# Gear Shift rattle during deceleration...



## tewasch (Nov 2, 2009)

While I've read along for a long time, but this is my first post.

I'm converting a 1981 Jeep CJ5 and got to drive it around for the first time last week. I have a number of things to work on.

It runs quite fine in all gears going forward and reverse. However, when I'm coasting or going down hill, the "back pressure" of the electric motor causes a rattle in the gear shifter (like it wants to pop it out of gear). If I apply a slight amount of pedal, it goes quiet. It also goes away if I go ahead and pop it out of gear (using the shifter). It sounds like teeth are chattering, but it stays in gear.

This is the same light-duty SR4 transmission that (I believe) the S10 pickup truck uses, so I thought I'd see if anyone had any experience and/or suggestions for this.

I must say, that I pulled the donor Jeep out of a guy's garage in peices, and it's taken me a long time to first restore it as it may have had some abuse (large tires, lifted, etc.---this is all removed now).

I have a twin 1981 CJ5 gas-powered 4-cyl with the same transmission and I don't get this kind of behavior when down-shifting. However, I don't have any experience with using this as a comparison to an electric application--especially with REGEN.

Any thoughts? I'm presently using the Curtis controller's stock settings (i need to build a cable and figure-out the command set to be able to make some adjustments here). 

Thanks. Tom.


Particulars:

Donor: 1981 Jeep CJ5, manual SR-4 transmission, stock (light duty) transfer case, manual brakes, manual steering
GM small-block adapter plate from Candian EV to stock bell housing
Presently removed front drive-shaft

34 200Ah Thundersky batteries
EV Display fuel gauge
MiniBMS (distributed) BMS
Curtis 1238-7501 controller
AC50 9" Ac motor
2/00 wiring


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## etischer (Jun 16, 2008)

Do you have enough fluid in the transmission (and transfer case)? My tranny makes a rattle when it is low on fluid. 

Could the rattle have something to do with the front driveshaft missing?


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## tewasch (Nov 2, 2009)

Thanks for the reply. Fluids are fine, but you have me thinking about the extra degree of freedom once I removed the front drive shaft. I have the transfer case in 2-wheel drive, but I'll take a look at that.

Again, thanks. Tom.


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## DavidDymaxion (Dec 1, 2008)

My Jeep Cherokee had a rattle. It was intermittent, and sometimes would go away if you cycled the clutch. It turns out the pilot bearing was missing! I'm amazed it worked as well as it did the majority of the time.


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## tewasch (Nov 2, 2009)

I learned that the hard way on another Jeep. It gave a painful sound in reverse (only). Nope, in my electric Jeep I soaked the bearing and installed it as required. Good thought though.

The missing pilot bearing was defintely a sound near the motor where this is a sound right at the bottom of the gearshift. Hmmmmm.

Thanks for the reply. Tom.


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## etischer (Jun 16, 2008)

Maybe your tranny is just worn out =) 

Does it change with temperature?

I thought had a clunk in my drivetrain, turned out to be software / tuning related. I was reducing speed demand and torque demand together which caused an instablity. 


If the motor is slowing down nearly the same rate as the car is slowing down, this can cause it to go in and out of regen and might cause the backlash in the gears to make a rattle. You might be able to tune this out.


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## EV-propulsion.com (Jun 1, 2009)

As long as your pilot bearing is in good shape as you say, I believe your transmission is worn, during decel you are loading the opposite side of the gearteeth thats why it doesn't do it on accel. The next phase of wear will be popping out of gear. It proably did that with the last owner and the ICE. You may want to ask this forum user FB Performance Trans who has a transmission shop, and could probably be more specific for that model.
Mike
www.EV-propulsion.com


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## tewasch (Nov 2, 2009)

Yep, this is what I think is going on (of course, the tranny could be questionable too). My experience with manual transmission problems typically is around shifting gears--not when I'm just staying in one gear. But I suppose one side of the teeth could be in really bad shape?

I have to dive into the controller next to understand all of what they're doing there. I know the controller supports REGEN and this smells of a weird feeback loop somewhere. The front drive-shaft is an interesting avenue to look at as well. I can check that out quickly.


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## EV-propulsion.com (Jun 1, 2009)

I think the teeth are ok, just that the thrust is the opposite way when decellerating(like pushing the mainshaft forward instead of rearward-or vice versa) against a worn thrust bearing. This would cause pressure on the shift collars because of excess play and transfering it up through the shifter. Just an educated guess though.
Mike
www.EV-propulsion.com


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## tewasch (Nov 2, 2009)

Thanks very much for your knowledge here.

What can/should be done about it or is this normal for this type of transmission? The noise from driving as-is would scare anyone as you started to go down a hill or on a longer coast.

Tom


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## EV-propulsion.com (Jun 1, 2009)

It's not normal for any transmission to do that, but it is somewhat common, I have seen it years ago on big trucks......
Does it get better or change if you put pressure on the gearshift lever one way or another? Also, does it do it in all gears?
Mike
www.EV-propulsion.com


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## FB Performance Trans (Dec 14, 2010)

EV-propulsion.com said:


> As long as your pilot bearing is in good shape as you say, I believe your transmission is worn, during decel you are loading the opposite side of the gearteeth thats why it doesn't do it on accel. The next phase of wear will be popping out of gear. It proably did that with the last owner and the ICE. You may want to ask this forum user FB Performance Trans who has a transmission shop, and could probably be more specific for that model.
> Mike
> www.EV-propulsion.com


Mike, I believe you’ve probably hit it right on the head. We don’t specialize in “stick” type transmissions but most transmissions will respond in the same way when going into a coasting mode. It’s typically called “engine braking” and it will apply more stress to the transmission. This effect becomes more obvious when the transmission is downshifted into a lower gear and then coasted. 

Because the automatic transmission is hydraulically operated and incorporates a torque converter the applied internal stress when the coasting is initiated will be somewhat reduced due to the fluid dampening.

Aside from the possibility of the transmission being worn, we would also recommend double checking the stability of both the motor and transmission mounts.


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## tewasch (Nov 2, 2009)

Mystery solved---

I thought it would be good form to post the solution here. In fact, the transmission was the problem (rattling out of gear when coasting). I pulled it and had it rebuilt including changing the 2nd and 3rd gears. By inspecting the teeth, we could see how poorly the wear pattern was (some shiny, some not) and that there was no longer any back cut in the tooth to help it stay in gear.

I just got the rebuilt transmission back in yesterday and all is well. Thanks all for the help.  Tom.


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## tewasch (Nov 2, 2009)

Mystery solved....

I thought I'd close this out and document it in case others ran into the same problem.

The issue with the transmission rattling itself out of gear was dramatically improved by rebuilding the transmission; however, the root cause was still present.

It ended up that the real problem was the pinion angle. I'm converting an older Jeep CJ5 and the donor had a high lift kit installed which I cut off. I made a mental note that the pinion angle was wrong at the time, but I hadn't fixed it yet. It was almost 20-degrees off. Once I tore it all down and rotated the leaf-spring perches, it fixed it beautifully. Everything is nice and smooth now.

Tom.


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