hard shifting 300sl

[greg walsh]

Thought I'd put this out again,I haven't gotten any replies earlier. When changing gears my 86 sl bangs fairly hard. More noticeable at lower speeds.Next weekend I'll change the transmission fluid and see if that helps,someone wrote about synthetic fluid maybe I'll try that.Vacuum lines seem o.k. Any help will be appreciated. Greg.

[Softball60]

What you are probably hearing is probably the rear end. Not familiar with the 300SL. I have a 1989 560SL. Years of wear make things loose.

When you do the trans also change the fluid in the rear end and check the driveline plus the half shafts check for play.

[Softball60]

Forgot, Make sure you change the filter in the trans!!

[SunGuy]

When I had this same problem in my '87 SL, the 'clunk' I was getting on shifts turned out to be the transmission shift modulator. Essentially, it's an adjustable vacuum fitting mounted to the passenger side of the transmission that controls shifting 'smoothness'. The vacuum line that feeds the modulator is the 'main' line that orignates from the rear of the engine manifold and runs to the trans. This line should be checked at the trans end to insure that it holds vacuum. Then using the adjuster on the modulator to increase or decrease, turn it 1/4 turn, then test drive the car. Repeat adjustments until it shifts the way you want. If it turns out that the modulator is bad, a replacement is under $50 and about 5min to install. Virtually any transmission tech can do this service for you; you don't need a Dealer or even an MB trained tech for this.

Re the trans service, remember to drain the torque convertor as well as the trans, install a new filter and pan gasket and a pan magnet should be installed if not already present. The magnet (around $8) serves to collect particles in the fluid.

Pls post how you make out with doing this adjustment, befor getting into flex disks, rear diff, drive shaft etc. In other words, start with the simplest (and cheapest) possible solution and go from there. Good luck w/your car.

Bob

[whunter]

Originally Posted by greg walsh

Thought I'd put this out again,I haven't gotten any replies earlier. When changing gears my 86 sl bangs fairly hard. More noticeable at lower speeds.Next weekend I'll change the transmission fluid and see if that helps,someone wrote about synthetic fluid maybe I'll try that.Vacuum lines seem o.k. Any help will be appreciated. Greg.

Here is a cheap common issue.

The rubber vacuum cap on the modulator valve becomes brittle, cracking and leaking = harsh shifting.

This cap is often overlooked, and causes needless replacement of the valve.

Rubber Cap - Modulator Valve
MB# 1262770081
Pelican Parts - Automotive Parts and Accessories - Porsche & BMW

related data
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[greg walsh]

Thanks so much for all the information, Greg.