Switching ABS to Conventional.

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gbabione

Registered User
I got everything installed and bled. It was a long hard fight getting booster in. I had to unplug sensors and move wire harnesses. Disconnect and move vacuum lines. I forgot about compressing rod. That probably would've helped. I dropped the steering column for easier access, but I still had to climb under the dash and use a wrench on one nut because a socket didn't fit. I installed self-bleeders in calipers. They don't work as well as I was led to believe. I was sucking air back in all four. I ended up doing it the old-fashioned way with someone pumping.
Now that they're bled, the pedal is soft until about halfway down. Then it takes everything I've got to push it the rest of the way down. That takes probably 10 seconds. What am I missing?
 
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35th

Registered User
I've herd because I'm looking into this for my SC that the rod between the booster and Mc is hard to get right and if the pedal is getting really stiff my thought would be not enough vacumm possibly or that your at the end of the boosters throw (from the rod not pushing Mc far enough) check that your getting adaquate vacumm then check to make sure the rod is long enough to push the Mc far enough if it's not then you may not have actually gotten all the air out so keep that in mind.
 
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MadMikeyL

SCCoA Member
FYI, I’ve done a few of these swaps, and on every one, the rod in the booster was too short to reach the master, and resulted in no resistance at the top of the pedal, and then started braking at the very bottom. Luckily the fix is very simple. Buy a cheap 7mm 1/4” drive shallow socket, slip it on the adjuster rod between the booster and the master, and put the master back on. The socket fits snugly on the adjuster rod, and lengthens it the exact right amount, and after a couple good stops, the socket winds up pressed on there and will never come off. And if you are worried about it holding up, I ran this exact setup with the lemons race car, actually figured it out at the track and did the 7mm socket originally as a temporary thing, but after the first race, I couldn’t get it off so just left it, and after 6 years of repeated hard braking from 140mph, the whole setup was no worse for wear.
 
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gbabione

Registered User
I bought a vacuum bleeder from Harbor Freight. It wasn't pulling any fluid. I tried pumping the brakes with that on. Put less fluid than I thought it should have into the cup. I removed speed bleeders thinking they might not work with vacuum pulling. I had fluid running out before I got old bleeders back in. I checked vacuum from hose. There's definitely nowhere near enough to pull fluid. I guess next is to check how much vacuum I have at power booster. How much do I need? If not enough, maybe I'll have to Tee right off of the intake plenum. Any ideas?
 
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gbabione

Registered User
I was getting 17" on my gauge and on a tester. I replaced the 5/16" tee with a 3/8". I checked on each piece as I put it back together. When I checked at the supply line between vacuum trees it jumped up to at least 25". There was no vacuum to inlet so that jump must've been from it being closed. Once the engine warmed up, it dropped to 16". Is that low for that supply line? It doesn't seem so because bypass valve is pulled completely open. Do I need to tee off right at the intake plenum?
 
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DOUG H

SCCoA Member
16 is too low if that's what you're looking for.

As I said before though, 18 is a general rule of thumb for any brake booster, any make/model. 16 may be enough
for your application? If you need to know where to get a stronger source, maybe see if you can get someone with
a 93-95 to post pic(s) of there set up
 
3

35th

Registered User
No not the pro. Valve see attached photo I circled the adapter
 

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talonhead

Registered User
As mentioned above, if your engine doesn’t build a lot of vac when idling, or when engine braking, you might need an electric vacuum pump to get the minimum vac.
When I rebuilt the brake system on my wife’s H2 after a braking failure (one cracked front line, both rear line were weeping bad). In case you are not familiar with GM truck/SUV ABS/Traction control systems—2 large lines from the MC to ABS unit then one line to each wheel.
New MC, 8 new SS lines pre-bent and 6 flex hoses and new pads. Bench bled the MC per instructions after I had the lines installed (unlike a bird, this stuff is installed BEFORE the body gets mated to the chassis!) I used a HF vacuum pump with a line with a needle valve to adjust the vacuum drag being pulled by the pump. Then attached this to a vacuum proof reservoir (allowing the fluid coming from system to collect without contaminating the pump). Getting the suction line to maintain a good seal is tough. QUESTION; is there a mechanical fitting (similar to a grease gun for zerk’s) that would work for bleeding? Anyways, I was able to suck fluid from the MC through the ABS/TC pump/control valve, fairly well. Aside from being able to cycle the pump, everything went well. Still had a soft pedal. Took it to the shop that did all my major servicing. He told me to hang out for a bit. He took it out to the lot and caused a couple of ABS events and brought it back. He said “the pump just needed cycled a few times, it’s all good”. No issues since.
Hoping I can get my ‘93 into the garage this summer to start the upgrades to support larger rotors, the BBF and T-56.
 
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