Looking to change drums to disc from 71 CBody to 68 - anything to know?

ayilar said:
Thank you for the link. What I am asking is, whether one brand is better than the other? I hope someone has experience with Centric or Dynamic Friction rotors.

PS: tons of good info in this thread, including personal experiences.
Click to expand...

I don't think it matters. Looking at the photos, the Centric and the Dynamic Friction look identical, and likely come out of the same plant. If I was daily driving a car there would be great temptation to spring for the protective coated ones, otherwise I would save my money and go with Centric. I've purchased plenty of Centric stuff in the past. It's no better or worse than any of the other brands who source everything from China these days.

On the plus side, I believe the design they are using would be considered a heavy duty rotor. My memory tells me that decades ago only the police and taxi spec rotors had the extra support ribs around the hub. These days it seems like most of the modern rotor castings have the ribs.

rotor 2.JPG


Jeff
 
69 300 vert said:
I checked it out after you mentioned it. I doubt the servo actually works, mebbe it can be repaired? I have no idea.

The '71 cruise will fit and work. The '68 servo is specific to 1968, TS switch and brake switch are specific to 1968 and 1969. The '69 servo is specific to 1969. After that they're pretty much alike.
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I imagine you can dig into the Servo, it might be in my FSM (although mine is 1968 instead of 1971, maybe they share enough parts to make it easier to carry over).
And if I'm reading this right, the 68 servo is specific to 68, but the later servos are backwards-compatible with the older systems? How would the brake switch fare? Not very familiar with cruise control intimately, just wondering how the mish-mash parts would fare.
 
It's VERY easy, don't even worry about 1968, that's for the numbers matching purists, just install that stuff in your car. Short of running into one of us at a show, NO ONE is going to realize it's not year correct. The brake light switch will replace yours directly, it has two extra terminals to disengage the cruise control, no more vacuum break like the '68 and '69's had. Be sure and get the little wiring harness that ties it all together. I just realized, you'll have to source the lost motion link and cable clamp, those came out with the engine. Get the bracket off the brake booster, don't leave it there.

Lost motion link pic:

lost motion link.jpeg
 
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Good to know!
Do you have a better source for that image? Having trouble seeing where the motion link is supposed to hook up on the carburetor linkage - I even wonder if that's a general part and not 4 barrel specific (I imagine it's not, on my car at least it still has the long stud for the accelerator pedal/kickdown/return springs).
 
Well, I guess I could be wrong...the link on the left is the only one I recall seeing...

cruise schematic.JPG


LostMotionLink.2.jpg


NOS-clamp.JPG
 
That 71 disc booster will bolt up to your 68, and will work fine, however, you will have interference with the shift linkage if you have column shift, and you will not be able to shift down to low 2 or low 1 with the shifter. I know, because I installed one of those boosters on my first disc conversion on my 66 T&C.

It's best to source the 65-70 Bendix dual diaphragm booster, but the single will work in the mean time. Have it rebuilt first.

Do NOT use the drum booster that you have in your 68 now, as it will not provide enough boost to properly energize the disc system, and will let you down.
 
Mine is column shift, so that presents an issue. Barring the cruise control linkage, I may just leave the booster alone. Maybe the master cylinder is still salvageable, however?
 
Do NOT use the original drum booster with a disc brake conversion system. Do not.

Yes, there are others who say that the drum booster is fine with a dsisc sytem, but it is not. The factory had two different boosters for the two systems because the disc system needs a greater vacuum boost to be able to fully energize and take advantage of the full brake system capability.

Think of it this way: using a disk system with a drum booster may make the difference between stopping in time, or not being able to stop as quickly as with the correct booster. That might be the difference between killing that stupid kid who runs out in front of you on his bicycle, or smashing into the back of that vehicle that cuts in front of you, filling up your safety zone, and then slams on his brakes, or not.

The other thing to think of is the liability issue. Nowadays in fatal or serious injury accidents there's almost always a mechanical inspection, especially if an old car's involved and any of the work done on the old car that might affect crucial safety systems could be suspect. The lawyers will have a field day if it's determined that braking system parts from two technically incompatible systems were used.

Do NOT use a drum booster on a disc brake system. I can't stress this enough.

It's unsafe.

Also, there are bore differences between drum brake and disc brake master cylinders, and early drum masters did not have the correct front reservoir size.
 
Ross Wooldridge said:
Do NOT use the original drum booster with a disc brake conversion system. Do not.
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Good post, but my question was more if the master cylinder from this donor car was savable, and then match it with the dual-diaphragm booster. Although in that case I think it would be far better to just get a NOS set, if possible.
 
I was gonna message 69 300 vert about cruise control since I didn't want to continue off-topic to the thread, but I couldn't so I'll say it here (might as well):
I was looking at the service manual for the 1970 model (mymopar.com didn't have 1971, but it looks like the exact same setup, as was mentioned), and the wiring diagram for it is pretty straight-forward, except for one part:

y5TYW1Y.png


Where would the accessory feed be in this case? I assume it's somewhere in the wiring harness, but it doesn't specify which wire black is going to - I guess it would be to whatever black is in this case. Even tried looking at all the wiring diagrams (there's several) and didn't really see anything mentioning accessories, maybe besides the interior controls. Also, interesting thing I just noticed is that the stalk here and on the 71 look the same as the 68 and 69 models, when did they get the later version with the sliding switch?
 
On my '68 I tied it into a switched power lead on the back of the fuse box. Where I put it on the '69 eludes me, completely blank. I_think_the sliding switch started in 1974 with the formal models. It wasn't too long after that the sliding switch superseded the rotary switch.

The switch for 1970 was new, it added the off position the earlier switch didn't have, hence the four wire connection vs the earlier three wire connection.
 
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I was confused what you meant by 'switched power lead' until I googled the term and found some car forums - so essentially what you were doing is running the wire to another part of an existing circuit that was a switched power source (such as ignition) instead of a constant? I've never heard the term before (most of my wiring and electrical knowledge comes from HVAC, not automotive, lol).

Interesting to know...correct me if that's not what you were saying. I guess running to ignition is the best choice?
 
I generally use the ACC fuse position. Tying into the back of fuse block is neatest, make sure you get the output (fused) side, fuse tap, acceptable, not great, or stuffing stripped bare wire under the fuse, nope.
 
Awesome! I understand now. And as it turns out, the ACC wire on the fuse block appears to be black as well (from another thread on this forum showing the inside of the block). Pretty good.

I hope the servo works in the parts car - I wonder if there's any quick way to test it without running power to it. As far as I know it's partly vacuum operated, maybe checking it by sucking on the vacuum line would be a good way to test? That's assuming the electricals are fine as well on the servo, which may be simpler, seeing if there's any corrosion on the connectors. Someone who has far more experience than me would have to chime in.
 
You can test the diaphragm for leaks, no problem. After that, I'm lost.

When you go to install it, the only adjustments are for the brake light switch and the accelerator cable (lost motion link). Any Chrysler service manual will have it in there. Don't mess with the adjustment screws on the servo, you'll never get them right. The servos either work or the don't. They don't have a high failure rate. The later ones are larger and made out plastic but work fine.

I believe in 1972, there was a master technician service booklet on cruise control, full of great information if you can find one. Imperialclub.com used to have them online, they appear to be gone now.
 
That service manual is amazing at explaining it. I'm surprised at how simple the concept actually is. Engineering does indeed make a difference!
 
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