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be careful who you let work on your car

SELLERSRODSHOP

SELLERSRODSHOP

Well-Known Member
stopped by a local shop yesterday where a couple friends work to visit for & few & the boss popped up & said "hey, you know a little about mustangs, see if you have any ideas on this". it was a 67 vert that was an original 6cyl 4 whl drum brake car. the owner lost a nice 73 vert in the big flood & long story short, the 302/c4 & front disc brakes were grafted onto the 67 & a 8'' 5 lug drum rear added. they couldn't figure out why the car had poorer braking qualities than it did before the swap. took one look & the original 4 whl drum master cyl & prop valve were still in place. told them "those need to be changed". boss said he could understand the prop valve, but said "the master should be fine as its a 1" bore master..." not sure if he ever understood the concept i explained about the volume differences between the new disc pistons vs. the original wheel cyls & the small bowls on the master not holding enough volume to work them properly....kinda scary if you think about it.
 
I agree 100% on the whole volume perspective... but is the smaller reservoir really THE issue? Once the system is primed, isn't the reservoir just there for long term replenishment such as when the pads wear down. I don't think the reservoir has much to do with the initial setup other than to prime the system. It's been a while since I've pressed a brake pedal with the cover off, but I don't ever recall seeing the reservoir level change with a fully primed / bled system.

According to Google, the 73 uses a 15/16" bore... not too far off from a 1" master.

If that's the case I'd be inclined to think that having the 1" bore is making the braking feel harder since it's throwing more volume into the caliper with a shorter stroke. This could be making the pedal harder to modulate... correct?

Another thing is the drums usually have 10# of residual pressure in the line whereas Discs typically are 2#. the drum master will cause the discs to drag more than the proper master / disty block would.

Lastly, If the distance between the brake pedal pivot and master cylinder rod attachment point is longer on the '65 pedal, it would also make the braking harder to modulate. Too much shorter and it probably will run out of stroke before applies good pressure to the calipers.

Just throwing out other ideas. Everything in the system needs to be considered and matched appropriately.
 
i think its a combination of everything. there isnt any real drag on the front brakes as he said they are pretty well nonexistent. says they only feel the rears grabbing, so i figured it probably was a volume or prop valve issue. i didn't look deep enough to see what was done as far as hoses. i did see the original 1967 hard lines were still in use, so they could be rust clogged & slowing fluid volume. all i know for sure is i wouldnt want to drive it!
 
"Grabber70Mach" said:
And does this Boss own the shop? Either way its amazing.
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boss isnt the owner & owner is hands off as far as the shop. both are good guys, just think this job was a little out of their spectrum as far as the norm around there...
 
Another thing is the drums usually have 10# of residual pressure in the line whereas Discs typically are 2#. the drum master will cause the discs to drag more than the proper master / disty block would.
Click to expand...

I tend to agree with Stangg. With an original MC designed for 4 wheel drums, this will cause screwy braking with disk brakes.
 
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