Engine and Transmission Tech

I posted this on mge just because there are a lot of guys over there with this tranny who never make it over here, but for the most part I consider this to be the home of the real experts. Let's see who has the better answer.

The Roadmaster tranny has taken a dislike to the 4-3 downshift bit it will go if properly double clutched. Otherwise it is fine. So...

What causes this?

What do we have to do to fix it?

How much will it cost us?

So far there is a suggestion that major surgery may be involved. That does seem rather vague.

Jim

Bad synchro?

T5 transmissions come in two very different types. The transmission in the Roadmaster is the later, "World Class" type. I believe World Class T5s only have two old-fashioned brass synchro rings, and as I recall the brass synchros are for the fourth-fifth interchange. Other than that, the World Class gearboxes use "friction lined rings" in lieu of regular synchros. They should be more durable... but they can fail. Unfortunately, that's about the limit of my knowledge of the subject. I've never had occasion to take my T5 apart.

Bad news is it's likely a synchro ring beginning to fail. Good news is that the T-5 is an easy box to dis-assemble and repair, the rebuild kits are not expensive and documentation on "how to" is plentiful. Before the I rebuilt my first T-5, the only other tranny I ever rebuilt was the box out of my '61 Minor 1000. The T-5 was vastly simpler (to this builder).

Not good, especially considering Mr. Automatic (Steve DeGroat) has the car! He has been waiting for such an opportunity.

1. Worn blocker ring/slider/dog teeth
2. Shift fork issue
3. Clutch/slave adjustment

Especially considering he has my (torn down) 2004r! ;-)

Definitely a synchro issue I would say from test driving it, and I do think I would know.

Jim

Why not try the clutch slave adjustment first? My "Old Mechanic" friend always said look for the simple thing first.Tim

Jim, have you drained and taken a look at the oil for different metals through it? Sometimes, it can tell a whole story.

I do not have the car, Steve does. So I cannot do any more diagnostics here. However I do not believe it is necessary as I think the cause has been identified accurately. I feel it is unlikely to be enough drag on the clutch to prevent the 4-3 downshift but still allow the 5-4 downshift and the 3-2 downshift. However I do not know what effect the different composition of the blocking rings might have so I will not go so far as to say it is impossible. It does take a full depression of the clutch pedal to disengage. Perhaps wear over the last few thousand miles has made that marginal. If that is the case what recommendations do we have for curing it?


Jim

Jim, what you just wrote matches my intuition. Someone can play with the clutch slave to see if it improves anything, but I'm skeptical that it will.

Can the Roadmaster's T5 be removed/replaced without removing the engine? How difficult? (Mine can be wiggled out. It's a little tricky to do, but doing so saves messing around with the cooling and exhaust systems.)

T5 boxes don't seem particularly intimidating to open and inspect. I don't recall hearing that any special tools are required. (That should be confirmed.) If it were my project, I'd probably inspect the box's internals before buying parts. I believe it's possible to buy specific repair parts instead of buying a complete rebuild kit. I don't know if that's advisable, but it might be a way to save money. If there's more internal wear than expected, another gearbox might be the way to go.

"How to Rebuild and Modify Your Manual Transmission" by Robert Bowen is available here for $13 (used). The table of contents indicates it includes a 30 page chapter specific to the T5...

[pomoforacing.com]

that's a really good article!

I used the Hanlon Motorsports video to rebuild my T5. It's very well done and has a wealth of information in it. The section on inspecting the synchros and the dog teeth on the gears for wear and suitability for reuse was especially good. You'll need a press, a couple of snap ring pliers and a dial indicator to complete the job.

It's interesting that the 2-3 up-shift works well but the 4-3 down-shift doesn't. The same synchro/blocker ring is used for both operations. Maybe the 3rd gear blocker ring is on the way out? I'd vote for ensuring the clutch is completely disengaging before tearing down the transmission. Don't the pressure plate fingers move away from the HTOB as the clutch disc wears? I wonder if the initial gap between the HTOB and the pressure plate fingers was too generous? Just a thought.

-- Scott

X2 on the Hanlon video if you end up rebuilding. That's what I used when I went through my T-5. I subbed out the press work but the rest is something anyone who is reasonably (operable word) careful can do if they follow the directions.

What about the pilot bearing or bushing in the end of the crankshaft? Is it new or old? Could it be causing binding on downshifting 4th to 3rd but not on upshifting 2nd to 3rd? I had trouble shifting my TR6 tranny even aftre rebuilding the shifter fork, throw out bearing ,pressure plate and clutch disc. After having the tranny out and in three times someone suggested looking there. A new pilot bushing cured the problem. If yor going to pull the tranny out maybr checking that would be good. IMHO Tim

I will adjust the slave when I have it on the lift.
the trans is easy to pull with the engine in place. Two people make it really quick, but I can do it alone if necessary.
I will not however try to repair the trans.

Steve