# Re: Knocking in the rear at low speeds and at shift change



## ddigital99 (May 3, 2005)

*Re: Knocking in the rear at low speeds and at shift change*

Hey Everyone,

I'm new to the board, I have a 88 300ZX Turbo Automatic and I'd like to know if any of you have had these problems or know what they could be.

Problem 1 - Car idles low with some backfire after highway use.

Problem 2 - Knocking or tapping in the rear at low speeds or at shift change between first and second gears.

Any help would be greatly appreciated. I'd hate to take it to a mechanic and get taken to the cleaners. Thanks in advance!

D


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## ddigital99 (May 3, 2005)

Actually Problem 2 - is a Knock or Tap in the rear is when I hit the gas or at shift change between first and second gears.

Thanks in advance.


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## BoBakTXL (Aug 30, 2004)

The Z31's had a tendency to have a defect I think inthe rear driveshafts, mine does the same thing. A loud thump in the back, dont forget... even with the clutch ALL THE WAY in to the floor, there IS still some pressure go the rear end, very un-noticeable pressure, its so low that it cant make a car move AT ALL, but anyways, that means that because the driveshaft needs replacment, meaning theres "slop" in the rear end, the thump wont ever go away.

Replacing I think the driveshaft will fix the problem, but wait for someone else to reply to know exactly what to replace.


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## Zen31ZR (Mar 24, 2004)

There is a plate on the back of the differential that connects the center pumpkin to the subframe. The connectors are made of rubber in its stock form and can conceivably wear out and break loose. Every time you shift, or the engine applies torque, the nose of the diff could be coming up and smacking the floor back there. This also creates a lot of strain on the U-joint back there, it could break eventually.


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## z31 (Oct 19, 2004)

problem 2 = most likely crossmember bushings and/or differential mount.


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## JAMESZ (Mar 12, 2004)

z31 said:


> problem 2 = most likely crossmember bushings and/or differential mount.


Yep. 

Worst case scenario the u-joint in the driveshaft is dead, but what z31 said is probably the cause.

Also run the codes on the ecu for problem number one and see what comes up.


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## Zen31ZR (Mar 24, 2004)

z31 said:


> problem 2 = most likely crossmember bushings and/or differential mount.


 Could be, it is an auto. But if the transmission was shifting around, he'd feel the thump right about where he sits, that's where the back of the transmission is.


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## Xorti7 (Dec 27, 2004)

Zen31ZR said:


> There is a plate on the back of the differential that connects the center pumpkin to the subframe. The connectors are made of rubber in its stock form and can conceivably wear out and break loose. Every time you shift, or the engine applies torque, the nose of the diff could be coming up and smacking the floor back there. This also creates a lot of strain on the U-joint back there, it could break eventually.


When i shift or take off from a stop, and really hammer on it, the back end makes a loud "thump". Is this what you're talking about? What can i do about that? I have a 88t manual if thats of any importance.


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## ddigital99 (May 3, 2005)

Thanks for all of the input fellas. Much appreciated!

Problem 2 - I took her to a Z mechanic today and he said it's probably the differential mount. I'll get an update tomorrow when he gets underneath there and I'll post his findings. 

*If it is the differential mount how much do you think I'll be looking at? I'd just like to have a ballpark figure so I know what to expect and I'll also be able to see if I'm getting an O.K. deal  * 

I'll ask him how the U joint and Driveshafts look.

Problem 1 - Codes on the EDU. will do. It only happens when I drive on the highway for more than lets say 20 min. It idles low and sounds like it wants to shut off. I'll usually give it some gas to make sure she doesnt stall. 

Thanks again! I'll keep you guys posted.


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## JAMESZ (Mar 12, 2004)

Xorti7 said:


> When i shift or take off from a stop, and really hammer on it, the back end makes a loud "thump". Is this what you're talking about? What can i do about that? I have a 88t manual if thats of any importance.


Replace the differential mount. The rubber bushings are bad.


