QuestionThanks Howard,
I tried double clutching yesterday when downshifting into 2nd, and no crunch. Do you think this would indicate air in the clutch system more than linkage slop?
Thanks Joe
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Followup To
Question -
Hello Howard,
I have a 1970 gt6+ with a 4 speed transmission. I had a problem with downshifting from 3rd to 2nd. I thought it must be a syncro, so I had the 2nd gear syncro replaced at a transmission shop. The technician said that the old syncro did not look too bad, but he installed the new one anyway.
I also installed a new throw-out bearing when assembling.
Anyway, I still have the same problem of the gear chunking when downshifting from 3rd to 2nd. It upshifts and downshifts fine when not running, and shifts up through all gears when running, but chunks from 3rd to 2nd when coming down. Could it be a slave cylinder problem, I did install a new kit in the master and slave .
Thanks for any thoughts.
Joe
Answer -
Hi Joe,
Down shifting from 3rd to 2nd is a slower shift than the other shifts due to the fact that you have to come across the pattern to get to 2nd. meaning the engine RPM gets further from the wheel speed so even when everything is in order, it is a difficult shift for the gearbox. My first question to you is do you rev your engine in between a down shift? This gets the engine speed up to what is close to the wheel speed of each gear that you are attempting to engage on a down shift. Downshifting use to be an art on older cars because syncros were not very good back then. So a driver had to get his engine RPM very close to what it should be for the speed he is going for the gear he is trying to go down to. An example was the early Jag E-type had poor syncros so a driver had to get the RPM very close to what was right for the gear he was trying to shift down to. Motorcycle riders and truckers had to learn to do this. Most motorcycles don't even have any syncros. So downshifting was dificult unless you learned how to rev the engine in between each downshift. It is not necessary on an upshift because the engine needs to slow down between shifts to engage a higher gear.
Several of the Triumphs did have a problem of the hydrolic clutch system just barely having enough travel to release the clutch so if you add in the delay of getting to 2nd from 3rd you can get a crunch. If you add in the factor that many British transmissions did not have an even step in gear ratio between gears.
I would do this,
be sure all the air is out of the clutch hydrolic system and check that no carpet is bunched up under the clutch peddle, Confirm that you have very little "Free Play" in the clutch peddle. and if you do not rev the engine between down shifts, try to locate a race driver (usually your local British car club will have several "Auto Crossers" or "SCCA racers") that will be glad to show you how to do it as it is a lost art on street cars.
I hope this helps.
HMF
AnswerLinkage slop is easily checked by feeling the free play in the peddle.
When I was young and indestructible I use to race motorcycles professionally and worked as a mechanic in bike shops. I then went to work in car dealerships on MG, Triumph, Jaguar, Austin Healey, Lotus, Ford, Sunbeam, Jeep and others and I came to an early conclusion that you should always rev an engine between downshifts. From what you have told me, if that car were mine, I would not even think about tearing it down and I would always rev the engine in between any downshift and forget the fact that you could get a crunch going into 2nd when you don't rev the engine. There are so many possibles like a bad pilot bearing, a wobble in the clutch disk, a too thick and soft disk lining, a pressure plate that is not releasing squarely, wrong trans oil. etc, etc & on & on. Read my section on "How to extend the life of a straight stick gearbox" on my website too. http://mg-tri-jag.net under " Tech tips"
One other thing I forgot to ask you. Is the problem worse while the trans oil is cold and is it better when you have been driving a long time. (trans oil warm)?
While working in a BLM dealership, we always used engine oil in the MG trans but BLM (British Layland) told us to start using gear oil. We then started having gear crunch complaints and we went back to engine oil and told BLM that they should try to learn something about cars and stop telling us how to work on cars. Ha! In the early 70s Dodge had the same problem. They used gear oil in their straight stick trans and all Dodge mechanics learned to put automatic trans oil in place of the gear oil and the trans would shift good then.
I haven't used automatic trans fluid in a BLM car but have solved many trans and overdrive problems using engine oil in place of gear oil.
Howard
