bolt in 4 speed replacement for t90 3 speed for F head?

I think my subject line says it all, and I know this gets covered a lot but was unsure what search terms to use to search for the right info.

Is there a standard 4 speed box upgrade for the F head that bolts right in and does not require serious driveline or floor panel or clutch modifications?

Now that Barney is running pretty well it would be nice to have an extra gear to drop the revs once i get to about 40 MPH. I don't ever plan to do much more than 45 LOL but it would be nice to calm him down at that speed...

Thanks in advance for info or a link to an old version of this conversation.

 

You want to drop the revs? Have you considered an O/D?

If I'm reading right, you want a trans with o/d, why not get a Warn or Saturn o/d.

 

Yeah, most 4speeds help on the lower end, not upper end.

 

Whoa, a new Warn or Saturn is near a $grand$ from Herm? sheesh maybe I will tolerate the revs....LOL

 

The overdrive unit from Herm is very nice. Fits perfectly, minimal alteration to your transmission cover, and the jeep now easily goes faster that I want to drive it...you can go 50 with fewer revs than the old 1:1 40 mph..I've had mine installed for about a week...

 

The T-90 you have is a 1:1 4th gear. The T-98 has a 1:1 4th gear. No reduction in rpm at the top end. Only way to do that is with an overdrive. Herm is your best bet.
If you do decide to go with the T-98 and can find one complete with all necessary adapters, driveline and floor mods will still be necessary.


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Have you considered changing the gearing in the differential? What ratio do you currently have, if it is a 5.38, it can be changed to a 4 something using standard used parts (ring and pinion). You would only have to change the rear one to see if you like it, as long as you only drive in 2 wheel drive. If it is acceptable, you could change the front diff as well. Changing from 5.38 to 4something would reduce engine rpm by about 20%. The downside is that you would have a higher 1st and 2nd gear as well, and the speedometer would be off by 20%, but that is easy to adjust with gearing on the speedometer shaft, or just eyeball estimation of the speedometer.

You could also go to a larger tire, or borrow a set of larger tires. Changing the dire diameter by 10% would reduce engine revs by 10%, say from a 28" tire (670-15 stock tire) to a 31x10.5x15 (31"tire). A 35" tire would be a 7 inch increase in tire over the stock size, and give a 25% reduction in engine revs.

Back in my college days (69-70), I drove a 59 cj-5 and put in a Warn overdrive to reduce the revs, and give me more speed. Cost me $300 back then. Overdrive was great on the flat, but had to downshift to standard high gear when any kind of a hilll or upgrade was encountered. That was with 8.25-15 tires.

Chuck

 

The Warn/Saturn overdrive is a great accessory for these Jeeps - it sounds like that's what you want. They are expensive new, but your Jeep will go up in value roughly as much as the cost of the overdrive installation. And it will make your Jeep more usable and enjoyable. There's no way you can do a transmission swap for the cost of an overdrive. And the overdrive has an easy installation. Seems like a no-brainer to me...

 

Try and find a used one they are out there. I'll have one for sale when I get to swapping my parts in April.

 

I am sold on the OD idea, but now I am also shopping plows so the OD may be next year!

 

I believe Herm has a Ford 4 spd ( where 4th is OD) and adapter plate but I am unsure of it's application. May be for V6 only. Might be worth a look.

 

He does or did. It's an RTS. Fair warning, if you ever have a problem with one good luck finding hard parts. Only used a couple years in Ford full size Bronco's and F-150's.
Had one I was going to adapt that needed one gear. Ended up selling it for parts as I couldn't get that part anywhere.


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