For those with vacuum and 12" front discs...

[novaderrik]

which booster is it- the big one or the smaller one?

 

[SNOWBIRD]

I believe booster is good unless you did not change pedal or have wrong pedal or pin is in the wrong hole on pedal.etc so when brake is to the floor you do not have the maximum travel you need ..i know it is a little far fetched BUTTTTT..Vacume at 15 in drive is more then perfect no wild cam in this engine...CHECK YOUR YOUR CHECK VALVE AT BOOSTER IF IT HOLDS VACUUM..VERY EASY TO CHECK ...start car run 30 secs.....stop engine and let rest for 30 secs to see if booster and check valve hold vacume try to remove the plastic check valve that is at the end of the vacume hose... you should hear a huge whoosh of air rushing into booster..this means booster and check valve are probably 99%working properly....

 

[SNOWBIRD]

PULSATING,comes from a badly turned disc or a oval drum...if your foot brake or emergency brake cables are free not seized slowly apply them with your left foot while the car rolls 2 to3 mph if the drums are oval you will feel it in the car...

 

[SNOWBIRD]

Why dont you stick on the right master cyl that matches those calipers redo the back with right shoes and drums if damaged ,and new spring kit ..voisla

 

[SNOWBIRD]

O ...bleed ..till your sure there is no more air

 

[stickybones]

Thanks for the tips guys. I have some things to think about and look in to. Unfortunately, I don't have alot of time right now to do this so it's likely to be a few weeks before I get to the bottom of this...assuming I get to the bottom of this.

 

[stickybones]

which booster is it- the big one or the smaller one?

Not sure what the big and small ones are, but I have the 9" diameter booster.

 

[stickybones]

Why dont you stick on the right master cyl that matches those calipers...

That's what the original question of this thread was. Since LS1s have four wheel discs, I can't assume their MC size is appropriate for my application. Searching, I did find a thread that discussed going up a size to 28.6/40mm and that seemed to work well for that particular individual. However, it seems that even application specific systems like a Baer use the smaller 24/36mm MC. Maybe it's a crap shoot or possibly, as discussed here in this thread, something else is not quite right leaving my brakes less than optimum.

If bleeding brakes wasn't such a PITA, I would play around with things some more and look into mixing/matching different combinations to see what the results are.

 

[SNOWBIRD]

Do a internet search MITYVAC BLEEDER HOLESHOT ,this is a vacume bleeder and you can do it alone and is clean ,almost no oil on floor ..HARBOR FRIEGHT sells a very similiar product

 

[RmvBfrFlght]

The LS1 f-body used a 1" bore M/C with a 9" dual diaphragm booster. So your set up matches the GM set up. The vacuum isn't the best, but sufficient.

Going to a larger bore M/C will decrease the braking capacity at the same pedal pressure. Going backwards so to speak.

A smaller bore M/C will increase the line pressure for more clamping from the calipers.

However, my thought is that the pads are the issue. Need to get some good high performance street pads. Try some Hawk's or Performance Friction pads.

Be sure to bed them in properly, and then give them some time to develop grip. The difference will be night & day.

RemoveBeforeFlight

 

[stickybones]

However, my thought is that the pads are the issue. Need to get some good high performance street pads. Try some Hawk's or Performance Friction pads. RemoveBeforeFlight

Actually I am using PFC front pads. I guess it's possible that they weren't bedded in properly.

 

[RmvBfrFlght]

Actually I am using PFC front pads. I guess it's possible that they weren't bedded in properly.

To re-bed them clean the rotors with some 80 grit emery cloth. Best is in a circular motion. A circular pad in a drill makes quick work of it. Then the same for the pad faces. Reassemble and re-bed and drive for a while easy on the brakes.

There is a possibility that the metering valve in the combo block is bad. This valve holds off the front line pressure until the rear shoes hit the drum. Then is supposed to allow full pressure to the fronts. A brake pressure gauge can be used to test this.

Front brake hoses can be an issue. For best braking use the stainless/Teflon lined hoses.

Push comes to shove, a lightly smaller bore M/C will help.

RemoveBeforeFlight

 

[stickybones]

OK let's close out this post. My brakes are good again, at least as good as I would expect them to be. They haul the car down from speed with some authority now. To recap what I did and what I think made the difference:

1. Cut the front discs, lapped the pads and bedded them together = no difference.

2. Replaced the rear AL drums with new steel ones (NAPA P/N 440-1359) = no more pulsations

3. Rebuilt my AL master cylinder (24mm/36mm) with a kit I got from RockAuto (Raybestos P/N MK1486) and bled it good on the bench = looks better in the engine compartment than the rusty cast iron one. See below.

