75 Vette

Not much life was left in the old 9 leaf spring on my 75 - so I rewired the rear suspension with a Monoleaf. Here is my new problem. I have a new vibration coming form the rear at about 70 mph. You can feel it in the seats. With the new spring the car sits about 1" higher in the rear as compared to the front.

I would love to hear what you have to say.

SuperBuickGuy

how are your u-joints?

gdh

Where/brand is the spring, did you use the longer bolts?

75 Vette

They were fine before I changed the spring.

75 Vette

That is what I thought. I think the half shafts are at an angle now with the higher height and may be the cause of the new vibration. I was thinking of going with longer bolts. There must be someone out there that has had the same problem.

Thanks

mrvette

I went plastic spring back in '95, when I bought my '72 vert, and wen with 8" bolts as part of the kit from VBP, been there since, but I do recommend the Bilstein shocks over any other I know of....like stock or KYB.....

gcusmano74

Very simply, with a full gas tank and nobody aboard, the half shafts should be near level with the ground.
Technically, the difference in height between the inner and outer lower strut rod mounting bolts (Chevrolet calls this the "D" dimension) should be 2" , plus or minus 1/4"..
When you are done, the frame should be very close to horizontal, front to rear. The rear can be down slightly- maybe 1/4" max.

75 Vette

Do you think an alignment is in order for the rear?

gcusmano74

If the tires are wearing evenly and the car does not feel squirrely, you are most likely fine.

MotorHead

gdh has a good question as to the brand pf spring you bought, why don't you go ahead and address that one it may give us some insight into your problem

75 Vette

Here is the link at Ecklers: http://www.ecklerscorvette.com/corve...1963-1982.html

Thanks

pauldana

thats a TRW

gdh

If you do a search on TRW springs I think that you will find a lot of the same issues that you are having regarding ride height. I and many others on here have a VBP rear mono spring and no such issues but did order the 8" bolts. Can you send that spring back?

muskegonbrake

Actually, that's a Hyperco, not a TRW

7T3C3TTZ07

Assuming the spring is installed exactly as the old one (centered and ride height) the new spring alone would not affect the rotating components in such a way as to cause a vibration. But working on the rear of the vehicle may have intensified a pre-existing situation (stress an old part, knock off a balance tab, . My experience with a U-joint that experiences a "flat" spot on the needle bearing is that the vibration or "rumble" is noticeable much before 70 MPH. Level half shafts is a good thing to check. I have not experienced it but there may be a little bit of a U-joint phasing issue causing a vibration. As I understand the phasing rule, the angle of U-joints at each end of a rotating shaft need to be at the same angle to be "in phase." In-phase would seem to be the normal case for the half shafts regardless of the ride height or spring rate but perhaps something got "bumped" during the install. Having the suspension "hang" by the side yokes can put some stress on old parts. I once lost a side yoke retainer by raising the rear. However, that did not generate a vibration. Best of luck on tracking down the root cause.

63mako

If your ride height is higher you changed your camber to positive. This requires an alignment. Before you take it in get your ride height wher. you want it. I would raise the car by jacking the trailing arm until the tire is just off the ground and check play at 12:00 to 6:00 It should be minor, and 3:00 to 9:00, it should be 0. Halfshaft alignment should be close to parallel.

75 Vette

Thank you

75 Vette

Thank you.

75 Vette

I'm picking up some 8" bolts today. I think the ride height is critical as its not like a straight axle where height makes no difference. My goal will be to get the shafts level. As a preliminary test, I should go and fill up the gas tank - take a ride and see if there is a difference. I'll keep you posted. Thanks Ken

redman76

Make sure they are Grade 8.