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Old 08-07-2017, 02:27 AM   #16
dsraven
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Join Date: Nov 2010
Location: calgary alberta
Posts: 7,773
Re: Any suggestions on a tire size

well with any diff swap there will be mods because the spring pads etc will probably not be in the same place.

try to get a diff with the same wheel bolt pattern as the front axle or else plan on different wheel sets or a redrill of the "new" axles to match what you have. remember a redrill means a headache if you need parts while on a road trip. try to stay with stock stuff, keep a pattern for the redrill in the vehicle or keep some cash handy.

unless you plan on deep dish wheels and are going to tub the box (make room for more back spacing on the wheels so you cut into the box and "tub" the area you cut out to make a narrower dimension between the tires), look for something with the same, or close, axle width. the track width of a 55 to 59 is 61.02". that is from the GM assembly manual and may not be the actual dimension that is from wheel mounting surface to wheel mounting surface on the axle. see this write up from crankshaft coalition on the subject that may help you pick an axle. looks like 1994 - 2003 chevy zr2 extended cab, four wheel drive is really close to the right width.

http://www.crankshaftcoalition.com/w...l_measurements

once you find a donor diff, plan on cutting all the brackets off the "new" diff and smooth the axle tubes to be ready for the new spring perches. be careful doing this because too much heat, like from a torch, can cause the axle tubes to warp and bring a whole new headache your way. a zip disc on a mini grinder is a good alternative because there is less concentrated heat compared to a cutting torch. move around to different areas too allow cooling after cutting off a bracket.
when the "new" diff is ready to go under the truck do a quick measure on the dimension between centers on the spring perches of the old diff and mock up the new spring perches on the new axle with the new ubolts etc. a trailer axle shop is a good source for these parts. you will need to know the axle tube diameter and the ubolt length. mock it up and get it centered etc but don't tighten anything up or weld on the new perches yet, just tighten stuff up enough to keep it all in place. set the truck down on the wheels and roll it back and forth a few times to get the suspension to settle into it's sweet spot. now do a drive line angle check. basically this is to match the angle of the engine and trans to the opposite angle for the diff pinion so the ujoint angles cancel each other out and you have less or no drive line vibration. check the link below to a good youtube demo on drive line angles. usually the engine and trans are angled down about 3 deg (at ride height, with the wheels and tires you will be running, measured on the oil pan gasket surface of the engine) and the diff is angled up 3 deg to compensate.

https://www.youtube.com/watch?v=gmV4qwLfOMY


when you get that all dialed in and the diff is centered side to side then tack weld the spring perches on to the axle tubes. make sure to put the ground clamp for the welder on the axle tube, not the axle flange, because otherwise the welding current will go through the wheel bearings and diff bearings and leave small "weld" spots on all those surfaces. that can mean a total diff rebearing andnew axles. tighten down the u bolts, assemble and bleed brakes, connect and adjust the park brake etc to make it all road worthy. road test it to ensure the wheels don't rub, there are no vibration issues etc and when satisfied do a final weld in on the spring perches. done.
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