Spindle interchange

[Tom H.]

Are the large bearing front spindles from the C3 fully interchangeable with the 1965 C2 w/disc brakes?

[Joe L.]

Re: Spindle interchange

Are the large bearing front spindles from the C3 fully interchangeable with the 1965 C2 w/disc brakes?

Tom------


No, they are not. There were other changes with respect to front suspension geometry between C2 and C3. I believe the C3 front spindle could be installed on a C2 but the suspension geometry would be changed.

A large bearing front spindle (i.e. those used from 1969-82) can be installed on a 1968, though, as long as the front hub is also changed.

[Tom H.]

Re: Spindle interchange

Thanks Joe

[Patrick B.]

Re: Spindle interchange

The C3 spindles look just like the C2 spindles except for the bearing size and the size of the holes for the steering arm bolts. The C3 brake backing plates, steering arms, steering arm bolts, and brake rotor hubs are required for the conversion. I do not think there is any suspension geometry difference. I have made this conversion without any problems.

[Joe L.]

Re: Spindle interchange

The C3 spindles look just like the C2 spindles except for the bearing size and the size of the holes for the steering arm bolts. The C3 brake backing plates, steering arms, steering arm bolts, and brake rotor hubs are required for the conversion. I do not think there is any suspension geometry difference. I have made this conversion without any problems.

Patrick------


They may appear the same but they are not the same. There is a difference between suspension geometry for C2 and C3 Corvettes even though most of the suspension parts are the same. For the rear suspension, the difference is effected by the configuration of the strut rod center bracket. For the front, the difference is effected by the spindles. I believe the spindle shaft location is slightly different between C2 and C3 spindles and, if I recall correctly, if a C3 spindle is installed on a C2 it will have the effect of slightly lowering the suspension. As I mentioned previously, the C3 spindle can be installed on a C2 but the suspension geometry is changed.

[Duke W.]

Re: Spindle interchange

The suspension geometry would only change if the ball joint holes changed location, and my understanding is that the front suspension geometry did not change from the C2, only the rear. However, if the spindle height was changed it would effect steering geometry, primarily the scrub radius, and it would also effect ride height.

I've heard of the larger bearing spindles being installed on C2s with no ill effect. I think a lot of racers did it.

Duke

Duke

[Patrick B.]

Re: Spindle interchange

The C3 rear strut rod bracket lowers the inner attachment point of the strut rod about an inch. This lowers the rear roll center and reduces the amount of rear camber change caused by suspension deflection. The change from the old 6.70-15 and 7.75-15 tires to the "wide" F70-15 tires on the C3 made the lower roll center desirable. I would think the modern radials used on most C2 drivers would also benefit from reduced camber change, so I also use the C3 strut rod bracket on C2's.


It would be nice to think that the C3 front spindles offer similar suspension geometry advantages for modern tires but I do not believe that it the case. They are just a little more robust.

[Joe L.]

Re: Spindle interchange

The C3 rear strut rod bracket lowers the inner attachment point of the strut rod about an inch. This lowers the rear roll center and reduces the amount of rear camber change caused by suspension deflection. The change from the old 6.70-15 and 7.75-15 tires to the "wide" F70-15 tires on the C3 made the lower roll center desirable. I would think the modern radials used on most C2 drivers would also benefit from reduced camber change, so I also use the C3 strut rod bracket on C2's.


It would be nice to think that the C3 front spindles offer similar suspension geometry advantages for modern tires but I do not believe that it the case. They are just a little more robust.

Patrick------


Yes, the 69-82 front spindles are definitely superior to the 63-64, 65-67, and 68 spindles in several ways. The bearing size is the most obvious improvement but there's another that's often overlooked. The 68-82 steering arms with 1/2" bolt attachment are considerably stouter and stronger than the 63-67 arms. The best of these arms are the 78-82 with forging numbers 465071 and 465072. These arms are so stout I don't see how they could be bent except in a massive crash. One caution, though: most, if not all, of the PRODUCTION versions of these arms are machined for only one tie rod position (the inner position for power or fast steering since all 78-82 Corvettes were originally equipped with power steering). 68-82 SERVICE arms manufactured from about 1978 on were machined for both holes but used the above-referenced forgings.

[Duke W.]

Re: Spindle interchange

The C3 rear strut rod bracket lowers the inner attachment point of the strut rod about an inch. This lowers the rear roll center and reduces the amount of rear camber change caused by suspension deflection. The change from the old 6.70-15 and 7.75-15 tires to the "wide" F70-15 tires on the C3 made the lower roll center desirable. I would think the modern radials used on most C2 drivers would also benefit from reduced camber change, so I also use the C3 strut rod bracket on C2's.


It would be nice to think that the C3 front spindles offer similar suspension geometry advantages for modern tires but I do not believe that it the case. They are just a little more robust.

The C2 front roll center is lower than the rear (but higher than modern cars), so it doesn't have as much camber/track change, and apparently GM thought it was okay for wider tires.

High roll centers increase roll stiffness for a given ride rate, so huge anti-roll bars aren't necessary. They also provide negative camber gain on the outside wheel, which somewhat offsets body roll to keep the tire closer to vertical with the pavement, but this generates track changes, which are detrimental.

Lowering the rear roll center in '68 with no significant geometry, spring, or bar changes at the front should have promoted more understeer and reduced the C3's tendency to transition to oversteer at the limit compared to a C2, but I recall riding in a friend's '70 L-46 (OE tires) on an aggressive drive down Mulholland. It actually felt more twitchy than my SWC on Pirelli CN72 radials, and I told him he was going to lose it. Sure enough, two corners later he did, but fortunately the only damage was a bruised ego.

IIRC the C2 front/rear roll centers are about 5/7" above ground level. The change to the '68 rear strut bracket lowered the rear roll center about two inches - to about the same as the front.

Modern cars usually have roll centers about 0-2" above ground level. Solid axles usually have fairly high roll centers, but don't have the attendant track and camber changes of high roll center independent suspensions.

Duke

[Richard F.]

Re: Spindle interchange

The so-called "dog bones" that reinforce the caliper carriers for F41 brakes have larger bolt holes after 68. Part numbers change after 68.

[Joe L.]

Re: Spindle interchange

The so-called "dog bones" that reinforce the caliper carriers for F41 brakes have larger bolt holes after 68. Part numbers change after 68.

Richard-----


There were THREE sets of J-56 front caliper reinforcements-----1966-67, 1968-only, and 1969-75. The 66-67 were GM #3882783, 4 and had 29/64" holes for 7/16" bolts. The 1968-only were GM #3925397,8 and the 1969-75 were GM #3948879, 80. The 68-only and 69-75 had 33/64" holes for 1/2" bolts.