How strong are the C3 parking brakes supposed to be?

[Michael L.]

[Joe L.]

Re: How strong are the C3 parking brakes supposed to be?

Guys,

I’m trying to adjust my parking brake on my 69 after complete the restoration. I followed the procedure in the CSM but it still didn’t work so I started to adjust it and then test it out. When I pull the brake handle there are basically two positions the handle can be in. The first is where the handle goes to if I don’t move the armrest cushion, which is about 60-70% of the total travel of the brake, and the second is all the way up till it cant move anymore. In my mind the brake should be effective in the first position (since most folks would be putting it on without moving the cushion) but it’s not. It will only hold the car on a very mild grade in the first position. Even in the second position, all the way on, it will slow the roll of the car on steeper grade (?20-25 degree incline) but it wont stop it. Am I expecting too much from this brake? Or should I keep adjusting until it holds in the first position on the steeper grade? Should it be able to hold on an even steeper grade, like 30-35 degrees in the first position? Thanks for any thoughts on this.

Mike

Mike------


The armrest cushion is strictly an aftermarket item. The design of the parking brake system was never done in such a way to accommodate the cushion. Follow the procedure in the FSM without the cushion in place.

When adjusted to exactly the direction of the FSM, the parking brake performance will be marginal.

[Leif A.]

Re: How strong are the C3 parking brakes supposed to be?

Mike------


The armrest cushion is strictly an aftermarket item. The design of the parking brake system was never done in such a way to accommodate the cushion. Follow the procedure in the FSM without the cushion in place.

When adjusted to exactly the direction of the FSM, the parking brake performance will be marginal.

/\/\/\THIS. The parking brake when adjusted correctly, will hold the car in place on flat ground with the car in neutral (if a manual transmission). Don't ever assume the parking brake is going to hold your car from rolling on any kind of hill...always put the car in gear along with the minimal parking brake. Picture below of my '67 for angle purposes only.

[Ed S.]

Re: How strong are the C3 parking brakes supposed to be?

/\/\/\THIS. The parking brake when adjusted correctly, will hold the car in place on flat ground with the car in neutral (if a manual transmission). Don't ever assume the parking brake is going to hold your car from rolling on any kind of hill...always put the car in gear along with the minimal parking brake. Picture below of my '67 for angle purposes only.

Not questioning your sound advice but.... just curious, what specifically does the owner manual state regarding the engagement of the parking brake? Does it advise against using it on a hill without putting the trans in gear or does it suggest that it can be used alone?

[Leif A.]

Re: How strong are the C3 parking brakes supposed to be?

Not questioning your sound advice but.... just curious, what specifically does the owner manual state regarding the engagement of the parking brake? Does it advise against using it on a hill without putting the trans in gear or does it suggest that it can be used alone?

Specifically, the owner's manual states to engage pull up on the handle, to disengage push button and release...that's about it. I would think that if GM knew of the lack of braking efficiency in the parking brake, they certainly wouldn't advertise it in the owner's manual. But, those of us who have owned several C2 and C3 over the years realize it's limited usefulness.

[Dan A.]

Re: How strong are the C3 parking brakes supposed to be?

Michael,

I owned my 72 for eight years before I even realized mine worked. It was only after we moved into our new house and tried it on the driveway which may have 10 degrees slope. It seems to hold but I wouldn’t leave it like that without it being in gear. I find your comments about the handle having only two positions interesting. I just went out and checked and mine has around 11 distinct “clicks”, or positions until it is full engaged. This may not be relevant at all but last year I noticed mine didn’t seem to ratchet any longer. I removed the console, lubricated the mechanism, worked it a bit and it has functioned properly since.

[Ed S.]

Re: How strong are the C3 parking brakes supposed to be?

Parking brakes on cars with drum brakes function completely differently. To engage the parking brake I was taught to apply the brakes hard with the foot pedal - this expands the shoes inside the drums. Then, while holding pressure on the brake pedal, pull the park brake handle. This allows the cable mechanism to expand out to the position of the shoes. Then release the foot pedal. Rear shoes, in the park brake mode are good and tight up against the drums. But....still put the trans in 4th gear as an added safety measure.

[John D.]

Re: How strong are the C3 parking brakes supposed to be?

I think the Engineers back in the day took the design to the point that it met the performance requirements once and then ran for the hills.

Happy Engineers week....https://en.wikipedia.org/wiki/Nation...eers_Week_(U.S.)

[Keith M.]

Re: How strong are the C3 parking brakes supposed to be?

Parking brakes on cars with drum brakes function completely differently. To engage the parking brake I was taught to apply the brakes hard with the foot pedal - this expands the shoes inside the drums. Then, while holding pressure on the brake pedal, pull the park brake handle. This allows the cable mechanism to expand out to the position of the shoes. Then release the foot pedal. Rear shoes, in the park brake mode are good and tight up against the drums. But....still put the trans in 4th gear as an added safety measure.

