GMT 400 Hydroboost swap

[1998_K1500_Sub]

The piston bores on both the master and calipers are larger on them.

For the record there are three caliper bore sizes:

3”
3.15”
3.386”

This post and associated thread discuss GMT400 brakes in some detail.

Post in thread 'Upgrade Front Brake Calipers'
https://www.gmt400.com/threads/upgrade-front-brake-calipers.58795/post-1251999

 

[whiteliard]

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.

Thanks for the info. I had seen info on the quick take up and that was the reason for the question. Since the HB conversion has forced me to change the MC, I will use this one:

www.amazon.com/dp/B000C9HK16?psc=1&ref=ppx_yo2ov_dt_b_product_details#customerReviews

Is is supposed to be for a JB5 or JD5 set up per rock auto and will work with the hydroboost I installed and then if I need to change the MC with the straight axle conversion, I will cross that bridge then.

Thanks again for all the responses and hopefully I'll be able to help answer questions when I finish it all up.

 

[1998_K1500_Sub]

Since the HB conversion has forced me to change the MC,…

Remind me: What forced the change? The existing MC won’t mate with the HB valve body?

 

[whiteliard]

Remind me: What forced the change? The existing MC won’t mate with the HB valve body?

Yes, the OD of the MC flange will not fit into the hydroboost I used. I needed one to match the pedal I got from a 1998 truck since they are hard to come by in my area. I used this HB:

www.amazon.com/dp/B000C4946A?psc=1&ref=ppx_yo2ov_dt_b_product_details

 

[Supercharged111]

Yes, the OD of the MC flange will not fit into the hydroboost I used. I needed one to match the pedal I got from a 1998 truck since they are hard to come by in my area. I used this HB:

www.amazon.com/dp/B000C4946A?psc=1&ref=ppx_yo2ov_dt_b_product_details

Did you start with a GMT800 master?

 

[whiteliard]

Did you start with a GMT800 master?

No, it was a 400 MC from a 1998.

 

[97VortecChevy]

Just curious but why doesn't the vacuum booster pedal work ? I see there's about an 1" difference in the pins.. My truck is a 1997 so i got a reman hydroboost for a 1997 with a MC and everything lines up. the rod does have a slight angel going to the pin but still has a full range of motion with no binding. I planned on just pulling the pedal and redrilling it but it lined up pretty good so figure i'd ask

 

[kylenautique]

Just curious but why doesn't the vacuum booster pedal work ? I see there's about an 1" difference in the pins.. My truck is a 1997 so i got a reman hydroboost for a 1997 with a MC and everything lines up. the rod does have a slight angel going to the pin but still has a full range of motion with no binding. I planned on just pulling the pedal and redrilling it but it lined up pretty good so figure i'd ask

Hey, if you dig how the pedal feels, then leave it. It changes the throw of the pedal and how high it sticks up, so generally you swap out the pedal or modify your stock one. Make sure you install the 1 ton calipers in the front along with the matching 1 ton master cylinder. You will really dig your brakes!

 

[Supercharged111]

Just curious but why doesn't the vacuum booster pedal work ? I see there's about an 1" difference in the pins.. My truck is a 1997 so i got a reman hydroboost for a 1997 with a MC and everything lines up. the rod does have a slight angel going to the pin but still has a full range of motion with no binding. I planned on just pulling the pedal and redrilling it but it lined up pretty good so figure i'd ask

Have you driven it that way? I do know a guy who did a HB swap but kept the original pedal, he didn't report any issues.

 

[97VortecChevy]

Hey, if you dig how the pedal feels, then leave it. It changes the throw of the pedal and how high it sticks up, so generally you swap out the pedal or modify your stock one. Make sure you install the 1 ton calipers in the front along with the matching 1 ton master cylinder. You will really dig your brakes!

I do plan on a big brake upgrade just not right now -- is this something I would have to do now ?

Have you driven it that way? I do know a guy who did a HB swap but kept the original pedal, he didn't report any issues.

Not Yet, I'm in the middle of doing a LS swap so was just doing the brake swap while i was at it