GM hydro boost brakes for newbies like me....

Renntag

Adventurer
Any idea how to look up which hydro unit a 98 2500 cummins dodge might have had?

I have sourced one for my 91 burb. This thread is very helpful. Thanks to all for sharing info.
 

Larry

Bigassgas Explorer
"The master cylinder I got had the holes for the lines swapped as compared to the old one. I asked him about this and he said it was normal to have to swap front/rear positions on the lines sometimes. The threads were correct, so no issues there."

So you are saying the front brake line attached to the new master cylinder where the rear brake line attached to the original master cylinder? If so, was this necessity based on the flare fitting size? Thanks.

His factory master (JB6 RPO code?) most likely had the large chamber (front brakes) towards the radiator and the small chamber (rear brakes) towards the windshield. The JB7-spec (1-ton SRW and heavy 3/4-ton) master he appears to be running now has the small chamber towards the radiator and the large one towards the windshield. Both have 1/2" primary ports (front brakes) and 9/16" secondaries (rear brakes), so just some bending the brake lines around some is needed to have them line up with the new ports position when you switch one for the other.

Thanks to everyone for the compliments!




The response from "underdrive" answers your question. The ports that the lines hook to are different threads, so they are not interchangeable. The front line must hook to the front, and the rear must hook to the rear. On the new cylinder these positions were reversed as compared to the old one, and required just a bit of bending to the lines to get them into the new positions. It was not a big deal, but I wanted to mention it so others would be aware if they were considering the swap.


Larry, the cam is stock right now. I put a goodwrench 350 in it, and when installing the distributor I didn't take the time to line it up in the normal orientation that is commonly seen. It runs good and I just wasn't bothered by it. My suburban has the 8.1. I like the power it produces but I don't think I will ever spend the money to upgrade to a big block in the pickup. I would like to get a bit more pulling power out of it with a cam swap or something, but it does a pretty good job as it is so upgrades are not on my short list at this time. Having the SM465 helps a lot with the pulling, so it helps to mitigate the power deficiency.

Oh yeah, I forgot about the brake lines at the master cylinder when moving to a 1 ton master cylinder. I had to flip them around on the K10 as well.

Yeah, a late model BBC swap isn’t cheap. I already have over $3000 in the 8.1L going into the Suburban plus I still have many more bits and pieces to collect and that doesn’t include the cost of the engine itself. In the end, they are still a worthwhile swap as there is only so much you can do to a carbureted small block if using them for hot weather, off camber/bouncy trails and high altitude. When the 8.1Ls are swapped into something else running custom tunes, exhaust and induction that actually breath they run entirely different than how a stock Suburban and my 2001 HD truck run. Night and day.…it is almost hard to believe it is the same engine.
 

Larry

Bigassgas Explorer
Any idea how to look up which hydro unit a 98 2500 cummins dodge might have had?

I have sourced one for my 91 burb. This thread is very helpful. Thanks to all for sharing info.

It will be the same Bosch hydroboost unit in these pictures other than it will have the period correct Dodge truck booster to firewall bracket and rods. The Bosch hydrobooster unit itself really hasn’t really changed at all in the past 30+ years. Some little things changed like thread connections but the unit internals and dimensions haven’t. If you want to swap one on to a 98 Dodge just find a truck of the same generation and grab everything.

Napa shows a hydrobooster for a 98 Dodge is a 527354 and lists for $498. One weird thing with older Dodges with Cummins was the fact many, if not most, still ran vacuum brakes operated by an engine mounted vacuum pump. This is a 1998 Dodge booster. Looks the same as every other Bosch booster used on GM and Ford as well outside of vehicle specific mounting bracket and push rods
NWM


NWM


NWM
 

Renntag

Adventurer
Thanks Larry.
I have a hydro unit from a 98 cummins dodge and would like to install it into my vac boosted 5.7 91 v2500 burb.
So it looks like I need to get a firewall bracket and pushrod for my square body.
 

Larry

Bigassgas Explorer
Thanks Larry.
I have a hydro unit from a 98 cummins dodge and would like to install it into my vac boosted 5.7 91 v2500 burb.
So it looks like I need to get a firewall bracket and pushrod for my square body.

You would probably be better off just doing some fabrication and creativity to use the Dodge fire wall bracket and push rod to brake pedal since you already have it. As I mentioned before, finding a loose square body GM truck booster to firewall bracket and push rod is practically impossible. To get the proper bracket and rods you would probably need to buy a complete used booster unit anyway. Again, the easiest swap for a direct clean bolt for bolt install is to pirate parts from the same exact vehicle otherwise fabrication is needed but a bird is hand is better than two birds in flight.
 

