The 75 and ZT Owners Club Forums - CDTI Undertray clips

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CDTI Undertray clips

Evening all.

My undertray is hanging down on my CDTI facelift contemporary. Half the clips are missing and as I dont have access to ramps it's a pain in the hoop to get the central 2 bolts/clips.

2 questions.

1. Is the undertray really that effective? has anyone took theirs off completely and the car suddenly rusted from bottom up??

2. I can find the clips on ebay for the front bumper. They're the long screws with what appears to be 1 incredibly course thread on the end. Are the 2 central screws the same as these?? as they completely missing and my undertray is hanging like a hammock!.

Cheers all.

Sorry those are hopeless..:D:duh:;

Had some .too soft and just jam up .

And single slot :duh::duh:
Well that's my experience .:o

Hello Robert,

To answer your questions:

Quote:

Originally Posted by DaylightRovery (Post 2759817)

1. Is the undertray really that effective?

Do you think that a car manufacturer would go to the trouble and expense of making and fitting a component that wasn't effective?

As I understand it, the undertray performs two functions:

Aerodynamics. It smooths airflow under the car which the theory probably tells us improves roadholding.
Protection. It stops rainwater splashing upwards causing corrosion and electrical faults.

Quote:

Originally Posted by DaylightRovery (Post 2759817)

2. I can find the clips on ebay for the front bumper. They're the long screws with what appears to be 1 incredibly course thread on the end.

The best fittings are not found on e-bay. They are the genuine MG Rover Dzus fasteners. These are released with a 180˚ turn of a Posidriv bit. The spigot is retained on the undertray with a nylon washer. Omitting these washers is the main reason why the fasteners are lost and the undertray hanging down.

I have the OEM Dzus fasteners on my car. I don't agree that the parts offered by DMGRS are superior. They require many turns because they're effectively screws. Unless you have a 4 post lift, that isn't an advantage. A 180˚ twist wins every time. ;)

Simon

Quote:

Originally Posted by SD1too (Post 2759830)

I managed to get some from ebay, which did work fine, they were just slotted instead of posidrive and bright plated, instead of black.

A couple of the spring nuts they screw into had failed on the sub-frame and they came complete with the nuts, so I replaced those two as well. They needed a bit of squeezing up, to get the nuts to properly stay put on the sub frame.

They do really need the plastic retaining washers to prevent fasteners getting lost. I made lots of them from a 4 pint plastic milk container, using a 25mm hole saw.

Quote:

Originally Posted by ceedy (Post 2759828)

Sorry those are hopeless..:D:duh:;

Had some .too soft and just jam up .

And single slot :duh::duh:
Well that's my experience .:o

Quote:

Originally Posted by SD1too (Post 2759830)

Hello Robert,

To answer your questions:

Do you think that a car manufacturer would go to the trouble and expense of making and fitting a component that wasn't effective?

As I understand it, the undertray performs two functions:

Aerodynamics. It smooths airflow under the car which the theory probably tells us improves roadholding.
Protection. It stops rainwater splashing upwards causing corrosion and electrical faults.

Sorry chaps, can't comment on the quality of those linked, just wanted to give the OP an idea of what he needed:shrug::D
Personally, I have similar to these https://www.ebay.co.uk/itm/LANDROVER...cAAOSwux5YKbVA

Cheers people, the under tray will stay as I supoose I wanted my own thoughts confirmed.

Suzublu many thanks. I dont suppose you know weather the 2 central fasteners use the litle gripper bit of metal or do they screw straight into a thread on the underside of the car??

My 2000 V6 has an immaculate engine compartment (always had the undertray). My previous 2005 car had no tray and a rusty underside and corrosion showing on the alloy parts of the engine underside (before I treated it!). The V6 engine noise is quieter than the 1.8 was!:shrug:

The standard undertray fittings are absolutely hopeless when the lugs for the Dzus fasteners corrode they don't hold, those LandRover ones are no better as they don't fit on some of the subframe fittings:mad:

What you really need to make the undertray secure are some of these instead of the standard clips:

https://www.ebay.co.uk/itm/M4-M5-M6-...S5sB70YEcXdGKA

M6 should do it combined with some M6 bolts and some suitable repair washers ;)

It shouldn't come adrift then ;)

My Volvo has them as standard for it's undertray and they do a far better job, they've never come adrift

Russ

Quote:

Originally Posted by BigRuss (Post 2759891)

... when the lugs for the Dzus fasteners corrode ...

That's easily prevented with a dab of Waxoyl or grease as you would for any threaded fitting in a vulnerable location. Alternatively, renew the corroded part, they are available from X-Part or BMW.

The undertray will not come adrift if the nylon washers are used and the spigots lubricated and positively fitted.

Simon