Knocking at the rear end of my TR4a

[Paul Garvey]

I recently bought a TR4a having been a T type MG man before so this is my first TR

The car has developed a serious knocking at the rear end.

If you put your hand on the floor behind the seats it feels like that is where the problem was.

To start with I put in new poly bushes in both trailing arms, no improvement.

The CV drive shafts are from Classic Driving Developments Ltd and they are relatively new, only done a few hundred miles.

I bought a reconditioned differential which was a 3.7 from a TR6 so I bought new TR6 rear mountings and Superpro bushes for this and it fitted the TR4a as you would expect. The noise went when the car is moving at a reasonable speed.

I then found the near side rear splined hub had some play so I replaced that, noise at low speed kicking in went.

What is the torque setting for the front 2 and the rear 2 axle mounting pins?

Also I put the grease on all surfaces of the poly bushes as the Superpro youtube video showed, could this be part of the problem. should I have put the grease all over each bush? Does this make torqueing the nuts an issue? Does the axle move?

As I said when I drive the car now at 20mph even up to 70mph I get no noise but the knocking occasionally kicks in when I slow down for a corner or poor road surface, could it be the axle moving on the superpro bushes?

With this knocking sound at low speed occasionally I am concerned about driving the car, thinking it may cause a bigger issue if not corrected.

Any suggestions will be appreciated

[brenda]

This may not be the problem but worth a look, check all exhaust brackets. I have the wheel barrow exhaust and it has a Y pipe this used to knock on the body and I had to put an extra bracket on to pull it away from the body. I don’t have the gearbox bracket fitted. Worth a look.

Mike Redrose group 

[RogerH]

Hi Paul,

 check the structure that holds the diff up in the air.

The bridge can break up - causing a clonk.

The pins in the bridge can break out - causing a clonk.

 

Roger

[Motorsport Mickey]

Hi Paul,

That sounds like a suspension related problem. As Mike says above the bodywork and front end of the diff flange intermittently try to occupy the same spot under certain suspension and bodywork movements and need spacing apart.

Check out underneath the rear of the transmission tunnel at the sides where floor is welded to the tunnel underneath the rear seat and the diff flange bolts to the prop flange looking for impact or bright metal that shows a problem.

Mick Richards 

[Phil Read]

13 hours ago, RogerH said:

Hi Paul,

 check the structure that holds the diff up in the air.

The bridge can break up - causing a clonk.

The pins in the bridge can break out - causing a clonk.

 

Roger

Yep, my 250 had a clonk. The  garage removed the final drive to fit oil seals and found cracked mountings. Mountings repaired and now no knocks or clonks.

[Z320]

Hi Paul,

your hand brake bowden cables could knock on your car from below.

Put a old towel or anything else soft between and make a test drive.

On my 4A I solved it with heating insulation cubes from the DIY market.

Ciao, Marco 

Edited July 8, 2023 by Z320
My poor English

[stuart]

Rear shocks loose?

Stuart.

[Paul Garvey]

Thanks for the replies.

The exhaust is the twin box system and I have checked that out

The 4 axle mounting studs have all been boxed in so they are OK.

I am going to check out Mick Richards suggestion.

The handbrake cable already had the grey plumbers insulation on it.

I had the suspension dampers off when first replacing the trailing arm poly bushes so they are rock solid.

 

Does anyone know the torque settings for the 4 nuts labelled 6 on the diagram below that are the mounting studs?

I got the diagram form a members old BL workshop manual but it did not give torque settings.

 

I look forward to your replies which has given me hope with Triumph TR's after years of T type MG ownwership

[keith1948]

Hi Paul

Check there is no play in the front and rear UJ's on the propshaft. Check rear gearbox mount is ok and fixing bolts tight. Are engine mounts at front of engine bay ok. Movement here could transmit back via propshaft. 

Exhaust moving is more of a rattle sound on my 4A. I just move it left or right a bit to cure that.

Keith

[Paul Garvey]

On 7/8/2023 at 4:45 PM, keith1948 said:

Hi Paul

Check there is no play in the front and rear UJ's on the propshaft. Check rear gearbox mount is ok and fixing bolts tight. Are engine mounts at front of engine bay ok. Movement here could transmit back via propshaft. 

Exhaust moving is more of a rattle sound on my 4A. I just move it left or right a bit to cure that.

Keith

Thanks I'll check the prop shaft and gearbox mount.

[DenisMc]

Hi Paul,

Regarding your request for the tightening torques for the four nuts that secure the diff on the mounting pins, I recently helped a friend refit the diff to his TR6. I believe it is essentially the same looking at Moss. If I remember correctly the four pins have a shoulder so that when the nuts are tightened the large washers are clamped against the shoulders meaning that this has no bearing on the loading of the poly bushes. We couldn't find a tightening torque either but as it is a  "hard" joint with no stretching of parts to be expected it is secure at quite a low torque.  The nuts are self locking.

My best wishes at finding the cause of the knock!

Regards,

Denis

[Paul Garvey]

Hi

Thanks for your help. it hadn't occurred to me that the large washers do stop at the shoulder and that means a secure fit when tighten up even though I had them on and off checked the fit, cleaned the threads on the mounting pins. School boy error on my side.

