Trumper Posted April 7, 2007 Share Posted April 7, 2007 HiI have a crunch when changing from 2nd to 3rd on my GT6 Mk3. Also similar problem on my Spit 1500 but thats 3rd to 4th.The GT6 had a gearbox rebuild a couple of years ago before i bought it.Im sure i have read somewhere that this can be a common fault on both cars and can be reduced/resolved by using fully synthetic oil in the gearbox.Can anyone help with some further advice please? is it a reasonable idea? any problems with the oil corroding internal parts?If its feasible what type of oil should i be looking at?I have a small leak from the gearbox drain plug so will have to drain down in the near future - thought it would be a good opportunity to make the change?Thanks - Andy Link to comment Share on other sites More sharing options...
jonathan binnington Posted April 7, 2007 Share Posted April 7, 2007 sounds like the synchros are weakening, synth gbox oil will make no diffrernce to that.j Link to comment Share on other sites More sharing options...
CharlieB Posted April 7, 2007 Share Posted April 7, 2007 Now that I'm an expert on gearboxes (only kidding!) it may be the springs in your synchro hubs. Either way I agree the oil won't make any difference, strip down time I'm afraid.Provided you've got a manual it seems to be fairly straightforward, just don't do it over a bank holiday weekend when the suppliers are shut!Charlie Link to comment Share on other sites More sharing options...
Deleted User Posted April 7, 2007 Share Posted April 7, 2007 post removed on request of author Link to comment Share on other sites More sharing options...
James Posted April 7, 2007 Share Posted April 7, 2007 Also - fully synth is meant to be bad for your overdrive. Link to comment Share on other sites More sharing options...
Trumper Posted April 8, 2007 Author Share Posted April 8, 2007 Smallfry - yes it crunches when changing up if memory serves me right - been so long since i have driven the GT6 as its been laid up for some work over winter.Thanks for all the info guys. Must admit to wondering about the quality of the reconditioning of the gearbox.Cheers - Andy Link to comment Share on other sites More sharing options...
CharlieB Posted April 8, 2007 Share Posted April 8, 2007 [quote by=jcarruthers link=Blah.pl?b=spit,m=1175973478,s=5 date=1175984375]Also - fully synth is meant to be bad for your overdrive.[/quote]I've been trying to find out about this. John Kipping on the Canleys site (& in the old Kipping catalogue) recommends synthetic oil for overdrive gearboxes, & lists a part synthetic GL5. (He also says use only GL4 in the diff.)However there's a note in the Moss catalogue that says "Hypoid oil should not be used even though it's recommended by Triumph, Laycock de Normanville specifically excludes oils with hypoid additives from its lubrication chart"I've only seen hypoid synthetic gear oil.I'm confused! Link to comment Share on other sites More sharing options...
heraldcoupe Posted April 8, 2007 Share Posted April 8, 2007 There has always been a conflict between Standard Triumph and Laycock. Triumph specifiesgear oil for their gearboxes, Laycock specifies engine oil. Exact reccomendations have varied down the years, but the basic differences have been constant.By comparison, BMC have (always?) specifed engine oil in their gearboxes, so there has been no conflicting advice.I've always run with an API GL4 mineral gear oil without problems, though others will be equally happy using engine oils. If I ran into problems then I would seek alternatives, but that's not happened yet.Cheers,Bill. Link to comment Share on other sites More sharing options...
CharlieB Posted April 8, 2007 Share Posted April 8, 2007 Thanks Bill. So does that mean an HP90 GL4? Link to comment Share on other sites More sharing options...
rotoflex Posted April 8, 2007 Share Posted April 8, 2007 Traditionally the crunch is 2nd gear.Until you rebuild the gearbox, double-clutch going up into the crunchy gear to stop the crunching & keep from having to make the rebuild more expensive.There Was A Time when synchros were new miracle things, & you can still drive the way they usedta before synchros & keep from tearing up your gearbox. Link to comment Share on other sites More sharing options...
Phil Wright Posted April 9, 2007 Share Posted April 9, 2007 Bill, I agree. I was told the same thing when I took my overdrive in for reconditioning at the specialist in Sheffield. Since then, i've run 20/50 engine oil in my gearbox and done about 5-6k since. The gearchange is slightly more positive and the o/d comes in nice and cleanly. Had no problem so far. Link to comment Share on other sites More sharing options...
Jason Posted April 9, 2007 Share Posted April 9, 2007 I'm going to try Red Line MT90 fully synthetic gearbox oil http://www.myaustinhealey.com/austin_healey_technical_articles.html I've got some coming in the post from one of my mates in the States. The theory seems sound, we'll see what the practice is when it arrives and I've put it in the gearbox! Link to comment Share on other sites More sharing options...
Phil Wright Posted April 9, 2007 Share Posted April 9, 2007 just watch it if you've got an averdrive - it might be too 'slippery' Link to comment Share on other sites More sharing options...
Deleted User Posted April 9, 2007 Share Posted April 9, 2007 [quote by=Trumper link=Blah.pl?b=spit,m=1175973478,s=0 date=1175973478]HiI have a crunch when changing from 2nd to 3rd on my GT6 Mk3. Also similar problem on my Spit 1500 but thats 3rd to 4th.The GT6 had a gearbox rebuild a couple of years ago before i bought it.Im sure i have read somewhere that this can be a common fault on both cars and can be reduced/resolved by using fully synthetic oil in the gearbox.Can anyone help with some further advice please? is it a reasonable idea? any problems with the oil corroding internal parts?If its feasible what type of oil should i be looking at?I have a small leak from the gearbox drain plug so will have to drain down in the near future - thought it would be a good opportunity to make the change?Thanks - Andy[/quote]Not 100% sure why no-one else has mentioned this but the crunch could be due to a worn Clutch causing some drag and hence a crunch when selecting/changin gear, has the clutch been replaced any time recently?? Link to comment Share on other sites More sharing options...
Phil Wright Posted April 9, 2007 Share Posted April 9, 2007 good point :) Link to comment Share on other sites More sharing options...
Trumper Posted April 12, 2007 Author Share Posted April 12, 2007 No idea when the clutch was replaced - its a good point though. It did cross my mind but i thought it would happen in all gears if the clutch was on its way out? Link to comment Share on other sites More sharing options...
Deleted User Posted April 12, 2007 Share Posted April 12, 2007 TrumperI have had a couple of Vehicles (non-Triumph) have this issue of crunching on certain gears and on one occasion for sure the Clutch was the problem, it was a combination of a little air in the system and the friction plate pretty much down to the rivets (also started to slip in the end), after the replacement/bleed the gearchange was just great. Certainly cheaper to look at this than pulling the GB for a re-build. Link to comment Share on other sites More sharing options...
rotoflex Posted April 15, 2007 Share Posted April 15, 2007 I think it's important if using a non-OEM gearbox lubricant to select a lubricant that is formulated for manual transmissions has friction modifiers to keep the synchros happy. There is unmistakably shortened lifespan of the synchros otherwise.Two aftermarket brands formulated to meet specs for a number of manual transmissions available in the US would be Pennzoil Synchromesh & Redline MTL. Redline MTL has a very good reputation among folks who are operating their cars in competition. Link to comment Share on other sites More sharing options...
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