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Triumph TR6 - Gears 'grinding' when shifting

As I run through the gears, driving normally, I have to shift slowly or the gears grind slightly before engageing. When down shifting, this does not happen. They never grind when parked, going into reverse or first.
Any ideas?
Jim Kinsella

1. make sure you are not using synthetic gear box oil. Synthetic is too slipery for old trans and will not allow the gear to be slowed down by the synchro

2Make sure your clutch is releasing fully

3. and if the above does not work, you have the classic worn synchro problem and a rebuild is necessary. I bet that you have the problem going from 1st to 2nd.

Think of a sychro as a brake (backwards to a concept of drum brake) inside the g-box. It slows or even stops the gear when shifting. If it is worn then it can't stop the gear quick enough when shifting fast and the gear will clash. When you shift slowly it allows the gear to slow with time. When you are parked the gears are not moving fast enough to cause the problem. 2nd and 3rd are usually the first sychro to go. While they are cheap to replace ~$25 ea the labour and re&re will kill you. I did mine myself and works beautifully

Did you know that you can shift gears (up or down) without using the clutch. If you're accelerating in 1st and you lightly let your foot off the gas with a gentle pull on the gear shifter, it will pull out of 1st and go to neutral as the rpm falls. Still with a gentle pull on the shifter, it will pop into 2nd when your engine rpm gets to the right engine speed (ie. synchronized) which is where the name synchro rings comes from. You can do it into 3rd and 4th too the same way.

Downshifting, you let your foot off the gas, smartly pull it out of say 4th, and while it's in neutral, give the gas a quick blip to increase the rpm (like for double de-clutching but without using the clutch) all the time with a gentle push on the gear stick and it will go into 3rd as the rpm drops back down (when it is synchronized). It will suddenly pop into 3rd. And so on and so on...

If you do this and get a smooth shift, it tells you that your synchros are probable in need of attention.

It's great to practice on a good gearbox so that when you find you have no more clutch or your synchro rings are worn, you'll already know how to do it - at least to get you home.

In the proverbial "good old days", gearboxes didn't have synchros. They were appropriately called "CRASH BOXES".

Don Elliott 1958 TR3A

Don Elliott

Thanks folks. I will do the 1-2-3 check list when things warm up and determine the problem.

How dificlut is it to rebuild the gearbox. I have the same problem, just babying it into second gear right now. I have the Bentley's Manual and I'm sure they go into how to tear down the gear box. I've peaked into it while changing my ring gear, not a very friendly looking place. Looks like one wrong move and the box is off to a professional.
Jeff Hall

The gearbox IS a bit hairy! But if you have a pro' as a back stop, why not give it a go? He can only take your money, not your pride, and think how proud you will be when you do complete the rebuild.

The best advice I got, from a pro',was to use petroleum jelly (Vaseline), not grease, to stick the needle bearings to a shaft while assembling and installing it. They don't drop off! Vaseline has a lower melting point and dissolves harmlessly in gear oil.
Good luck!

Jeff, I just did my '76. It was very easy. I used a Haynes manual as a guide and it was a lot less intimidating than book shows. I did the rebuild because I was able to find an OD and wanted to make sure I had a 100% tranny. Just keep all the gears,syncros, etc in the right order and right direction as you take them off of the mainshaft. I just used an old broomstick, as I took a piece off, I put it on the stick. Good luck, Mike
Michael Parkhill

Jeff I did my '75 about 2 years ago and surprisingly it was really easy. I used the Haynes manual inconjunction with TRF parts guide for a detailed explode diagrams. I used a coat hanger tie together to keep pieces in order and onto another one as I cleaned them. You want to keep the same order and orientation. The hardest thing is to get the spit spacer ring off the mainshaft (there is a specific tool for that which makes the job easier...perhaps a tranny shop may one it to take that off once you have it disasembled. Make sure you use a brass drift to hammer in the main berrings; ALSO when you take apart the synchro hub gears do it inside a plastic bag, the 3 ball berrings will fly across the room). The Haynes does an excellent job of walking you through. Once apart I would replace all synchos, all bearings and thrust washers and check the constant gear for wear on the facing. Also the top hat bushing in 69-73 is made of bronze and wears so replace it...'74 on it is made of steel and does not wear but still check the freeplay. Also you may want to replace the reverse idler gear b/c of grinding into will not believe how many of the teeth are damaged chipped or missing. ALSO change the tappered pin for the clutch throwout arm shaft bushings (use TR3) and the release bearing because the re & re is the worst of the job and you don't want to have to yank it out later b/c of a sheared clutch fork pin...AND THESE DO FAIL

I am not a mechanic but good with tools and mechanically inclined, it took me with the unit is out about 2 hrs to disassemble , 2 hrs to clean and about 3 hrs to put back together. The nut at the prop shaft flange can be a bitch to undo because it is torqued on with significant ft/lbs. Transmission w/o OD is only about 65-75lbs so it is easy to move.

This thread was discussed between 16/01/2002 and 20/01/2002

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