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LTX and LSXPutting LT1s, LS1s, and their variants into Third Gens is becoming more popular. This board is for those who are doing and have done the swaps so they can discuss all of their technical aspects including repairs, swap info, and performance upgrades.
While you may have already found a solution to your braking issue (and I'm in the same boat as you yet haven't addressed it) somewhere buried in my files are the bore diameters of several 3rd/4th gen master cylinders as well as piston area(s) of several of the popular 3rd gen brake upgrades.
Of course its entirely likely that you have that info as well however if you don't, I should be able to dig it up.
I guess I will share what I did with my stock V6 tachometer as well. This might seem overkill to most people but it is cool. Basically, I have the most accurate stock tachometer in the world.
Unlike Camaro gauges, the Firebird gauges look cool and are worth keeping. Especially the V6 tach because it has a 6K redline and sweeps up to 8K rpm. I just happen to have a friend with a waveform generator. Everybody has one of those, you know. Anyway, he reverse engineered how the tach works and found that there are two resistors in the back of the tach that effects calibration. He used the waveform generator to simulate a V8 engine signal and played with resistors until the tach worked the way we want. When the tach was stock it worked okay, but it wasn't very accurate. Now the tach is darn accurate from 500 - 8000 rpm.
So I guess what this boils down to is the way I fixed my tach is I handed it to somebody smarter than me.
Do you know what you changed to make the v6 tach work with v8? I bought a busted up cluster off ebay and it has a v6 tach i'd love to use in my car. (also other gauges i'm about to go crazy scientist on.)
The erod kit puts out Tachometer Signal (WHITE) - This is a 2 pulse/rev output (see features above).
My tachometer worked on the bench but doesn't operate in the car. I haven't spent hardly any time yet trying to figure it out.
Your GM engine PCM might be able to send a V6 signal. If so then there are no mods needed to your tach and you only need something like HP Tuner to access the feature.
I know it is basic but are you sure you have all the air out of your brake system? I only ask because I did the same thing when I put my engine in (4th gen master). Bled them all the way around twice and when I went to start it up brake pedal went to the floor. Bled them again and decent pedal feel but still not as hard as it should be. I assume there is still a little air in there and will just have to keep bleeding them until it works its way out. But at the same time with a bigger cam I know I've lost some vacuum pressure. I'm running the 4th gen master with the 1LE prop.
Maybe the fourth gen master is as hard to bleed as the LT1 coolant system
I bought one of these and have never gone back to bleeding brakes any other way.
This looks pretty legit.
Originally Posted by mw66nova
i gravity bleed. i almost never have to do more than a couple of pumps.
How long do you leave it cracked on the right rear when the system is totally empty? I know it is overkill but I might cycle through another round of fluid just to make sure all the air is all out. Don't want to keep chasing dumb stuff like this.
I had bought one of these dealies, worked good on the clutch res, but doesn't seem like it is holding vac enough to pull the brake fluid.
Last edited by grngryoutmyway; 06-10-2016 at 07:39 AM.
I had tried every method conceivable to bleed brakes. Even went so far as to modify a master cylinder cap to accept an air fitting (as it's done on the assembly line). That didn't work too well. But the pneumatic bleeder...hook it up, go inside the house for a beer, come back, top up the reservoir, soon you've managed to not only bleed the brakes but also flushed the entire system of old fluid.
(Warning: Harbour Freight products may not work as intended).
This time I went all out and did everything I could the best I could -- removed the master cylinder and bench bled it, installed a new proportioning valve, bled the heck out of the lines. Hardly feels any different and still can't lock up the rear brakes. I guess I will have to measure rear line pressure if I want to investigate further.
Had a short moment of glory tonight with AC filled and working..... then there was oil all over the floor. The compressor oil was leaking out the middle of the case of my used AC compressor. I am so through buying other people's used junk! I will repeat once again in the near future with a new compressor.
The bad thing is the car now has other problems. I accidentally left the IAT unplugged when filling the freon. Didn't realize it for a while and then the car started running badly. It backfired through the intake manifold and stopped running and was flooded out horribly. Found the IAT connector undone and had to clear the flood by disconnecting fuel injectors and spraying starting fluid in the throttle body. Car would start but die again shortly after and had to keep repeating the flood clearing with starting fluid. I figured the tune had learned bad habits so I reloaded the original tune and car seemed to run okay. I went for a drive just to really clear things out and the car died again couple miles from home.... and wouldn't restart. Loaded the old tune again and baaaaaarely got the car running and revved the snot out of the car all the way home. Something isn't right now.
The tune may have learned something different, but until you apply it to the other tables it shouldn't go into effect.
