P6 3500S- manual gearbox trouble

#1
Hi all.

My 3500S has been haunted with gearbox problems during my entire ownership. I started with a gearbox that was extremely noisy- and this was replaced with a gearbox that jumped out of reverse. Last winter this was replaces with gearbox number 3 - that turned out to have a high clonk-clonk sound as soon as the clutch is released - even in neutral.
Now I am fed up with used "worked perfectly when car was parked"-gearboxes. So I disassembled the noisy gearbox I started with - as this shifted as it should and the noise sounded like bearing noise. So the plan was to change the bearings (even the costly special rear bearing) if no other problems found.

But unexpected surprises was found. The internals seems in very good shape as far as I can judge - even the syncro rings looks very good. But the surprise is approx a tea spoon quantity of very small magnetic steel balls of approx 0.2 mm in diameter found inside the roller bearings and especially in the drive entrance for the oil pump.

First question is where do these small balls come from? My theory is that the box has been overhauled but the balls is from blasting and not cleaning the housing afterwards. They have certainly entered the gearbox from "outside".

The needle bearings have no signs of damage or wear but I will naturally clean it all and replace if in doubt. But the oil pump is not feeling like it is spinning smoothly as I would expect it. But it is a riveted unit. Any one having experience with with taking these oil pumps apart (and back together again) ? In theory most of these strange steel balls will have ended inside the pump so I need to take it apart or to replace it.

IMG_20210712_131143 (Small).jpg IMG_20210712_131158 (Small).jpg IMG_20210702_193825 (Small).jpg

Thanks in advance
Frank, Denmark
 

quattro

Administrator
Staff member
#2
I had a similar issue when I had the injection bits (Plenum, tower base and manifold) cleaned and polished by a company specialising in aluminium engine bits. I used a dremel to remove the 3.9 badge, and I suspect the vibration loosened this little lot.

IMG_E6585.JPG

I don't know the oil pump on your gearbox but I do know that you need to remove every single steel ball out of there, but I'm sure you realise that.

Have you thought of taking it to an engineering shop?
 

colnerov

Well-Known Member
#3
Hi, I would think that given the different sizes of the balls that they are one of the types of media used in vibratory tumbling to de-burr and finish the castings, they can do it wet or dry. I would guess these have been done wet and have been holed up in a corner somewhere.

Colin
 

Demetris

Well-Known Member
#4
If you have 2 gearboxes available, i think it is better to take both of them apart, and use the best parts between the 2 to assemble a good one. Perhaps the gearbox that jumps out of reverse has a good oil pump.
 

jp928

Active Member
#5
^^^ what he said. Its not like the oil pump needs to match anything else, as in gear pairs. Is the pump rivetted to the plate seen in the parts book?
 
#6
The gearbox has now been flushed with brake cleaner, blown with compressed air and swiped with powerful magneto until no further alien objects have showed themselves. I did not take the mainshaft apart as this will require reshimming etc - so I have a fear that some steel balls are still hiding in there somewhere. It is also clear that the output bearing (that is no longer obtainable/very expensive) has taken some beating so it will require replacement. Replacing all the bearings is still an option but if some of the alien steel balls are still in there somewhere and destroys the bearings again I will be in bad mood :(

I will take the gearbox currently in the car (the box saying clonk-clonk) out and dismantle it in parallel and see if I can mate something together.

Looked closer at oil pump and as I said it is riveted together.
IMG_20210726_164610 (Small).jpg IMG_20210728_091038 (Small).jpg

One can peak into the input and the output "ports" and it looks as if the internal is a sort of fiber disc without any wings or teeth. So in my terminology it is not really a "pump" but more a device that simply is trying to give a sort of flow of oil through the box.

Thanks for the input - it will but be until autumn that I will be able to do progress on this issue. I will then update the thread with my conclusions and the decisions i will make.

