TR2/3/3A Problem with angle drive for overdrive

I am having problems with the angle drives I have installed on my TR3 since I installed the A-Type overdrive. As can be seen in the attached picture, they are twisting off on the "spring" part of the stem that goes into the overdrive speedometer drive pinion and bearing assembly. This is the second one that did that in just a few months. I have a new speedometer cable and I cut out the transmission tunnel cover to allow a fairly straight flow of the speedometer cable from the angle drive to the speedometer. (Note that I did not use the 96 inch cable nor the original hole in the floor.) I have read that a defect in the speedometer can cause the angle drives to fail, but have not seen what problem that actually causes with the angle drive. The angle drives I'm using came from TRF and they have circlips that hold the angle drive gear covers in place. So that makes it easy to open up the angle drive to see what failed. Is it worth the high expense of sending the speedometer for rebuild without knowing that is what is causing the problem? Or could the problem be with the overdrive pinion and bearing assembly? Thanks for any ideas!
Bob

TuffTR250,
This solution might be off base but it is a complaint we have heard for decades and might your problem. The Angle Drive is supposed to be fitted with a spacer (washer) or there is too much preload on the angle drive resulting in failure that can manifest itself as you have shown. There is even a factory TSB on this issue.

Here is a link to the PDF and instructions we supply with a new angle drive. I hope your solution is this simple.

https://www.mossmotors.com/graphics/products/PDF/021-511.pdf

Best,

Shawn

Why not just use the factory configuration (without the angle drive) ?
Yes, twisting off the stub cable is exactly the failure I've seen when the head binds. To check, remove the head and find something suitable to turn the mechanism, then spin it between your fingers. It should spin easily, any stiffness likely indicates the source of the problem.

Thanks Shawn! I have installed the spacer washer on all the angle drives that have failed, so in this case, that is not the problem.

Randall, when I installed the overdrive I considered using the 96 inch speedo cable, but I could not find a route through the original hole in the floor to the front of the car without putting the cable under the frame of the car. I did not want the cable hanging under the frame of the car. Unfortunately I did not ask on the forum how to avoid that situation with the 96 inch speedo cable. I know that the angle drives have been used on Triumph's for a long time so that seemed to be a good option.

I did notice when I disassembled an angle drive from my TR250 that stopped working, but did not completely fail that the gears are not well made and the meshing of the gears is not very good. In my opinion the angle drives as a whole are not of a robust design. I believe that General Motors used the Laycock overdrives, did they use angle drives and were they more robust? If yes, would they fit a Triumph overdrive? Thanks!
Bob

The Type D & J Laycock ODs were used by Volvo, but I'm not sure they used an angle drive.

M.

I have also had this happen and it was a binding speedo that was the cause -- apparently that wiry section of the angle drive is the weak point among the speedo drive parts. I was able to repair the one that did that for me using a short length of old speedo cable (still had a good square tip).

Thanks Geo! How did you repair it? Did you drill a hole in the gear end of the "big" gear and then spot weld the new piece into that hole? And did you have to get your speedometer rebuilt to avoid the problem after you fixed the angle drive? I guess maybe they make the angle drive weak so if the speedo binds it doesn't totally wipe it out. BTW, I put a drill onto the speedometer cable and the speedo seemed to turn ok. How would I tell if the speedo is binding bad enough to break the angle drive? Thanks!
Bob

This is going to sound pretty crude - but I yanked out what remained in the unit after it broke, those wiry bits you see here:



I then cleaned it well and cut the squared end off of an old speedo cable and stuck in there with some JBWeld. The original bit of cable was swaged in there but the JBWeld worked for me.

I did get the speedo head rebuilt as I could tell it was binding. I think the angle drive is designed to break first and 'save' the $15 cable.

I am talking to a company in Texas that makes angle drives for old GM cars with overdrives. Can anyone confirm the thread on the Triumph angle drive end that goes to the speedometer cable, and the corresponding thread on the overdrive "pinion/bearing assembly" thing that the angle drive goes into? I measured them and I believe they are 28 threads per inch and 3/4 outside diameter. Is that correct? or is the thread 26 per inch? Thanks!

Thanks Geo! That is an interesting fix.
Bob

I've never used an angled drive before, but I do note that there are a lot of posts about problems with them. I'm with Randall. If the original drive was straight, why not just use a straight drive and be done with it? Follow the pics in my TR2 recipe thread to see how it routes without running below the frame.

