1981 auto trans shifting issue
Thread Starter
Heel & Toe
Joined: Oct 2015
Posts: 21
Likes: 0
From: Sun City Center Florida
1981 auto trans shifting issue
1981 original automatic trans delayed shift into each gear with clunking (?) sound when shift does occur. Had been running fine, no unusual driving events. Fluid change (can't find trans fluid dip stick), linkage problem??
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
Transmission dipstick is at the right rear corner of the engine. 3 speed auto (TH350 or TH350C) could be a poor vacuum signal to the trans. 4 speed auto, (700R4) the TV cable may need adjustment.
Drifting
Joined: Aug 2019
Posts: 1,334
Likes: 225
How many miles on this car? Has the vacuum modulator ever been replaced? The original was blue. What is the condition of your fluid?Can you tell where the clunking is coming from? Does it change based on throttle position? If you did a fluid change, how did you add fluid?
The dip stick is right along side of the distributor shield on the passenger side.
The dip stick is right along side of the distributor shield on the passenger side.
Thread Starter
Heel & Toe
Joined: Oct 2015
Posts: 21
Likes: 0
From: Sun City Center Florida
37,056 miles - can only find 1 dip stick and it appears to be oil and shows full. Have mechanical work done for me and no bills show vacuum modulator so no. clunk comes from below my feet when gear is being shifted. Owned car for 3 years and trans fluid changed frequently but not in last 6 months. Looking for potential causes to tell mechanic so thank you for responding
Race Director
Joined: May 2006
Posts: 18,690
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The first problem is why can't you find the dipstick?
It is pretty obvious if it is there, did your mechanic fail to reinstall it?
Passenger side of car near firewall, please look to see if you see the tube with no dipstick inserted.
It is pretty obvious if it is there, did your mechanic fail to reinstall it?
Passenger side of car near firewall, please look to see if you see the tube with no dipstick inserted.
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Thread Starter
Heel & Toe
Joined: Oct 2015
Posts: 21
Likes: 0
From: Sun City Center Florida
I have searched in the cold light of day and with a flashlight and see only one dip stick (with green handle). No open tubes either only wire harnesses and sparkplug wires. While I no longer do mechanical work, I have some aged experience so it is either buried under the back of the motor cage or not attached???? In either case I will have someone check it out along with your other suggestions
Thread Starter
Heel & Toe
Joined: Oct 2015
Posts: 21
Likes: 0
From: Sun City Center Florida
Thank you for your help - and I'll eat crow (and have my eyes uncrossed) if the mechanic shows me the dip stick sitting right where you said it should be. I will let you know.
Drifting
Joined: Aug 2019
Posts: 1,508
Likes: 495
Transmission dip stick is hiding underneath the Distributor Cover right next to the distributor on passenger side
Shifting late and hard sounds like the vacuum Modulator hose fell off . Does the engine still running good ?
Shifting late and hard sounds like the vacuum Modulator hose fell off . Does the engine still running good ?
Thread Starter
Heel & Toe
Joined: Oct 2015
Posts: 21
Likes: 0
From: Sun City Center Florida
Found it, now know what I'll be eating for dinner (crow) pushed back black shield covering distributor cap and walaa!
fluid looks clean and very full. engine still running fine.
Where is the VM hose located?
fluid looks clean and very full. engine still running fine.
Where is the VM hose located?
Thread Starter
Heel & Toe
Joined: Oct 2015
Posts: 21
Likes: 0
From: Sun City Center Florida
Found location of vacuum modulator and will get younger half of our team to check it out and will let you know if loose hose is the culprit. Thanks again to everyone who responded.
Race Director
Joined: May 2006
Posts: 18,690
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If yes and too full the fluid will aerate.
Drifting
Joined: Aug 2019
Posts: 1,334
Likes: 225
While your under there, check the trans mount and bolts. Also check the driveshaft u joints for play.
Thread Starter
Heel & Toe
Joined: Oct 2015
Posts: 21
Likes: 0
From: Sun City Center Florida
no sir, just checked cold after being happy I found dip stick. We will be looking over hose, trans mount and bolts and drive shaft tomorrow provided the hurricane stays on the same path. If we don't find any fault there I will have it looked at by a mechanic and ask specifically if the amount of trans fluid is correct. I will post any significant findings.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
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From: Cool Northern Michigan
The modulator is connected by a short piece of vacuum hose to the tranny. Sometimes they have hose clamps, some don't. Due to the heat from the nearby exhaust, that chunk of hose will dry rot and crack open. The crack could be on the invisible back side. This creates a vacuum leak and effects shifting.
If you want to change your shift-points, (up or down) the modulator is available in a adjustable unit, with a allen key.
If you want to change your shift-points, (up or down) the modulator is available in a adjustable unit, with a allen key.
Thread Starter
Heel & Toe
Joined: Oct 2015
Posts: 21
Likes: 0
From: Sun City Center Florida
Jacked the car up and found the modulator and everything is connected but a previous owner sprayed silver paint over everything in that area so we couldn't see the true condition of the hose or if it is the original unit (blue?).
My plan is to take it to the shop to replace the modulator and go from there.
Thanks again to everyone and I will make another post with what fixes the problem only if a new modulator is NOT the fix.
My plan is to take it to the shop to replace the modulator and go from there.
Thanks again to everyone and I will make another post with what fixes the problem only if a new modulator is NOT the fix.