Clunking/thudding while shifting/rough idle

How-to's and repair secrets for your 4WD can be found here. Have a question? Ask it in here!
Post Reply
rex
Newbie
Posts: 4
Joined: Fri Apr 13, 2018 2:55 pm
My tercel:: 1983 4WD

Clunking/thudding while shifting/rough idle

Post by rex » Sat Apr 27, 2019 1:37 am

Hi all,

First off, thanks in advance for this rad forum! I recently bought a ‘1983 Toyota Tercel 4WD manual transmission, and I’m really excited to get her back in shape.

1st question: I just did some work checking vacuum leaks, as it was failing smog, and I found it had a poorly functioning TVSV. I replaced it and checked the EGR, etc, and got her to pass! Now, however, the idle seems to struggle even after warm up. It doesn’t stall, but I definitely notice the vibration and that it seems to struggle, also I was cruising in 2nd gear yesterday (going downhill) and she seemed to backfire-but ever so slightly. It has been timed to 5deg BTDS, and stays roughly around 900RPM. Time to clean the carb? I checked for leaks around the intake manifold and base of carburetor, but didn’t notice anything significant.

2nd Question: The car has a rebuilt transmission (with about 20,000 miles on it)-but I notice a lot of clunking when I shift gears, unless I shift very very slowly, which I still get the thudding/clunking from (especially when going from 1st-2nd, and 2nd to 3rd. If I am completely stopped and shift super slow I can limit the thudding. It’s kind of a dull sound, a thump? But I can feel it, as if the transmission is moving when I shift. Maybe bad synchros? I was also thinking it could be the CV axles. NOTE: I am pretty sure the ball joints are near-shot, because I can hear the car clunking/feel vibration in a sharp turn-could all these loose parts on the front end contribute to the thudding of the transmission? Any help would be much appreciated!

Thanks,

Rex

User avatar
dlb
Highest Ranking Member
Posts: 6545
Joined: Mon Jul 06, 2009 9:03 pm
My tercel:: none currently, 7 previous
Location: shawnigan lake, bc, canada

Re: Clunking/thudding while shifting/rough idle

Post by dlb » Sat Apr 27, 2019 9:06 am

Hi rex. Despite being the factory recommended setting, I usually found 900 was a little low for idle in T4's so I would first try increasing it to 950 rpm or so and see how that goes.

When it backfired, did it come out the carb or exhaust? That will indicate whether it was detonating too early or too late. I usually found it was related to timing so you may want to double check your timing (make sure you have the vacuum advance disconnected and plugged when you check it).

A rebuilt trans with only 20,000 miles on it shouldn't clunk. Either someone did a lousy job or they lied to you. Regardless, you should check the transmission oil level and make sure there is plenty of it because low oil in there will kill a trans fast. Look up how to check it on here, it's not hard. If you find the level is ok, you might want to try a different trans oil. There is an ongoing discussion here about what to use -- some people swear by full synthetic, some people swear against it, so you just have to read a bunch and make a decision for yourself. But from what you describe, it does not sound like front end components are the cause of your thudding (being completely stopped and still getting thudding is the big giveaway).

Good luck.

rex
Newbie
Posts: 4
Joined: Fri Apr 13, 2018 2:55 pm
My tercel:: 1983 4WD

Re: Clunking/thudding while shifting/rough idle

Post by rex » Sat Apr 27, 2019 10:07 am

Thanks, per question 1: The backfire came out the exhaust, so maybe too late? Also, it doesn’t happen often, and I remember that I may have been in a rush to get home after a long night at work, and not let the car warm up properly. It often takes a good 3-5min to warm up after its been sitting for more than a few hours (which I figured was normal?).

Per question 2: To clarify, the thudding happens when accelerating from a stop, 1-to-2, and from 2-to-3-but I’ll double check and see if it thuds when it’s in first gear from a full stop. I agree that it could be a crappy rebuild, I have a receipt for it from the previous owner, but other work done on the car seems half-assed. My buddy and I checked the trans oil about a week ago, and gear oil came out of the filler hole clean, I’ll check it again, and make sure it’s topped up.

I do think the ball joints need to be replaced, but I know that’s a separate issue, definitely getting vibration and a “clunk clunk clunk”/loose feel when turning sharply.

I also be checking the motor mounts/transmission mount/u-joint, and I’ll update upon inspection.

Thanks again!

User avatar
dlb
Highest Ranking Member
Posts: 6545
Joined: Mon Jul 06, 2009 9:03 pm
My tercel:: none currently, 7 previous
Location: shawnigan lake, bc, canada

Re: Clunking/thudding while shifting/rough idle

Post by dlb » Sat Apr 27, 2019 1:54 pm

It shouldn't backfire ever, whether it's warmed up or not, so do double check the timing.

Ah, thanks for the clarification. Clunking on starts, stops and shifting is usually due to worn front end stuff: CV axles, tie rods, ball joints, strut mounts, engine mounts, etc. If you get a clunking on sharp turning, you definitely have a bad CV axle so that may also be the source of your shift clunk. It's important to note: ONLY BUY NEW CV AXLES, do not buy remanufactured ones! Many of us here have had remans that are garbage out of the box. New ones are still available on rockauto.com, and you can usually find the latest 5% discount code for that site here on the forum. If you get the clunking when turning left, it is the right CV that is bad.

You can check and replace the ball joints if necessary when you do the CV.

User avatar
Petros
Highest Ranking Member
Posts: 11265
Joined: Sun Jan 28, 2007 6:31 pm
My tercel:: '84 Tercel4wd w/extensive mods
Location: Arlington WA USA

Re: Clunking/thudding while shifting/rough idle

Post by Petros » Tue Apr 30, 2019 1:27 am

welcome to the form:

backfiring, likely the fuel cut off solenoid is not working. when down shifting it should cut off the fuel supply and prevent back fire, either the vac hose is not routed properly, or it is leaky or disconnected, so it is getting the incorrect vac signal. soloing and vac lines are an is an easy check, see the factory service manual procedure (free down load from elsewhere on this site).

there is a procedure for setting the throttle linkage and the throttle breaker. There is a small diaphragm with a push rod that keeps the throttle from slamming shut on the front of the carb, opposite from the throttle cable. if not adjusted properly it will cause stalling possibly back firing. easy adjustment, but important to have it correct. check operation of choke as well, if not opening it will be too rich, and be down on power and back firing. See the service manual for these procedures, they are easy once you know what to check/adjust.

Also, I suggest advancing your timing to 10 or 12 deg BTDC to improve power and economy, and lower exhaust temps (high exhaust temps have been known to cause exhaust valves to fail and can cause catastrophic engine failure when the valve head breaks off). the 5 deg setting is for emissions, so you put it back there before the next test, but the factory setting can cause you to wreck the engine, and require a replacement (whey the valves break loose in side the engine it almost always results in the engine needing to be scrapped, it can not be rebuilt).

bad sycros do not cause clunking, usually the trans does not either (you get bad grinding noises out of a bad trans, not clunking). but the engine and trans mounts (if bad) or the cv axles can cause clunking. also check all of the front suspension mounts, bushings, rubber parts, ball joints and tie rod ends, as well as the upper strut mounts. if bad they can clunk (it will be obvious, no need to replace them if they are in tight and there are not shreds of rubber hanging out of them). Also, check the u-joints on the rear drive shaft, and the center bearing. it is mounted in a big rubber bushing, so it should have some give, but the joints should be tight and no play in the center bearing.

Good luck.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)

Post Reply