C2 disc brake conversion

[Dennis H.]

I want to change my 64 to front disc brakes. Is there a set of spindles other than 65-67 Corvette that will work without changing the track width? The aftermarket kits and 68 up spindles change the track width as much as 1 inch per side. Thanks for your help. Dennis

[Wayne K.]

Re: C2 disc brake conversion

Dennis,

I don't have the answer to your question but within the last 30 days if you check the archives there was a lot of discussions with regard to this. I don't know what your reason is for wanting to do this but after readfing the discussion you may want to stay with the drum system.

Wayne

[Michael H.]

Re: C2 disc brake conversion

Dennis,

If you've thought this over and decided this was what you want to do, why not just use 65-67 spindles? I'm not 100% sure but I believe the dim's are the same so the track shouldn't be affected.

If you do change to front disc with rear drum, be SURE to find and install a proper dual circuit master cylinder designed for this application as the single circuit 64 cylinder will definitely not work. (Chevelle may have a cyl that might work) The disc/drum arrangement is completely different than drum/drum or disc/disc and would use a unique cyl.

There was a great string of posts on this same issue a few weeks ago and I think, in the end, it was agreed by all that the conversion was not near worth the aggrevation. A properly setup drum system is more than satisfactory unless you are amature road racing.

Michael

[mike cobine]

Re: C2 disc brake conversion

I think you have based your choices on erroneous information.


If you look at the chart below, you will see that the track changes as the tire and wheel change. This is because track is defined as the center of the tread on one side to the center of the tread on the other. Changing the tire changes track. Changing the wheel changes track.



Year Front Rear Wheel Tire
1964 56.3 57.0 15x5.5 6.70x15
1965 56.8 57.6 15x5.5 7.75x15
1967 57.6 58.3 15x6 7.75x15
1968 58.3 59.0 15x7 F70-15
1969 58.7 59.4 15x8 F70-15
1973 58.7 59.5 15x8 GR70-15
1977 58.7 59.5 15x8 GR70-15





I don't believe you have any change due to the spindle.

[Duke W.]

Re: C2 disc brake conversion

Tire size has NO EFFECT on track since track is measured from the circumferential center of the tire, which does not change with changes in tire width.

Track is determined by the distance of the hub wheel mounting plane from vehicle centerline AND wheel offset.

Though '64 (drum brakes) and '65 (disk brakes) base steel wheels have the same +0.44" offset, disk brake cars have slightly wider track because the hub wheel mounting plane moved slightly outboard with the new disk brake system.

'67 Rally Wheels (and C2 optional KO/bolt-on aluminum wheels including adapter) have +0.06" offset; '68 7" Rally wheel offset is -0.28", and 8" Rally and optional aluminum wheel offet is -0.50".

Track changes after 1965 through the end of C3 production were solely due to wheel offset changes.

Duke

[mike cobine]

Re: C2 disc brake conversion

That would be true IF you were measuring where the hub tracks, however, the reason it is called Front Track and Rear Track is this is where the TIRE tracks on the ground, and is measured on the ground plane.

Vehicle dynamics are not in space but upon the ground, specifically the road surface.

As such, the change in size and construction of the F70 belted tire and the GR70 Radial tire allows the GR70 to sit at a slightly different spot on the ground.

The same would be true of the geometry of the taller 7.75 tire as opposed to the 6.70 tire. Being taller, it reaches further out due to the camber of the wheel and tire.

Vehicle Dynamics, Pages 5-18 and 5-19, Chevrolet Power Manual, 2nd Edition.

[Gary C.]

Hood Clearance issue with power dual master cyldr

If a power brake 67 power brake master cylinder is install the nose will be higher and the hood will not clear. Two choices; 1 - make a thinner hood or 2 - redrill the firewall holes to lower the power brake booster. Also, when adding front disk brakes to a '64 a porportioning valve will be required or you will lock up the rear brakes.

Good drum brakes will work just as well unless you are road rallying and really abusing the brakes. I converted my '64 for rally reasons. It's a heck of alot more expensive than good Heavy Duty drum brake shoes.

As others pointed out, there's been lots of previous posts about this on '64's & C1's.

Good luck,

Gary
....

[Duke W.]

Re: C2 disc brake conversion

The OEM track specs are based on design camber and design ride height and rounded to the nearest tenth inch.

The difference in track for a 6.70-15, which is about 0.4" larger OD and 0.2" larger static loaded radius than a 7.75, F70, or GR70-15 would be noise level with the OEM specified slight positive front camber and slight negative rear camber.

If hub distance from centerline was the same for both '64 drums and '65 disks, the '65 front track (slight positive camber) would be minutely more and the rear track (slight negative camber) would be minutely less because of the slightly shorter tire, but '65 track is speced speced about 0.6" wider because the hub wheel mounting plane is further outboard with disk brakes.

