where to find a transmission ratio adapter

[rigon4]

I'm looking for a adapter for my truck ac part number 1565208 ratio 1:0.833 no luck finding it can someone give me some places to look I Googled it and checked eBay with no luck thanks

[geezer#99]

http://www.transmissioncenter.net/sp...n_______va.htm

[wideopen1967]

http://www.texasindustrialelectric.c...on_Adapter.asp

[rich weyand]

I have used both of the vendors listed above with no issues.

I can't find the AC Delco part either, which means getting an aftermarket part.

Be careful figuring percentages. .833 is 16.7% less than 1, but 1 is 20% more than .833. GM lists ratio as the speedometer side, so .833 out to the speedometer for 1.000 in from the xfer case. So you should be reading 20% high on speed (reading 60 mph at an actual of 50) to need a 17% step-down adapter.

The first vendor listed above has a 17% slow-down adapter. (From 60 down to 50 is 17% slower.)

The other option is ACDelco #3950352, which is 1:.8241. This will be 1% low, or 1/2 mph at 50. I couldn't find one of those either.

[RedRoad]

Would these adapters be the same for 4x4? Im running a NP205 T/C and the speedo reads 7mph slower due to larger tires, anyone have a part number?

[RIDE-RED 350r]

Wish mine was only 7mph slow... Reading about 48 I'm actually going 60.

I was kicking around here yesterday and saw another speedo ratio adapter thread... Gave myself a brain-ache trying to figure out the math to determine what % to speed up my guage....

I give up... Just read the tach! LOL!

[hatzie]

I put together a spreadsheet to take some of the pain out of it. You can find it on the manual page.

[biggsteve97]

Speedometer shops can build them.

[RIDE-RED 350r]

I'll check it out Hatzie. Thanks!

Woops... Downloaded the Apache files and I couldn't open it due to "sharing violation"....

[RIDE-RED 350r]

Just got it figured out and got the spreadsheet open... WOW that's confusing! Never used a spreadsheet before.

[rich weyand]

To figure a new ratio, and look up the part number, I need 1) the speed indicated, 2) the actual speed, and 3) the ratio of the adapter that is already on there. The existing adapter should have the ratio stamped on the housing.

An alternative to the speed indicated and actual speed is to drive 10 mile markers on the Interstate somewhere, recording the odometer reading (to tenths) at both ends, then subtract them. You will come up with something like 10.7 or 9.5.

Anyway, give me that info and I will calculate it and look it up.

[rigon4]

I got mine working for about 50 miles but then stopped and the Speedo was off also so what ratio would I need my GPS said I was going 50 the trucks Speedo said 56 and that was with the 1:833 adapter

[rich weyand]

To get it to display 50/56 of what it is displaying now, you need a 50/56 step-down, or something like 1:.893. You already have 1:.833 on there, so to get one ratio adapter that incorporates what you have plus the additional you need, that is .893 * .833 = .744. So you need a 25.6% slow-down adapter.

Closest period GM part is 3952220, at .7333. This will be about 1% slower than what you need, so will show 49.5 at 50. This was a common adapter for Corvette's with low rear-end ratios, like 4.56:1. I found a used one here:
http://www.parts123.com/parts123/yb....5Z50000050n~~~

That same exact ratio is also available here as "slow down 26.7%":
http://www.transmissioncenter.net/sp...n_______va.htm

[11555wally]

Hi Rich. Where do you find the ratio stamped? Is it on the little box between the transmission and the speedo cable? Didn't see anything on mine but I could take another look.

[rich weyand]

The little box between the transmission and the speedo cable is probably a ratio adapter. That should have a ratio stamped on it if it is a GM/AC Delco item.

I think they normally did the speedometer ratios in the drive and driven gears of the transmission without ratio adapters in the C trucks. In the K trucks, there were fewer ratios available, and so they had factory speedo ratio adapters.

[11555wally]

I'll get a better look at it tomorrow. I'm sure the truck didn't come with the rally wheels and big tires. It's an 86 Custom Deluxe. I know the engine was originally a V-6 but now is a 305. I checked the speedometer this morning against my GPS and when the speedometer said 65 the GPS said exactly 60. Down and around 25 there didn't seem to be any difference. Thanks for the info as usual.

[rich weyand]

So it is probably an aftermarket ratio adapter to correct for some changes along the way. Best is to take that off and put the cable directly into the tranny and see what you have. While you do that note the color of the driven gear the cable plugs into. They are color coded, and a new gear is cheap and easy to replace. On a transfer case, there are fewer choices, and the driven gears are expensive and unobtainable, so there you normally go with the adapter.