SAS GMT400

[Pig]

First, hello. First time posting. I have looked and looked and even searched your site and am quite surprised no one posted about a solid axle swap on a GMT400. Now, I have the idea I want and the parts gathered to begin. Now....Before I continue, I ask to please curb criticism about the direction I want to go and the parts I am using. Based on what I have read in your forums, that does look like its kept to a minimum.

About the rig. Its a 1988 C1500. The history to this truck is in depth and extensive and not really relevant to the build. I will not be doing anything with the 5.7L engine. It was built about 5 years ago. Mated behind the 5.7L will be a GM variant NV4500. Behind that will be a fixed yolk Borg Warner 44-70 transfer case. Drive shafts will be made once the truck is sittiing on the axles. The axles will be the 1999 era Superduty Dana 60 with the 36.5 spring pad spacing. The rear will be the matched axle AAM 10.25. These axles were chosen due to the large availability of parts and the ease of replacement. I am not gonna run extremely large tires so the issues with the wide perches are moot. The tires will be 35x12.50x17. Since I am running a 33x12.50x15 on it now with minimal rubbing issues....with the truck lifted....I wont have any at all.

About me....I am an extremely capable tech already. My fab skills are good, but not the best. But I can fab things to last. So if something is technical, speak it. I get it.

So....First question....pretty basic....What hydroboost and master cylinder combo would be ideal for a dual piston caliper setup on all 4 wheels? I rather not run a vac brake booster. These trucks brakes were always iffy on the best of days. I want to have better than great stopping power.

Second question.....I am not running a crossover steering set up. Again....great if youre hard core off roading....I am not. Ford uses an inverted T set up that works on their trucks and goes UNDER the leafs. Ford uses an inside frame steering gear box GMT400s do as well. The difference is the pitman arm. GM it points back towards the engine. Simply turning the GM pitman 180* would cause reverse steering. Ford it points foward toward the radiator. I could probably make the GM gearbox work.....But I am thinking a Ford steering box would be the way to go since it points out far enough to clear the leafs. What Ford steering gear box would bolt up? What box would require minimal modifications?

Third question.....What source would you use for aftermarket drop pitman arms?

Fourth Question.....The rear shackle bracket on the front leaf springs on the Superduties are inside the C channel of the frame. Like I said....I am going this route....If I need more lift to clear, I can always get the shackle extenders and get the height I need. I digress....On the Superduty, like the GMT400s, the frame goes open C channel to the rear of the vehicle. Ford solved the issue by adding a section of frame inside the channel to add rigidity. Since the leafs I am using dont go as far back to the fully opened C channel, its still inside the "boxed" portion of the frame. Do you think this part of the frame is strong enough to accommodate the rear shackle without reinforcement? A sub question to this, With the springs in the unloaded position, which way would I mount the shackle so when its loaded, there wont be any issues. I read that the proper end position would be about 25 degrees front or back depending if I want a stiffer or softer ride. Since I will be drilling a 2" hole in the frame, I would like to measure a million times and cut only once. So placement....paramount.

Fifth Question.......I am no fan of alloy rims. Especially where I live, vehicles will get stolen with Pepboy rims if they look nice enough. I like the durability of steelies. What Ford steelie offers that GM rally wheel look in a 17" rim? 17 is the choice as there are more options for tires. 16 is pretty slim and expensive from what I was looking at. Overall tire size goal is 35x12.5x17. Since 33x12.5x15 work on my 2WD truck now with minimal issues....the extra height will be no big deal once all said and done and with the gearing, transmission I have sorted out.....will give me a similar RPM and power band expectation. I know fuel mileage will be worse....But if I was worried about gas mileage, I would drive a Prius. Besides.....I paid $4 a gallon before for that beast. 36 gallon tank......C note every fill up.....you get the idea.

I know this is ALOT from a noob to the site. This project has been in the phases of getting done for the last 7 years. I have owned the truck for 15. This truck is not gonna get replaced anytime soon. So I would like to thank each and every one of you who offer your help.

[WILLD420]

You have to set shackle angle with weight on it. It won’t be right if you guess and it’s a lot of work to fix if you guess wrong.

The frames are pretty strong. I’d suggest looking at other build threads on the Gma websites for more info.

[Pig]

Well....I cannot set weight on it. How do you set weight on something that doesnt exist? The rear shackle has yet to be positioned and installed. Someone has to know how to set the angle properly without weight.

As for looking at other sources....I have. But none address the questions I have cause no one is doing the build like me. Everyone uses the shackles under the frame. This would lift my truck higher than it would be functionally useful. Thats why I am opting towards the Ford approach. The rear shackle going through the frame of the truck.

[WILLD420]

You have to hang all the rest of the suspension pieces and axle, then jack the axle up till you can get the rear of the spring positioned at the height you are looking for. I use a spacer between the frame rail and the spring eye to get it close. A 2x4 block works most times. Then you jack up the axle till the vehicle weight is on the spring. That will give you the static ride height location of the spring eye. Then you figure out the angle you want and do your measuring for putting the hole in the frame rail.

Ton's of build threads out there doing exactly what you are looking to do. You don't have to reinvent the wheel, just adapt it to your application.

http://www.fourwheeler.com/how-to/12...-buyers-guide/

Check out the picture down by the Deaver leaf spring ad. Is that the type of shackle mounting you are looking for?

[Pig]

Yes. That is what I am going for. Set up the same way the 99+ Superdutys are set up as well. I have looked and look for those thread doing the build I am doing and have come up short. Hence why I signed up for this forum. I feel I will get the best help here from every other site out there. When I did sign up, I was just surprised that no one mentioned a SAS swap before.

Anyway.....The positioning of that bracket going on the inside of the frame is a one shot deal. As you can imagine....I dont want to re-drill the frame to accommodate the shackle mount. I have done my homework on workable final product angles but have not found anything reliable enough to say....I will do this over that. While I repair vehicles for a living, I understand the theory and logic behind why things are done, I dont do custom or fabrication work. So while its familiar work with installing parts, its unfamiliar to working angles that will provide years of trouble free service. With setting the leafs on say a 2x4, after that, I get it about the positioning. At that point, I think I am back to where I come back to the shackle angle. What should the angle be at that point and why?

I know all about the ride quality of leaf springs, the extra weight to the vehicle and the extra body roll.....I am prepared for that. I just dont want a spring binding on me, flexing excessively to mess up the drive angles and what not. Pretty much just need to know do I set like(for example, not actual) the shackle back 10 degrees and why that would be the starting point. I know that the spring rate, spring arch and weight on the spring come into play at these points. But this is why I am asking. If the answer was easy to find elsewhere, I wouldnt be asking.

And Will, dont think I am being combative towards you. I am not. Just looking for understanding and I tend to be direct about it. So thank you for your help on this with me. Its really appreciated more than you know.