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TF Main Shaft Gearbox Rebuild

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TF Main Shaft Gearbox Rebuild
#1
  This topic is about my 1955 MG TF 1500
55-60MG4KM Avatar
55-60MG4KM Silver Member Keith Meyer
Corvallis, OR, USA   USA
I am working my way through the Main Shaft rebuild having completed the gear cluster / layshaft. When I disassembled the mainshaft there was no washer (Moss 324-480) on the main shaft outboard of the 1st / 2nd sliding hub and between the circlip. Barrie Jones, in his video, calls this a "spacer" and says "that it is put there becasuse there was too much movement in the gear and you might or might not find one of those". Since I am replacing the entire 1st / 2nd sliding hub assembly and my original sliding hub did not have a spacer how do I determine if I require a spacer with the new sliding hub? Thanks, Keith

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Declan Burns Avatar
Duesseldorf, NRW, Germany   DEU
Keith,
I had a problem with my gearbox with third gear. I could only change down when the revs dropped below 2000rpm otherwise it crunched. When I took it out I measured the end float at about 1.5mm or more. I contacted Barrie Jones about it and sent him photos. He said that that same missing spacer was my problem so I installed it. I then changed to a 5 speed box and sold on the repaired gearbox. The person who bought it never came back to me so I assume it is OK and that Barrie was right. I set the end float at 0.05mm during the repair.
Regards
Declan

55-60MG4KM Avatar
55-60MG4KM Silver Member Keith Meyer
Corvallis, OR, USA   USA
Declan: I've been away from the TF transmission for a bit so sorry not to have responded. Today I installed the 1st/2nd sliding hub and installed the circlip. I then took my "feeler" guages and measured the distance between the circlip and the hub face. If I am measuring the correct location then I came up with an "end float" of .043" and converting from inches to MM that equals 1.0922MM. Based on your response the gap is dramatically larger than your reccomended dimension. However, I cannot find anyone who offers a "spacer" much less do they discribe what the dimensions of the spacer are. Do you have any reccomendations on how to acquire the spacer or construct one? Thanks, Keith

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55-60MG4KM Silver Member Keith Meyer
Corvallis, OR, USA   USA
Here are a couple of pictures of the gap between the 1st / 2nd hub and the circlip referenced above.


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Overview.JPG    48.3 KB
Overview.JPG

Up Close.JPG    29 KB
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Declan Burns Avatar
Duesseldorf, NRW, Germany   DEU
Keith,
According to the booklet "Barrie Jones's notes" (well worth buying!) the 2nd gear end float should be .004" to .006" (0.1 … 0.15mm). He writes that a shim should be added to achieve this. Your end float is 10 times greater!
I suggest you purchase a shim which is thicker than required and grind down to meet Barrie's specification. I don't know the size but measure the inner diameter required. The outside diameter is not critical. Standard shims should be available online.
Regards
Declan



Edited 1 time(s). Last edit at 2019-02-03 06:24 AM by Declan Burns.

GB3 George B
Winter Haven, USA   USA
Remember that the shift fork position is fixed by the detent balls, etc. The fork needs to be centered in the groove of the outer hub passively when in neutral. It is possible to shim to eliminate play, but then the fork is continually rubbing/wearing in contact with the hub. A little play would be better than constant rubbing. George

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55-60MG4KM Silver Member Keith Meyer
Corvallis, OR, USA   USA
Thanks everyone for your help. Keith

MGTF1500 Ardeche France Avatar
MGTF1500 Ardeche France Thierry SUCHIER
TOURNON SUR RHONE, Rhône-Alpes Auvergne, France   FRA
In reply to # 3885130 by Declan Burns Keith,
According to the booklet "Barrie Jones's notes" (well worth buying!) the 2nd gear end float should be .004" to .006" (0.1 … 0.15mm). He writes that a shim should be added to achieve this. Your end float is 10 times greater!
I suggest you purchase a shim which is thicker than required and grind down to meet Barrie's specification. I don't know the size but measure the inner diameter required. The outside diameter is not critical. Standard shims should be available online.
Regards
Declan

