I just brought a 100% stock 51 chevy 3/4 ton and want to up grade the rearend, I plan on keeping the truck as original as possible but would like to be able to drive it a little faster the current 50mph top speed! Obviously im not looking for a race car but it would be nice to be able to comfortably cruise at 65 without destroying the engine! I'm wondering if I am best to switch out the rearend to something else and if so what is best and easiest or if i would be best (or if I can even get parts) to switch out the gears in the diff? Any thoughts and advise would be greatly appreciated.
hang on.. somebody will have an answer...there are also .. a bunch of forum posts on this or a very similar issue.. you might want to search for them using the search link above left.. next to the active posts link..
hang on.. somebody will have an answer...there are also .. a bunch of forum posts on this or a very similar issue.. you might want to search for them using the search link above left.. next to the active posts link..this is probably for a 1/2 ton... rear end for my 350 sb PRO51GMC PRO51GMCNew User | Posts: 4 | Joined: 02/09Posted: 02/17/0901:29 PMhey guys need some help finding a rear end for my 51 gmc half ton. i have a 350 sb. I need some help on what to look for at my local junk yard any info woold be greatThanks,PRO51GMC PackRatWrecker PackRatWreckerEnthusiast | Posts: 262 | Joined: 09/08Posted: 02/17/0906:48 PMCan't say what later axle is the correct width.I can tell you that flipping the rear springs end for end will put the center bolt in the right place for the later axle. **********1949 Chevy 1 1/2ton, home-built hydraulic wrecker. Rustoleum industrial black, with flames. Flamethrowers out 5" dual stacks.1962 Chevy C-20, 402BB, 4-speed, 3.90 positrack. Hauls my camper.... among other things.Kaiser M35A Deuce, 4x4 4 wheel steering *work in progress* haroldrussi haroldrussiNew User | Posts: 4 | Joined: 03/09Posted: 03/03/0906:05 AMI installed a 1979 Firebird 10 bolt rearend into my 1948 P/U houston54 houston54User | Posts: 55 | Joined: 03/09Posted: 03/23/0912:30 PMThe 2nd generation F-body (camaro/firebird) rear axle works well. The 2nd gen ran from 70-81 but the 70 rear axle is an 8.2" ring gear and not as strong as the later years which are 8.5". The hookup of the parking brake cables can be tricky but I used sailboat rigging clevis' to attach them to the stock cross-bar. Works fine. There are other solutions to that also.The rims/tires are another area that will need caution on. I have found the minimum backspacing for a 15 x 7 inch rim in this application is 4". Any more and you will be rubbing your tire against the bedside. Tire width I am running is a 235 but a 255 could fit but your backspacing would need to be about 3.75 to accomodate it. Some people install wheel tubs to permit wider rubber. This comes from my experiences on a 1954 truck project. Your results may vary.
Thanks Wayne, I'm going to start hunting around for something that will work... Does anyone know 1) if ring and pinion set ups are available anywhere that I could switch out to keep the original rearend? And 2) how do I find what the current ratio is so I can calculate a suitable ratio to run. I guess i need to know this no matter what direction I go.
thats something i don't know off the top of my head..you might call some of the ring and pinion suppliers...there are probably some parts available someplace...in my family there are trucks with 4:56 gear and 4:11 gears.. both of which were greatly improved by going to tires over 30 inches tall.. usually with 16 inch rims as 16.5s are hard to find in sizes other that 12.5 31.5 x 16.5..going to increased size tires on just the back will result in brake bias issues.. where the rear brakes might cause the rears to skid.. or the fronts to skid during panic stops..and if you intend on driving one of these are CURRENT highways speeds.. please make sure that all your brake hydraulic components are NEW or stainless steel sleeved.. there is also a neat site called GMPARTSWIKI dot com.. that has old truck parts catalogs.. you can page thru and see what parts were available.. to make some of what you are doing easier..
Brilliant! Why are the easiest things always the last to cross my mind? I never even thought about looking into larger rear tires... I'll take a look at my tire size tomorrow and try to figure out if that is an option for me... The truck came with brand new tires but I certainly don't mind having a spare pair for the front laying around. I'm definitely looking at upgrading the brake system... I just need to work out what will be best for me, actual freeway speeds in my area of California seem to be about 85mph but I'd be happy with 60ish so hopefully I can get away with a relatively straight forward upgrade there... Time will tell! Thanks for the web site too, I'll take a look
yea.. freeway speeds in my area vary also.. from a total parking lot to about 70 or 75..except late at night as caltrans surfaced the freeway.. so its like glass.. and the motorcycles go past at a buck and a half..the freeway here is 4 lanes in either direction and enough on and off ramps to take the lane count to 13 lanes.many heads work better together
You asked about how to find your current gear ratio. Either take the diff apart and count teeth (yeah, I don't think you want to do that). Or to get the approximate ratio, jack up the rear end put it on jack stands, (front wheels blocked or course) transmission in neutral and brakes off, rotate the drive shaft by hand and count the revolutions for the wheels. If wheels move in opposite directions, get some help and rotate the wheels at the same time in the same direction and count the drive shaft revolutions. ratio= (drive shaft revolutions)/(wheel revolutions) good luck. This assumes you have an open drive shaft, my 54 gmc had a torque tube, so that option was out of the question. Since I had to replace the rear end anyway, I did some research and found the best/strongest/easiest to work on rear end was a Ford 9", it comes in a variety of sizes and configurations, you need to measure back plate spacing and spring perches then go to the junk yard, and find it. Of course that won't be anywhere near stock.