Author Topic: irs swap  (Read 2729 times)

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Offline beetlemandan

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irs swap
« on: December 08, 2011, 01:03:40 PM »
so i have a 69 beetle and i want to put a 73 transaxle into it for  better hwy cruising. other than the 3 bolt nose cone difference, is there any other mods involved in the swap?
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Offline Geoff

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Re: irs swap
« Reply #1 on: December 08, 2011, 03:54:52 PM »
If it's already IRS then Just a pressure plate change to a 71 and later as the t/o bearing is different.

Offline Bruce

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Re: irs swap
« Reply #2 on: December 08, 2011, 08:09:23 PM »
so i have a 69 beetle and i want to put a 73 transaxle into it for  better hwy cruising. other than the 3 bolt nose cone difference, is there any other mods involved in the swap?
A 73 Bug gearbox does NOT have a taller hwy gear in it.  Swapping in that gearbox won't help reduce your rpms. 
When VW changed from a 4.12 R&P to the taller 3.88, they also put in a shorter 4th gear to compensate.  The result is taller 1-2-3, with the same overall final drive ratio on 4th gear.

IF you do this swap, you need to be aware of the potential interference between your early 2 bolt nose cone and the cage for the mainshaft ball bearing (top one).  The later nose cone has clearance.  You may have to clear your early nose cone.

Offline Jerome

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Re: irs swap
« Reply #3 on: December 08, 2011, 09:08:49 PM »
so i have a 69 beetle and i want to put a 73 transaxle into it for  better hwy cruising. other than the 3 bolt nose cone difference, is there any other mods involved in the swap?
A 73 Bug gearbox does NOT have a taller hwy gear in it.  Swapping in that gearbox won't help reduce your rpms. 
When VW changed from a 4.12 R&P to the taller 3.88, they also put in a shorter 4th gear to compensate.  The result is taller 1-2-3, with the same overall final drive ratio on 4th gear.

IF you do this swap, you need to be aware of the potential interference between your early 2 bolt nose cone and the cage for the mainshaft ball bearing (top one).  The later nose cone has clearance.  You may have to clear your early nose cone.

I have to say I love all this nerdy info..... Some of these minds are obsessive compulsive hoarders of nearly useless VW info.... I LOVE IT!  :clap:
Sucks to your assmar.

Offline silas

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Re: irs swap
« Reply #4 on: December 08, 2011, 10:34:09 PM »
good times!

Offline beetlemandan

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Re: irs swap
« Reply #5 on: December 09, 2011, 06:42:02 AM »
so i have a 69 beetle and i want to put a 73 transaxle into it for  better hwy cruising. other than the 3 bolt nose cone difference, is there any other mods involved in the swap?
A 73 Bug gearbox does NOT have a taller hwy gear in it.  Swapping in that gearbox won't help reduce your rpms. 
When VW changed from a 4.12 R&P to the taller 3.88, they also put in a shorter 4th gear to compensate.  The result is taller 1-2-3, with the same overall final drive ratio on 4th gear.

IF you do this swap, you need to be aware of the potential interference between your early 2 bolt nose cone and the cage for the mainshaft ball bearing (top one).  The later nose cone has clearance.  You may have to clear your early nose cone.


 :017:  so could i build a frankenstien freeway flyer out of the two? having to do 3800rpm just to hit 110kph is really getting old
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Offline Bruce

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Re: irs swap
« Reply #6 on: December 09, 2011, 10:29:04 PM »
Taller tires.

Offline Jerome

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Re: irs swap
« Reply #7 on: December 10, 2011, 08:15:39 AM »
any good solution costs $$$$$.....

http://www.californiaperformance.com/md5s.htm
Sucks to your assmar.

Offline Geoff

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Re: irs swap
« Reply #8 on: December 10, 2011, 09:14:23 AM »
For a taller 4th you can install a 4th from a 71 bus (with some work) with the 3;88 trans, taller 4th, 195-65-15's and 2275cc  this worked great in my 59 but made it difficult to go on long trips with other VW's as they couldn't keep up.

Offline beetlemandan

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Re: irs swap
« Reply #9 on: December 10, 2011, 04:30:16 PM »
well thanks to jerome, that 2275cc is now closer than ever! maybe i'll make a baja and toss some 33" mudders, that'll make for taller gearing...
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Offline Bruce

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Re: irs swap
« Reply #10 on: December 11, 2011, 12:37:18 PM »
What tires do you have now?

Offline beetlemandan

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Re: irs swap
« Reply #11 on: December 11, 2011, 06:26:28 PM »
205/60 15s
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Offline Bruce

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Re: irs swap
« Reply #12 on: December 11, 2011, 09:32:55 PM »
having to do 3800rpm just to hit 110kph is really getting old
Now we're getting somewhere.
Your tires are the same dia as stock.  That means you have a 4.37 R&P in there now.  If you just switch to a stock 4.12 gearbox, you will be happy.
If you absolutely know you have a 4.12 right now, your tach is way off.

Offline beetlemandan

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Re: irs swap
« Reply #13 on: December 12, 2011, 05:10:17 AM »
i've had 2 vdo tachs in the car and both show the same, so i'm guessing its the r+p. all i know about the tranny is that it came from a 71 and it had a reverse gear, which is better than what was in the car at the time. thanks for the info bruce!
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Offline Bruce

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Re: irs swap
« Reply #14 on: December 12, 2011, 10:43:58 PM »
Here's the way to prove it without removing anything.
Jack the car up on stands. 
E-brake off
2nd gear
Turn the engine to TDC (or some other notable point)
Turn one tire so the valve stem is at 12O'Clock.
Now start turning the engine, counting engine revolutions needed to make the tire go exactly one rev.

8 turns of the engine = 3.88
8½ turns =                    4.12
9 turns =                       4.37
9½ turns =                    4.62

If your rear brakes drag it will mess up this count, so maybe check that both tires go exactly one turn.

Offline beetlemandan

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Re: irs swap
« Reply #15 on: December 13, 2011, 04:59:33 AM »
how the hell do you know this stuff bruce?!?!?
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Offline Bruce

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Re: irs swap
« Reply #16 on: December 14, 2011, 10:41:26 PM »
Start by taking them apart!

 

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