I don't get it either.
Why use an angle drive since one was never intended for a TR3?
I had no problem routing the speedometer cable to avoid interference with the frame or any other component.

My Healey uses an angle drive of the overdrive without any issues.

Hi

So I have now blown up my third angle drive - all of them installed properly with the washer. Speedo was rebuilt in both 2004 and 2014 so doubt that is the problem. Was using 66" speedo cable with it. Definitely going back to the 96" speedo cable and routing it under the chassis in a big loop using zip ties. Very disappointed in the quality of those angle drives.

Bob

Sounds like something was binding. I agree a 3-year-ago rebuilt speedo shouldn't bind but sometimes things happen that shouldn't. Fault could also be the cable.

I used a homemade P clamp fit to the bottom of frame using the body to frame blot in the corner of foot well similar to the factory one that holds the cable in front of the battery box.
No angle drive, no zip ties.
I did have to roll the rear edge of the cutout for cable back for more clearance,probably due to the later 4 syncro trans being slightly longer.
Tom

After inspecting the area near the transmission tunnel, I simply do not see how I can attach a speedo cable to the OD tailshaft w/o angle drive. So, this led me to do a bit more research as to why these angle drives keep failing on me and I think I have an answer. There was a Triumph TSB dated Feb 29, 1967 which talked about failures and the need to insert a washer between the angle drive and where it connects the tailshaft. My feeling is that even one washer is not sufficient. I believe the input shaft on the angle drive is too long. When screwed into the output on the OD tailshaft, it bottoms-out and places an excessive end load and premature failure of the angle drive pinion.

So, I have ordered yet another angle drive and three washers. This time, before installing I will measure the depth of the OD output with a probe and compare it against the input shaft on the angle drive. Then I'll use multiple washers to get the proper clearance and avoid the binding (bottoming-out).

Bob

Tom, what length speedometer cable did you use?

I tend to agree with RJS even though I have not measured the input shaft on the angle drive, but I have noticed how long they are, based on the failure mode this seems to be at least one of the causes of the problem. I also believe the gears in the angle drives are poorly made. If Triumph felt the input shaft was too long way back in 1967, why didn't they and the Big three take action with the vendors to correctly fix the problem rather than apply a "fix". Is it because the "pinion & bearing assembly" (#97 in Moss TR2/3/4 catalog) is different on different cars?

I'm just now thinking that for the A-Type overdrives, it may be that we have to pull the "pinion & bearing assembly" out of the overdrive and carefully measure the "hole" in the pinion&bearing assembly and the input shaft on the angle drive to ensure the "correct" length of the input shaft that needs to protrude into the pinion&bearing assembly so it does not bottom out.
Bob

OK, so I took some measurements. The depth of the hole is ~26mm. And the length of the input shaft on the angle drive is ~19.5mm. So, maybe that is not my issue. Thus, I opened up the angle drive and NOW think I found the problem. I removed the large circlip and removed the large pinion. See photo. I found the tiny weld on in the center of the pinion has failed which allows the shaft to spin freely inside the pinion gear. I'm going to attempt to re-weld that and repair it. I may still insert an extra washer when I attached it to the tranny. Won't know results for several weeks as I have the cylinder head off the car right now.

Bob

RJS, my next to last failure was exactly the same as yours. So I spot welded the top of the larger gear and ground it smooth. The last failure shortly after the previous was that it twisted off inside that larger gear, apparently because after my weld the input shaft could no longer turn freely inside of the gear as it had done for the previous failure. And BTW, for both failures I had one copper washer inside the angle drive. I'm out of usable angle drives now. I may just do what has been suggested and forget the angle drive on my TR3 and go with the 96 inch speedo cable. However, I still have an angle drive on my TR250 and I've had two failures on those. And on the TR250 I don't think there as an alternative to the angle drive.
Bob

I used the TRF listed TR3 W/overdrive cable which is 96"
Tom

RJS said:

After inspecting the area near the transmission tunnel, I simply do not see how I can attach a speedo cable to the OD tailshaft w/o angle drive.

Click to expand...

That would be because you apparently have a TR4A. The original poster Bob said he was working on a TR3. The TR3 has specific provisions for not using an angle drive; 4A does not (and the 4A factory setup was an angle drive).