Chris Wilson Posted October 23, 2015 Share Posted October 23, 2015 (edited) You have only to look at YouTube and videos from Jap car meetings to see that some people feel Toyota so over engineered the Getrag 6 speed that it will survive supposedly huge power increases, drag racing, drifting and God knows what else. I have read "bulletproof", "unbreakable", "built like a brick ****-house" and other OTT descriptions that are patently wrong, which is why Jack's Transmissions or whatever they are called rebuild so many of the things. The aftermarket have many suitable gearboxes designed and able to hold the torque and abuse, that really should be used for these sort of uses, but I doubt many would want to spend the right sort of money. The sort of money that makes sending a Getrag to Jack's Transmissions look like a piffling amount! Car makers don't build in unnecessary amounts of overhead, one only has to look how the aerly M5's from BMW had strict warnings about not fitting a tow bar. It wasn't because the M5 chassis was any less able a tow car than a 535, it was the manual gearbox used in them was at its limits and towing a caravan may well have taken it over the edge. It's amazing just how well this elderly manual Getrag has survived in the MKIV, seeing what people do to it. It's amazing the W58 survives at all, when turbo torque is put through one that already whines and whirs and has slow synchros. Edited October 23, 2015 by Chris Wilson (see edit history) Quote Link to comment Share on other sites More sharing options...
Hitbox Junkie Posted October 23, 2015 Share Posted October 23, 2015 All in mate That isn't as bad as I first thought. Of course not something I'd like to spend but it's good to know and would refresh the box. Will watch your thread be nice to hear your thoughts and impressions when the box is returned as well as thoughts on there service ect. Quote Link to comment Share on other sites More sharing options...
Luxluc Posted October 23, 2015 Share Posted October 23, 2015 I have to admit that I only smashed the 3rd gear syncro on the drag strip. On the road, I never had an issue. However, I feel that a stage3 overhaul will be ok for a 20 year old box. Quote Link to comment Share on other sites More sharing options...
herbiemercman Posted October 23, 2015 Share Posted October 23, 2015 Why are Gearboxes only an issue on Toyota Mk4 Supras ?, I have lots of friends who have several makes of cars, they tune them and hammer them, BUT, no mention of any gearbox failures ? I just find it difficult to see why a company who over 24 years back built a car which was 20 years ahead of it's time, and in more recent times been tuned to modern day and above levels of BHP, why would the gearbox not be like the other cars ? I think i can see Chris's point about Toyota designing for what was FFP ( Fit For Purpose) at the time, but there is a qualatative bit which asks the question, what is high mileage and what is gearbox abuse ? The torque bit is easy to understand, but if the driver wants to avoid the sudden torque impacts, then the box, IMHO, should cope with it ? If some of the owners are dropping the clutch and floorboarding in gear changes etc, then the failure is understandable, especially if the design spec was for 250 lbs/ft torque and then we increase this to 400 lbs/ft. In the USA a indestructable replacement box would be designed, IF, enough punters wanted this,many mk4 supra upgrades are available and very good and cost effective, IMHO, in the days we live in, we should not be tolerating broken basic transmission parts and repair costs being a complete joke, that is , if you can get a repair.? for this car, other makes of recon boxes are readilly available for all cars, at reasonable cost. May be iam forgetting, the mk4's are very old now ? herbiemercman. Quote Link to comment Share on other sites More sharing options...
GazDoran Posted October 23, 2015 Share Posted October 23, 2015 All this talk of broken synchros has got me interested. I have never experienced a broken synchro, or gearbox failure in any car I have owned, so I have a couple of questions. The broken synchro seems to be defined in this thread by a crunch, so what is the difference between a broken synchro crunch and a poor gear change/grinding of gears crunch? A broken or worn synchro seems to also be widely defined by it being hard to put a car in to gear - My gearbox can be fairly notchy (especially at low rpm) but given that the 6 speed is often described as agricultural, I would assume that a little notchiness (inventing words now) is natural to the Supra? Quote Link to comment Share on other sites More sharing options...
