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1990 K5 Duramax Blazer (BroDozer)

LB7 Duramax and Allison 1000 5 speed in a 1990 Chevy K5 Blazer
Overview Gallery Discussion
Truckman4life said:
Sucks about the parts issues. Part of it I feel is that people just don't give a crap to help each other out and actually do a good job with parts and such. They just take the easy way and if it's wrong no skin off their back.
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I couldn't agree more. I often have no issue paying more for a part from a company i know stands behind there product and customer, but it just seems harder to find these days. I mean i know it is probably hard dealing with shit customers from a business stand point but part of it is working to find a resolution. I am so grateful for the vendors we have and support on this site. I have yet to have any issues with them and always seem to get great customer service.
 
So i knew i was going to need to convert to hydro boost. This would require the replacement of the brake pedal, which i will address later, and the replacement of the vacuum booster. I decided to use and rebuild the hydro boost unit that came off the parts truck (2004 duramax). I'm pretty sure they are the same as the ones that are on most Chevy's other than the accumulator maybe. This would require a new firewall mounting plate and input rod, both of which i was able to source from my friend whom we found the K20 parts truck for.

I then learned it requires a special socket to remove the mounting plate and the original tool cost $80-$100. After a little digging i was able to locate a company making their own socket. Linked below. I believe i paid less than $50 after tax and shipping and it was worth it!


I also knew there was a special tool to change the input rod, however most people were just making there own which i did. Both the socket and tool i made are pictured below. Other than that, nothing to complicated here. Pulled her apart cleaned or replaced all parts and seals, added a fresh coat of paint and put her back together.


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I used this 1/8 adhesive rubber gasket stuff i had laying around on the back of the mounting plate for a seal to the firewall and i installed the new input rod by mounting the unit in a vice and using a dead blow hammer. I coated both of those in Eastwoods Brake Gray Aerosol and love how it turned out. I also ordered up the adapters to convert the fittings to AN. They are listed below.

www.eastwood.com

Eastwood Brake Gray Aerosol

Durable, heavy-duty coating resistsDOT 3 brake fluid; up to 400°F
www.eastwood.com www.eastwood.com

6AN To 16mm x 1.5 flared O-ring​

6AN to 18mm x 1.5 flared O-ring​

6AN x 5/16-24 O Ring​


Amazon.com: Everbuilt 6AN To 16mm & 6AN to 18mm Power Steering Fittings With O Rings Compatible for GM Chevy Buick Cadillac Power Steering Pump Gear Box Adapter fittings -6 To 16 & -6 to 18 : Automotive

Buy Everbuilt 6AN To 16mm & 6AN to 18mm Power Steering Fittings With O Rings Compatible for GM Chevy Buick Cadillac Power Steering Pump Gear Box Adapter fittings -6 To 16 & -6 to 18: Cooling Lines - Amazon.com ✓ FREE DELIVERY possible on eligible purchases
www.amazon.com


This is where i hit a snag. My original plan was to use the master cylinder from the 2004 duramax but after test fitting it i am pretty confident it is to tall and wont fit under the hood. Ill try to add a picture later. I then tried the stock master cylinder and it wont fit on the hydro boost. I really want to stay with a bottle and cap style reservoir so i am thinking about using one from a 2004 F250 but i am defiantly looking for any input on this or things to consider.

Are all/most hydro boost units of this style the same? I don't imagine they would make them with different bores that receive the master.

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Looking good! I think you can modify the brake pedal to accept the hydro setup. Just another hole needed with a new pin. I will look and see if I have a HB pedal. Also don't forget the small return spring.
 
Shawn said:
Looking good! I think you can modify the brake pedal to accept the hydro setup. Just another hole needed with a new pin. I will look and see if I have a HB pedal. Also don't forget the small return spring.
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O i did not know that. Makes sense though. I was given a full hydro boost pedal assembly so i just went that route. I should be posting that next when I'm all done with rebuilding it. Thanks tho!
 
If you have the full hydro pedal assembly, thats even better. I went that route when I converted from manual to automatic trans. Used a HB brake pedal assembly. It was a bitch to swap out but worth it in the end. then used flexible stainless lines for all the HB lines and brake lines.
 
I tried a master like yours on my '83 hyrdroboost and the pilot that goes in the booster was too big for mine. If you do some digging I think there's a different res or something that you can run on your setup but I'm not sure.
 
I did the Wilwood master but would not go that route again. When compared to the m1008 with its stock HB brakes, I liked the feel of it better. Wilwood looks nice but thats about it. Here you can see my AN fittings and I made the lines going to the HB. The brake lines were bought pre-made.


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Ya, i was tempted to use the Wilwood because bling bling but im not attracted to the idea of not being able to see the fluid level in the res or be able to add fluid quickly. :dunno: I think i just have to keep looking for something i like. Im also toying with the idea of putting the stock ABS system back on but im not sure it is even worth it.

@Shawn how do you like Wilwood's adjustable proportioning valve?
 
Fancy said:
Ya, i was tempted to use the Wilwood because bling bling but im not attracted to the idea of not being able to see the fluid level in the res or be able to add fluid quickly. :dunno: I think i just have to keep looking for something i like. Im also toying with the idea of putting the stock ABS system back on but im not sure it is even worth it.

