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IRS trans gearing
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mammbush
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PostPosted: Tue Mar 28, 2023 10:44 am    Post subject: IRS trans gearing Reply with quote

I have a 6/1973 beetle. I’m running 31s out back. I want to replacechange gearing to help with the final drive. Suggestions? 4:57? Who do I contact?
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mcmscott
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PostPosted: Tue Mar 28, 2023 1:21 pm    Post subject: Re: IRS trans gearing Reply with quote

4.57 would be a bus box. You could do a 4.86 if it is available. I think I would just change 3-4 out using a gear calculator to determine ratios.
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PostPosted: Tue Mar 28, 2023 3:28 pm    Post subject: Re: IRS trans gearing Reply with quote

This is a useful calculator for figuring out the ratio you want:

https://spicerparts.com/calculators/transmission-ratio-rpm-calculator
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PostPosted: Tue Mar 28, 2023 3:39 pm    Post subject: Re: IRS trans gearing Reply with quote

A lot depends on how much power the engine has and the intended use of the vehicle.
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PostPosted: Tue Mar 28, 2023 3:40 pm    Post subject: Re: IRS trans gearing Reply with quote

Better yet one from the folks who provide and manufacture VW transaxle components:

https://weddleindustries.com/gear-calculator
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PostPosted: Tue Mar 28, 2023 3:58 pm    Post subject: Re: IRS trans gearing Reply with quote

If you were to stay with your present 3.87 ring and pinion then a 1.02 4th gear would put you at 70 mph at 3000 rpm. Do you have enough engine to handle that?

A 4.12 ring and pinion with a 1.02 4th would run 66 mph at 3000 rpm.

I must ask... why the monster tires? Off road car?
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PostPosted: Tue Mar 28, 2023 5:24 pm    Post subject: Re: IRS trans gearing Reply with quote

1835, pertronix vacuum advance, flame thrower coil, C45 cam, 32/36 carb 40/35.5 valves. Not sure the power. Just Boggs in 4th if there’s any resistance. Bridges, heavy head wind etc. It’s a city car.
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PostPosted: Tue Mar 28, 2023 6:02 pm    Post subject: Re: IRS trans gearing Reply with quote

Just changing tires to something in the 25" to 26" range would fix it and be far cheaper than a transaxle gearing change.

Just an idea...
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PostPosted: Tue Mar 28, 2023 6:12 pm    Post subject: Re: IRS trans gearing Reply with quote

No I don’t want smaller tires. Looks too good with the big tires. I’ll spend the money to do it the way I want. All good.
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PostPosted: Tue Mar 28, 2023 6:13 pm    Post subject: Re: IRS trans gearing Reply with quote

Solution #1 - Aftermarket 4.86 R&P with stock gears.
Solution #2 - Your stock 3.88 R&P with 1.48 - 3rd & 1.13 - 4th gears.
Solution #3 - My choice would be 4.12 R&P with 1.48 - 3rd & 1.04 - 4th gear.
The 4.12 R&P would be a little easier driving in heavy city traffic.


You didn't ask but you would get a noticeable increase in power if you installed dual 40 IDF's on your engine.
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PostPosted: Tue Mar 28, 2023 7:05 pm    Post subject: Re: IRS trans gearing Reply with quote

Runnong 31's on my rail. 4.375, stock ssc 1st and 2nd. 1.46 3rd and 0.93 4th. If I had it to do over, I would have went with a steeper 4th gear. Gps says about 3200 rpm at 65 mph.
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PostPosted: Tue Mar 28, 2023 7:14 pm    Post subject: Re: IRS trans gearing Reply with quote

mammbush wrote:
No I don’t want smaller tires. Looks too good with the big tires. I’ll spend the money to do it the way I want. All good.


I get this. When I ran 31s with 4.12, I treated it like I was driving a 3spd with over drive.
But, would like it regeared.

Bwajaja has a 1680cc. With a w110 and dual Kads.
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PostPosted: Tue Mar 28, 2023 7:44 pm    Post subject: Re: IRS trans gearing Reply with quote

The higher the ring and pinion ratio get, the smaller the gear teeth are, the less able to tolerate any abuse they'll be. I would keep you strong 3.88 and change your 3rd and 4th gears to one of the combos listed.
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PostPosted: Wed Mar 29, 2023 6:14 am    Post subject: Re: IRS trans gearing Reply with quote

Aren’t there some Thing irs transaxles out there with 4.37? Just for a cheap solution.
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PostPosted: Wed Mar 29, 2023 7:50 am    Post subject: Re: IRS trans gearing Reply with quote

NJ John wrote:
Aren’t there some Thing irs transaxles out there with 4.37? Just for a cheap solution.


No.

Things with IRS were 4.12. Earlier Type 181 sold outside the USA were swingaxle.

slalombuggy wrote:
The higher the ring and pinion ratio get, the smaller the gear teeth are, the less able to tolerate any abuse they'll be. I would keep you strong 3.88 and change your 3rd and 4th gears to one of the combos listed.


Yes it's true 3.88 are stronger than a 4.12, but that does not mean the 4.12 are weak. I've run hundreds of full 1/4 mile passes in my heavy street Ghia with a 4.12. He'll be fine with a 4.12 in his 90 HP street car. The spider gears are the weak link. With the 3.88 & 31" tires, he'll be lugging the engine in 1st & 2nd gear in heavy street driving with his 90 HP 1835 engine. The 4.12 will be a lot more enjoyable driving around town 20-30 MPH.
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PostPosted: Wed Mar 29, 2023 8:01 am    Post subject: Re: IRS trans gearing Reply with quote

vwracerdave wrote:
Earlier Type 181 sold outside the USA were swingaxle

With reduction boxes if I remember correctly.
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PostPosted: Wed Mar 29, 2023 8:34 am    Post subject: Re: IRS trans gearing Reply with quote

oprn wrote:
Just changing tires to something in the 25" to 26" range would fix it and be far cheaper than a transaxle gearing change.

Just an idea...


mammbush wrote:
No I don’t want smaller tires. Looks too good with the big tires. I’ll spend the money to do it the way I want. All good.


Once again styling triumphs over engineering. Rolling Eyes


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We'll re- visit the "How many 175 hp burnouts can a stock '67 swingaxle endure?" story.

In this case our transaxle took exactly one burnout to become useless albeit expensive junk. The detail I tend to omit is we tried to keep the tire sizes reasonable with 29/9.50-15s on the back. Truth of the matter is VWs were designed to work properly with narrow tires 26" tall or less. Too much rubber meeting the road causes more wear and tear on the drivetrain, the transaxle in particular. Not to mention the situation where only one gear out of four is drivable some of the time.

We were ready to do the "money is no object." thing until we were quoted $5000 (plus core charge, plus shipping both ways) for a transaxle we can't break.

.
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oprn
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PostPosted: Wed Mar 29, 2023 9:01 am    Post subject: Re: IRS trans gearing Reply with quote

I find that in most cases my right foot is directly connected to my wallet. The harder I use the right foot the emptier my wallet becomes! Wink

To fix that I like to insert my brain in the loop between the right foot and the wallet. Seems to have helped in later years... didn't work when I was younger though! Laughing My brain was the weak link back then. Rolling Eyes
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PostPosted: Thu Mar 30, 2023 8:48 am    Post subject: Re: IRS trans gearing Reply with quote

Thanks for the good advice and recommendations. The opinions are, well, like assholes, everyone has one and some of them stink.
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