Author Topic: Manual Gearbox Problem (G72)  (Read 1134 times)

BobWeststrate

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Manual Gearbox Problem (G72)
« on: September 17, 2024, 19:26:49 »
Hi all,

I have been reading a lot of stories on this forum and have learned so much from you already. Unfortunately I have come across a problem that I could not find a solution for on this forum yet. A few years back I have overhauled the manual gearbox (G72) but skipped the top cover and the shifting forks. I have renewed the master and slave cilinders and the pressure plate/disk. Now the following issue occured:
my first and second gear are hard to engage and even harder to disengage. Only when the car is Idle is when I can change gears. Reverse is troublesome too but not so much. Third and forth are enaging and disengaging fine.

To fix the problem I did the following:
- Renewed all the bushing from the shifting rods
- Flushed the brake fluid in the clutch system (bled the system too). I noticed that the brake fluid was pretty much black when it came out. Does this mean that seals in the master / slave cilinder have gone bad?

After doing the above the problem persisted so I removed the gearbox and opened the topcover. I noticed that the Shifting fork responsible for gear 1 and 2 has a lot of wear on it. This results in the shift fork coming very close to touching the gear. After removing the rods I saw that the selector plate had a lot of wear on it too. The two squares are damaged (see pictures).
Questions I have:
- I found online that a new plate costs close to 500 dollars, do you guys have any suggestions for other places?
- Do you think that fixing this will resolve my issues with the gearbox?
- Why does the shifting fork have so much wear on it? Is the shimming incorrect in the topcover? If so, Is there a manual on how to shim it correctly?

Thank you in advance for your answers to my many questions!

Bob
« Last Edit: September 17, 2024, 19:32:49 by BobWeststrate »

Jonny B

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Re: Manual Gearbox Problem (G72)
« Reply #1 on: September 17, 2024, 20:13:53 »
As a full member, take a look at Pagoda Notes Volume 1 and 2, this is a review of the rebuild one of our members did on a four-speed tranny.
Go to the Technical Manual and scroll down to find the Premium Content piece for the past issues of Pagoda Notes.
Jonny B
1967 250 SL Auto, DB 568
1970 280 SL Auto, DB 904
1966 Morris Mini Minor

BobWeststrate

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Re: Manual Gearbox Problem (G72)
« Reply #2 on: September 17, 2024, 21:05:50 »
Hi Jonny,

Thank you for your fast response. I just read both volumes and I found that a loose slotted nut might cause some problems, I will look into that. However I could not find anything on the shifting forks and selector plate. Do you have any ideas on that?

Thanks!

Bob

ja17

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Re: Manual Gearbox Problem (G72)
« Reply #3 on: September 18, 2024, 04:45:32 »
Most issues are a result of the loose slotted nut and the resulting damage and mis-alignment of the upper shaft key. The factory has a special set-up fixture for the exact adjustment of the upper shift cover forks.
Joe Alexander
Blacklick, Ohio
1969 Dark Olive 280SL
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2002 SLK32 AMG (350 hp)
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1989 flu419 Mercedes Unimog (US Army)
1998 E430
1974 450SLC Rally
1965 220SE Finback

BobWeststrate

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Re: Manual Gearbox Problem (G72)
« Reply #4 on: September 18, 2024, 06:22:55 »
Thanks! I will get on it!