LS1 MC needed for rear LS1 brake swap?
05-20-2014, 02:06 AM
#1
LS1 MC needed for rear LS1 brake swap? Posting this here since I got crickets in the brakes section.
I'm running OEM LS1 rotors/calipers with Hawk HPS pads on all 4 corners, LT1 MC and LT1 ABS block currently. The brakes have been bled thoroughly.
After searching I could not find the info I was looking for. I seem to remember someone mentioning that the LS1 brake MC is needed when swapping from LT1 to LS1 rear brakes, but I can't remember why. Possibly something to do with a different piston or valving design.
I'm running OEM LS1 rotors/calipers with Hawk HPS pads on all 4 corners, LT1 MC and LT1 ABS block currently. The brakes have been bled thoroughly.
After searching I could not find the info I was looking for. I seem to remember someone mentioning that the LS1 brake MC is needed when swapping from LT1 to LS1 rear brakes, but I can't remember why. Possibly something to do with a different piston or valving design.
05-20-2014, 12:21 PM
#2
I'm running LS1 rear brakes on my car with LT1 parts from lines forward... seems fine. I did read that the valving is different but I don't see the point in changing if my brakes feel fine (but then again I only have the rears b/c I needed them for my 9").
https://ls1tech.com/forums/14613573-post5.html
https://ls1tech.com/forums/14613573-post5.html
05-22-2014, 07:32 AM
#4
YES! The master cylinder needs to match the rear brakes.
The LT1 calipers with the integral parking brakes have a spring to pull back the pads. The master cylinder has a residual pressure valve just like drum brakes have.
The master cylinder needs to be swapped. The LS style reservoir bottle has the fluid level sensor hole, you can swap bottles.
One hard line from the master cylinder to the ABS valve block has a different thread and you'll need to make up the line with the matching fittings.
The LT1 calipers with the integral parking brakes have a spring to pull back the pads. The master cylinder has a residual pressure valve just like drum brakes have.
The master cylinder needs to be swapped. The LS style reservoir bottle has the fluid level sensor hole, you can swap bottles.
One hard line from the master cylinder to the ABS valve block has a different thread and you'll need to make up the line with the matching fittings.
05-23-2014, 09:28 AM
#5
Well, crap. My problem wouldn't be as bad as yours, but the rear brakes would end up dragging a bit because of the residual pressure then. However, there could be the issue also of the LS1 MC having a slightly larger bore for the rears, since the line is also bigger. I'm a stickler for doing things the right way (especially since it's as important as brakes), so I guess that's my new little project when I get home.
Unfortunately, in my exhaustive search I could not find an adapter fitting for the LT1 line to the LS1 MC, so looks like I get to make a new line. Yay.
For anyone that might run into this issue later, the LT1 brake MC fittings are M11x1.5, while the LS1 MC has one different. The front brakes line is still M11x1.5, but the line for the rears is M12x1. Thanks, GM.
I'll try to remember to update this with results when I finally get around to it. Thanks for the info Paul.
Unfortunately, in my exhaustive search I could not find an adapter fitting for the LT1 line to the LS1 MC, so looks like I get to make a new line. Yay.
For anyone that might run into this issue later, the LT1 brake MC fittings are M11x1.5, while the LS1 MC has one different. The front brakes line is still M11x1.5, but the line for the rears is M12x1. Thanks, GM.
I'll try to remember to update this with results when I finally get around to it. Thanks for the info Paul.
Trending Topics
05-25-2014, 06:06 AM
#9
Ok, so after even more research, I'm convinced that changing to an LS1 MC is not needed.
Paul, your description of how the LT1 rear disc caliper works is incorrect. The GM manual states "Parking brake application is completely independent of the hydraulic braking system."
If you read the description of the LT1 parking brake's function and examine the drawings carefully, you will see that there is a separate parking brake collar that is engaged, which compresses the pad. The actuation of this collar in no way interacts with the piston or hydraulic circuit, they are not disrupted in any way. There is no spring pressure to "overcome" by the hydraulics.
While you are correct that older cars with disc/drum setups need residual valves, I cannot find any info that this is true in newer cars with ABS. It seems that the ABS combo valve takes the place of any need for residual valves.
Also, I cannot find any indication in the blowout diagram or part listing of the brake MC for a residual valve. The GM manual does not list different part numbers for the master cylinder for drum or disc.
So now I'm curious, did you physically see a residual valve installed in the LT1 MC you installed?
Paul, your description of how the LT1 rear disc caliper works is incorrect. The GM manual states "Parking brake application is completely independent of the hydraulic braking system."
