How many people out there have raised their differential per the Greenwood VIP article and drive their car on the street? I am looking at doing this, but I am concerned that there will be a bad vibration getting rid of the rubber bushing and mounting the cross member solid.

Second question I had about this modification is that the article calls out for a hole in the 1/4" plates to be 23/32's in diameter, but the bolt is only 7/16". I would think this would allow the differential to shift with the holes being oversized so much?

Lastly, on the upper part of the frame it bends down a little bit. I assume that this needs to be bent up in order to set the cross member flat.



I was thinking of adding a 1/8" thick piece of rubber or hard durometer plastic between the sombrero and the plate, as well as between the crossmember and frame just for some isolation similar to what Jason Staley had done. Any opinions on this?

Here is what I got when I mapped out my rear suspension. I don't think the toe is completely correct. Has anyone else done this?

 

Prior to putting in my C4 suspension, I considered raising the differential. Modifying the bushings seemed like a lot of hassle, whereas modifying and and rewelding the center section of the crossmember seemed easier. (The pinion mount would have to be tweaked also to keep the driveshaft angles correct.)

 

Not quite sure what I'm looking at here. The frame piece that the crossmember mounts to shouldn't have a gap in it, and the piece that curves down on the right side of the photo should go all the way around. In addition, the ears of the crossmember should be flat - it looks like they may have been bent down when someone pried the crossmember down. I can take some pics of my frame this weekend if you like so you can see what the stock setup looks like. I have a rolling chassis in the garage so everything is exposed.

EDIT: After looking at my frame I see that the gap and hat on your frame are fine. The end of the crossmember should be straight across though, but the bends shouldn't affect anything.



Rick B.

 

thats what i did. raised 1.5" to get car low enough and still keep half shafts level. 10" bolts also

 

I'm working on the same issue. I can't see how a little flex makes a big difference as it is only up and down, not side to side. I have poly bushings in my front mount and the thing doesn't move much. I would like to raise the diff a little, I have 10 inch bolts. SCCA rules won't let me cut and reweld the brace. Can you just remove the rubber bushings and put in a big steel washer? I'm taking it apart tomorrow and MIGHT understand it a bit better then.

 

Check my archived posts. I installed an old set of Greenwood (I think) solid mounts, and I know I posted the dimensions at one point. They don't raise the crossmember too much, but it is a solid, rubber-less connection.

 

Quoting Bat's post on the solid mounts...

...They appear to be based off of something noted (but not pictured very well) on page 6-4 of the Chevy Power Manual, 5th edition. They totally eliminate the rubber bushings - the stepped portions fit snugly into the crossmember bores. I'm fairly sure that they're steel, but I'm not 100% certain. All dimensions are approximate.

Upper ring dimensions:
total thickness - 9/16"
thickness of wide section - 7/16"
thickness of narrow section - 1/8"
diameter of wide section - 4"
diameter of narrow section - 3 13/16"
diameter of hole - 2 9/16" (it appears to taper a bit as it goes downward - it's around 2 1/2" - 2 17/32")

Lower plate dimensions:
total thickness - 7/8"
thickness of wide section - 7/16"
thickness of narrow section- 7/16"
diameter of wide section - 4 1/4"
diameter of narrow section - 3 13/16"
diameter of hole - 1/2"

BTW, I talked to Guldstrand about these not long ago. They used to sell them, but don't bother asking for Dick to scrounge (yes, he's been known to do that when he thinks he might have something) for a set as apparently there aren't any just laying around. Haven't asked Greenwood...

 

Isnt smart struts answer to you camber change question:

 

72LS1Vette - Then ends of the cross member are bent down from me using a 6ft prybar trying to get the rubber bushings out

Vesa - I plan on doing the smart struts or some variation, I was just curious if this is close to what others have checked.

TheSkunkWorks & I'm Batman - Does this look like what you are describing?



This is the way I understand the Greenwood VIP article. (except I reduced the hole from 23/32nds to 1/2")

 

This isn't about camber curve, rather combating toe-steer during rear suspension travel. Be careful how much camber gain you dial out.

mpettus, I understand the whys and wherefores and have this on my list, but so I don't make a false assumption and give you inaccurate info you'll have to ask the Bat to verify this, as I've yet to perform this one...

 

Looks just like the Guldstrand plates I have installed, except that the upper donut isn't jammed that tight against the frame. I think the lower plates may have hit the cones.

 

This is lowering the frame. The differential is in the same place.

 

So with the crossmember solidly mounted do you notice a large increase in the amount of noise, etc? I will probably do something more like what is mentioned in the VIP article due to lowering the car.

Thanks,

 

I haven't had the car running again yet. Hopefully, this week or early in the next.

 

I finally got around to taken everything apart. The male insert on the frame looks like it bottoms out in the diff crossmember bushings. It looks like the design is for the diff to be able to rock up and down a little at the front mount. I have poly front diff mount which probably stops if from moving much. I also have the aluminum cross member reinforcing donuts which I don't think do any good. Seems to me that cutting a hole large enough in the aluminum donuts to fit over the male frame locators would make a pretty firm set up. The only way I see to raise the diff is to remanufacture the cross member. I'm not sure any of this is worth the trouble.

 

The cross member can be raised up to 3/4" without modifying it, but the rubber bushings have to be removed and the metal flange on the frame has to be hammered flat. I got 5/8" because I placed a 1/8" piece of rubber between the cross member and frame to keep gear noise to a minimum.

 

Jason;
How does the cross member stay centered. I haven't removed my rubber bushings so don't know what it lookd like with out them. Also did you then put a spacer between the diff and strut bar bracket to make up for the difference. I assume the strut rods are way out of alignment since they have been raised?

 

I believe you can raise the diff pretty easily if you weld in a plate like I have modeled earlier in the thread. As far as being worth the trouble, I think it depends on if and how much you lower the car. If the half shafts get horizontal or angled down towards the diff, then the toe starts to do bad things. For you being in BSP I don't believe raising the diff is even a "legal" option.

The rear diff would be centered by the plate I mentioned above, but brings me back to one of my original questions about the hole diameter called out in the VIP article being much larger than the crossmember bolt. Here is a pic of the crossmemer in the car w/o the rubber bushings.



I don't believe raising up the rear differential should change your suspension curves, just your starting point in the curve. Your relationship of half shaft pivots and strut bar pivots will remain the same. With that said lowering the strutbars with either a plate or the "smart struts" will change that curve.

Jim,
I saw you were at Nationals last year in Topeka. I am sure I checked out your car at one point throughout the week. Hopefully I will get to make it out there again next year (although it won't be in the vette).

 

Keep in mind how poorly edited those articles were. Lot's more errors made it too print back then.

 

I haven't researched the SCCA rules about raising the diff. Since the car has been lowered then adjusting the diff to match would seem OK. Smart struts aren't legal because they change the locating points of the struts. Putting in a plate 1/2 inch between the diff and bracket would take it back to about the stock angles. A reall y grey area in the rules. I really should just sell the car and buy something newer, but ol red is the longest relationship I've ever had.:o I really need to falir the car and go to 315 rubber. Back to the orginal subject seems the best way to mount the cross member is to machine a plate that has the correct center hole and and a flange that goes into the large hole and centers the cross member. I'm just going to put mine back together and live with it. I'm not worried about the half shafts angle as the car is a trailer queen. I control the toe issue by having 3/8 toe in.