May be how to do it in other cars but not a C3. C3 primary brake system and parking brake are completely independent. Disc regular, drum parking brake.

[Richard K.]

Re: How strong are the C3 parking brakes supposed to be?

I seem to remember reading somewhere to drive down the road slowly and pull the parking brake on lightly while holding in the button. Do this for a short distance. This is meant to burnish the brake pads and set them in, so to speak. It could be that not a lot of the parking brake's pad's are making contact with the drums. Sorry this is a little vague, but might be worth a try as a possible quick fix.

[Duke W.]

Re: How strong are the C3 parking brakes supposed to be?

As above. Over time the linings develop a "glaze" that reduces their Cf. My '88 MBZ 190E 2.6 has the exact same rear parking brake design, but a smaller disk. When new the parking brake worked well, but lost effectiveness over time, so to correct this I would lightly drag the parking brake on a down grade, but with each of these "adjustments" I had to pull the lever a little further and after several the lever was at the limit of travel and the brake wouldn't hold, so it was time for a real adjustment about ten years ago

The adjustment procedure is identical to vintage Corvettes - loosen the cable then adjust the shoes to achieve a slight drag, just like and old car with non-self adjusting drum brakes, then adjust the cable to spec - something like three or four clicks with 20 pounds of force or whatever.

It's worked fine since, but I've only driven it less than 10K miles since then.



Duke

[Duke W.]

Re: How strong are the C3 parking brakes supposed to be?

Guys,

I’m trying to adjust my parking brake on my 69 after complete the restoration. I followed the procedure in the CSM but it still didn’t work so I started to adjust it and then test it out. When I pull the brake handle there are basically two positions the handle can be in. The first is where the handle goes to if I don’t move the armrest cushion, which is about 60-70% of the total travel of the brake, and the second is all the way up till it cant move anymore. In my mind the brake should be effective in the first position (since most folks would be putting it on without moving the cushion) but it’s not. It will only hold the car on a very mild grade in the first position. Even in the second position, all the way on, it will slow the roll of the car on steeper grade (?20-25 degree incline) but it wont stop it. Am I expecting too much from this brake? Or should I keep adjusting until it holds in the first position on the steeper grade? Should it be able to hold on an even steeper grade, like 30-35 degrees in the first position? Thanks for any thoughts on this.

Mike

Grades are usually expressed in percent - the rise over a given amount of level travel times 100 so a 45 degree angle is a 100 percent grade and a conventional car would likely be unable to climb. The steepest grade you are likely to encounter on a public road is about 15 percent and IIRC interstate highways are limited to six percent.

It's not clear to me if you're doing the adjustment properly even though you said you used the CSM procedure. I suggest you do the "drag adjustment" to burnish the linings and then go through the shop manual adjustment procedure.

Duke

[Mark F.]

Re: How strong are the C3 parking brakes supposed to be?

Per John Hinckley's C2 Assembly Process Presentation (available in the Database of Restoration Documents [DoRD] Sticky Post), that's what they did as the third step of the Roll Test at the factory to burnish the shoes before final adjustment...I doubt the C3 process was any different...

RT-3	Driver moves back to the smooth-road side of the rollers, accelerates to 60 mph, and . Driver then slows to a stop on the rollers and pushes the button on the pedestal; the rollers retract and the driver proceeds into the toe-in machine.

[John D.]

Re: How strong are the C3 parking brakes supposed to be?

After burnishing the shoes at the roll test I wonder how the final cable adjustment performed ? The car was off the end of the line presumably with no access underneath. Maybe there was a pit ?

[Mark F.]

Re: How strong are the C3 parking brakes supposed to be?

After burnishing the shoes at the roll test I wonder how the final cable adjustment performed ? The car was off the end of the line presumably with no access underneath. Maybe there was a pit ?

Good question, John...

I just searched for that "park brake final adjustment (if needed)" step and did not find it.

The front cable is installed at step 28 on the Hard Trim Line (before Body Drop).

HTL-28

Parking brake lever/handle assembly and front cable

The rear cable is installed at step 7 of the Chassis Line (before Body Drop)

CL-7	Install rear parking brake cable

Here's what John said for step 9 on the final line, which is 48 steps BEFORE roll test.

FL-9	Connect front parking brake cable to rear cable with equalizer and adjust tension.

There is a Chassis Pit on the final line, but that's before roll testing.
The only "Pit" after the roll test is the toe-in pit, which would be a logical place to do it with the car on the ground on its wheels.

Seems to me such adjustments would be non-typical, so the Driver would have to lean over the sill and yell at Pit guy that it needed adjustment, though ?

Having worked in toe-in pits myself, this could also be semi-dangerous...you don't want the driver peeling off the toe-in machine while the pit guy still has his hands up adjusting a cable !