 

[Paul Garvey]

On 7/8/2023 at 9:45 AM, Z320 said:

Hi Paul,

your hand brake bowden cables could knock on your car from below.

Put a old towel or anything else soft between and make a test drive.

On my 4A I solved it with heating insulation cubes from the DIY market.

Ciao, Marco 

Hi

Just had the car up in the air and the plumbers insulating grey tubing on the car was to stop the hand brake rubbing on the fuel line. Once under the car again I lifted and lowered the hand brake cables and they do make a knocking sound, I put the plumbers grey insulating pipe om each cable but I couldn't push it in the gap where it goes to the car hand brake. You mention insulation cubes what exactly are these? I'll try them.

[Z320]

Sorry, my poor English writing!

Tubes, not cubes. They are „pre-slotted“, I opened them and pushed , closed, pushed, closed ….them (closed with tape) in several steps of 10 cm+10 cm+…. from the drums to the car body

Edited July 10, 2023 by Z320

[Paul Garvey]

Hi everyone.

The diff was the biggest culprit for the knocking, once the replacement was fitted the knocking went when driving the car but still an occasional "smaller" knock at low speed or poor road surface.

I had changed one of the hub spline extensions, I went through the car history and new hub spline extensions were fitted with the new 195 wire wheels 2 years ago. I bought a new one for the rear near side from the same supplier in London. Today I bought another one as the new one was "knocking ' I learned a lesson, the first one I bought was "cheap" in price and quality and lasted a matter of days . From today I will only buy from Moss to get quality even though the price with Moss is almost 50% more. You get what you pay for and avoid Chinese rubbish.

[Ralph Whitaker]

9 hours ago, Paul Garvey said:

Hi everyone.

 From today I will only buy from Moss to get quality even though the price with Moss is almost 50% more. You get what you pay for and avoid Chinese rubbish.

Hmmmmm!

Ralph

[Paul Garvey]

Hi

To keep you in the loop. The reconditioned diff made a big difference but there was still a knocking at low speeds, bumps in the road. It was CDD CV half shafts that had a massive amount of play. As they were relatively new, less than 10000 miles and still looked like new I never expected another big bill to replace them. Car is now all good at the rear end. 

[stuart]

1 hour ago, Paul Garvey said:

Hi

To keep you in the loop. The reconditioned diff made a big difference but there was still a knocking at low speeds, bumps in the road. It was CDD CV half shafts that had a massive amount of play. As they were relatively new, less than 10000 miles and still looked like new I never expected another big bill to replace them. Car is now all good at the rear end. 

Thats interesting, have you contacted the supplier?

Stuart.

[monty]

17 hours ago, stuart said:

Thats interesting, have you contacted the supplier?

Stuart.

Yes many of us have fitted the CDD units. Were these the actual real culprits? It would be nice to know exactly what the problems were with them.

[Motorsport Mickey]

Paul,

I presume if you contacted the supplier and they stood on their products ? At 10,000 miles I’d hope any of them would.

Who fitted the driveshafts ? Have they EVER been unrestrained ( even by yourself removing a shock absorber and not supporting the driveshaft and trailing arm no lower than it should go), and allowed the driveshaft to go outside their operating range ?

On CV driveshafts If you want to work on a wheel or trailing arm and wish to drop the arm unrestrained, it is good practice to undo and remove the inner drive flange from the diff. Then the whole trailing arm can be allowed full drop without damage.

Mick Richards

[Paul Garvey]

On 10/8/2023 at 10:41 AM, monty said:

Yes many of us have fitted the CDD units. Were these the actual real culprits? It would be nice to know exactly what the problems were with them.

It was the diff end. I never expected these to be the problem . I was baffled so I took the car to TRGB. Up on the car lift Wayne was baffled until he put his had on the CV at the diff end and was surprised at the movement. He had never seen this before?

TRGB are agents for CDD so CDD are send the parts to fix it.

[Paul Garvey]

On 10/7/2023 at 5:02 PM, stuart said:

Thats interesting, have you contacted the supplier?

Stuart.

Yes TRGB are sorting it.

[Paul Garvey]

Hi Everyone

 

As you know I have had a "knock" at the rear of my TR4a that I bought earlier in the year at a price that reflected the "knock".

Via TR classified I was able to source a new TR5/6 style diff. that was reconditioned by a MG/TR specialist garage.

This reduced the knock considerably but still a niggly knock when driving slowly.

I tried all the suggestions on this site.

The CV drive shafts were from CDD looked brand new, I had the receipt so I never suspected the CV drive shafts.

In the end I relented to take it into TRGB who did an excellent job. On the car lift even they were baffled at first until finally they looked the CV drive shafts and like me never thought they would be the culprit because they looked brand new.

They contacted CDD and CDD gave the same excellent service as TRGB. They sent replacement parts for TRGB to fit so I only paid labour. Which if I had bought new CV drive shafts from CDD would have cost much more so a win win situation.

All sorted now so I can get on taking the engine out........why take then engine out? Because I want to know this car backwards when driving up Stelvio and the Dolomites next year.