Can you load the last tune from the shop where it was running it's best?
Are there any error codes?
Yes, that's what I did was load the old tune to get the car running again. Learn tables are always in effect, doesn't matter whether or not you transfer to base. Learn tables are just an extension of the base fuel tables where the (total fuel) = (base) + (learn).
I am going to venture out and try a little idle tuning for myself. Can't keep paying pro's hundreds of dollars at a shot for little improvement here and a little there. Reading some helpful material right now and will see if I can put it in effect to improve things.
Ya, I should take some pictures. I don't have any for myself yet other than this one I took in the driveway a couple weeks ago. I don't think anybody has actually seen the car yet!
Yes, that's what I did was load the old tune to get the car running again. Learn tables are always in effect, doesn't matter whether or not you transfer to base. Learn tables are just an extension of the base fuel tables where the (total fuel) = (base) + (learn).
I am going to venture out and try a little idle tuning for myself. Can't keep paying pro's hundreds of dollars at a shot for little improvement here and a little there. Reading some helpful material right now and will see if I can put it in effect to improve things.
Yea, the learn tables are always compensating if you have them enabled, which I assume you do. But until you hit the "transfer to base fuel" button they won't perminently change the base fuel map.
PM me your e-mail address I have a couple pdfs I've saved that might help.
Is that the torque arm mount hanging down?
At about the middle of the door?
Excellent ride hide height too! Were the GC springs fairly easy to adjust?
Yes, that is the torque arm. The ground clearance sucks didely ucks. I'd like to ride lower but do not dare. Edit: The lack of ground clearance was too hard to live with that I ended up removing the torque arm and having a custom torque arm fabricated for me, Post #789, https://www.thirdgen.org/forums/ltx-...ml#post6149848
Springs are easy to adjust when new at least. The adjusting rod has Acme thread so you have to unweight the suspension to turn it. I used a 1/2" ratchet driver on the front without too much effort. The back comes with a spanner to turn the collar, but the springs are so short that I could do it by hand because there is no load on the springs when axle is at full droop.
Originally Posted by mw66nova
looks like some adjustable lca's are in order to recenter that rear wheel in the wheel well, unless it's an optical illusion?
Just a visual trick on your eyes. Tires are centered with adjustable control arms.
Got brave enough to try a little tuning myself and got the car idling better. Basically got rid of the surging. That built my confidence a bit to keep tweaking things on my own.
I think AC is going to be a challenge and I may have to add a wire to enable AC idle kick. That is actually a lot of harness work as things sit right now. I'd rather spend some time on idle quality to see if I can keep things alive with AC compressor turning on.
And a short walk around the car. Nothing real fancy here, just a clean, stock body Firebird with a 22 year old paint job. I think she still holds her own in a crowd.
looks like some adjustable lca's are in order to recenter that rear wheel in the wheel well, unless it's an optical illusion?
Thanks, now it keeps bugging me. I looked at it again and it is both centered and set back depending on reference point. The overall appearance to the eye is set back. I'm just going to leave it for now.
No, I haven't done anything with the brakes since we last spoke. Next step is to remove the rear calipers and make sure that everything functions properly and slides easily. Anything after that probably means spending money.
I have a growing list of things to do. I'm not inclined to do much of anything this summer that takes the car down so it will probably be done over winter.
* brake pedal feel and front/rear balance
* fabricate a strut tower brace
* redo torque arm mount -- increase ground clearance and lower car
* custom camshaft & upgrade rocker arms
* fix tachometer (all new gauges ?)
* wiring for AC idle kick, if not already done
* engine oil cooler? depends what oil looks like at end of summer
No, I haven't done anything with the brakes since we last spoke. Next step is to remove the rear calipers and make sure that everything functions properly and slides easily. Anything after that probably means spending money.
Pretty much the same boat I'm in although I have LS1 fronts, PBR rears, original 86 IROC MC and prop valve, (disc/disc).
My guess (a semi-educated one) is that it's a mismatch between the MC, prop valve and the calipers used. At some point (probably next winter as well) I'll work my way through those charts I mentioned earlier and figure out what's going on. When (if) I do, I'll post my results. I think there are more than a couple of members here that have similar issues.
Rowdy is good, that's what makes a normal drive fun. I just hope it makes power this time. I know that I'm putting a lot of hope in just a cam swap, but I suspect my current cam is so wrong that the engine is going to be a whole new beast. If not, then I'll just have fun with it anyway because it's not like it is a turd.
No, I haven't done anything with the brakes since we last spoke.