SlowJoe

New member
I forgot to include a photo of the bracket that came with my unit that I sent to Vanco to show the modification necessary to the holes. It would be easy to make one like this if someone needed one.


 

underdrive

jackwagon
The ports that the lines hook to are different threads, so they are not interchangeable. The front line must hook to the front, and the rear must hook to the rear. On the new cylinder these positions were reversed as compared to the old one, and required just a bit of bending to the lines to get them into the new positions. It was not a big deal, but I wanted to mention it so others would be aware if they were considering the swap.
I'll just put this here for general information - the mid-'80s 3/4-ton trucks with diesel engines had a 1-1/4" bore master cylinder that has the large chamber on the front and the small one on the rear, however the port thread sizes are switched around to 9/16" primaries (front) and 1/2" secondaries (rear). To make it worse, this being a factory hydroboost application such a master will bolt up to any GM hydroboost unit. Thus, if one is not careful, and simply rearrange their brake lines to match port thread sizes, they will end up with the large chamber and its respective piston feeding the rear brakes, and the small chamber and piston feeding the fronts. Not likely to be any fun whatsoever every time brake pedal is depressed.

It will be the same Bosch hydroboost unit in these pictures other than it will have the period correct Dodge truck booster to firewall bracket and rods. The Bosch hydrobooster unit itself really hasn’t really changed at all in the past 30+ years. Some little things changed like thread connections but the unit internals and dimensions haven’t.
I always wondered if that is indeed the case, why are there different listings for the hydroboost units between some 3/4-ton and 1-ton trucks of the same model year. And it's not a matter of different reserve accumulator pressures (IIRC it was 350 psi for the gold ones and 450 psi for the blue ones, not sure what the spring rate is for the silver ones) as they both have the same color accumulators, hydraulic line port threads are all the same as well, so I figured it must be something internal, but what?
 

toddz69

Explorer
I always wondered if that is indeed the case, why are there different listings for the hydroboost units between some 3/4-ton and 1-ton trucks of the same model year. And it's not a matter of different reserve accumulator pressures (IIRC it was 350 psi for the gold ones and 450 psi for the blue ones, not sure what the spring rate is for the silver ones) as they both have the same color accumulators, hydraulic line port threads are all the same as well, so I figured it must be something internal, but what?

There are also differences between power piston diameters internally between models.

Todd Z.
 

barefoot boy

Observer
And I am pretty sure some of the master cylinders have a step bore, with different primary and secondary piston diameters. Underdrive, your last post about being careful about just switching the brake lines is why I originally posted my question; I was pretty sure it was possible to end up with a wrong combination, but I figured someone would know for sure if I posted the question. Thanks everyone for the info.
 

Larry

Bigassgas Explorer
There are also differences between power piston diameters internally between models.

Todd Z.

I stand corrected. You’re correct, there are some internal power piston differences as it turns out. I was basing my info from a A1 Cardone sales presentation on booster rebuilding I got through our service parts group at work where they made the internals sound to be the same across the board for all units with the biggest difference in mounting brackets, rods and accumulator size. Learn something new every day! Now I wonder what difference the power pistons make and what vehicle GVWR, etc. drives different piston sizes. The more we learn about these the more we find out there is more to learn. I wonder how much attention to piston diameters paired to the right vehicle spec rebuilders really pay attention to...Hmmm
 

toddz69

Explorer
Now I wonder what difference the power pistons make and what vehicle GVWR, etc. drives different piston sizes. The more we learn about these the more we find out there is more to learn. I wonder how much attention to piston diameters paired to the right vehicle spec rebuilders really pay attention to...Hmmm

Somewhere in my hardcopy files (probably can be found somewhere online too), I have some listings that show the various piston diameters for different applications. Not surprisingly, the larger GVWR vehicles have larger pistons in them. I don't remember if the different applications have different casting numbers on them or not. I'd think maybe that might be one way to tell them apart. I have an acquaintance here in Phoenix that owns a huge recycling company that sells to all the rebuilders and it's really a spectacle to see all the different parts sorted and stacked ready for rebuilders. They have large cardboard bins about 8-10' in diameter and about 3-4' deep that are filled with unique part numbers and stored floor to ceiling in large warehouses. Big business!

Todd Z.
 

superbuickguy

Explorer
Subscribed. I want to put this in the Woofwagon.

it's really easy to do, CPP tends to have the best prices on them as well (conversion). If you know the vehicle you're getting parts from, then do get used stuff - but you can spend a lot of money buying used parts that don't work.
 

chilliwak

Expedition Leader
Thanks for all the input guys. This is really what I need to understand the system. A member here on the board is getting me hooked up with a pedal assembly and such so that I can do my swap this summer. He is also the guy that has helped Larry. Cool to have people that can help you out...:)
 

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