5 Speed gearbox flaw repair

[DMC-81]

Happy to help Dana! I really hope this is the end of this saga.
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As it turned out, the sound was coming from one of my brake pads.
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Just something to consider. Either way, I hope the tapping is soon to disappear!

Thanks Nick! Me too! I'll check them out.

How many miles is there on the gearbox? The bearings don't look scored so much as heavy wear which is normal. If foreign objects got into the bearings they would look MUCH worse. The wear on the differential races can be explained by an improper adjustment more than anything else.

Thanks David. There are 27K miles on it. You probably can't see it from the picture but running your fingernail in the race shows that it is actually scored. The thrust bearing as well, although less so. I wouldn't expect heavy wear at 27K, and because both carrier and thrust bearings were scored, it led me to the debris theory, even though it wasn't run long under those conditions. I was pretty particular about the adjustment last time (in post 73), but who knows.

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New bearings:

I had a nearby Mercedes/Porsche repair shop press the new races on the differential (and the 1 / 2 slider hub). There was one shim on the opposite side of the bolt side that's pictured that I needed to ensure was put back:


With the new bearings in place, it was time to set the pre-load. The specification for new bearings is 3 to 7 pounds of force measured on a force gauge. I set mine at the lower end... 3 pounds :


I used the correct tool borrowed from Nick to adjust the pre-load:


Set and locked (I used a new o-ring):


Thrust Bearing:
I installed a new SNR thrust bearing ( FC 10893 ) on the secondary shaft. This doesn't have to be pressed on. It included a new spacer that goes between the races. The old one is on the table and the new one is installed:


Breather:
In this round, I finally found a new gearbox Breather (103047) at DeLoreanGo. For a flexible plastic piece, this looked pristine and pliable. Mine was cracked and mostly missing. Trial fitted:

Installed:

[Rich_NYS]

Hate that you had an issue, but I love looking at your projects & pics!

Fingers crossed for trouble-free miles, brah!

[DMC-81]

Hate that you had an issue, but I love looking at your projects & pics!

Fingers crossed for trouble-free miles, brah!

Thanks Rich!

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Assembly: (selected steps...more details are in the Manual Transmission Repair & Restoration " album on my profile)

I meticulously cleaned the case halves after the races were installed, including removing the bearing retainer and anaerobic sealant residue and cleaning/ chasing the threads for both end covers:


I trial fitted the gears before bearing retainer is applied and re-assembled. Everything looked great and was clean and tight:


After assembling the case halves and installing the 2 locknuts with red Loctite , it was time to put the covers on. I used new NOS paper gaskets from P.J. Grady. I found that these ones don't shrink/distort when the Indian Head gasket shellac that I used is applied.


As before, I used blue Loctite on the M10 bolts for the clutch housing and made sure the threads were cleaned to get an accurate torque reading:


Bearings replaced and the transmission is ready to go back in the car...again!:


I refreshed the grease/anti-seize mix to the input shaft/ throw bearing area:


Mated to the engine and installed. I temporarily used four M10 x 80mm bolts as Dennis suggested in post 19 to help align things which was VERY helpful:


Here is a view of my transmission tag. It was only serial number 000086 after DMC switched to the 369-08 type of UN-1 which, I suppose explains why I had the rare nut backing off flaw.... Mon Dieu!! Also, "boîte pont" or literally "box bridge", is French for gearbox/transaxle:


On to linkage...

[David T]

Looking good! I don't have a whiz-bang digital scale, I use an old spring scale, but whatever works. If you did feel something on the bearing races you are correct in trashing them, it wasn't visible in the picture. Unusual for them to be trashed at 27K miles so something out-of-the-ordinary went wrong. Was the box ever run dry? Did anyone every have to add a lot of gear oil because of a leak? When you drained the box was there anything in the oil? Did you find any fragments when you disassembled and cleaned the parts?

[DMC-81]

Looking good! I don't have a whiz-bang digital scale, I use an old spring scale, but whatever works. If you did feel something on the bearing races you are correct in trashing them, it wasn't visible in the picture. Unusual for them to be trashed at 27K miles so something out-of-the-ordinary went wrong. Was the box ever run dry? Did anyone every have to add a lot of gear oil because of a leak? When you drained the box was there anything in the oil? Did you find any fragments when you disassembled and cleaned the parts?