I got my brakes working. Low pedal is gone. Tons of effort to get to the point where I found an air pocket trapped in the upper part of the rear brake system that would not purge. I released it by cracking open the nuts at the master cylinder (with the lid off the master cylinder). I guess you could call it a gravity bleed of the upper system.
It was a simple thing with a simple solution, but let me tell you it was anything but simple to find that problem. I am going to spare you all the details but I had literally checked all the hardware in the system, even down to the pushrod in the booster. For example, I now have a $70 tool just for measuring rod clearance to the master cylinder.
I didn't know anything about brakes when this began so I had to do a lot of learning to understand how things work and how to troubleshoot. I'm just going to post some of the more useful info I found in case it helps somebody else.
One of the things I had to sort out was this whole 3rd gen versus 4th gen master cylinder thing. Which is better? As far as I can tell the answer is, "depends". The 3rd gen master has a quick take-up feature. The 4th gen does not. What is this quick take-up thing, you ask? Well, I wondered too and this is what I learned....
Normal disc brakes produce a little drag on the rotors when the brakes are retracted. In other words, there is zero clearance between the pad and rotor. Back in the 1970's GM decided it would be a good idea to pull the pads away from the rotor for less drag and better fuel economy. They did this by changing the design of the piston seal. The only thing that pulls the piston back is the rebound of the piston seal. GM designed a new seal with more rebound so that the piston was pulled further back, and they called this new invention a "low drag brake". Problem is a little movement of the pad is a big movement of the brake pedal. They needed a way to restore a normal pedal feel by pushing a lot of fluid into the brakes very quickly when somebody first touches the brakes -- Enter the quick take-up master cylinder. The video I linked below explains how that works.
The outcome is if you have low drag brakes, then you must have a quick take-up master cylinder or else you will end up with a low pedal. As far as I can tell, GM stopped using low drag brakes some time in the 1990's. All the brake upgrades we use (LS1, C5, C6, etc...) are normal brakes and do not require a quick take-up master cylinder.
So the next question is, do modern brakes need a modern master cylinder? I'm no expert, but as far as I can tell the answer is no. You can use a quick take-up master on normal brakes with no abnormal effects. In fact, I believe it will feel pretty much the same as a 4th gen master. The 4th gen master is a 25.4 mm straight bore. The 3rd gen master is listed as a step bore with 24 / 31.75 mm, or 25.4 / 36 mm depending on the year. That 3x.xx number isn't the bore size of the high pressure bores that do the braking, it is the bore size of the quick take-up cavity. That means 3rd gen and 4th gen have the pretty much the same bore size and same feel when braking. The exception is early and mid-year 3rd gen masters that are for drum brakes only, those masters don't push enough fluid to operate rear disc brakes.
It is worthy to point out that the 4th gen design is more simple and inherently more reliable. There are a lot of things that can go wrong with that 3rd gen quick take-up valving. The other thing about a quick take-up master is it is a bit more tricky to bleed brakes. You should not pump the brakes and you need to wait about 15 seconds between pedal strokes or you can aerate the fluid in the master cylinder. You don't need to worry about this with the LS1 master cylinder.
If you know for certain that something I said is wrong then go ahead and correct me. But honestly, if you're not 100% certain then don't clutter this thread with different info because that kind of thing is exactly why it was so damn hard for me to figure this out in the first place.
Now that the brakes are working well, I am still not happy with how the car stops. I have the prop valve cranked all the way to max pressure and it feels like the front brakes are still over powered. Maybe I don't have enough line pressure in the back, but my gut feel is this is a case of too much front bias.
I can run a simple experiment by swapping front and rear wheels. Putting the drag radials on the front should reveal if the rear brakes are worth anything. If so, then I'll order up some grippier brake pads for the back and see how much that helps. It may be that eventually I just need more traction on the front tires.
No, I'm not locking up the front a lot because I have control of my foot. But yes, when the front locks up it doesn't feel like the back is participating enough. I have 255 Nitto NT05 tires in the front and 275 NT05R drag radials in the back. Major difference in traction.
My rear brakes are 40 mm piston and I notice everything from 4th gen Camaro to C6 Corvette uses 45 mm piston. I don't think I have a bad setup per se, but I think it will take more effort to get it right.
You may or may not find this interesting however I think it has quite a bit to do with how the LS1/PBR brake combo behaves when driven by the 3rd gen master.
The chart attached shows that the stock 3rd gen caliper piston has an area of 4.43 sq./in. (or 4.91 depending on the stated piston diameter). The LS1 has 2 pistons with a combined area of 4.81 sq./in.
The stock Delco Moraine rear caliper piston is 2.8 vs 1.94 for the PBR. The LS1 and C5 Vette has a 2.46 sq./in. piston.
