GMT 400 Hydroboost swap

[Mildphil]

Does anyone know about swapping from the OBS hydroboost to the NBS hydroboost? I have a k2500 with the factory hydroboost but would like the better pedal feel of the newer unit.

 

[GordonCustoms]

I believe that the outer diameter of the nbs master cylinder is to big to fit into the obs hydro-boost, you may need a nbs hydro unit and swap out the mounting plate to bolt up to the obs firewall. Or that could be my case cause I'm using a nbs master cylinder for a 3500hd and the 1500s ones might fit fine.

 

[Mildphil]

I believe that the outer diameter of the nbs master cylinder is to big to fit into the obs hydro-boost, you may need a nbs hydro unit and swap out the mounting plate to bolt up to the obs firewall. Or that could be my case cause I'm using a nbs master cylinder for a 3500hd and the 1500s ones might fit fine.

Yes the piston is a different size, but I was planning on swapping the entire unit anyway since my hydroboost unit is leaking drops of power steering fluid inside the truck by the pedal rod. Speaking of, is the OBS hydroboost rod the same length as the NBS rod? I know that the obs vacuum to nbs hydroboost guys need to modify the rod to reach the pedal.

 

[GordonCustoms]

Yes the piston is a different size, but I was planning on swapping the entire unit anyway since my hydroboost unit is leaking drops of power steering fluid inside the truck by the pedal rod. Speaking of, is the OBS hydroboost rod the same length as the NBS rod? I know that the obs vacuum to nbs hydroboost guys need to modify the rod to reach the pedal.

Now that you mentioned it I believe there is something different about the rod and its crimped on so its not easily swapped, I just took them both apart and swapped the whole rod assembly(power piston). Its been so long so I'm forgetting alot of the details.

 

[Mildphil]

Now that you mentioned it I believe there is something different about the rod and its crimped on so its not easily swapped, I just took them both apart and swapped the whole rod assembly(power piston). Its been so long so I'm forgetting alot of the details.

So instead of modifying the rod, you swapped in the assembly where the rod is housed? interesting, i'll have to see how that works whenever I go to the junk yard. What MC did you use? I have read that the rear disc/drum trucks have different masters? Or is there just an additional valve on the master?

 

[GordonCustoms]

So instead of modifying the rod, you swapped in the assembly where the rod is housed? interesting, i'll have to see how that works whenever I go to the junk yard. What MC did you use? I have read that the rear disc/drum trucks have different masters? Or is there just an additional valve on the master?

I don't know if the master cylinders are different for disc and drum. I'm using a master cylinder with the biggest cylinder size that I could find I believe it was out of a 2006 3500hd, I swapped in a 02 9.5 14 bolt for disc brakes and used a adjustable proportioning valve.

 

[Mildphil]

I don't know if the master cylinders are different for disc and drum. I'm using a master cylinder with the biggest cylinder size that I could find I believe it was out of a 2006 3500hd, I swapped in a 02 9.5 14 bolt for disc brakes and used a adjustable proportioning valve.

How's that working out for you? As my truck sits right now with the factory HB, if one hits the pedal with some authority, that thing will plant you against the windshield. Only issue I have is the play in the pedal before it actually gets firm.

 

[GordonCustoms]

How's that working out for you? As my truck sits right now with the factory HB, if one hits the pedal with some authority, that thing will plant you against the windshield. Only issue I have is the play in the pedal before it actually gets firm.

It works pretty good, I believe the biggest thing to fix the soft/spongy pedal problem is the nbs master cylinder cause so many people just do that swap onto the obs vacuum boosters with great results, hell there are some disc conversion kits that come with a nbs master cylinder and the kit calls it a "firm feel master cylinder"

 

[Mildphil]

It works pretty good, I believe the biggest thing to fix the soft/spongy pedal problem is the nbs master cylinder cause so many people just do that swap onto the obs vacuum boosters with great results, hell there are some disc conversion kits that come with a nbs master cylinder and the kit calls it a "firm feel master cylinder"

I'd be fine doing a NBS master and just replacing the hydroboost when it finally goes. Only issue I'm seeing is people saying that the NBS master won't work with the OBS HB (hydroboost). Although I do know that the OBS master will work just fine on a NBS HB. I've also noticed that the acdelco reman gmt400 HB units are actually just gmt800 units with the obs backing plate, pretty interesting.

 

[GordonCustoms]

I'd be fine doing a NBS master and just replacing the hydroboost when it finally goes. Only issue I'm seeing is people saying that the NBS master won't work with the OBS HB (hydroboost). Although I do know that the OBS master will work just fine on a NBS HB. I've also noticed that the acdelco reman gmt400 HB units are actually just gmt800 units with the obs backing plate, pretty interesting.

Well I just picked up a k2500 with hydroboost and I have a nbs master cylinder for it, I'll see if it will bolt up with no issues. Might have to wait till weekend before I can get to it and let you know through. I know the bolt holes line up I think its just the part that fits into the HB is bigger on the nbs MC so thats where the problem is. Unless the HB on my 2000 K2500 is different or was replaced before I got it.