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## z31 (Oct 19, 2004)

http://www.thespecshop.com/solid_diff.asp


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## ddigital99 (May 3, 2005)

Nice!

Thanks!


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## ddigital99 (May 3, 2005)

*I got my bill today from the mechanic*

I got my bill from the mechanic today for that issue i posted regarding a knocking in the rear when takin off or between 1st and second gears in my automatc transmision 88 Turbo,

Here's the breakdown - 

Replace rear crossmember bushing - $112(parts) - $280(labor) = $393
Replace differential mount - $166(parts) - $35(labor) = $200
Nodify crossmember for camber adjustment - $0(parts) - $140(labor) = $140
computer 4 wheel alignment - $59 - = $59

+ $35 shop fees
+ $60 tax

and a grand total of $886.00

is this a fair deal?

All input greatly appreciated.


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## Zen31ZR (Mar 24, 2004)

ddigital99 said:


> I got my bill from the mechanic today for that issue i posted regarding a knocking in the rear when takin off or between 1st and second gears in my automatc transmision 88 Turbo,
> 
> Here's the breakdown -
> 
> ...


Labor is always expensive. It cost me $1000 to have a broken exhaust stud drilled out of a head once......


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## ddigital99 (May 3, 2005)

z31 said:


> problem 2 = most likely crossmember bushings and/or differential mount.


Dead on it appears!

Good call.


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## Zen31ZR (Mar 24, 2004)

ddigital99 said:


> Dead on it apears!
> 
> Good call.


Mentioned that in the 4th post, thanks.


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## z31 (Oct 19, 2004)

ddigital99 said:


> Replace rear crossmember bushing - $112(parts) - $280(labor) = $393


$112? For $40 bushings?

http://www.zcarparts.com/store/merchant.mvc?Screen=PROD&Product_Code=23-4148&Category_Code=PSDC06D


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## ddigital99 (May 3, 2005)

z31 said:


> $112? For $40 bushings?
> 
> http://www.zcarparts.com/store/merchant.mvc?Screen=PROD&Product_Code=23-4148&Category_Code=PSDC06D


Thanks man! I appreciate you picking that up. I'll bring that up and see what he says.

Are those bushings(on the link) the same as crossmember bushings? 

Any other input would be appreciated.


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## ddigital99 (May 3, 2005)

ddigital99 said:


> Thanks man! I appreciate you picking that up. I'll bring that up and see what he says.
> 
> Are those bushings(on the link) the same as crossmember bushings?
> 
> Any other input would be appreciated.


I think he said the turbo crossmember bushings were more, but I'm not sure. Anyways I'll bring it up. 

Thanks again.


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## z31 (Oct 19, 2004)

ddigital99 said:


> I think he said the turbo crossmember bushings were more, but I'm not sure. Anyways I'll bring it up.
> Thanks again.


They're the same. The poly ones are at least.


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## JAMESZ (Mar 12, 2004)

z31 said:


> They're the same. The poly ones are at least.


They are the same stock. Price is about right if you figure labor in and all. If you can do it yourself it would be far cheaper. Also look other places for parts some of the prices are alittle steep.


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## ddigital99 (May 3, 2005)

Thanks fellas. Work is done and she feels great!

I spoke to the mechanic about it and I feel he justified the price good enough. At least it gave me something to bust him on, so he wont get too loose with the billing in the future.

Thanks again!


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## z31 (Oct 19, 2004)

JAMESZ said:


> They are the same stock. Price is about right if you figure labor in and all. If you can do it yourself it would be far cheaper. Also look other places for parts some of the prices are alittle steep.





> Replace rear crossmember bushing - $112(parts) - $280(labor) = $393


He quoted $280 for labor. The $112 for parts is where i took issue. :cheers:


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## Darkstar (May 31, 2005)

my god, mine does the same thing, i never thought it was anything more than my transmission though. as it is my transmission needs replacing. it's that or rebuild it mainly for second gear and its syncros. it usually happens only after a long highweay drive when i'm stopped at a toll and wanna inch up.

i need to replace something else?


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