Blazer Speedo gears

[BBrendal]

Ok so I put the 33 x 12.50 x 15 BFGs on and love them. Now I need to get my speedo right. I havent checked with a gps how far off the speed is but it is registering 9/10 of a mile when I traveled a mile. So I know the speedometer is slower then the truck is actually going. I know someone who can figure out the gear combo that it has to be on a transmission but on a 4x4 how do you get the speedo gear out of the 205 transfercase? A socket does not fit on the housing in transfer case. Has any one put these tires on and changed the gears. Any help is appreciated. Oh and also Im running a 3.73 gear.

[1972k5blazer]

I hope someone chimmes in on this for you and for me too ! Im in the same boat my 70 has 33 s and i took a gps out and it was right at 5 to 6 mph off at every speed ! I thought i read a thread on here where a guy removed the reducer on the trans case and just hook his cable right into the trans case and it spead his cable up 5mph . I wanted to try it but my cable was nt long enough with the reducer removed . Can anyone sure enough verify if this will work if the reducer is removed ?

[BBrendal]

I dont have a reducer on mine. It is direct do the transfer case and mine is off. Ill see how far with a GPS over the weekend.

[47thriftmaster]

You will have to change the speedo gear, were it goes into the trans case. I saw them for sale, but can't remember where, will have to look into it. They are made though, different colors for different set ups. Should be able to find or order at a trans shop.

[BBrendal]

Originally Posted by 47thriftmaster

You will have to change the speedo gear, were it goes into the trans case. I saw them for sale, but can't remember where, will have to look into it. They are made though, different colors for different set ups. Should be able to find or order at a trans shop.

Yea I know I have to change them but cant get the speedo housing off. A socket or wrench does not fit on the housing. Thats what Im trying to find out. Also if anyony knew the color of the gears needed for my combo and are the gears similar to whats used in a trans.

[Firebirdjones]

Every blazer I've ever owned with a 203-205 transfer case has always had the gear reducer on it before the cable connects to the case, including my current 72 blazer.

As far as I know there isn't anyone making the speedo gears for these old transfer cases anymore, they are completely different from what you would find in a transmission.

What I had to do when I switched to 33" tires was have a company build me a completely new reducer, they didn't even use the old one. Cost about $70 to do so but it's the only option I'm aware of.

I'd have to dig through my receipts as I can't remember the name off the top of my head, they are all over the internet though. Took them about 3 weeks to build one and it's worked perfectly.
They will ask you to bypass the current reducer (you don't have one) and they want the speed recorded straight from the transfer case at 40-50-60 mph and compare that to a GPS. Tell them your findings and they simply build the reducer. Easy as that.
Just make sure this is the tire size and gear ratio you are sticking with. If you change something down the road it's another $70 and a 3 week wait for another reducer.

[Firebirdjones]

Here is a link to the place I used.

http://www.transmissioncenter.net/sp...gTAod41hNNw#gm ratio adapter


On the highlighted list click on "ratio adapters" which is 3rd from the left top row. It takes you right to the adapters. Scroll down and you will see the custom adapters they off with a 2-4 week waiting period. You'll have to call to order and they will ask for the info I mentioned above.

[BBrendal]

That is what Im talking about. I believe the speed up 11% is what I need. Thanks Firebirdjones! I love this site!

[Firebirdjones]

Originally Posted by 1972k5blazer

I hope someone chimmes in on this for you and for me too ! Im in the same boat my 70 has 33 s and i took a gps out and it was right at 5 to 6 mph off at every speed ! I thought i read a thread on here where a guy removed the reducer on the trans case and just hook his cable right into the trans case and it spead his cable up 5mph . I wanted to try it but my cable was nt long enough with the reducer removed . Can anyone sure enough verify if this will work if the reducer is removed ?

Yes you can hook straight to the case, and I did that with mine back when I was having another reducer made because that's how they wanted the speedo error measured.

I can't remember exactly but I think you are right, it did speed up the speedo slightly. It wasn't near enough in my case however. I'm pretty sure I needed something like a 35% change or more which is why I had to do a custom reducer.

My cable had enough slack to reach the case without the reducer, but if you find that not to be the case, you can buy short little cable extentions with male/female ends to lengthen your existing speedo cable. I used to have a GM part number around here somewhere just for that. But I'm sure it can be found just about anywhere on the net.

[Firebirdjones]

Originally Posted by BBrendal

That is what Im talking about. I believe the speed up 11% is what I need. Thanks Firebirdjones! I love this site!

You are more than welcome.