Ring gear bolt "lockplates"

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Vic Skirmants
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Ring gear bolt "lockplates"

#1 Post by Vic Skirmants » Thu Jun 06, 2019 8:22 am

For years, Porsche tried various methods to keep the ring gear bolts from loosening and breaking. They finally settled on adding a groove in the bolt head and using a "lockplate" in the groove. Years ago I determined that the "lockplate" really couldn't keep the bolts from loosening, but it would keep the broken head of the bolt from dropping out and doing further damage. I have had one example of this on the shelf for years. I just dismantled a transmission with SIX broken bolts, and three perfectly intact "lockplates". Pictures below.
I do not use the lockplates in the race cars; I think they promote oil foaming. Just Red Loctite and 65 ft-lbs torque.
I do use the lockplates in customers' street transmissions. Wouldn't want some future mechanic thinking I forgot them. I do tap them down to be more "aerodynamic".
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C J Murray
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Re: Ring gear bolt "lockplates"

#2 Post by C J Murray » Thu Jun 06, 2019 8:45 am

Take it to your local Certified Porsche Classic Dealer and have them repair it under warranty. The only hitch will be if they download the data from the CPU and find out that you have been doing burnouts. I have met one modern Porsche owner that had an engine warranty denied because they found evidence of track day usage in his CPU.

In about 1972 my 6 ring gear bolts failed in my 62 Super coupe. I replaced them with the trans in the car. Vic is the master but the changes Porsche made from 6 to 12 bolts and the improved bolt specs show that they were chasing a reoccurring problem.
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Al Zim
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Re: Ring gear bolt "lockplates"

#3 Post by Al Zim » Thu Jun 06, 2019 10:57 am

I would think that more foaming of the gear lube would be because of the oil change in the gear oil when the sperm whale was considered an endangered species, that was a long time ago. That has been overcome by additives to the oil. The real cause of the foaming to hypothesize will be because the ring gear acts like a paddle wheel steam boat throwing the oil around the gearbox. My theory for the ring gear bolts breaking has to deal with the manufacturing tolerances on the ring gear and the differential housing. A situation that I do not believe cannot be corrected using the VW and its derivatives of cast iron housing. al zim 2019/06/06
 

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Jacques Lefriant
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Re: Ring gear bolt "lockplates"

#4 Post by Jacques Lefriant » Thu Jun 06, 2019 11:45 am

Hi Al
Interesting that Porsche I believe continued the use of the grooved bolts and lock plates until the 1987 G50 gear box long after VW abandoned the lock plates/wires.
j
 

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Re: Ring gear bolt "lockplates"

#5 Post by Mike Wilson » Thu Jun 06, 2019 12:26 pm

I find this an interesting topic. From the pictures, these bolts don't break off at the heads. Porsche and VW obviously knew of a problem but rather than addressing the breakage, wired or lock plated the bolt heads so when the bolts did break, it was a larger rather than smaller piece of metal in the case.

Wouldn't harder bolts solve the problem of breakage with lock plates or safety wire as an additional measure?

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Vic Skirmants
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Re: Ring gear bolt "lockplates"

#6 Post by Vic Skirmants » Thu Jun 06, 2019 12:44 pm

"Wouldn't harder bolts solve the problem of breakage with lock plates or safety wire as an additional measure? "
Harder bolts would be more prone to breakage.
I do have one other "lockplate" that contains a bolt head perfectly broken off at the shank.

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Re: Ring gear bolt "lockplates"

#7 Post by C J Murray » Thu Jun 06, 2019 12:53 pm

I agree Mike. I don't think they accepted that they would break and needed to be contained but I do think that the design of the bolt and the seating of the bolt was not good. The bolts breaking on the threads seems to suggest that the threaded section is too long vs the smooth section. Porsche did upgrade to a stronger bolt, right? I was told when I bought the parts back in 72 that Porsche had a rash of bad bolts around 1962.
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Re: Ring gear bolt "lockplates"

#8 Post by C J Murray » Thu Jun 06, 2019 12:59 pm

Porsche must have theorized that the bolts loosened and backed out and then broke at the thread. I think that is wrong. A tight fit of the smooth shank of the bolt pretruding into the ring gear should be strong. Did they do that Vic?
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Re: Ring gear bolt "lockplates"

#9 Post by Vic Skirmants » Thu Jun 06, 2019 1:05 pm

C J Murray wrote:
Thu Jun 06, 2019 12:59 pm
Porsche must have theorized that the bolts loosened and backed out and then broke at the thread. I think that is wrong. A tight fit of the smooth shank of the bolt pretruding into the ring gear should be strong. Did they do that Vic?
There's really no room in the ring gear for an unthreaded shank. The threads start immediately at the surface.

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Re: Ring gear bolt "lockplates"

#10 Post by Mike Wilson » Thu Jun 06, 2019 1:17 pm

Maybe "harder" was an incorrect description on my part. I meant stronger but the threaded part of any bolt is weaker than non-threaded, correct? The bolts in the pictures look like they just snapped. Was this due to the stress of the rotational force exerted upon them causing fatigue and failure?

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Re: Ring gear bolt "lockplates"

#11 Post by C J Murray » Thu Jun 06, 2019 1:48 pm

Vic Skirmants wrote:
Thu Jun 06, 2019 1:05 pm
C J Murray wrote:
Thu Jun 06, 2019 12:59 pm
Porsche must have theorized that the bolts loosened and backed out and then broke at the thread. I think that is wrong. A tight fit of the smooth shank of the bolt pretruding into the ring gear should be strong. Did they do that Vic?
There's really no room in the ring gear for an unthreaded shank. The threads start immediately at the surface.
Perhaps a thicker ring gear with room for a tight shank and a machined thinner VW carrier to match would have been stronger?

I now have 25000 miles on a Cadrobi(spelling?) conversion with 160hp 2133cc engine. It hasn't blown up yet and seems like a good solution. VW must have been having diff problems also since they updated their diff..
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Re: Ring gear bolt "lockplates"

#12 Post by Jeffrey Leeds » Thu Jun 06, 2019 4:39 pm

Are these 10.9 strength?
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Re: Ring gear bolt "lockplates"

#13 Post by Vic Skirmants » Fri Jun 07, 2019 7:55 am

Jeffrey Leeds wrote:
Thu Jun 06, 2019 4:39 pm
Are these 10.9 strength?
They are 12 or 12.9, however you want to designate them.

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Re: Ring gear bolt "lockplates"

#14 Post by Jeffrey Leeds » Fri Jun 07, 2019 5:38 pm

Thanks, Vic.
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