One Time Opportunity: Upgraded (“bulletproof”) transmission coupler order

[Nicholas R]

No, I don't think anything was e-mailed out yet. Ed told me on July 6 that he had placed the order for 20 couplers and that the leadtime is about a month so it may be until early August until you hear from him.

Thats correct. You will hear from Eddie for order information.

Eddie and I are kind of teaming up on this. I made a drawing for a coupler a while back when I pulled mine out of my transmission to swap for my one piece shaft. Always thought I may have them made but didn't know if there was interest, and I've been very invested in producing my 1 piece shaft (which is still happening). My company is also sending me out of the country for about 5 months so I figured it would be some time after that. However, since the need is here, I'm having the couplers made and shipped to Eddie since I'll be out of the country, and Eddie is handling all of the orders, and installing them in the cars at his shop that require them.

I spoke to the manufacturer yesterday and they said that they had acquired the material and were in the process of machining them now. They have a transmission shaft that I sent them so that they can test fit the splines before they are sent. They said that they are still shooting for early August for shipping (to Eddie) barring any major issues.

I have always hated the idea of taking money ahead/pre-orders so I will not accept money until the parts are complete and ready to ship. Sometimes there are problems, delays, etc. in the process, and though often unavoidable, they are a pain; but to me that pain is amplified exponentially when customers have already put money on the line.

For those curious, I performed some Finite Element Analysis (FEA) on the part for steady torsional loading on the fully splined coupler with the 4340 material at the heat treatment level I have chosen, and the principle and shear stresses are below the yield strength of the material up to 500ft/lbs of torque. [PLEASE NOTE I AM NOT RECOMMENDING PUTTING 500FTLBS THROUGH YOUR TRANSMISSION] That being said, steady torsional loading isn't usually what breaks things, it is typically shock/impact loading (aka: your burnouts, potholes, quick changes in traction, railroad tracks, etc.) and fatigue. Still I am confident that in this specific part should no longer be the weak link in the input shaft line.

Coupler FEA Simplified.jpg

The weak link will much more likely move to one of the low cross section areas of the shaft where the shaft was necked down so that splines could be rolled, the worst of which being where it is down to ~17mm-17.5mm diameter coming out of the coupler. The other known issue is at the overhung 5th gear as under heavy load the 2 shafts can begin to spread apart causing the teeth to improperly engage, or an excessive alternating stress in the shaft causing fractures.

Original Shaft Cross Section Dimensions.jpg

Here is a stripped 5th gear from a transmission of mine.
Failed 5th.jpg

I have performed the similar FEA on the original shaft and it doesn't fair anywhere near as well at that level of torque. Not knowing the exact material for the original shafts makes it a little difficult (it's clear that its nothing special, likely just general alloy steel), but I can make some assumptions about it based on the case hardening and the tested hardness. The stresses calculated are far beyond the tensile strength of the material for steady load (not even considering fatigue). I would still recommend that people drive responsibly as they approach the 300hp/300ftlb area.

Original Shaft FEA Simplified.jpg

Also bear in mind that this part is useful for not just higher powered cars. I have talked to multiple owners and vendors about transmissions that have failed on stock cars at the coupler. A transmission in my possession failed at the coupler due to fretting corrosion (which occurs at non-lubricated connections where vibration/movement is present) and broke the main shaft at the roll pin. This happens in the coupler because the main shaft is case hardened, where the stock coupler is significantly softer (it is not a hardened part), and the connection is completely dry as its outside the lip seal.

Here is a photo one of the transmissions I have where the coupler splines corroded away due to fretting, eventually putting all of the load on the roll pin, shearing the end of the main shaft (the end of the shaft is still inside the coupler). This is a shame because the result was that the main gear shaft was sheared, which is the most expensive shaft to replace. Some say that the coupler is a "mechaical fuse" but to me, if it's failure leads to the most critical and expensive shaft becoming damaged and unusable, it's not serving that purpose. That roll pin is only there to control axial positioning and not meant to carry torsional load; but when the splines fail, thats where the load goes.

Failed Coupler.jpg

Broken Shaft.jpg

Anyway, here's hoping the machining process continues smoothly!

[Josh]

Great post Nick! I really appreciate it.

I will comment that driving responsible with an excess of 300hp/300ftlbs torque is not an easy task! Its just too fun!

[Nicholas R]

Great post Nick! I really appreciate it.

I will comment that driving responsible with an excess of 300hp/300ftlbs torque is not an easy task! Its just too fun!

Absolutely!

And I know what you mean! I had the coupler in my car for almost 3 years with the LS1 mostly stock. There were definitely times where I pushed it but I still always had the transmission in the back of my mind. I was also careful to let off the throttle around potholes, uneven roads, train tracks, etc. It was when the Car Fix episode happened and the Lingenfelter heads and cam went in that I REALLY started getting nervous; not necessarily for the coupler, but for the main shaft components. That was what the single piece input project was born out of.

The other weak point I'll mention in the transmission is the 2 spider gear differential. Later UN1s (after the 369) came with 4 spider gears, which distributed the load in the differential a lot better. I've talked to several others about instances of those components failing, and in several cases it was stock DeLoreans (some high powered too). I know for myself, the Quaife limited slip diff will certainly be my next drivetrain upgrade. I think its smart for both power distribution, and to limit the loss of traction under heavy load. So far Eddie is the only person I know to install on in a DeLorean as he put one into the 2JZ Supra Engine car.

[Nicholas R]

Small update on these.