stevie_b Posted October 23, 2015 Share Posted October 23, 2015 The broken synchro seems to be defined in this thread by a crunch, so what is the difference between a broken synchro crunch and a poor gear change/grinding of gears crunch? They're kind of the same thing. A synchro will help the gear match the speed of the engine. Poor gear change will be caused by very aggressive changes I suppose. But if the synchro is worn, no matter how carefully you nurse the gear change, it will crunch, unless you match the engine and gearbox speed. Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted October 23, 2015 Share Posted October 23, 2015 Gears are in constant mesh, they don't crunch. Sometimes reverse is not constant mesh, but all forward gears are in 99% of car gearboxes. Gears can strip teeth, or their support bearings go noisy or fail. But they don't crunch. SYNCHROS crunch, or dogs in dog boxes crunch. Contrary to common opinion the gears do NOT slide in and out of mesh with each other, the change in drive ratio drive is done by the synchro hubs and synchro teeth locking a gear to its shaft. Quote Link to comment Share on other sites More sharing options...
herbiemercman Posted October 24, 2015 Share Posted October 24, 2015 Hi Chris, This is meant to be a compliment, you are a know all. Quote Link to comment Share on other sites More sharing options...
GazDoran Posted October 24, 2015 Share Posted October 24, 2015 Gears are in constant mesh, they don't crunch. Sometimes reverse is not constant mesh, but all forward gears are in 99% of car gearboxes. Gears can strip teeth, or their support bearings go noisy or fail. But they don't crunch. SYNCHROS crunch, or dogs in dog boxes crunch. Contrary to common opinion the gears do NOT slide in and out of mesh with each other, the change in drive ratio drive is done by the synchro hubs and synchro teeth locking a gear to its shaft. That's not really answering my question though as it is possible to get a crunch or a grind without a broken synchro surely?! I.e. If I fully engage the clutch, move the out of gear into neutral then partially or fully disengage the clutch before putting the car back in to gear it's going to grind like shit...but that's driver error not a broken synchro... So my original point is still what defines a broken synchro? Would there be a grind no matter how well executed the gear change? Will the gearbox feel particularly knotchy or difficult to select a gear? And how can you define that on a box that is frequently described as knotchy and agricultural? Sorry to hijack the thread by the way. Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted October 24, 2015 Share Posted October 24, 2015 http://auto.howstuffworks.com/transmission4.htm Loads more with Googling. Quote Link to comment Share on other sites More sharing options...
herbiemercman Posted October 25, 2015 Share Posted October 25, 2015 (edited) Good links and very interesting, this takes me further along the road of me changing my agressive clutch, i am learning to live with the ergonomics but as an engineer i worry about the accelerated ware on my gearbox. If the "price" is me experiencing a bit of clutch slipping, then this may have to be ? there are mixed views and experiences from members on whether slipping will happen on certain organic clutches. Also the cost of gearbox repairs is extortionate. Edited October 25, 2015 by herbiemercman (see edit history) Quote Link to comment Share on other sites More sharing options...
tross Posted October 26, 2015 Share Posted October 26, 2015 A company local to me said I'm looking at £1100 to strip and rebuild + parts on top but doesn't want to get involved due to the power in running through it Alright minge Where was that? Have you talked to Thames Transmissions on Canvey? They did my Skyline box and it's who dad used to use for most of his work. Sending it to the States sounds a bit retarded lol. Quote Link to comment Share on other sites More sharing options...
johnd-mkiv Posted October 26, 2015 Author Share Posted October 26, 2015 Alright minge Where was that? Have you talked to Thames Transmissions on Canvey? They did my Skyline box and it's who dad used to use for most of his work. Sending it to the States sounds a bit retarded lol. Lol think it's newwood transmissions in Southend have a good rep but I'll give them a ring also, they all get a bit scared when you say the horse power Quote Link to comment Share on other sites More sharing options...
Hitbox Junkie Posted October 26, 2015 Share Posted October 26, 2015 Lol think it's newwood transmissions in Southend have a good rep but I'll give them a ring also, they all get a bit scared when you say the horse power Why they scared do they all use gummy bears for internals Quote Link to comment Share on other sites More sharing options...
johnd-mkiv Posted October 26, 2015 Author Share Posted October 26, 2015 Lol the supra community are not fazed by large horsepower, just spoke to Thames transmissions he said about £500 to strip an rebuild with parts on top I've emailed Steve at Toyota from the first page but no reply if I can get the parts I'm all good to go Quote Link to comment Share on other sites More sharing options...
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