If you read the description of the LT1 parking brake's function and examine the drawings carefully, you will see that there is a separate parking brake collar that is engaged, which compresses the pad. The actuation of this collar in no way interacts with the piston or hydraulic circuit, they are not disrupted in any way. There is no spring pressure to "overcome" by the hydraulics.
While you are correct that older cars with disc/drum setups need residual valves, I cannot find any info that this is true in newer cars with ABS. It seems that the ABS combo valve takes the place of any need for residual valves.
Also, I cannot find any indication in the blowout diagram or part listing of the brake MC for a residual valve. The GM manual does not list different part numbers for the master cylinder for drum or disc.
So now I'm curious, did you physically see a residual valve installed in the LT1 MC you installed?
05-25-2014, 12:30 PM
#10
No I did not see the difference or dissect a master cylinder myself. I had been told and learned from other threads and/or websites that there's a difference. I had issues when I used the non-matching master cylinder and changing to the one that matches the rear brakes was the fix.
I'm not the only one that's done this.
I don't care what any diagrams might say, I had a problem that went away after the swap to the matching master cylinder.
I'm not the only one that's done this.
I don't care what any diagrams might say, I had a problem that went away after the swap to the matching master cylinder.
05-26-2014, 08:41 AM
#12
I currently don't have any issues, Catmaigne as well it seems, so I think I'll be saving myself the time and money of swapping.
05-26-2014, 09:38 AM
#14
Teching In
Join Date: Oct 2003
Posts: 32
Likes: 0
Received 0 Likes
on
0 Posts
No I did not see the difference or dissect a master cylinder myself. I had been told and learned from other threads and/or websites that there's a difference. I had issues when I used the non-matching master cylinder and changing to the one that matches the rear brakes was the fix.
I'm not the only one that's done this.
I don't care what any diagrams might say, I had a problem that went away after the swap to the matching master cylinder.
I'm not the only one that's done this.
I don't care what any diagrams might say, I had a problem that went away after the swap to the matching master cylinder.
I have done a number of swaps from LT1 to LS1 brakes and never had an issue.
05-26-2014, 10:01 AM
#15
The problem I had using the LS1 master cylinder with the LT1 rear brakes was the brake pedal would first drop without any resistance almost an inch before it "caught" and braking could occur. The system was bled properly several times to make sure there was no air in the lines.
This dropping of the pedal was because the rear pads were being pulled back from the rotor. The first movement of the brake pedal was because the rear pads had to first get back to the rotors. My research resulted in discovering there was something with the parking brake parts in the caliper that was causing this. I was told (it's been a long time so I don't remember by who) that swapping to the LT1 master cylinder would fix the problem.
The explanation I was given at the time was that the LT1 rear calipers needed retained pressure. I didn't ask for or need further explanation, drawings or textbook diagrams because it seemed plausible and made sense. It seemed to be a valid explanation and I didn't demand written proof.
Following this advise and swapping to the LT1 master cylinder completely cured the problem. This led me to accept that the explanation about LT1 rear calipers needing retained pressure was accurate.
The entire process from discovering the problem to research then doing the master cylinder swap work was over about two weeks. This was not a spur of the moment, knee-jerk or "let's try this and see what happens" modification.
Although it can't be found in a system description guide or GM publication, my research into the issue, explanations offered to me and the fact that following the advise to swap the master cylinder fixed the problem makes this what I consider an actual needed modification when swapping brakes, based what I went through, not on hearsay.
This dropping of the pedal was because the rear pads were being pulled back from the rotor. The first movement of the brake pedal was because the rear pads had to first get back to the rotors. My research resulted in discovering there was something with the parking brake parts in the caliper that was causing this. I was told (it's been a long time so I don't remember by who) that swapping to the LT1 master cylinder would fix the problem.
The explanation I was given at the time was that the LT1 rear calipers needed retained pressure. I didn't ask for or need further explanation, drawings or textbook diagrams because it seemed plausible and made sense. It seemed to be a valid explanation and I didn't demand written proof.
Following this advise and swapping to the LT1 master cylinder completely cured the problem. This led me to accept that the explanation about LT1 rear calipers needing retained pressure was accurate.
The entire process from discovering the problem to research then doing the master cylinder swap work was over about two weeks. This was not a spur of the moment, knee-jerk or "let's try this and see what happens" modification.
Although it can't be found in a system description guide or GM publication, my research into the issue, explanations offered to me and the fact that following the advise to swap the master cylinder fixed the problem makes this what I consider an actual needed modification when swapping brakes, based what I went through, not on hearsay.
