swap the whole crossmember or just control arms for disc brake upgrade

[Jeffvega]

I have a 79 donor truck to use on my 70, would it be better to swap the whole crossmember or just do the arms. Also it looks like the rearend will fit since my 70 is also a leaf spring rear. I'm also taking the ps box off the 79

[SCOTI]

If anything needs rebuilding, just swap the parts. If the 'replacement' c.member has all fresh parts, swap it as a unit.

I've never read anything about the rears being a direct swap so I can't help there. I would measure the C/L of the spring perches on both housings to know for sure.

[Spray-Bomb]

79 rear is most likely a 10 bolt instead of a 12 & in 71 the axles became wider by 3/4" per side IIRC

[Jeffvega]

Thanks for the help. The 79 looks physicaly the same as far as the back cover goes but I'm still not sure. The 70 rear is in better shape but I would like the five lug axles. If I understand correctly though you say that the 79 is wider by 3/4 each side so I guess I'm back to square 1

[SCOTI]

Originally Posted by Jeffvega

Thanks for the help. The 79 looks physicaly the same as far as the back cover goes but I'm still not sure. The 70 rear is in better shape but I would like the five lug axles. If I understand correctly though you say that the 79 is wider by 3/4 each side so I guess I'm back to square 1

It depends . . ..... 1970 was the year when the switch occurred to the wider housing. Housings built 'early' in the year were narrower..... then they switched to the wider housing. Best to measure the perch C/L. ECE & CPP sell replacement 5-lug axles if your budget allows.

[Jeffvega]

so if the perches measure the same then the next step would be to remove the axles from both and measure them

[SCOTI]

Originally Posted by Jeffvega

so if the perches measure the same then the next step would be to remove the axles from both and measure them

If the perches measure the same, swap the entire housing.

[bodydropped68]

Originally Posted by Jeffvega

I have a 79 donor truck to use on my 70, would it be better to swap the whole crossmember or just do the arms. Also it looks like the rearend will fit since my 70 is also a leaf spring rear. I'm also taking the ps box off the 79

just swap the control arms, steering linkage, steering box, sway bar and don't forget the brakets on the frame if your truck doesn't already have a sway barand just leave the crossmembers alone. as far as the rear goes if the spring perch's don't match up cut them off and weld on new ones you may already be doing that if your going to flip the axle to lower it anyway.

[ERASER5]

Is your engine in or out? If the engine is still mounted, you will not be able to swap the cross member. Well, maybe you can if you just like squishing into very tight places!

As Scotti said, if anything needs replaced, just swap in the parts. I did it that way. I replaced every wear item except the rubber A-arm bushings. They were OK. I also kept the 6 lug with McGoughy 6 lug rotors.

Oh! Since no one has mentioned it, make sure you have Heavy Duty brakes. The HD brakes will measure 1.5" across the rotor edge. Do not waste your time with the light duty rotors (1"). The aftermarket specialty stuff is all made to the HD specs (drop spindles, drilled rotors, etc.).

The wider rear end was done to match the wider front disc brake setup in 1971. You are getting ready to widen the front suspension with the disc brake setup. Matching it with rear end is a good thing.

[SCOTI]

HD 1/2-ton = 1.25" rotors. Lt duty came after 1980 & were 1.00".