The machining is going well. The test fits have been successful (see pictures).
Coupler 1.jpgCoupler 2.JPG

Each one is inspected and test fit before being deemed "good".

They are hoping to ship them out to Ed next week. I was hoping to be around when they would finish but unfortunately my international trip starts this Friday so I will just miss them. Still, as long as my VPN is up and running, I should be able to hit up DMCTalk from time to time. Meanwhile my car will be covered, battery tendered, and fuel stabilized, in my garage awaiting my return.

[Texas Twister]

Small update on these.

The machining is going well. The test fits have been successful (see pictures).
Coupler 1.jpgCoupler 2.JPG

Each one is inspected and test fit before being deemed "good".

They are hoping to ship them out to Ed next week. I was hoping to be around when they would finish but unfortunately my international trip starts this Friday so I will just miss them. Still, as long as my VPN is up and running, I should be able to hit up DMCTalk from time to time. Meanwhile my car will be covered, battery tendered, and fuel stabilized, in my garage awaiting my return.

I was trying to order two but never got any response to a personal message I sent. Is there any way to still get two couplers?

[SEO Motorsports]

At this time DPI ordered ten, I am using one and we will be going down the list after that. Payment will be PayPaled to Nick and I will ship them out when he gives me the OK and shipping address.

-Ed

[Nicholas R]

Alright, I need some help from the community. The machine shop that is making the couplers has made an error that is going to affect the timeline of this project.
I was told yesterday that the couplers were being finished up, and received several photos of the finished parts. When I examined one closely however, I noticed a critical error in the alignment of the roll pin hole and the splines.
These photos should show what I mean.

Here is the shaft. Notice that there is a spline recess that goes through the center of the hole.

Shaft Alignment.jpg

To line up correctly, the coupler needs to have a spline peak going through the center of the hole, to mate with the recess in the shaft. Unfortunately this is not the case. If you look at this photo, you’ll notice there is also a spline recess going through the center of the hole. This means that the hole is misaligned, 1/2 of a spline. This misalignment is too great to allow the roll pin to be installed (especially since each coupler will come with a spiral roll pin which is less forgiving than a standard roll pin). I believe there may have been a couple that were made correctly, but my understanding is that after I bought off on the first one, at some point a different machinist took over, and cut the splines backward.
Photo

IMG_5132 Adjusted.jpg

So there are 2 options.

A. Scrap the parts, make them again. Obviously the machine shop doesn’t want to have to do this but to me they did screw up. The consequences are that the timeline will reset. It may take a little less time since they have the process worked out, but they still have to procure the proper material, let me buy off on the paperwork, send the material for heat treatment and testing, and perform all of the machining. Probably looking at another month or so, maybe a little less.

B. Work with the parts. The misaligned hole would be abandoned, and another correctly aligned hole would be drilled at the other end of the coupler, roughly 90 degrees offset from the current hole. This option would allow the couplers to be completed hopefully next week. The resulting couplers would look like this. Truthfully, from a strength perspective, I think this will have little effect on their performance. However, I also know that there is value in having the part made the way it is supposed to be. The resulting part would look like this:
Extra Hole.jpg

I’m still trying to talk to them about the cost implications of both options and whether there can be a cost reduction for option B; I would hope there would be some.

What I need is answers and opinions from the folks that want them. What do you prefer?

I am very sorry about this delay. I wish I could have caught this sooner but short of watching over their shoulder as they were machined, I'm not sure theres much that could have been done. Still I take responsibility for it. Issues like this are why I wont take money up front.

Let me know your thoughts and thanks for the support,

Nick

[refugeefromcalif]

Hello Nick.
While I didn't pre-order one of these couplers, I do work in a machine shop that cuts splines, (Internal and External) up to 16".
If the shop was supposed to preserve the orientation of the hole, (Based on a blueprint), to the spline, They ARE at fault.
If a different machinist took over the job, He wasn't informed, (or too Lazy to read the blueplint), on the Correct orientation he was Supposed to maintain.

We sometimes deal with shafts for the mining industry(s) that have splines on each end that have to be within .005, (along center line), of each other, and do a Lot of them.
When holes have to be within the same tolerance to splines, we make fixtures or jigs, to accomplish that.

My .02

George

[Nicholas R]

Hello Nick.
While I didn't pre-order one of these couplers, I do work in a machine shop that cuts splines, (Internal and External) up to 16".
If the shop was supposed to preserve the orientation of the hole, (Based on a blueprint), to the spline, They ARE at fault.
If a different machinist took over the job, He wasn't informed, (or too Lazy to read the blueplint), on the Correct orientation he was Supposed to maintain.

We sometimes deal with shafts for the mining industry(s) that have splines on each end that have to be within .005, (along center line), of each other, and do a Lot of them.
When holes have to be within the same tolerance to splines, we make fixtures or jigs, to accomplish that.

My .02

George

Thanks George; it was clearly indicated on the drawing. Both a section view, a detail view, and a field note indicating the that the spline peak align with the center of the hole. Honestly not sure what happened but whats done is done. I like these guys as the have done very good work for me before. They made my full transmission shaft which is FAR more complicated than this part. Guess everyone has an off day...

[Mario]

If it was specified correctly in the part drawing and you had signed off on the initial (correct) parts, then the bad ones are completely their fault. They should be making new ones for free or a very reduced price.

I say get new ones. If they'll let you keep the bad ones, they could perhaps be re-drilled and sold at a lower cost. Doubt they'll give them to you, though.

Disclaimer: I won't be needing one for many more months anyway, so I have no issues with waiting longer. But I think it's better to have them made right.