Brake bleeding & hair pulling
Le Mans Master
Joined: Jun 2019
Posts: 5,326
Likes: 2,094
From: Loveland
Try driving the front up on ramps, remove rear wheels and lower the rear as much as you can. This will improve the angle of the rear calipers.
I use the Motive bleeder at the MC and about 12 psi to bleed the calipers, helps a lot.
I use the Motive bleeder at the MC and about 12 psi to bleed the calipers, helps a lot.
Last edited by kodpkd; Apr 25, 2022 at 11:59 AM.
Thread Starter
Instructor
Joined: May 2021
Posts: 222
Likes: 73
From: Missouri
Ok I had to get away from this for a bit just to take a break. So here's where I'm at. I've bled bled and more bled using all the tricks mentioned here and elsewhere. I cannot get any bubbles to come out of the calipers or MC. I've bled the MC multiple times, banging it with my rubber mallet which worked good at getting the last tiny bubbles out. Same on the calipers. Went for test drive. I have brakes now but still a lot of pedal travel....not to the floor but pretty far for sure. I checked all the calipers and I still have some slight weeping out of bleeders and also a couple of the proportioning valve connections. Again, it's very slight but there. I will try and carefully see if there's anymore room to tighten but I already know I'm close to the limit. So, would that very small amount of weepage be the reason for the long pedal travel? Could there be something not right with the MC or the rod possibly? When I took the MC off, the rod is only about 1-1.5" long. This is on an '81. Does that sound about right for this year? Any other thoughts?
Thanks guys.
Thanks guys.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,809
From: Cool Northern Michigan
The question is not about the booster rod length, but rather the gap between the rod and the MC.
Should be 0.060.
Too tight, brakes drag constantly.
Too loose, extra pedal travel.
Should be 0.060.
Too tight, brakes drag constantly.
Too loose, extra pedal travel.
Thread Starter
Instructor
Joined: May 2021
Posts: 222
Likes: 73
From: Missouri
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,809
From: Cool Northern Michigan
You can leave the lines attached.
Remove the two nuts and pull the MC away from the booster within reason.
There is a special tool that measures and sets-up that critical booster rod gap.
Or.
Go to Wlamart toy section. Get a egg of Silly Putty. Place a gob of it on the end of the booster rod. Reinstall the MC, just snug the nuts down.
Remove MC and try to retrieve and measure the thickness of the clay. That is your gap.
Remove the two nuts and pull the MC away from the booster within reason.
There is a special tool that measures and sets-up that critical booster rod gap.
Or.
Go to Wlamart toy section. Get a egg of Silly Putty. Place a gob of it on the end of the booster rod. Reinstall the MC, just snug the nuts down.
Remove MC and try to retrieve and measure the thickness of the clay. That is your gap.
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Thread Starter
Instructor
Joined: May 2021
Posts: 222
Likes: 73
From: Missouri
Yep, I pulled the MC and removed the gasket that someone had put on there. It's been raining for days here so I won't get to test that change until Sat. Will let you know the results. BTW, the rod on my '81 is non-adjustable....
Thread Starter
Instructor
Joined: May 2021
Posts: 222
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From: Missouri
The rod from the booster to the MC is non-adjustable. At the pedal, I tried to take a look yesterday but couldn't really get a good view of it. The service manual shows a nut there, but gives no explanation on adjusting it. I'll try again this weekend when I have better light.
Le Mans Master
Joined: Jun 2019
Posts: 5,326
Likes: 2,094
From: Loveland
I would start with the, rod to MC, measuring tool. If you have a "very small" gap between the rod and the inside of the MC, you should be good. In reading about the 81 vet, it very important the MC and booster are made to go together.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,809
From: Cool Northern Michigan
The rod from the booster to the MC is non-adjustable. At the pedal, I tried to take a look yesterday but couldn't really get a good view of it. The service manual shows a nut there, but gives no explanation on adjusting it. I'll try again this weekend when I have better light.
Especially in the brake category:
Combination Valve > Proportioning Valve, Master Cylinder piston design, Brake Pedal Assembly, Booster Rod, etc.
I have a service manual that states '74 - "77 had only four bleeders. Then six bleeders starting in '78.
H-m-m-m-m-m.
So think of a service manual as general knowledge, not specific.
Thread Starter
Instructor
Joined: May 2021
Posts: 222
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From: Missouri
Ok I had to back the corvette out of the garage and the pedal felt much better. It engages much quicker now. Will do a more detailed test tomorrow but one quick question. How much brake drag is acceptable? Here’s a quick video. Is this ok or do I need to back off the rod clearance a bit more?
Last edited by sci85; May 6, 2022 at 02:56 PM.
Le Mans Master
Joined: Jun 2019
Posts: 5,326
Likes: 2,094
From: Loveland
That does seem like too much drag. I wondered about my caliper drag also, I drove about a mile without braking,, and touched the disc, it wasn't that hot. Check both sides to be sure they are the same. Make sure it isn't the bearings that are too tight. Kind of hard to see but I assume that is the front.