Propshaft "rubber Donut" removal

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badlyworntoy

Propshaft "rubber Donut" removal

Post by badlyworntoy »

I think this will interest a few people :)

After reading and contributing to several discussions in various threads lately about failure of the rubber (as we all call it) "Donut"or to use its correct term "drive coupling" I learned how just a little amount of miss alignment can cause catastrophic failure to these couplings and lead to some serious damage to the underside of our cars. With this I decided to see what options the technology of 2012 had to offer. After consulting with my preferred Prop shaft manufacturer Bailey Morris in St Neots Cambridgeshire we came up with this :-

Its the standard Lada 2 piece prop shaft which has been shortened 90mm for the Fiat Twin Cam conversion......par the course... but the interesting points to note are its been fitted with what’s called a Slappasy sliding universal joint which has a flat steel flange in place of the donut.this then bolts directly to the output Yoke on the Fiat 131 gearbox via 3 x M12x50mm bolts, the yoke its self has had minimal modification to the three ends to give it a machine fit inside the drive flange. The yoke is still attached by its retaining nut to the gearbox but the final 30mm of ouput shaft on the gearbox has been cut off due to clearance issues. The universal joint will happily run with up to 28 degrees of miss alignment on all plains with no issues and can work at up to 50 degrees MA but speeds and load are restricted. You'll note it maintains its sliding design for Live axle application.

Secondly the rear section of the prop shaft is made from what’s called Resilent tube his is to do the job of the Rubber on the old drive coupling and remove some torsional stress from sudden acceleration. It’s a tube inside a tube bonded together with hard rubber.

I’m hoping it won’t break me or my car and I won’t be able to break it!!

Any thoughts People?

Ian
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Urbancamo
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Re: Propshaft "rubber Donut" removal

Post by Urbancamo »

Ian

I don't see a reson why this wouldn't work. There are many cars in the world which have three U-joints in propshaft. With similar design than yours. Only one old example to mention, Volvo 140-series had exactly the same propshaft desing than yours. Three U-joints, one placed directly behind the output yoke.

As long as U-joints are phased correctly and propshaft balanced, there should not be any issues.
Test drive will tell you how you succeeded.

Good thing is that flexible part in the rear. If the whole propshaft would be completely solid, it would be very harsh to gearbox output shaft and other parts in the drive line. Not a good thing.

That donut isn't the best solution there. As long as pieces are straight, it will last long and hold up lots of torque (200 Nm+ isn't any issue). But misalignments can cause it to explode with terrible consequences as you've seen an heard. And I have experienced that twice...since lining the parts again, no more explosions has been occurred.
Rally guys usually use special thick sheet metal flange bolted directly to that donut. It will hold the pieces together and keep car running even the donut has been disintegrated. But that's a whole different story.

More comments are welcome for this interesting topic!

T
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WhizzMan
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Re: Propshaft "rubber Donut" removal

Post by WhizzMan »

Even though the U-joint will happily transfer torque at 28 degrees, it will not do so linearly. You don't see a lot of u-joints in front wheel drive cars; usually those use CV joints to deal with the more "extreme" angles you get with a driven wheel being used to steer the car. If you're building a setup that requires constant dis-alignment that is more than a few degrees, a CV joint may be smarter to use.

The tube-in-a-tube that is vulcanized together sounds like a proper alternative to dampen the drive train and a lot safer than using donuts.
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Urbancamo
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Re: Propshaft "rubber Donut" removal

Post by Urbancamo »

Of course that front U-joint will never see huge angles as that front part is bolted between gearbox and front support bearing. That's why the rubber donut works if parts are lined correctly.

One thing to remember is that U-joints will require some slight angle to operate. If parts are completely straight the needle bearings wont roll at all and the lifespan of U-joint is greatly reduced.
There is always some angle in two rear U-joints when you drive.
Common recommendation for U-joints is not go under 0.5 degrees.

One important thing to notice is that pinion and transmission output shaft angles should be the same. As I'm driven over 30 Ladas, I would say there's some misalingments in almost every single one.
Ladas are the only RWD cars that have very odd driveline based judders, vibrations and noises even the things seem to be in good condition. Propshafts aren't always even balanced properly from factory! Same thing applies to crankshaft balancing, but that's an another story.

So when you do these thing properly, results are usually satisfying.

T
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turbofiat
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Re: Propshaft "rubber Donut" removal

Post by turbofiat »

Very interesting. Where can these be purchased?

I've always felt this was the weakest link in a 124's drivetrain.

I've had one of these bust on me on my 124 Spider. Luckily I was having exhaust work done on the car and the car was up on a rack and I was showing the guy what I wanted done and noticed a big chunk missing. I did not even feel any vibrations. Who knows how long I had been driving around on that thing. I managed to get the car home without incident and replace it before it gave way and damaged the transmission.

This coupling had been on the car for just 4 or 5 years. The original coupling was 17 or 18 years old and showed cosmetic cracking and I replaced it just for the inappropriate of it. I was concerned that 150 BHP might be pushing the limit or new rubber components for Fiats are just junk.

I was looking into having some of these replicated out of urethane by a company in Texas. Problem was he had to make a batch of 100 at a time and was not sure if I could recoupe my investment by selling them on an internet auction site. A friend did manage to make some money by having a batch of Lancia Beta/Monte Carlo gearchange bushings which were out of production made out of some sort of material used in human joint/hip replacements.

Regarding the 124 driveshaft setup:

I've got a 1968 Ford Fairlane. Typical American Tank, 5 liter V8 w C4 automatic. One of the U-joints failed and I had to pull the driveshaft. It took me longer to raise the car, support it on stands than it did to pull the driveshaft. Four bolts from the differential, slide the splined yoke out of the transmission and it was off the car.

On this car the driveshaft consists of 2 U-joints and a splined end. That's it.

Now I ask why a 124 Spider has 2 U-joints, a carrier bearing, and a flex coupling? Why would all of these components be required for such a short driveshaft? Why did Fiat think all this poor was nessessary?

Even full size Chevrolet pickup trucks do not use a carrier bearing on their short beds. Only their long bed (8 foot) models use carrier bearings. And no flex couplings. And I know of no RWD American cars that use these and they manage to work just fine.

How did Ford manage to get away with a longer driveshaft with only two U-joints and not having any vibration issues?
124 Spider, Yugo,131
WhizzMan
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Re: Propshaft "rubber Donut" removal

Post by WhizzMan »

The higher the RPM, the more balance you need. Also, a V8 engine will not pulse as much as a 4 in line engine. And "no shudder" can be relative, of course.
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