and my car, that either the 5/8" or 1/2" grommets could have been used and would have served the purpose. Regardless of which size used make sure the inner edges of the filter hole have no sharp edges or burrs. The 1/2" version took a bit more effort to install on the pickup tube, but provided a tighter seal. The 5/8" grommet was easier to install and seemed to also seal OK, even if not as tightly as the 1/2" grommet. Based upon that I would GUESS that originally a 5/8" ID grommet was used as ease of assembly probably took precedence over the "super" seal. However this is just a guess on my part so apparently we still can't really be sure what size grommet was originally supplied "back in the day".

I hope this helps someone. See my next post for more general observations about my filter and fluid changes.

CentralCoaster

Sorry, forgot about this thread.

Let me know if you still want the shifter. It is sloppy, just like to the one I removed from my 85 before tightening it up on a press.

The owner said it was fine until he had the reverse lockout rod welded/repaired, as if the heat caused the slop.

I'd hate to sell junk. At worst, you could use the shifter handle and button assembly still.

What zip code are you in? Does $40 shipped sound reasonable? The shift **** and button look good cosmetically.