/Frank, Denmark
 

jp928

Active Member
#7
How can you see into the outlet port, when its a small hole in the side of the shaft bush hole?
Google lt77 oil pump and you will see how they work - originally fibre, but replacements are steel - disc with internal teeth, driven by a smaller gear offset from centre, inside the big gear. It looks to me that the rivets are in countersunk holes, so I would bet that any halfway capable engineering shop could drill them out, and replace with c/sunk head bolts, once any internal issues were dealt with.
You might test it by submerging the inlet in oil and manually spinning the drive key (ccw), and check that oil comes out of a hole in the top bush that the mainshaft goes through. Then check the mainshaft by pumping oil from an oil can into the rearmost side hole and checking that it comes out under each of the gearsets. If this works its probably OK, dont open it.. The fibre gears in LT77 apparently broke up and lost their teeth, hence the steel replacements.
Can we assume you have been using the correct SAE20 oil ?
 
#8
I use one of those small inspection cameras with a small color screen and a long fibre "neck". One can even record the video for later viewing on a tv-set or a computer. I can see - pretty clear - the fibre disc from both input and output. Thanks for the info - as it has internal gears I will have to take it apart to verify the damage and/or trapped steel balls inside. It does not sound nor feel good when turned by hand and if these steel balls have been in between the teeth it will have taken its toll..... I have equipment to drill out and taper the holes - no problem.
I have had the car for many years - bought it dismantled some +15 years ago. In the recent years I have put it together. Gearbox was laying in the trunk/boot when I bought it and I have only driven some 20 miles with it. And with SAE20, indeed. Because of the noise it was replaced with the next gearbox ... and the next...... :)
 
#10
I finally found the time to drill out the alloy rivets and separating the oil pump. To my surprise it looks to be in surprisingly good shape and I also did not find any of these foreign objects (steel balls) inside it. The car has very low milage and the pump shows very little wear and no harm seems to have been done by the fault.
I will still rebuilt one functioning box using 2 of my faulty ones and this pump will be put back together and probably used in that rebuild.
For reference I have shown a measurement of one of the pump wheels below.

IMG_20210810_192626 (Small).jpg
IMG_20210810_192820 (Small).jpg


Thanks
Frank, Denmark
 

jp928

Active Member
#11
Good result, keep it up!
The spare pump gears I have for LT77 - OD of large gear 49.9mm , small gear 29.5mm, 8.5mm thick. The drive peg is a just a square section piece.
 
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#12
The measurements on mine is 50.0 mm, 29.3 mm and 8.5 mm respectively. Probably the same as on the LT77 - or at least surely modifiable to fit - should anyone ever come in the situation.....

/Frank
 
#13
A short follow up on this issue.....
To recap I have a manual P6 gearbox that contained many small steel balls of unknown origin - and therefore extremely noisy. Somebody here locally mentioned that these steel balls look like the ones used for "shot peening" which is used to make gearbox components less prone to teeth breaking of the gears. In fact it is mentioned that these P6B manual boxes did get that treatment at the factory (Rover P6 Manual Gearbox).
I am not implying that these balls have been inside the box since birth - but it could be that the box during a rebuild - someone had access to this process - but failed to clean cavities afterwards.
--
I have a second box that was installed after the above - but gave loud clonk-clonk as soon as the clutch was released. The update here is that I have now taken that box out of the car and taken this apart as well.
And I found two teeth broken of the main shaft - so that explain the noise and make me glad I did not drive the car with that box. In general the gears shows several small signs of damages. Many of these cars can have had a harsh ending of their live when rust had doomed them to be scrapped anyway.
--
So the conclusion follows my earlier post. I will use the cleaned internals from the first box but renew the bearings that is obtainable - and the seals - and just use the oil pump from the "clonk-clonk" gearbox - as I took the other one apart by drilling out the rivets to check if alien objects was trapped inside it. This will be a winter project so updates on the end scenario will be postponed when the long winter evenings have been enjoyed in the shed :)

/Frank, Denmark
 

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jp928

Active Member
#15
Considering how shot peening of a gear shaft would be carried out, I find it hard to see how the shot might get into the box. Surely the gear shaft would be mounted inside a cabinet (like a sand blasting unit), shot peening done, shaft removed, cleaned, oiled and stored until it was assembled into a gearbox.

Teeth broken off the mainshaft - my old mainshaft (2000tc) and the 3500 parts book do NOT show ANY teeth on the mainshaft - splines at front, centre and rear, but no actual gear teeth. ??
 
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