GMT 400 Hydroboost swap

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Did you install that $100 Booster in an 89? I need a replacement for my 97 but dont want to waste money if it wont fit.
It's currently bolted to the firewall. The pushrod adapter, combination block, and AN adapters should be here later this week so I can finish it up.

FYI if anyone is looking at this booster - the two pressure lines are 18mm-1.5 & 16mm-1.5 O-ring and the return fitting is a 5/16-24 ORB to 3/8" barb. The center bore is 1.820" diameter, master cylinder mounting bolts are spaced just over 86mm around 3.392" at the centers, all the bolts are M10x1.5, and it's angled down 4.5 degrees in relation to the backing plate.
 
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whiteliard

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Rebuilt unit and new master cylinder, I have new hoses as well. Note to everyone, rebuilt units do not come with the push rod to reach the master cylinder. There are two different kits also and it all depend on the bore of the hydroboost unit.
Do you have the part numbers for the push rod kits? I have the rebuilt Cardone 52-7358 brake booster but I don't have the push rods and am having a hard time finding them?
 

whiteliard

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Question on best master cyclinder for the hydoboost for my truck. My 1994 K1500 has JB5 as stock but there are options for JB5 and JB7 master cylinders that will work with the hydro (hydro is 1998 JB7 to match the pedal). Is there any down side to using the JB7 master cyclinder in a stock brake configuration with the JB77 hydro for now? I am planning to straight axle the truck in a few months which will have the JB7 drums and a D60 with larger disc.

Any advice is appreciated.
 

L31MaxExpress

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Question on best master cyclinder for the hydoboost for my truck. My 1994 K1500 has JB5 as stock but there are options for JB5 and JB7 master cylinders that will work with the hydro (hydro is 1998 JB7 to match the pedal). Is there any down side to using the JB7 master cyclinder in a stock brake configuration with the JB77 hydro for now? I am planning to straight axle the truck in a few months which will have the JB7 drums and a D60 with larger disc.

Any advice is appreciated.
JB would be a vacuum boost system. JD is hydroboost. I went from a vacuum boost JB6 to a JD7 hydroboost and matching master. I then put the SRW aka Police Tahoe front calipers on. I know have the same booster and a DRW front caliper using a wider 01-02 3500 van rotor setup on my 97 Express.
 

HotWheelsBurban

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JB would be a vacuum boost system. JD is hydroboost. I went from a vacuum boost JB6 to a JD7 hydroboost and matching master. I then put the SRW aka Police Tahoe front calipers on. I know have the same booster and a DRW front caliper using a wider 01-02 3500 van rotor setup on my 97 Express.
I think some years GM used JB/JD interchangeably. My crew cab has the hydro boost system for power brakes, and the VIN report says JB8, not JD8. The Burb has JB6 brakes, with vacuum booster.
 

1998_K1500_Sub

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Question on best master cyclinder for the hydoboost for my truck. My 1994 K1500 has JB5 as stock but there are options for JB5 and JB7 master cylinders that will work with the hydro (hydro is 1998 JB7 to match the pedal). Is there any down side to using the JB7 master cyclinder in a stock brake configuration with the JB77 hydro for now? I am planning to straight axle the truck in a few months which will have the JB7 drums and a D60 with larger disc.

Any advice is appreciated.

The JB5/JB6 brakes used "low-drag" calipers and "quick take-up" MCs. The heavier-duty JB7/JB8 brakes did not use "low-drag" calipers and were not paired with "quick take-up" MCs.

Mixing parts can yield less than optimum results. See attached.

Is your head spinning yet? Just wait...

The calipers on your D60 will, I expect, NOT be the "low drag" type that requires a "quick take-up" MC, as I assume it will use different calipers entirely from what GM offered on the GMT400 JB5/JB6 brakes (please correct me if I'm mistaken... in fact, if you know what calipers you'll be using on it, do tell). Given my assumptions, you would want an MC from the JB7/JB8, or perhaps JD7/JD8 (see @HotWheelsBurban's post above), as appropriate for the hydroboost valve body.

AFAIK, the only difference in the HD and non-HD MC is that the HD MC has a slightly smaller bore (edit / correction: The HD MC seems to have a slightly LARGER bore, e.g., JB6 vacuum boost w/ 1.125" bore MC and the JB6 hydroboost w/ 1.25" bore MC) There may be other differences, e.g., the non-HD may or may not mate properly with the HB "booster" valve assembly b/c of dimensional differences. Somebody else (@Schurkey?) might comment.

