Why does my transmission shift poorly?

Important: If your clutch is dragging, stop driving the car immediately. Read Jack's transmissions Clutch Drag Kills Syncros.

Poor shifting is a hallmark of 1G cars. 2G owners have vastly improved transmissions, and do not generally suffer from bad shifting. If you have a 2G that has shifting problems, you must read  about possible problems with crankwalk on the 2Gs.

For 1G cars, there are several fixes.  There are also several TSBs on this problem, for various years.  Check the NHTSA site for TSB information.  Remember, TSBs are neither warranties nor recalls.

Solution #1 came up in 1992 when the first TSB called for adding a 'friction modifier' to the transmission fluid.  The modifier increases the frictional coefficient of the fluid, so the synchronizer rings (synchros) match speeds faster.  There have also been several synchro design updates throughout the various years, intended to improve the crunchy shifting.  Of course, to take advantage of these requires a transmission rebuild.

Many DSMers recomment using Redline MT90 or Genuine Mitsubishi DIA Queen in place of the Redline MTL from years ago. Not many are left using BG Synchroshift or GM Synchromesh days due to claims of early syncro failure among the majority.  All of these fluids have the same purpose - to increase friction, just as the Mitsu fluid modifier is intended to do.  Most owners report at least some improvement with the new fluids, but most experience significantly better shifting. Opinions and experiences vary.

Recent experience suggests that Redline MTL gains in shifting performance by sacrificing synchro longevity. This is not exactly news, but more and more owners are reporting this problem with MTL now that there are alternative fluids available. Many owners considered the tradeoff to be well worth it. However, more people are now recommending a mix of Redline MTL with MT-90 gear oil, to combat both problems at once or just use straight MT-90.

Poor clutch disengagement has recently become a suspect for poor shifting in DSM cars. Refer to [[What are the symptoms of poor clutch disengagement?]] for more information. There is a great writeup on hotrod.com | How to Diagnose Your Own Clutch System Problems - Be Your Own Disc Doctor (or download archive PDF)

Problems have sometimes been found in the shift linkage as well, leading to the Tighter Shifter Page (90-94) (or download archive PDF) that describes how to rebuild the linkage in 1G DSMs for improved performance. Kyle Jones even found that an incorrect aftermarket lower radiator hose was interfering with his shift cables and causing crummy shifting; cutting the hose shorter did the trick.

The Last Word: Eric B. would like to add:

"On the topic of Redline gear oil eating away the syncronizers in your transmission, there is a reason for that. It is the wrong API service grade (GL-5). Chemically, GL-5 isn't friendly with brass and will deteriorate your syncros, which is why differentials and transfer cases seemingly only call for it. Almost all (if not all?) transaxles require a GL-4 service oil. This is most overlooked by everyone. I found out the hard way also from my other car's transmission. I verified this being the cause of failure from a handful of machinist and transmission specialists. By mixing it as stated on the page, it is merely being dilluted and the corrosive effect is still existing, but reduced."

Sean Costall: "Personally, my car has had MTL and Syncroshift in it since '96, and it still shifts fine on the original tranny. YMMV. [Thanks, Eric!]"