Mine is natural color i think 36 tooth
It’s pretty accurate, but i think the faster i go its off a tiny bit. Is there a way to know the exact color/ tooth count for rear end ratio?
I changed the o ring and seal but she started leaking again so i wanna try the gear next.

 

you need to know the number of teeth on the transmission drive gear, your gear ratio and the tire diameter.
https://www.tciauto.com/speedometer-...xo7WOAAmwyVln8

 

you’re right I forgot about tire size unless you’re sticking with the factory size then I guess you can’t go by the color

 

What size are your tires? That will make a difference as to what gears to run in the tans.

 

This will get you where you need to go. Cross the tires listed with your tire diameter and you should be good to go. That's what I did with my 255/60/15 BFG's

I swapped out the old drive gear as well to the 18 tooth listed. I think it's green.

 

I have 235/60/15 in the rear and the front I have 225/60/15

 

It’s off by a percentage, so the actual MPH error will get larger as the vehicle speed increases.

 

Those are shorter than anything that came on the car by .4" . The shortest tire that came on these cars was 26.5" tall. That's the F78-14. That would mean a 18 tooth drive and a 45 tooth driven gear would be your closest match.

 

Correction, I have 255/60/R15 in the rear and I have 245/60/R15 in the front

 

Ok, then you're looking at 18/44 drive/driven.

 

OK, I did some quick calculations and the 18/44 ratio is 2.444444444.
IF your current drive gear is a 15 tooth, with the 36 tooth driven you are at a 2.4 ratio. If you just change the driven gear up to a 37 tooth that would be a 2.4666666667 ratio. That would slow the speedo down just enough to be where you need it without needing to remove the tail housing, replacing a HARD to find drive gear AND getting the larger tooth count housing for the driven gear.

 

Hey Randy thx, question the drive is the one you cannot easily remove correct? how do i know if it is in fact a 15? by color also?
So my speedo seems accurate until i get up to about 45-50 it seems to drop of 1-2 MPH thx for the help

 

Yeah, they are color coded. I think the 15 tooth is grey.

 

So I bought a new 36 tooth gear part number 135-9270 AC Delco I got the part in and it’s only an inch and a half round not an inch three-quarter and the guy selling it on eBay will not take it back does anybody know the correct part number for a 1970 turbo 400 other than AC Delco 1359270

my original one is on the left. The one I bought is on the right it’s an inch and a half versus an inch and three-quarter. Does anybody have a part number for the inch three-quarter?

 

There are different speedo housings for different gear tooth. I don’t recall the breakdown, but as gear tooth count changes, so does the diameter. To keep the gears in mesh, the housings are cast with different offsets.

Look at the end of your current speedo housings, it will have a group of numbers, those are the gears tooth count compatible with that housing.

 

thanks Matt if it leaks again, I’ll take it apart and check it out

 

All right so I put the correct gear back in and the seal I bought for the speedo cable. The outer smaller seal is still too big. Is there a better brand I bought this one off of Amazon and it’s just too big you could see it seeping right out the speed cable.
Amazon is just like Ebay. You really don’t know what you’re getting unless you get the correct part number for something that works. Anybody have a part number or brand I could look up.

 

Go to your nearest transmission shop, chances are the builder has a box of them.

 

For a car that's over half a century old?

 

Why not? They use the same seal/oring on the 700, and that transmission isn’t half a century old. And even if they don’t have one, they could definitely order the correct part.

 

Hey Matt is this the number i need?
40,41,42,43

 

The breakdown for the two housings are
34 to 39 tooth gear
40 to 43 tooth gear.
For a 36 tooth gear you need to get the 34 to 39 housing

 

So my housing is wrong for my gear? so when this last owner had the transmission resealed the builder did not use the correct hosing?
because the previous owner kept bringing back this trans for the same leak several times? I guess he never caught it.
thx, so now where and what do i get?

 

If I am following along correctly, the gear that was in the transmission was 1.75 ( that size is for the 40 teeth and up gears ) so the housing is correct for the gear that was in the transmission.
Now that you want to put a 36 tooth gear in, that housing is not correct., the correct housing is available new from various vendors runs about $70.00.

 

well maybe not, i thought i had a 36 tooth gear maybe i don't, I just want to stop the leak, i already put i new o ring and seal and assumed i needed a new plastic gear because is still leaked after the new seals.
wondering now if i bought the wrong seal guess i will start over. i was going by the color of the plastic gear assumed it was a 36 light green.

 

I like to use the seal that has a spring , I haven't had on leak yet.
The industry number is 44078a. The seal is about 2.50 but shipping just one would cost stupid money.
The gears a usually marked on the long stem side with the teeth count.

 

Thats cool did not know they made one with a spring

 

Sorry I know that I'm alittle late in posting this, however here is the various gear and as they were called Sleeve that was used at the time.

Any transmission shop should be able to get these gears. This page is from a Dealership Parts Book.

Here is the Sleeves the the gears were used with. As you can tell by studying them there is only a couple that will work.

 

thx mine is 1362077

 

Ok so i am starting over on this issue.
I bought New a seal with a garder spring as suggested by Nicks1966
and going to count the teeth on the gear this time i assumed it was a 36 tooth by the color of the gear.
going to try the garder spring with my current gear then maybe buy the correct gear.
if that all fails i will buy a whole housing.

 

Ok so the smaller garder seal seems to work but the larger seal still needs replace the one i bought was tooo big “loose” anyone lnow one that will fit properly thx. The initial one I tried that was still leaking was probably the smaller seal so I took both of those out and put the original larger seal in because like I said the larger one that I put in was loose.


as you could see in the picture, it’s not leaking from the cable no more, but the outer seal looks wet on the bottom

 

Here are the numbers I have for the oring seal
GM- 25501478
ATP- SO-38
Pioneer -- 762004
Wittrans / cobra transmission 34369A

 

thx i will give one a try