Given that the bias has shifted greatly in favour of the front (when compared to stock) and being driven by the same (stock) piston in the master cylinder, doesn't it stand to reason the fronts will be very active compared to the rear?
The force exerted by the piston area of the MC is going to be multiplied by the piston area of the caliper. Bigger pistons equal greater clamping force. If you reduce the size of the piston, as is the case when going from stock rears to the PBRs, the resulting force will be less in comparison.
From this, wouldn't it make sense that a different MC is needed? One which restores the bias that came from the factory.
I find the column on the far right the most telling. If I'm reading it correctly, it calls for 27% more pedal effort for the same decel rate when comparing the stock Delco calipers to the PBRs.
On a similar note, you had discussed the need to increase the rear brake bias and possibly through the use of a different brake pad. I have a link to what I had thought would provide a performance pad for the rear PBR calipers but unfortunately, the pads in question are only available for the stock 3rd gen calipers. Here's the link regardless. You may find something of interest there. For what it's worth the pads I'm referring to are the Stillen Metal Matrix.
You made mistakes with your numbers but I understand what you're trying to say.
No, changing master cylinder won't change the pressure ratio front to rear, but it can change the pedal feel. A master with a larger bore size can move more fluid for the same stroke of the pedal but it develops less line pressure from the same force of your foot. This will make the pedal feel hard, with short stroke, and you'll have to push really hard to make the brakes work. A master with a smaller bore moves less fluid for the same stroke but develops greater line pressure. This will make the pedal feel soft with a long stroke. Experts are going to recommend 1" bore for the stuff we're talking about. If you went crazy with 6 piston race calipers then you'd probably have to step up to a larger bore master cylinder to move enough fluid to operate the brakes.
I suppose you could tweak the front and rear braking independently by using custom dual master cylinders from Wilwood. But almost none of use are willing to do that.
Not sure where the mistake comes into play here.
The point I'm trying to illustrate is that for a given size piston in the MC, you will realise greater clamping pressure at the rotor if the caliper piston in that rotor is larger than the next one. (I believe that's part of Pascal's Law of fluid dynamics). Comparing the stock 3rd gen caliper's larger piston to the smaller PBR's piston shows the difference in area and the resulting decrease in clamping force. That's also illustrated by the chart which indicates 27% greater effort to get the same deceleration rate.
That's all I'm trying to say here. This possibly explains why I have poor rear brakes. There's also probably not enough bias adjustment available in the prop valve to compensate for the smaller PBR piston.
Isn't that why racing calipers have a greater number of pistons? To increase the effective area applied to the rotor (via the pad). The MC bore size don't change all that much when you compare it to the vastly increased caliper piston area(s). But a little would go a long way when compensating for the mods in question.
Now if I have it all wrong, I'll excuse myself and not muddy the situation any further but I think that's the gist of it.
You're only looking at how a different master cylinder bore effects the rear brakes. Changing the master cylinder effects both front and rear brakes at the same time. Net change of nothing, other than how the pedal feels.
Sorry, Skinny, I misread your post. Agreed, a different piston diameter in the caliper will change the clamping force on the rotor.
You mentioned to me that your rear brakes literally do not grab when you put the car on jack stands. That is not because your brakes are too small, that is a failure to get pressure to the rear. My personal opinion is that you either have air in the system (I swore I didn't either and you know how that ended) or your prop safety valve is thrown.
Regarding that spreadsheet, I found the physical data very useful (made my own spreadsheet from it) but I don't come up with the same results as whoever made that spreadsheet. My worksheet is based on equations from the white papers at the Stop Tech website and I have more confidence in my own work. I would be careful believing too much of what you see in the "Results" columns.
I'm with you on all points.
What I was really trying to illustrate was why my (our) braking systems have become more forward biased. Smaller rear calipers and somewhat larger front calipers will do that given the same MC and prop valve.
Like you, one day I'll get to the bottom of this.
My plan, also like you, is to go for the LS MC. (I like the looks if nothing else). I have the 1LE prop valve that I should install too. I'll address the bleeding issue as well.
None of this means much though as long as my engine is in pieces.
06-09-2016, 07:57 AM
Anyway, he reverse engineered how the tach works and found that there are two resistors in the back of the tach that effects calibration. He used the waveform generator to simulate a V8 engine signal and played with resistors until the tach worked the way we want. When the tach was stock it worked okay, but it wasn't very accurate. Now the tach is darn accurate from 500 - 8000 rpm. 
I will repeat once again in the near future with a new compressor.
But yes, when the front locks up it doesn't feel like the back is participating enough. I have 255 Nitto NT05 tires in the front and 275 NT05R drag radials in the back. Major difference in traction.