4. Bleed the brakes twice. The first time made no difference. I did them again using a different technique. I vacumn/gravity bled them this time. I put the mity vac on each bleeder (one at a time of course) and pumped it up. I then cracked the bleeder and let it flow. While it was flowing I tapped on the respective wheel cylinder or caliper. I also tapped on the proportioning valve before I started in the rear. I tapped the steel lines also. The logic here was dislodge any possible air bubbles hiding within. After this last bleed job which occurred after the MC rebuild replacement, my brakes were back to very good again.

I've been riding the GN like this since the summer when I finally finished doing all this stuff and I'm happy to say it was mission accomplished. Thanks for all the little tips that got me thinking of which ways to go. I think the biggest difference, which is probably the solution for many others who also have brake problems is a real good bleed. I haven't been to the track since so I don't know how much boost they'll hold at the line, but I can hold ~7 psi in my driveway with street tires which is pretty decent in my book.

 

[Red Regal T]

OK let's close out this post. My brakes are good again, at least as good as I would expect them to be. They haul the car down from speed with some authority now. To recap what I did and what I think made the difference:

1. Cut the front discs, lapped the pads and bedded them together = no difference.

2. Replaced the rear AL drums with new steel ones (NAPA P/N 440-1359) = no more pulsations

3. Rebuilt my AL master cylinder (24mm/36mm) with a kit I got from RockAuto (Raybestos P/N MK1486) and bled it good on the bench = looks better in the engine compartment than the rusty cast iron one. See below.

4. Bleed the brakes twice. The first time made no difference. I did them again using a different technique. I vacumn/gravity bled them this time. I put the mity vac on each bleeder (one at a time of course) and pumped it up. I then cracked the bleeder and let it flow. While it was flowing I tapped on the respective wheel cylinder or caliper. I also tapped on the proportioning valve before I started in the rear. I tapped the steel lines also. The logic here was dislodge any possible air bubbles hiding within. After this last bleed job which occurred after the MC rebuild replacement, my brakes were back to very good again.

I've been riding the GN like this since the summer when I finally finished doing all this stuff and I'm happy to say it was mission accomplished. Thanks for all the little tips that got me thinking of which ways to go. I think the biggest difference, which is probably the solution for many others who also have brake problems is a real good bleed. I haven't been to the track since so I don't know how much boost they'll hold at the line, but I can hold ~7 psi in my driveway with street tires which is pretty decent in my book.

Hey Mike, glad you got them squared away. I'm almost finished my second LS1 brake installation, now on my dark red T. I did the fronts first, of course. Less of a job than the rear, and I was going to wait to do the rear but one of my rear wheel cylinders was leaking, so rather than fix it I opted to complete the installation by changing over the rears. By the way, since I went with the high performance pads on my GN, my brakes are nothing less than awesome, but I digress. I didn't want to spend $85 just for front pads this time around. As you know, the autozone pads wouldn't stop the damn car, so I thought, just for the hell of it, I'll buy the cheapest pads ADVANCE sells ($22) and give it a whirl. Surprisingly, they're not bad at all. No fade as with the $45 Autozone pads. Spiffy, huh?

 

[stickybones]

Hey Mike, glad you got them squared away. I'm almost finished my second LS1 brake installation, now on my dark red T. I did the fronts first, of course. Less of a job than the rear, and I was going to wait to do the rear but one of my rear wheel cylinders was leaking, so rather than fix it I opted to complete the installation by changing over the rears. By the way, since I went with the high performance pads on my GN, my brakes are nothing less than awesome, but I digress. I didn't want to spend $85 just for front pads this time around. As you know, the autozone pads wouldn't stop the damn car, so I thought, just for the hell of it, I'll buy the cheapest pads ADVANCE sells ($22) and give it a whirl. Surprisingly, they're not bad at all. No fade as with the $45 Autozone pads. Spiffy, huh?

You trying to be the LS1 brake conversion king?

I'm contemplating a rear disc conversion, but it won't be happening any time soon. My kids and their needs come first. Maybe someday, like in 2025, my boys will be cruising the streets in the GN.

Merry Christmas

 

[GN owner]

Sticky,

What did you bleed first? In other words what wheel (left or right front or left or front rear) did you start the bleeding process and what was the last one to be bled? I have a vacuum brake conversion also and like you the car does not stop like a normal GM vehicle from that era and I will probably be re-bleeding the brakes again after reading your post.

 

[stickybones]

1. Passenger rear
2. Driver rear
3. Passenger front
4. Driver front

Doing the vacuum technique, I did not pin the proportioning valve plunger.

Also, it's critical that the master cylinder gets bled properly on the bench before it gets installed. Slow and steady, over and over again until there are no bubbles.

Good luck.

 

[Red Regal T]

I have never pinned the proportioning valve plunger to bleed brakes. Yeah, MC properly bled is very important.

 

[RmvBfrFlght]

stickybones, good to hear that you have the brakes squared away. For some reason these cars need good brakes.

I also learned something. I've always thought that air in the system would only produce a soft pedal. Apparently not so. Thanks for the follow up.

RemoveBeforeFlight