Another ABS Bleeding question

megatronz0r · Jun 9, 2023

I recently purchased a 1988 GMC GMT400 Singlec ab Short Bed 2wd that has been frankensteined to say the least. It has a 400sbc, 95 dash and seat and the rest appears to be 88. The guy i bought it from knew absolutely nothing about it.

Driving home i realized how sketchy the brakes really were so I replaced the master cylinder with the NBS model and i did Russell brake hoses.

Now i'm to the bleeding part and i have some sort of Kelsey-Hayes ABS unit that i've read are a nightmare to bleed or need to be taken to a dealer. Ive considered deleting the ABS but ive only found guides videos of the RWAL. I have also read that I can buy a scanner on amazon for about $100 that will bleed to brakes in OBD2 vehicles but with all the hackery on this truck i have no idea if my truck is OBD1 or OBD2.

OBD2 Scanner with ABS Auto Bleed FOXWELL NT630 Plus

So i guess my main questions are:
Did 1988 have this ABS (pictured below) as an available option
Is 1988 OBD1 or OBD2 (pictured below of what it looks like in my truck)
Are there any guides of removing this type of ABS and replacing it with a proportioning valve
Any additional information would be greatly appreciated i'm feeling a little overwhelmed currently.

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Caman96 · Jun 9, 2023

96 up is obd2. Your definitely obd1.

megatronz0r · Jun 9, 2023

Caman96 said:
96 up is obd2. Your definitely obd1.

Doesn't that look like OBD2 Port though?

xXxPARAGONxXx · Jun 9, 2023

megatronz0r said:
Doesn't that look like OBD2 Port though?

Harness including port came with the dash, I'm sure. What makes something OBD-1 versus OBD-2 comes down to the VCM (ECU). It's the software. You can have a harness for an OBD-2 vehicle installed, but if the software on the VCM is for an OBD-1 vehicle, the VCM couldn't care less if there's an OBD-2 port on the vehicle.

megatronz0r · Jun 9, 2023

xXxPARAGONxXx said:
Harness including port came with the dash, I'm sure. What makes something OBD-1 versus OBD-2 comes down to the VCM (ECU). It's the software. You can have a harness for an OBD-2 vehicle installed, but if the software on the VCM is for an OBD-1 vehicle, the VCM couldn't care less if there's an OBD-2 port on the vehicle.

So would a shop or dealer even have the ability to bleed the abs with with this port?

xXxPARAGONxXx · Jun 9, 2023

megatronz0r said:
So would a shop or dealer even have the ability to bleed the abs with with this port?

No idea. There's a lot of variables in your Frankenstein. First would need to hook up a scanner to the port and see if it actually communicates with the VCM and/or ABS module.

Schurkey · Jun 9, 2023

Are you sure this is an '88?

The '88s had RWAL with an iron body. The iron RWAL system had a single bleeder screw that made the RWAL easy to bleed.

You have a later-model ABS, a later-model dash, later-model computer diagnostic connector...one wonders how much of this truck is actually from '88. That ABS system will require front-wheel speed sensors, which the '88 did not have.

Given the carburetor, the computer is almost certainly starving for info and setting codes. Perhaps disconnected entirely. God only knows what you're gonna find. Being a naturally-suspicious and naturally-grumpy old man, the first thing that comes to mind is a dishonest seller combining together old wrecks, and then instead of getting a "Salvage" title, sells it while claiming no knowlege of the vehicle's history. Given the change to the dashboard, do you have an '88 VIN number, or a '95 VIN?

Don't get me started on the evil of installing a two-chamber master cylinder when using low-drag front calipers that need a three-chamber master cylinder. And if this actually has '88 front brakes, there's a really good chance that you've got JN3 brakes, the weakest, crappiest power brakes ever installed on a GMT400. Aside from the inherent issues with JN3, I bet the bigger problem is that you have no way to bleed the ABS unit, and it's got air inside.

If you bought the same Russell brake hoses that I bought, you'll want to verify that the hoses cannot rub on the upper control arm no matter how the wheels are steered or whether the front springs are compressed or extended. I had to wrap my control arms with rubber to prevent them abrading on the hoses ('88 K1500, not '88 C1500 like yours.)

Existing rubber wear-guard isn't tall enough.

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Additional protection applied.

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megatronz0r · Jun 9, 2023

Schurkey said:
Are you sure this is an '88?

The '88s had RWAL with an iron body. The iron RWAL system had a single bleeder screw that made the RWAL easy to bleed.

You have a later-model ABS, a later-model dash, later-model computer diagnostic connector...one wonders how much of this truck is actually from '88. That ABS system will require front-wheel speed sensors, which the '88 did not have.

Given the carburetor, the computer is almost certainly starving for info and setting codes. Perhaps disconnected entirely. God only knows what you're gonna find. Being a naturally-suspicious and naturally-grumpy old man, the first thing that comes to mind is a dishonest seller combining together old wrecks, and then instead of getting a "Salvage" title, sells it while claiming no knowlege of the vehicle's history. Given the change to the dashboard, do you have an '88 VIN number, or a '95 VIN?

Don't get me started on the evil of installing a two-chamber master cylinder when using low-drag front calipers that need a three-chamber master cylinder. And if this actually has '88 front brakes, there's a really good chance that you've got JN3 brakes, the weakest, crappiest power brakes ever installed on a GMT400. Aside from the inherent issues with JN3, I bet the bigger problem is that you have no way to bleed the ABS unit, and it's got air inside.

If you bought the same Russell brake hoses that I bought, you'll want to verify that the hoses cannot rub on the upper control arm no matter how the wheels are steered or whether the front springs are compressed or extended. I had to wrap my control arms with rubber to prevent them abrading on the hoses ('88 K1500, not '88 C1500 like yours.)

Existing rubber wear-guard isn't tall enough.

You must be registered for see images attach

Additional protection applied.

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I am not sure this an 88 the only thing I’m going off of is the vin number and title. What other sure fire things could I look at to determine what year this truck is?

Schurkey · Jun 9, 2023

I've purchased TWO vehicles where the title VIN number did not match the VIN plate on the vehicle.

In one case, someone had exchanged a "Z" for a "2", and in another I think it was an "I" for a "1". The rest of the numbers matched. The Highway Patrol inspected the cars, issued paperwork, and the title got corrected without much hassle.

In your case, I'd want to compare the VIN plate on the dash to the VIN on the title. There are "secret" VIN numbers stamped into the frame, and perhaps on the cowl/firewall on the lower right side, and probably other places as well. My '92 and '93 Luminas had VIN stickers on the fenders, trunk lid, and other easily-replaced parts.

Caman96 · Jun 10, 2023

My 96 has vin on drivers door sticker, not sure about 88’s.

Another ABS Bleeding question

megatronz0r

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Caman96

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megatronz0r

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xXxPARAGONxXx

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megatronz0r

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xXxPARAGONxXx

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Schurkey

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megatronz0r

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Schurkey

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Caman96

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