The referenced pages in the second edition Power Manual discuss roll couple distribution and roll steer and toe change. Other than just showing track in Figure Two and defining T sub F and R, they don't go into any more detail on track measurement or track sensitivity to other parameters.

Duke

[mike cobine]

Duke, you steered from his question to your own

His original question concerned finding something with the same track as the '65-'67 front disc brake spindles.


You have directed it to the difference between the '63/'64 spindles and everything else.


You are correct in the tire being "noise" in the equation, as that is why the '69-'72 with F70 is Front 58.7 and the same as '73-'77 with GR70 at 58.7 while the back differs at '69-'72 rear 59.4 but larger on '73-'77 rear 59.5. The difference in the tires was not enough to round over in the front, thus the same 58.7, while in the rear, it was at the point to round to the next highest tenth, thus 59.4 and 59.5.


If your measurement is to tenths, it is noise. If it is to inches, then all differents here are noise. But the tire size is still part of the equation.


I should not have confused you by including the '64 track measurments as a reference.



Year Front Rear Wheel Tire
1964 56.3 57.0 15x5.5 6.70x15
1965 56.8 57.6 15x5.5 7.75x15
1967 57.6 58.3 15x6 7.75x15
1968 58.3 59.0 15x7 F70-15
1969 58.7 59.4 15x8 F70-15
1973 58.7 59.5 15x8 GR70-15
1977 58.7 59.5 15x8 GR70-15






Duke: The OEM track specs are based on design camber and design ride height and rounded to the nearest tenth inch.


Quite the profound statement. By altering the camber on the tire, the track changes. If the tires did not factor, then a requirement as you stated would not be necessary.


Now back to Dennis' original question, Is there a set of spindles other than 65-67 Corvette that will work without changing the track width?


Answer - '68-'82 front spindles will produce the same results as the '65-'67 spindles. The differences in measurements are due to tire and wheel changes and not the spindles. There MAY be a difference due to the use of larger bearings and thicker materials on '69 and up, but the difference would be insignificant in actual use.

[Duke W.]

Re: Duke, you steered from his question to your ow

Like I said, the increased '65 track over '64 is due to increased lateral distance from vehicle centerline to the wheel mounting plane of the disk brake hubs; '65 wheel offset is the same as '64, and the slight difference in tire OD and nominal camber, if any, between '64 and '65 has no meaningful contribution to the track increase.

So that the answer to the question is that if one installs the spindle/disk-hub from a disk brake model on a '64, the track will increase by about 0.6" relative to the OE drum brake setup, assuming use of wheels with the same offset

Also, the original questioner may find it useful to know that'64 steel wheels will not fit over disk brakes; '65 steel wheels were redesigned to clear the disks, but they have the same offset as '64 steel wheels.

I will also add, that I don't think it is advisable to make this modification. The drum brakes are a good system, and a thorough overhaul with modern linings should yield a very good system. Carbon-metallic lining materials are also availalbe, which rival the old J-65 metallic linings in fade resistance for high performance use, but are much less temperature sensitive.

Duke

[Bill Stephenson]

Re: Hood Clearance issue with power dual master cy

Gary,

--------I must be confused by the body of your post. All 63/67 Corvettes had optional power brakes. To my knowledge all 63/67 Corvettes used exactly the same mounting position for the masters, and all 63/67 Corvettes used the same position for the power booster. You do have to drill new holes for the addition of a power booster, but the booster stays in the same position relative to the hole in the firewall used for the master cylinder. I have added many a power brake set-up to mid-years and never had any kind of hood interference. Im sorry if I am not looking at your post correctly!!!.........Bill S

[Gary C.]

Reply to Bill icw ref to hood clearance issue

No problem until you install a '67 dual master cylinder and power brake booster. The combo makes the front nose of the '67 dual master cylinder to be higher than the hood opening. At least it did on my '64. Gary....

[Dennis H.]

Re: C2 disc brake conversion

I want to thank everyone for their comments but I don't need a course in track width 101. Let me restate my question. Does anyone know of any spindles that will keep the same hub to hub distance as the stock 64 drum brakes other than 65-67 Corvette. These pieces are scarce and I wondered if any other GM Vehicle used a spindle that would work. Thanks Again Dennis

[mike cobine]

Re: C2 disc brake conversion

Dennis,

As Duke has stated several times, the distance on the '65 is WIDER than the '64, so the answer is, no.

However, '65-'67 is the same as '68-'82, so if you can live with the '65-'67, then you can live with the '68-'82.

[mike cobine]

Re: C2 disc brake conversion - I should add

that the difference is only about 1/2 inch on the track, so that is 1/4 inch on each side further out.

If your tires are so tight that 1/4 inch will cause a problem, then you need to check everything on your front end, including the body, to find out why.