Hi Declan,
I allow myself to intervene thinking that there is a small mistake.
Here is the page in question
b. Insert spring and plunger
c. Slide 3rd gear over the plunger
d. Slide the collar over the plunger, slots to the outside, holding the plunger down with a fine screwwdriver through one of the holes in the 3rd gear synchro cone.
e. Turn the collar 30 degrees to release the plunger.
7) Check the 3rd gear end-float. Ideally it should be .004 "to .006".
If it is significantly larger, you may need to make up a spacer.
8) Slide on the 3rd / 4th hub assembly, noting that the deeply recessed side goes against the 3rd gear. Later hubs should have one hall protruding inside the hub, which shc depression in the handshaft.
9) The handshaft can now be inserted into the gearbox.
10) Reassemble the input shaft:
at. Replace the bearing shield, convex side towards the bearing.
b. Replace the bearing.
c. Slide on the lock-washer.
d. Screw on the threaded collar (left hand thread).
e. Hold the shaft gently in a vice, tighten the collar and secure it by bending over the lock washer. Be careful not to damage the polished portion of the shaft - the oil seal runs on it.
11) Stick the spigot to the inside of the shaft with Vaseline. Note that these are the longer 28mm needles
41 Barrie's Notes

and I see that it's third gear that you're talking about when you've noticed it's the second gear? But that may not be important.
Indeed, I recommend to everyone this wonderful booklet from Barrie's
Sincerely, Thierry de l'Ardèche



Edited 2 time(s). Last edit at 2019-02-04 05:23 AM by MGTF1500 Ardeche France.

Declan Burns Avatar
Duesseldorf, NRW, Germany   DEU
Thierry,
The only mistake I can see is the mistake in the workshop manual. The spacer Keith is referring to is Item 18 in the workshop manual. The workshop manual states for Item 18 Guard-bearing-first motion shaft. This should read Guard-bearing-main shaft and not first motion shaft. This is the Moss item 324-480 that Keith is referring to and Barrie Jones refers to this as a spacer. It is too small in diameter to guard the bearing. According to the workshop manual it is fitted between the circlip Item 40 and the bearing Item 16. The discussion was about if the spacer should be located in front of or behind the circlip
Regards
Declan

Lonnie Cook Avatar
Orlando, FL, USA   USA
Here is a post by Keith McKenzie on the other MGT forum in 2012 in response to a similar question about inserting a shim between the circlip and the 1-2 hub. A similar question on the website gained a similar response. Based on the responses, I didn't add a shim to my TF gearbox.

In a word " NO " I did this fix last year . Made my problem noticeably worse. After talking to FR Millmore from this site this was his reply. Hi Keith -
From what I can see, the laygear looks quite good, certainly replaced at least one more time than the first gear. The chipping/wear at the engaging end of the teeth is not a real problem. I've seen gears chipped a third of the way back, no problem, but a sign of rough driving or dragging clutch. It is wear of the tooth contours that IS trouble, and I do not see any. As I said, use ball bearings or other accurate round things as gauges, if you have any doubts.
Your old first gear IS a problem, due to that same tooth wear, and may be the entire problem,
HOWEVER:.
I told you that the spacer has no locating effect, and suggested you leave it out. Examining things more closely, it may in fact have a disastrous negative effect, leading to your problem. If there is clearance between the hub and spacer when in first gear, good. It could be .010 or a foot, makes no difference. However, if there is NO clearance, or negative clearance, then the hub could be preloaded against the synchro detent ball/springs, fighting the first gear detent on the shift rail. The overall length of the hub makes no difference; it is the length from the back of the hub to the synchro detent holes that matters. As I said before It is the fork that determines the gear position, and the hub position is determined by the synchro balls from the gear position. BE CERTAIN that there is definite clearance between the back end of the hub and the bearing bits WHEN it is in first gear. This must be enough that any slop in the mainshaft bearings cannot reduce it to less than zero. If the clearance is negative under either steady state or dynamic conditions, the synchro balls will be pushing it OUT of gear while the rail detent attempts to KEEP IT IN GEAR.
This is where we started, and I repeat <<<LEAVE the spacer OUT>>>

