I'm new to this site. I have a 91 honda accord that the transmission shakes or "shimmers" at 40 mph. It DOESN'T SHAKE WHEN IN "SPORT" MODE. I know it's not a tire or bent rim. Both axles are basically new " a year old or newer". I. I changed the fluid (not flush). I used actual honda ATF. It has been shaking before I changed it. I was hoping it would fix it but no luck. I'm a fairy good back yard mechanic. But I don't know much on Honda's or automatics. I've always had standard shift trucks. There are no flashing lights from the indicator lights, no check engine lights. It has about 278,000 miles bit has been maintained well. Any info would GREATLY APPRECIATED.

 

Being new to the site is awesome, I remember when I first joined years ago. Its a great common ground for ideas, problems and solutions.
I'd like to see a super clean, organized forum but I'm sure that will happen some day. It just gets full of brief, un-self respected redundancies so when I see your post here with YOU, then thats what we want.

Heres what I'm thinking,
If it doesn't shake in sport mode, ya know what that tells me? it's your computer, the TCU or "transmission control unit".
That doesn't mean it has to be your real problem though, it just could be...
The sport mode button is simply an activation of a different shift logic within your TCU.
All the same internal transmission components are used in either mode, sport on or sport off, I do know that.
The components ARE used differently however from mode to mode.
What we need to differentiate is what the changes are in operation between the two modes.
If for example in sport mode there is a design built into the TCU's logic that increases fluid pressure for example to certain clutches then we may find our problem, a clutch that slips.
(they would do this for a change in the shift duration or a harder shift if you were wondering)
Your problem however is that it shakes and that is almost certainly due to a slipping clutch.

Heres some other things I'd say:
278,000 miles is pretty much the time when you'd start to see a problem like this
Changing the fluid was a good move
Axles that have worn joints can vibrate and cause this symptom, good check there, also make sure they are fully seated in the transmission's differential and that the axle nuts are tight

Hope this helps,
-Ian

 

thanks man. It's weird it doesn't do it all the time now I'm guessing electrical (TCU). I've got a all honda junk yard about 20 mins from me. But is there a way of checking these things before installing the same problem from another car or maybe something even worse

 

The fact that it doesn't shutter @ 40mph all the time and is intermittent makes me think it might not be a clutch slipping due to the failure of the actual clutch but because
there is some sort of blockage in the valve body of the transmission, like fluid flow is intermittently interrupted by something.
There is a filter but it is internal and requires alot of work to access. Other possibilities are a failing clutch or bad TCU. Apparently the 90-91 Accords are known to have a couple internal TCU parts that go bad (resistors and capacitors). You can find TCUs for like $60 on eBay. Do be careful in fully diagnosing what you can first though because a failure of the TCU can also be caused by the failure of one of the components it controls like a solenoid. It doesn't hurt to try and see if there are any codes stored in the TCU's memory even if you don't have a lit indicator light.

Retrieving Codes:
Find the connector shown in the picture, it's just chillin down there not connected to anything.
Short the two terminals A and B together and watch the 'S' light or 'D4' light on the dash.
Codes are read by the length of flashes of either the 'S' or 'D' light, the 1's digits are short flashes and the 10's digit are long flashes.
For example, if you get two consecutive short flashes, you have a code "2", if you get two consecutive short flashes and a long flash, you have a code "12".
There is a 1 second pause between codes if there are multiple codes stored.

1-Lock-up solenoid 'A' circuit open or shorted.
2-Lock-up solenoid 'B' circuit open or shorted.
3-Throttle Position Sensor circuit open or shorted.
4-Vehicle Speed Sensor open or shorted - No signal from speedometer.
5-Shift Lever Position Switch circuit shorted.
6-Shift Lever Position Switch circuit open.
7-Shift Solenoid 'A' circuit open or shorted.
8-Shift Solenoid 'B' circuit open or shorted.
9-Counter shaft or transmission speed pulse generator open or shorted.
10-Coolant Temperature Sensor open or shorted.
11-Engine RPM ( signal) open or shorted.
12-(No code 12 used)
13-Main shaft speed pulse generator open or shorted.
14-Linear (line pressure control) solenoid open or shorted.
15-Kick down switch circuit shorted.

Another thing you might want to check is the throttle valve. Connected to the engine's throttle body are two cables, one of them is the actual accelerator pedal's throttle cable,
the other is a cable that runs to a little arm on the transmission called the throttle valve. Basically when you push the throttle, this cable is used to move throttle valve on the transmission allowing it to understand how much demand is being applied. If the cable or throttle valve arm itself are stuck or sticking, or if the cable is not correctly adjusted then the transmission may be attempting a shift or torque converter lock up when your just at a cruise due to incorrect throttle valve input to the transmission. Real easy to check out.