Newbie with another disc brake swap question. . . . .

[dennis111]

I have enjoy checking out the forum an the different reader's rides. Since this is my first post, I decided to make it a good, challenging one.

After reading several articles and the FAQ about converting my 68' GMC PU (see sig.) to disc brakes I purchased a complete 1978 Chevy 1/2 ton V8 PU with PB and PS. I also has a 12 bolt rear which is similar to mine, except it has the desired 5 lugs.

I understand that it is easiest to change out the whole crossmember assembly in the front. I also understand that the engine will need to be lifted up or removed and to use the 78's proportional valve. This leads to some specific questions that the various articles didn't cover.

1. Apparently the 78' crossmember will fit fine, if new holes are drilled in the frame. How does one know where to drill the holes in the frame? Are there holes or anything that will help for forward/rear alignment?

2. Which motor mount metal bracket works best? If I decide to reuse the original 68' brackets, do the holes in the 78' crossmember match?

3. Do I use the 78's pitman and idler arms? I have the late 68' type steering similar to the newer trucks.

Any other words of advice?

Now as far as the rear end. What will I need to do to put it in my 68'? I am led to believe that the leaf springs pads might be the same distance apart. I have noticed that the shocks in the 78' are in different directions and they are located outboard of the frame.

1. Should I try to mount the shocks outboard or should I reweld the old mounts/bumper pads on the new rear and use the original 68' locations? I am looking for the "easiest" way.

2. Is there anything else that I have missed that would put a monkey wrench in the swap?

Now for my last question:

The leaf springs appear to be the same width. Are they swapable without major modifications?

Thank you for your input and suggestions. Hopefully your answers will help future newbies too. . . . . .

Dennis

[Nick's683/4]

For the front cross member you only i have to drill one new hole all the other hole line right up. I used a 79 3/4 suburban with a 454 and a th400. I used all the same motor mounts and stands that were on the suburban. I havnt got it all together yet but i got the cross member in and it fit like a glove. The streing box fit in and i used the pitman and idler arm off the suburban.

Hope this helps
Nick

[krue]

Welcome to the board from South Mississippi!

[dennis111]

Thanks Nick, you gave me the answers that I needed for the front end swap. Much appreciated!

Krue, thanks for the welcome. My 68' and I are world traveler's (literally.) In the 30+ years that I have owned it and we once called Biloxi "home" (from the mid to late 1970's.) We finally settled down now in Central, PA.

Best of luck to both of you with your projects!

Dennis

[Blue Beard]

Welcome from SW Washington State....

Be sure to post some pics, before...during...and after stages of work.

Being how the suspension issue is a FAQ it might be a good idea to take photos during the process and post them in the FAQ section.

Good luck

[Tx Firefighter]

All but two of the bolt holes line up. Just install the crossmember with all of the bolts but the two. It will be aligned properly with the frame this way. Than, you egg out the last 2 holes. They will be close, but not perfectly aligned. A little slotting and you're done. I have even left those last 2 bolts out with no ill effects. There are like a dozen other bolts holding the crossmember in anyway.

Use steering box and idler arm off of the donor truck.

I always used the older style original motor mounts. Just leave the engine bolted to them, remove the two lower bolts (1 per side) that go into the crossmember, and lift it a tad with an engine hoist. Leave the rest of the motor mount bolts in place while doing this. Kind of hang it there while the crossmember is gone from beneath it. After swapping crossmembers, the stock motor mounts will set down onto the the crossmember just fine. There will be 1 hole to drill on either side of the crossmember for the bottom motor mount bolt. The mount will be right there, so all you have to do is drill down through the hole.

I have never swapped any rearends on these trucks with the leafsprings, so I can't offer any suggestions about that.

Welcome to the board, and very well though out intelligent question, I can tell you took the time to research this beforehand.

[Putter]

Welcome from Central Mississippi. Sounds like you are well on your way to getting this portion of your project done. Tons of good "know-how" here on the board. If you get stuck part way through, just post the questions and sit back. The answers are on the way.

[dennis111]

Thanks for the welcome's and for the advice. I think I have the crossmember swap pretty well whipped (mentally.) About the only other thing I haven't thought much about are the hydralic brake line routings. What is the best way to route them?

Would it be easier to copy the 78' routing with the proportioning valve (78') on the frame under the radiator or should I try to make it more like the 68' style and run the lines across member, placing the 78's valve near the master cylinder?

I already own a double flair tool and some tubing.

Dennis

[Nick's683/4]

I havnt had much time to look at that yet but i was planing on puting it just like the 79 that i got my stuff from. There is spot on the proportioning valve for the stock 68 braket and there is holes in the very front cross member for it.

Nick