The only other things that affect the issue are the state of the shift fork - bent or loose. Bent will cause the gear to misalign with the laygear, but should be obvious. Loose in the groove shouldn't matter much within reason,
IF the gears are good. Loose on the rail could cause it to not go all the way into gear, which would cause it to jump out easily.
OR the condition of the first gear detent on the shift rail. This includes spring load as assembled, and condition of the detent notch. These notches can be touchy, as can modifications to them. The only check is to know the force required to move the rail out of the various detent positions. As far as I know there are no specs anywhere for this, it being a matter of "sufficient". I can judge by looking at the notches. Compare to the other detents, by eye and by feel when shifting (both into and out of gear). Maybe send me a really clear pic of the notches for this. And remind me where the "extra" spring/ball went.
Might help if Quantum or somebody has real specs for the detent spring load/length. This can be corrected or modified with the gearbox in the car, just remove the cover.

Best.
FRM
I hope this is of some use to you and Fletcher does not mind my reproducing his email. I put a new first gear in from Quantum Engineering now Moss has them.Mind you the gear box is going back together today so I have not personally tested the results. But will try to post back in a month or so when the new pistons and roller cam are all back in ol'Betsy.
Cheers, Keith


Lonnie
TF7211



OLD STUFF ... houses, furniture, cars, wine ... I love it all

55-60MG4KM Avatar
55-60MG4KM Silver Member Keith Meyer
Corvallis, OR, USA   USA
I have communicated with 6 knowledgable people on this subject and I keep getting conflicting information. I now have 4 votes for: Yes, install a spacer and 2 Votes for No, dont bother with the spacer. So, I asked and received an email from John Twist on this subject. His answer was also: Yes, install a spacer. Plus he offered that the reason to install it was to keep the inner hub from moving so far on the mainshaft that the ball bearings might pop out to far and prevent the outer hub from sliding forward when you enter second gear. He commented that the spacers he has seen are commonly not as thick as a quarter dollar (I miked one at .0675"winking smiley but thicker than .025". He also reccomended not to use a material that is to soft as it will eventually be beaten thin by the repeated stikes of the inner hub. Although my gearbox didnt have one (but someone was messing around it it previously) I'm going to install the spacer.

I have a gap of .043". Barrie Jones says you should have a gap of .004-.006". I think that is pretty tight and I'm going to look for something with a thickness that gives me a gap larger than that. Maybe around .030 - .032". I bought a 1.185" x 1.75" x 18 guage (.049"winking smiley machine bushing that is pretty hard. I have been trying to file it, sand it, reduce its thickness but I can't keep it consistently flat across the diameter of bushing. Might have to take a new one to the machine shop and have them grind it down to my preferred thickness.

Oh, by the way of rebuilding, I replaced all my hub / synchro ring pieces and one mating gear. I found out that I should have lapped in the synchros to the new and old gears I installed. Time to back up and redo!

Keith

Ormolu Avatar
Ormolu Barrie Jones
Okehampton, Devon, UK   GBR
1955 MG TF 1500 "Emily"
1973 MG MGB GT V8
Barrie Jones here.

Second gear end float can be quite large and a clearance of about 1mm is normal.
The one in the photo looked OK to me.

Third gear end float is critical.
Ideally, it needs to be between .004 and .006 inches.
Note that you must have SOME clearance. If it is less than .004" then you have a problem.
If it is considerably more than .006", then you need to make up a spacer.
I would not worry if it was .012"

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