@Shawn how do you like Wilwood's adjustable proportioning valve?
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Yep, thats another thing about the Wilwood. PITA to get the cap off with its small allen screws. I wish they did a site window or something. I'd probably consider the newer alum C30 HB GM master with the plastic reservoir unless there is something better. The brake light switch was removed since it was not being used and a plug is now there. I do like the Wilwood adjustable proportioning valve but that led up to another thing you have worry about... removing the stock proportioning valve on the frame rail in front of the engine without running all new brake lines. I found some adapters so I could remove it but don't like how it looks.
 
Shawn said:
Yep, thats another thing about the Wilwood. PITA to get the cap off with its small allen screws. I wish they did a site window or something. I'd probably consider the newer alum C30 HB GM master with the plastic reservoir unless there is something better. The brake light switch was removed since it was not being used and a plug is now there. I do like the Wilwood adjustable proportioning valve but that led up to another thing you have worry about... removing the stock proportioning valve on the frame rail in front of the engine without running all new brake lines. I found some adapters so I could remove it but don't like how it looks.
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Well, lucky for me, it was a 90 Blazer and did not have a proportioning valve on the frame rail. Mine came with the ABS and proportioning valve at the MC. This should make it easier to use the Wilwood valve. However if i go with the F250 MC the outputs for the brake lines are on the other side. I believe the 2004 F250's had 4 wheel disc so i was thinking i may not even need one but the extra adjustability can't hurt. How do you like the braided stainless lines coming of the proportioning valve? I was thinking of doing something similar but heard the breaded line allow more play in the brake pressure than a solid line.

Below is the MC off the Silverado. Was not anticipating it being that tall and get a strong feeling it wont fit under the hood. No sure where the hood falls but you can see the MC sticks up quite a bit.

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Fancy said:
Well, lucky for me, it was a 90 Blazer and did not have a proportioning valve on the frame rail. Mine came with the ABS and proportioning valve at the MC. This should make it easier to use the Wilwood valve. However if i go with the F250 MC the outputs for the brake lines are on the other side. I believe the 2004 F250's had 4 wheel dick so i was thinking i may not even need one but the extra adjustability can't hurt. How to you like the braided stainless lines coming of the proportioning valve? I was thinking of doing something similar but heard the breaded line allow more play in the brake pressure than a solid line.

Below is the MC off the Silverado. Was not anticipating it being that tall and get a strong feeling it wont fit under the hood. No sure where the hood falls but you can see the MC sticks up quite a bit.
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Oh even better! Good to hear the ABS makes it easy. Also I hope the Ford does not have 4 wheel dick. That sounds like it rides rough... :D Looks great!
 
muddybuddy said:
maybe you can swap to a lower profile reservoir?
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That was a good thought! I started looking into it and i didn't seem to find any options. Also, the more i read it seams like this master is probably not a good idea anyway, due to the bore size.

Shawn said:
Oh even better! Good to hear the ABS makes it easy. Also I hope the Ford does not have 4 wheel dick. That sounds like it rides rough... :D Looks great!
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I think auto correct saw "Ford" and assumed something :haha:
 
So after doing some homework on braking systems I think I have a solution. From what I have read you want a pedal ratio between 5:1 and 7:1 and you want your master cylinder to front caliper piston area ratio to be pretty close to your pedal ratio. Again, this is just from what I have read and my interpretation of the information.

I started by finding my actual pedal ratio. Using the diagram below it is simply Pr=(A/B). For the hydro boost pedal that is Prh=15.75/2.875=5.48:1. for the vacuum boost pedal it is Prv=15.75/3.5=4.5:1. Already I’m leaning toward the hydro boost pedal since it falls in the recommended range, but now I need to see how my master cylinder to brake caliper piston ratio compares.

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For this I’m told you look at your front caliper on one side and find the piston area. In my case I have a 79 Ford dana 60 with dual pistons. The piston diameter is 2.18” and you start by just looking at one piston. I also know the original master cylinder in these trucks was a 1.0625” bore size just for reference.

To find the area of the piston you use A=pi(r^2) so half of 2.18 =1.09 thus Ac=3.1416(1.09^2)=3.73 now multiply this by 2 since you have 2 pistons leaving me with Ac=7.47.

Im looking to use a master cylinder from a 2004 F250 that has a bore size of 1.375”. half of that is .6875. So Am=3.1416(.6875^2)=1.48. Making the ration Ac/Am=7.47/1.48=5.05:1 I though this was pretty close to the 5.48:1 pedal ration I have. The other master I was looking at was out of a dodge with a bore of 1.25” resulting in a 6:1 ratio which to me is just as big of a difference. So if the master cylinder out of the ford does not work I al least know I need to be somewhere between the two.

Next question is with the master fit my hydro boost? IT is on order so to be continued i guess lol
 
The one I'm running has a 1.34" bore, bolted up to my factory hydrobost and factory lines. And has a bolt on aluminum res. Made for a disc/disc 1983 Chevy P30 with a 6.2L diesel and hydroboost. This guy...
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@Truckman4life That one looks beefing and not a bad price!

I actually ended up swapping over to a 2004 F250 Hydroboost and master cylinder because i was able to score them for free and the math seemed to line up. The Ford MC did not fit on the Chevy Hydroboost. I painted and replaced the hydroboost and bolted everything back up. Much happier with the clearance here.

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