Ring and pinion

[ecbert]

Does anyone know where I can get a higher (lower numerically) ring and pinion for my 70 GMC 5500? either new or used, whole take out third member would work. I believe it has the H150 / H170 two speed rear, currently it has the 6.50:1 ratio and I'd like to go to the 4.83:1 ratio.

[Pvmt-Pndr]

LKQ is where I've been able to find gear sets or 3rd member for my rear end. There are a couple of other places that have found too but it seems like LKQ bought all of them anyways. A phone call to them should get you whatever you want if it's out there for sale. In a 24 hour period they called me back with 3 different options

[ecbert]

Pvmt-Pndr, thank you for the reply. I actually have an inquiry into them already and I did manage to find some NOS stuff out there from various suppliers but they wanted over $1g just for the ring and pinion. For that price I can get a complete newer Eaton rear but that's not the way I want to go.

[Pvmt-Pndr]

I'm in the same boat as you are. I was quoted around the same price for 4:88s and 4:56s all between 1000-1400 if I recall correctly. That will probably be the last big thing I do. Once I rebuild my engine I'll be able to determine which of the two I want.

[ecbert]

I didn't even see the 4.56's in the GM book, only the 4.88's (I thought the book said 4.83's but I could be wrong). Can you send me a link as to where you found the parts? Changing from 6.50's to 4.88's or 4.56's would be like adding an overdrive transmission! I also need to rebuild (tank) my 366, I have found a 427TD block and I plan on using that in the future.

Thanks for your advice / replies.

[Pvmt-Pndr]

The 4:56 and 4:88s i mentioned were for my rear end, I have a 17221. I currently have 6:50/8:87 low.

That's exactly why I want suck a high gear but before I pull the trigger I need to make sure I'll have the power to make up whatever drop in rpm they will create.

I highly recommend you find a gear calculator and punch in all the info to it to see if you'll have the power for the split too. I wrote out 4 different gears. 6:50 (for direct comparison), 5:29 (a member has a set for a great price), 4:88s and 4:56. Then I laid them all out on a table to see where I would be and how many mph split there was between gears. I also noted where 60/65/70 mph was and what rpm I would be at so I can ride the torque curve of the engine while cruising. I found that 4:88s puts me in the happy spot in 5H while 4:56 drops the rpms low enough to act as an OD and I can always down shift. The biggest gap I believe was 13 mph which may be a little too much but I'm not sure. That's why I'm not wanting to buy gears until I rebuild the engine. Since the day I bought the truck something wasn't right and now I know I lost the cam and have low compression in one cylinder.

[sweetk30]

http://www.grimmjeeper.com/gears.html

good calculator here for the offroad guys . but can be used a lot with others . if your tans is not listed just type in the #'s and it will compute from there .

[ecbert]

I already made an RPM calculator in Excel, the TD 427 that I have it going to make 3x the power that my current 366 does, without much difficulty. I don't use the truck for hauling anymore so I don't really need the low gear ratio. I found some gear sets online but they are not high enough, anyone have any sources?

[Pvmt-Pndr]

You may be better off swapping the whole rear end.

[sweetk30]

just cause you go gear ratio for better rpm and more speed dont forget these old trucks have old brake system designs and steering also . up grade one watch out for the other .

as said maybe swap to newer axle pair and get better brakes and ratio all in 1 .

[ecbert]

Well, I found a GM Clark 280VO trans that was behind a 366 and I'm going to start there by swapping out my SM465, so that'll give me a .8 OD - not a bad start. I currently have just the shifter and the trans, need to get the parking brake assy and a PTO for it. I've also located a 5.57:1 ring and pinion for a reasonable price.

I will be posting pictures of the swap.