huug
Member
Hi Guys,
I live in the Netherlands and I have a 1958 Chevrolet Bel Air with the 348 engine.
That engine got a major rebuilding last winter. Behind it was a TH350 transmission attached. As I had it out of the car, together with the engine, I wanted that TH350 rebuilded also. So I contacted a transmission guy over here, and he offered me to exchange it with a rebuilded one, instead of rebuilding mine, as they were the same, both in dimensions and price. And indeed, it bolted right to the engine and had the same short tail.
Now that I have the car up and running again, after 6 months of work, the transmission performs very well and shifts very smooth. But my speedometer showed way too less. So I did some searching about speedometer gears here and on the web, and learned a lot about driven and drive gears, different ratios, colours, teeth and so on. But to some questions I couldn't find an answer.
The first one was: can I get that drive gear out of the tranny without draining it? But I found out: yes, you can. Some ATF will come out, but it will not drain.
So my next question is: can I get that tail housing of my TH350 without draining the transmission? I presume it can, but I'm not sure.
My new TH350 has got the large 1½" speedometer gear housing, that shows 36 37 38 39. This large gear housing tells also that this TH350 is NOT from a Chevrolet, but that's OK. It isn't original anyway.
And what came out was a broken blue 38 teeth driven gear, and the hole showed a 9 teeth green drive gear.
To calculate what gear I need on http://www.bgsoflex.com/speedo1.html I filled in the diameter of my P205/75R14 tires, which is 26.10 inch.
Then I need my rear axle ratio. Where ever I looked on my axle, I could find any serial number or ratio on it. But looking at the original condition of the axle, in combination with the 348 motor and the Gr on the indicator on the steering column, what reveals it had a turboglide once, I presume it has a ratio of 1:3.36
I read about a tip to jack up the rear weels and count the revolutions of the rear wheels and drive shaft in order to get the ratio, which is a nice one, but very hard to count it two digits secure.
The last input I need to know is the speedometer revolutions per mile. Is this 1000 for the 1958 Chevrolet? Could it be less?
Presuming it is 1000, I calculated the ratio 2.60, that goes with the combination 15/39, a grey 15 teeth drive gear with a brown 39 teeth driven gear.
No combination is possible with my current green 9 teeth drive gear, so I need to replace that also.
My other question is why that blue driven gear of mine got broken. Did my speedometer had too much resistance? Should I lubricate it? I know my odometer has some difficulties to come in a new number in the 2nd and 1st digit, so maybe this can be the problem. Is removing and rebuilding the speedometer out of a 58 easy? The cable moves freely, when removed.
Is my above stated thinking correct? Any input on this mather is welcome.
I live in the Netherlands and I have a 1958 Chevrolet Bel Air with the 348 engine.
That engine got a major rebuilding last winter. Behind it was a TH350 transmission attached. As I had it out of the car, together with the engine, I wanted that TH350 rebuilded also. So I contacted a transmission guy over here, and he offered me to exchange it with a rebuilded one, instead of rebuilding mine, as they were the same, both in dimensions and price. And indeed, it bolted right to the engine and had the same short tail.
Now that I have the car up and running again, after 6 months of work, the transmission performs very well and shifts very smooth. But my speedometer showed way too less. So I did some searching about speedometer gears here and on the web, and learned a lot about driven and drive gears, different ratios, colours, teeth and so on. But to some questions I couldn't find an answer.
The first one was: can I get that drive gear out of the tranny without draining it? But I found out: yes, you can. Some ATF will come out, but it will not drain.
So my next question is: can I get that tail housing of my TH350 without draining the transmission? I presume it can, but I'm not sure.
My new TH350 has got the large 1½" speedometer gear housing, that shows 36 37 38 39. This large gear housing tells also that this TH350 is NOT from a Chevrolet, but that's OK. It isn't original anyway.
And what came out was a broken blue 38 teeth driven gear, and the hole showed a 9 teeth green drive gear.
To calculate what gear I need on http://www.bgsoflex.com/speedo1.html I filled in the diameter of my P205/75R14 tires, which is 26.10 inch.
Then I need my rear axle ratio. Where ever I looked on my axle, I could find any serial number or ratio on it. But looking at the original condition of the axle, in combination with the 348 motor and the Gr on the indicator on the steering column, what reveals it had a turboglide once, I presume it has a ratio of 1:3.36
I read about a tip to jack up the rear weels and count the revolutions of the rear wheels and drive shaft in order to get the ratio, which is a nice one, but very hard to count it two digits secure.
The last input I need to know is the speedometer revolutions per mile. Is this 1000 for the 1958 Chevrolet? Could it be less?
Presuming it is 1000, I calculated the ratio 2.60, that goes with the combination 15/39, a grey 15 teeth drive gear with a brown 39 teeth driven gear.
No combination is possible with my current green 9 teeth drive gear, so I need to replace that also.
My other question is why that blue driven gear of mine got broken. Did my speedometer had too much resistance? Should I lubricate it? I know my odometer has some difficulties to come in a new number in the 2nd and 1st digit, so maybe this can be the problem. Is removing and rebuilding the speedometer out of a 58 easy? The cable moves freely, when removed.
Is my above stated thinking correct? Any input on this mather is welcome.