Bear in mind, if your existing front calipers are "stock JB5", then they are the "low-drag" type which require a "quick take-up" MC... "require" is the operative word here. They'll still work with a non-quick-take-up MC, they just may not work as well (e.g., low-pedal). See attached.

Barring new information to the contrary, I would suggest you install the MC I suggested prior b/c you're planning to install the D60 "in a few months". In the meantime, if you note any braking anomalies (low pedal) with your new MC and "old" JB5 calipers, you can swap JB7/JD7 calipers (which are NOT low-drag and and will work properly with a non-quick-take-up MC) onto the truck in the meantime.
 

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  • Low drag calipers - Quick Take-up.pdf
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L31MaxExpress

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The JB5/JB6 brakes used "low-drag" calipers and "quick take-up" MCs. The heavier-duty JB7/JB8 brakes did not use "low-drag" calipers and were not paired with "quick take-up" MCs.

Mixing parts can yield less than optimum results. See attached.

Is your head spinning yet? Just wait...

The calipers on your D60 will, I expect, NOT be the "low drag" type that requires a "quick take-up" MC, as I assume it will use different calipers entirely from what GM offered on the GMT400 JB5/JB6 brakes (please correct me if I'm mistaken... in fact, if you know what calipers you'll be using on it, do tell). Given my assumptions, you would want an MC from the JB7/JB8, or perhaps JD7/JD8 (see @HotWheelsBurban's post above), as appropriate for the hydroboost valve body.

AFAIK, the only difference in the HD and non-HD MC is that the HD MC has a slightly smaller bore. There may be other differences, e.g., the non-HD may or may not mate properly with the HB "booster" valve assembly b/c of dimensional differences. Somebody else (@Schurkey?) might comment.

Bear in mind, if your existing front calipers are "stock JB5", then they are the "low-drag" type which require a "quick take-up" MC... "require" is the operative word here. They'll still work with a non-quick-take-up MC, they just may not work as well (e.g., low-pedal). See attached.

Barring new information to the contrary, I would suggest you install the MC I suggested prior b/c you're planning to install the D60 "in a few months". In the meantime, if you note any braking anomalies (low pedal) with your new MC and "old" JB5 calipers, you can swap JB7/JD7 calipers (which are NOT low-drag and and will work properly with a non-quick-take-up MC) onto the truck in the meantime.
My JB6 brakes did not have low drag calipers or a quick take up master on either my Van or Tahoe. I swapped both to SRW 1-ton hydroboost with matching master cylinders and 1-ton (JB7?) front calipers. The piston bores on both the master and calipers are larger on them.
 
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1998_K1500_Sub

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My JB6 brakes did not have low drag calipers or a quick take up master on either my Van or Tahoe.

How odd. My understanding is ALL 5/6 we’re of low-drag / QTU type. Evidently it's not the rule.

(edit) @Schurkey remarks here about low-drag calipers, from which I probably adopted my opinion:

https://www.gmt400.com/threads/mc-upgrade-question.55664/post-1204231

Quoting from that post:

"I'd expect low-drag calipers on any of the 6-lug trucks, unless they're ordered with a "heavy duty" or "trailer towing" brake package.

"For example, JN3--JN5--JB5 brakes standard on half-ton pickups, with the horrible leading/trailing shoe rear drums.
JB6 standard on half-ton Tahoes/Blazers/Suburbans which is the same as the JN5/JB5 up front, but with the good Duo-Servo rear brakes. (maybe this varies by year...I've heard of Tahoes having JB/JN 5 Leading-Trailing rear brakes.)
JB6 standard on 6-lug "light duty" 3/4 ton pickups.

"Far as I know, the low-drag calipers and the three-chamber master cylinders were NOT available on any 8-lug or 10-lug GMT400-series vehicles. Those trucks got JB/JD7, JD8 or JF9 brakes."
 
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HotWheelsBurban

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My JB6 brakes did not have low drag calipers or a quick take up master on either my Van or Tahoe. I swapped both to SRW 1-ton hydroboost with matching master cylinders and 1-ton (JB7?) front calipers. The piston bores on both the master and calipers are larger on them.
My 1 ton is JB 8 even though it's hydro boost, but the "8" may be because it's a crew cab.
 
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