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View Full Version : TR4/4A Trying to replace TR4 transmission mount



Mark_Barton
04-12-2009, 04:53 PM
Do I need to remove the gearbox cover to do this?

As with most jobs I take on myself, I always find one blasted nut I can't get at. This time it's the right-hand bolt attaching the gearbox to the mount; the cross-member's in the way, and so is the downpipe when I try to get at it from underneath.

Found partial access on the right hand side of the gearbox cover where a rubber seal has disintegrated, but there's not really enough room through it to do more than stop the bolt rotating when I try to undo the nut.

Does anyone have any experience with this, any advice? I'll remove the cover if I have to, but that seems like a lot of dismantling for what should be a quick and easy swap.

Thanks...

sail
04-12-2009, 05:07 PM
I did my 4a from underneath. It was the left side I found awkward due to the strap to the top of the trans limiting movement. No tricks other than to get the right size open ended wrench which I did not have. Easy with gearbox cover off but better off to lay on your back for a bit than do all that.

Mark_Barton
04-12-2009, 05:14 PM
No tricks other than to get the right size open ended wrench which I did not have.

Interesting you should say that... Are they different sizes on each side? I was beginning to think they might be, but dismissed that as my own ineptitude trying to get anything on it!

The 3/4 inch on the left was a bit of a fiddle, but once I got the bolt stopped with a socket, I was ok on the other end with a wrench.

I can get the socket on the bolt on the right, just nothing on the nut...

TR3driver
04-12-2009, 05:36 PM
Sizes should be the same on both sides, but as I recall the bolt has a different size head than the nut, at least on my TR3/A.

Only way I've done it is either with the cover off, or drop the crossmember. But that was on a TR3A, so your TR4 might be different.

Geo Hahn
04-12-2009, 05:52 PM
We had a local email tech session on this very subject just a few days ago to answer a question from one of our local club members who was hoping to replace the mount on a club 'lift day'. We found one guy who had replaced it from below but he recalled thinking at the time it would have been easier to just remove the cover.

Staring at mine from underneath I could see that even with the car overhead on a lift this would be a tricky shot.

sail
04-12-2009, 06:01 PM
I just looked on my 4a and both nut and bolt are 3/4". I guess I just needed a second open end wrench. I remember the fat Harbor Freight wrench would not fit on top and the thinner better wrench just fit but I could not turn it. I also took off the 4 bolts on the cross piece.

Geo Hahn
04-12-2009, 06:04 PM
Okay -- I reviewed my (cryptic) notes from when I last did this.

I show that I used a 13/16" wrench on the nut and a 19mm (@%#?) on the bolt.

But -- depending on what type exhaust mount you have isn't the righthand nut actually welded to the exhaust bracket and thus captive requiring the bolt to be turned to remove? Or am I thinking of something else entirely?

sail
04-12-2009, 06:16 PM
I have exhaust bracket on right but no weld on either side.

TR3driver
04-12-2009, 06:20 PM
and a 19mm (@%#?) on the bolt.19mm = .748", plenty close enough to 3/4"

TR4nut
04-12-2009, 06:37 PM
I'd remove the cover. The passenger side does use the exhaust hanger with a welded nut, getting to that would be a real pain, and remounting might be even tougher.

Randy

Mark_Barton
04-12-2009, 07:17 PM
OK - I've got the cross-member off (2 skinned knuckles, several unrepeatable expletives) which has given me slightly improved access and a much better view.

The passenger-side nut is bigger than the 3/4" I took off the other bolt, and I can't fit any of my wrenches onto it. I think I have Sail's fat wrench problem though, rather than it being bigger than 7/8" (which is as large as my small collection currently goes).

There's certainly an exhaust hanger there, but I can't see if the nut is welded or not. I'll clean it up a bit tomorrow and have another look.

Does anyone know if the welded nut was pre- or post- a certain commission number, or is it just a question of if it was re-welded when it was replaced?

TRMark
04-12-2009, 08:38 PM
I would not remove the entire cover. What I did was mark the cover (mine is plastic) at the front (cockpit side) of the facia support bracket, removed the bracket and cut the cover and removed the rear part. I cut a length of aluminum strap and bent it to the shape of the cover, the part still attached, I put the strap in place half under the front cover. I drilled some holes in the cover and strap and riveted it to the cover using some sealant. The rear cover can now be removed to adjust the od solenoid, maintenance whatever. You may have to use some sheet metal screws on either side of the cut where it mounts to the floor to assure the covers fit snug. Later I found you could buy two piece covers.

TR4nut
04-12-2009, 09:24 PM
There's certainly an exhaust hanger there, but I can't see if the nut is welded or not. I'll clean it up a bit tomorrow and have another look.

Does anyone know if the welded nut was pre- or post- a certain commission number, or is it just a question of if it was re-welded when it was replaced?

Not positive, but I think the welded nut was on the exhaust hanger for all TR4s. Here's a link to a TR3 topic where I posted a picture of the hanger - if yours looks like that, chances are it is welded.
TR3 exhaust hanger post (https://www.britishcarforum.com/bcforum/ubbthreads.php/topics/540036/Re_Tranny_rear_exhaust_mount_F#Post540036)


Later I found you could buy two piece covers.
True, but I've only seen them for sale over in the UK, and I bet anything your modification is better than what you can buy - sounds like a good thing to try.

Randy

Geo Hahn
04-12-2009, 09:43 PM
and a 19mm (@%#?) on the bolt.19mm = .748", plenty close enough to 3/4"

Most likely it wanted a 3/4" but my 19mm wrench was a bit thinner or skinnier or something like that. My greasy notes only tell how I did it, not why I did it that way.

The bracket is item 15:

https://www.mossmotors.com/Graphics/Products/Schematics/TRI-008.gif

Item 17 is, of course, the bolt that holds the right side of the gearbox to the mount.

AFAIK, all TR4s had that bracket and welded nut -- inconvenient (IMO) compared to the bracket used on the TR3s.