Thanks! I doubt the box was run dry. Before my ownership, it was well cared for by the original owner. But, when the event happened, and I drained the oil, it had some small metal flakes in it. When I disassembled it the first time, it had some pieces of the broken spring caught up in the gears, and stuck to the magnet (see post 44). So, that's why I'm thinking about the debris cause. Since then, the oil has been changed 3 times, so the box is well flushed.

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Linkage

Rob Grady felt that my 2nd gear rattling noise was likely in the Bellcrank assembly. He said that he's seen more than a few make that noise as the original pivot bolt gets loose as described in this thread:
http://dmctalk.org/showthread.php?13...vot+bolt+depth

Indeed, there is also a Service Bulletin on it, ST-19-10/81 Gearshift Action

This made total sense to me. I remembered that my rattling noise only happened when I was accelerating lightly, and I heard it in multiple gears. I supposed a hard acceleration would tighten up the linkage and therefore it would not make the noise. Plus, if the pivot bolt /Bellcrank was the source of the noise, it would be magnified/radiated throughout the frame based on where it was. That would explain why it seemed that the transmission was self-destructing below me.

I looked at my Bellcrank and sure enough, it was loose. There was also excessive play laterally between it and the pivot bolt. There is a brass bushing in it that may be slightly worn in addition to the pivot bolt. Noise problems aside, I didn't want to get stuck with a sheared or missing pivot bolt.

So, to address the issue, I chose to replace the Bellcrank assembly (100549), and get the improved grade 12.9 Shift Pivot Bolt & Hardware ( 105844GA ) from PJ Grady that was discussed in the above thread. Here are the new parts:

(Note: the pivot bolt washers are out of sequence in this picture)

Here is the new Bellcrank and improved pivot bolt installed with a 50/50 mix of grease and antisieze between the bolt and the crank. I applied red Loctite to the jam nut. I learned from Rob Grady that my strip of missing epoxy paint was intentional. The factory workers put on a strip of tape before painting the frame and removed it after the paint was done to avoid extra material that would interfere with the Bellcrank operation. The rust protection applied to the strip was grease. So after cleaning off the old grease, I liberally applied my 50/50 mixture to the strip as well. Now the Bellcrank is tight but free moving.


I also removed the gear change assembly and front gear change tube to clean, lube, and install the DMC bushing kit:

I also cleaned the mounting area:


Finishing up....

I finished re-installing the rest of the shift linkage with all new bushings, and I had to do a cross-gate cable adjustment again:


I added a DMC M/T Noise Isolator (108903) as this was a running change after my early car was produced:


I also replaced my tired and torn Shift Boot with DMC's improved version ( 100688 ) with the metal bracket. I noticed that it snapped on tightly..nice! I finally aligned and tightened my OEM shift ball:


The gear change action seems tight and smooth! Ready to test drive...

[dn010]

The bushing kit is one of the best things I did to my car, it removed so much slop/play in the shift linkage, it was a night/day difference when I did it.

Looking very good, hopefully you'll have a very uneventful future and can enjoy driving instead of repairing!

[DMC-81]

The bushing kit is one of the best things I did to my car, it removed so much slop/play in the shift linkage, it was a night/day difference when I did it.

Looking very good, hopefully you'll have a very uneventful future and can enjoy driving instead of repairing!

Thanks Dan!

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Well, I drove the car over a few days and the results are excellent. The car shifts as smooth as butter with an extra tightness in the linkage and there is no noise at all at any speed or acceleration scenario. It has only been a few miles, but I'm cautiously optimistic.

I have also noticed that the noise isolator did make a difference in the cabin noise levels. It's actually quieter. And just like that, I love the car again.

I'd like to sincerely thank everyone again who helped me through this problem. It really took a collection of several experienced people to help me sort through the impacts of this rare problem. Through several vendors, I got the parts for a completely refurbished and strengthened transmission.

I hope this thread is helpful to other owners either in fixing the flaws/weaknesses or in general refurbishment.

I'll repeat my advice to the community:

If you ever start to hear gear whine, (especially in 3rd and 4th gears) on deceleration/ coasting, that's more than likely a sign of the shaft nut beginning to back off. If so, I strongly recommend you immediately park the car, drain the gear oil, take the back cover off the transmission and inspect/ deal with the nut(s). That's much easier and less expensive to do before the damage inevitably happens...trust me on that.

Even better: If you have or acquire an early car, especially one with a fairly low serial number on the transmission I would strongly recommend doing the above service proactively.

Let my pain be to your benefit.

Cheers,