Taking the 5th (Re-purposing the B4 Snub Bracket for B3 Use)

[Lago Blue]

Some further drive-line slack, shunt and shift related reading...

https://www.s2forum.com/forum/techni...gearbox-weight

https://www.s2forum.com/forum/techni...mounts-porsche

[Lago Blue]

TSB outlines possible electronically enhanced drive-line shunt issue for some...

Found this related topic while searching for something else and am sticking it here. While it specifically applies to B3 7A ECMs, it also serves to reinforce the point that from the perspective of the driver's seat, in order to find and quell the most feaseable total perceived drive-line shunt sources, their possible elimination may be best achieved by examining a broad search field, to encompass areas external to the actual drive-line's primary rotating bits and which may also include this third source area:

Application: 90 Quattro 20V L5-2309cc 2.3L DOHC (7A) (1990)

Powertrain Management > Relays and Modules - Powertrain Management > Relays and Modules - Computers and Control Systems > Engine Control Module > Component Information > Technical Service Bulletins > Customer Interest: > 249102

Engine Control Module: Customer Interest

ECM - Deceleration to Acceleration Hesitation

Group: 24
Number: 91-02
Date: April 30 1991

Subject: Engine - Minor Load Slap In Drive Line Occurs When Changing From Deceleration To Acceleration While Driving

Model(s): Coupe Quattro, 90 Quattro M.Y. 1990

Condition: Deceleration fuel shut-off remains momentarily activated during acceleration.

Production: Introduction of improved ECU software for MPI engine management system. ECU P/N 893 906 266D

As of: April 1990

VIN:
8A_LA208061
8B_LA13615

Service:
A) For vehicles produced after the above date/VIN, the new style ECU (893 906 266D) should be used.
B) For vehicles produced before the above date/VIN, replace ECU 893 906 266B with P/N 893 906 266BA (ECU has improved software to correct shortcoming).

Note: Replace ECU with zone approval only. Part numbers are for reference only, contact your parts department for verification.

Powertrain Management > Relays and Modules - Powertrain Management > Relays and Modules - Computers and Control Systems > Engine Control Module > Component Information > Technical Service Bulletins > Customer Interest: > 249102

[Bowie69]

Porsche 915 / 930 engine mounts are another good option for an OEM rubber isolated but significantly stiffer gearbox / diff mount. These are near-as-dammit the same installed height as OEM. The through-bolt is 12mm not 10mm. The outer circumference needs very slightly reshaping to fit the Audi subframes. These are what I run.

s-l300.jpg

Hey Alex,

When you fitted these, did you just use the 10mm bolt in the 12mm hole, or drill/tap it out, or sleeve it or.... anything?

Thanks!

Peter.

[Error404]

I use a 12mm bolt

[Lago Blue]

Audi S1 flexible drivetrain connections.png

It’s funny, I just came across this photo (above) again the other day while looking for something else, and thought about this very thread and how I think about all our many drive-train connections.

Imagine firstly:

At rest, the bare but totally assembled torque delivery system, run-able and ready to go, all the spinable shafts of the system (engine / tranny / 3 x diffs / 6 x drive-shafts / 10 x CV’s / 4 x hubs, discs, wheels and tires, etc.) suspended in zero-gravity space without any means of physical support. Kind of like that photo but minus the suspension and sub-frames shown, it’s just floating there.

Now secondly:

Give that system air, fuel and electricity, and start the engine. Engage a gear. Open the throttle, and let it close. The whole 5-armed mechanical creature will writhe and twist like the soft interior being one finds inside a grass-hopper; with its’ exoskeleton removed.

The car’s chassis is that exoskeleton, the suspension - the creature's limbs. Without those, the drive-train is a powerful but helpless and wriggling quint-o-pus. So to best harness that torque, the chassis needs equally powerful power-train attachment points and somewhat flexible connections to control that train. If they were solid, there'd be breakage, more noise, and less fluidity of control.

All the drive-train’s mounts and bushings are the critical links that attach to and direct all the train’s energy. That’s quite a list (snub, engine and tranny mounts, main shaft bearing support, 3 x rear diff mounts, 4 x top-mounts, 8 (or more?) x A-arm bushings, perhaps even the steering and rear-link bushes, etc.,). That is also why they all best need to be very strong, but still have some degree of flexibility, to smoothly and quietly (and one could argue, this list would even include the sub-frame bushes) best take-up, damp, release, spread out and diffuse the energy for those tasks. All those soft bits (and all of them wear-points) are the connective tissue, perhaps analogous to our own joints, cartilage, tendons and ligaments. If you where thinking some of those original (an evolved and world-beating design, BTW) resilient connections ought to be made completely solid, fuse a couple of your own healthy vertebrae and tell me how that improves your athleticism for doing exactly what?

This is why any injury (deficiency, weakness, slack or damage etc., or ill-conceived replacement) in these necessarily resilient connective tissues, to continue the analogy - like an sprain or strain to one of our own aging body’s joints, are so deleterious to the fundamental and overall performance and chassis capability; and the collective characteristic feel and enjoyment of driving the car. They (all those buried dull soft bits) don’t often get the respect they are due. As a fundamental starting point, ensuring they are all in the best shape possible ought to dominate one’s necessary to-do list, and be done really well first; prior to much of anything else. You may be pleasantly surprised how really good refreshed to new and very near to stock can be.

[Bowie69]

I use a 12mm bolt

Thanks Alex, think I was having a brain fart moment, had in my mind there was a captive nut in the subframe! With a fresher head this morning, yes, it should be fine....

Thanks