Last edited by Paul Bell; 05-26-2014 at 10:16 AM.
05-26-2014, 03:44 PM
#16
While I'm glad that swapping the master cylinder on yours fixed the issue, there is still no evidence that such a residual valve exists. While it may in fact exist, the way you describe the operation and design of the LT1 rear brake caliper is flat out wrong. I find it amusing you so easily toss out GM's explanation because of your presupposition.
Your explanation for a need to change the MC is plausible, except that it rests on LT1 calipers actually needing a residual valve. Unlike drums, LT1 calipers do not use a spring to retract the pad. There are 3 springs on the LT1 caliper. One of them is external, and is the large outer return spring for the cable and actuator lever. The other two are internal, and attach to the parking brake actuator collar boot retainer. These return the parking brake collar to its rest position. However, this does not disrupt the piston, because the piston, actuating collar, and clamp rod are not directly attached.
I believe I have a spare LT1 MC at home, and maybe out of further curiosity I'll pull it apart. But without hard evidence of the existence of a residual valve, I still believe the LT1 MC is fine with rear LS1 brakes.
Since your experience on the subject is having a problem running an LS1 MC with LT1 brakes, and with the evidence I've put forward, I don't think it would be fair for you to continue to recommend swapping to an LS1 MC for those of us LT1 guys that have swapped rear brakes. Especially since more than myself have come forth saying we experience no real issues with this setup.
However, since you did have success swapping to an earlier MC and you say others have as well, and I have no experience with that, I can't fairly tell you you're wrong in that regard.
Your explanation for a need to change the MC is plausible, except that it rests on LT1 calipers actually needing a residual valve. Unlike drums, LT1 calipers do not use a spring to retract the pad. There are 3 springs on the LT1 caliper. One of them is external, and is the large outer return spring for the cable and actuator lever. The other two are internal, and attach to the parking brake actuator collar boot retainer. These return the parking brake collar to its rest position. However, this does not disrupt the piston, because the piston, actuating collar, and clamp rod are not directly attached.
I believe I have a spare LT1 MC at home, and maybe out of further curiosity I'll pull it apart. But without hard evidence of the existence of a residual valve, I still believe the LT1 MC is fine with rear LS1 brakes.
Since your experience on the subject is having a problem running an LS1 MC with LT1 brakes, and with the evidence I've put forward, I don't think it would be fair for you to continue to recommend swapping to an LS1 MC for those of us LT1 guys that have swapped rear brakes. Especially since more than myself have come forth saying we experience no real issues with this setup.
However, since you did have success swapping to an earlier MC and you say others have as well, and I have no experience with that, I can't fairly tell you you're wrong in that regard.
05-26-2014, 04:52 PM
#17
We didn't dismiss GM's explanation-we couldn't find one.
What was advised seemed to work and that's what I went with.
Over time, there's been a few who've contacted me with the same problem and swapping the master cylinder to match the rear brakes always seemed to be the fix.
It appears that some cars with mismatched calipers & master cylinders work just fine and some cars don't. I was one of the lucky ones with a car that didn't work right and I needed this swap.
If you have calipers with the wrong master cylinder and you have no problems, great!
What was advised seemed to work and that's what I went with.
Over time, there's been a few who've contacted me with the same problem and swapping the master cylinder to match the rear brakes always seemed to be the fix.
It appears that some cars with mismatched calipers & master cylinders work just fine and some cars don't. I was one of the lucky ones with a car that didn't work right and I needed this swap.
If you have calipers with the wrong master cylinder and you have no problems, great!
05-27-2014, 12:32 PM
#19
Are those just guys with LT1 brakes and LS1 MC's, or both sides? I just find it odd, although entirely possible, that GM left info out of the service manual. I guess as long as the brakes work the way they should, it doesn't matter which MC you end up with.
05-27-2014, 01:39 PM
#20
As paul has already said, the LS and the LT master cylinders are different.
The front circuits are exactly the same but the rear circuits are different as seen in this pic
LS on top
LT on bottom
When I changed to the LS MC, my brakes simply worked better and the pedal was a bit firmer. Clearly the GM engineers had a reason to redesign the MC for the LS cars.
The front circuits are exactly the same but the rear circuits are different as seen in this pic
LS on top
LT on bottom
When I changed to the LS MC, my brakes simply worked better and the pedal was a bit firmer. Clearly the GM engineers had a reason to redesign the MC for the LS cars.
Last edited by wrd1972; 05-27-2014 at 01:45 PM.