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gearbox shifts more difficult in hot weather


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Hi all, I have a question about my gearbox from my TR4 (1962). Does anyone know why my gearbox is harder to switch in hot weather? It's harder to get into gear. Sometimes from three to four a little crack. Not Always. Just that it's not completely synced. In the spring I never had this before. And only if he's been riding hot. The next day everything is back to normal :)

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Jo - almost certainly to do with the oil you are using getting thinner as it gets hotter - what oil are you using and I'm assuming it's a non overdrive gearbox? Whatever, drain the oil and refill with new oil ( if it's old) and/or a thicker oil . Ultimately your synchros are probably a little worn, but so long as you recognise that and take your time when changing gear in the suspect ratios, you should be fine 

Cheers Rich

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2 hours ago, rcreweread said:

Jo - almost certainly to do with the oil you are using getting thinner as it gets hotter - what oil are you using and I'm assuming it's a non overdrive gearbox? Whatever, drain the oil and refill with new oil ( if it's old) and/or a thicker oil . Ultimately your synchros are probably a little worn, but so long as you recognise that and take your time when changing gear in the suspect ratios, you should be fine 

Cheers Rich

Hi, I am using 80W90 GL5. It is a non overdrive gearbox. The oil is from august 2019. Thanks for the info!!

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If I were you I’d drain it and replace with GL4. GL5 additives might be attacking the synchromesh teeth. That’s the opinion of many in the past. I’m no oil engineer though. 

Edited by peejay4A
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14 minutes ago, peejay4A said:

If I were you I’d drain it and replace with GL4. GL5 additives might be attacking the synchromesh teeth. That’s the opinion of many in the past. I’m no oil engineer though. 

My mistake, i just checked the bill. It's indeed 80w90 GL 4. 

They used 80w90 gl5 for the diff

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The clutch master cylinder has a small rubber seal that blocks the reservoir feed when the pedal is pressed... if that little seal degrades then it leaks more when soft/hot...meaning that as you push the clutch some fluid flows back to the reservoir...so less fluid goes to slave cylinder...slave moves less...clutch doesnt disengage...gears difficult to select. When stationary (engine running) can you select reverse without crunching when hot? if not then gearbox is not properly disengaged.

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On 6/25/2020 at 5:43 AM, ctc77965o said:

The clutch master cylinder has a small rubber seal that blocks the reservoir feed when the pedal is pressed... if that little seal degrades then it leaks more when soft/hot...meaning that as you push the clutch some fluid flows back to the reservoir...so less fluid goes to slave cylinder...slave moves less...clutch doesnt disengage...gears difficult to select. When stationary (engine running) can you select reverse without crunching when hot? if not then gearbox is not properly disengaged.

Had the same symptoms in reverse gear on the MGTF for a few weeks but didn't bother, then the master failed completely. Opened the reservoir: full of black fluid. Rubber seals had disintegrated, yet at the slave cylinder fluid was clear. Might worth taking a look at the fluid colour at master cylinder to confirm/discard.

Edited by Geko
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17 hours ago, Jo Neyskens said:

My mistake, i just checked the bill. It's indeed 80w90 GL 4. 

They used 80w90 gl5 for the diff

There are yellow metal thrust washers behind the sun & planet gears in the standard differential so GL5 spec may not be suitable.

Cheers

Peter W

Edited by BlueTR3A-5EKT
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