retrac

I reciently bought a 1987 Chevrolet C20 Chevrolet Suburban with the 454ci engine and 4.10 rear end ratio. It has The Turbo 400 Transmission, transmission cooler, oil cooler and factory towing package. I know that this is going to sound crazy but I would like to get the rear end ratio changed. I dont have a tach hooked up to it yet, so I don't know the rpm at each speed, but after 55 mph the engin rev's are so high you can't carry on a conversation or listen to the radio. I know that the rear end ratio can be reduced to something that would be better for me. This vehicle will only be occasionally used for towing a car trailer to a car show. The rest of the time it will be in general use and I would like it to be something enjoyable to drive. My questions are what ratios are available to me for this vehicle and what the cost would be to do the job? Are the parts for this age vehicle going to be difficuilt to find or are they pretty much available?

Eggert

Hi,
I have a 2001 Yukon XL K2500 with the 6.0 liter engine and a 4.10 rear end for towing a 10,000 lbs camper.
The only time mine gets too noisy is when it tows going up a hill at 55 mph in 2nd gear at 4,000 RPM.

4.10 is optional for greater towing power, 3.73 is standard and gives a 9% reduction in RPM, hardly much of a change.

Please don't be upset, just to cover the basics:
I am not familiar with your model and presume that the tranny is a 4 speed or 3 speed with overdrive.
Does your tranny check out and shift into high gear / overdrive?
I hope there is no slipping.

On mine, 4th gear at 70 mph is about 2,400 RPM.
Take care, Eggert

gregory914

There should be tons of parts for that vintage, just look at the sites below in "Related Links".

The turbo 400 is a three speed so you won't have the advavtage of the overdrive like in the newer ones so you can probably get away with a 3.42 or 3.23 ratio. If you go to a 3.73 I don't think you'll see much difference.

Get a portable tach and see what your RPMs are at the speeds you drive at then talk to rear end shops or mechanics and see what would work, remember the taller the gears the less guts your burb will have.

A buddy in SO CAL put an R700E (I think that's the #) tranny, four speed w/overdrive, in his 89 3/4 ton and it works fine but he had to play with the OD shifting electronics cause his Burb didn't have the computer the tranny needs to work like the factory wanted.

From my muscle car knowledge I know that the turbo 400s take about 30 to 40 HP to power to the wheels. However, it is a much stonger trans than just about anything out today. Remember they were the trannys that were in LS-6 Chevelles (465 HP) and lets not forget the Buick GS Stage 1, GSX (485 HP w/510 ft.# of torque) or the (500+ HP) COPO and Yenko Camaros. Sorry I just love those cars, automatic or not!!

retrac

The Turbo 400 Transmission is a 3 speed, NO OVERDRIVE. I do have a R700 that I took out of 84 3/4 ton C20 Pickup that I receintly restored after 270,000 miles. I was thinking that I could have it gone through and rebuilt and put it in the Suburban. The truck did not have a computer, but the Suburban does. Would this be a better change than the rear end change?

retrac

Thanks for your response to my question. I do have a R700 transmission that I took out of my 84 C20 that I just restored after 270,000 miles. The Truck came with a 350ci engine and the R700 transmission. When I restored the truck I replaced the 350 with a 30 over 400ci engine and a turbo 400 transmission pull a heavy duty utility trailer. The truck doesn't sound anything like the Suburban at high speed. The Suburban only has 113,000 miles on it and I just had the transmission in serviced. It shifts good and it doesn't seem to be slipping any, but I am not sure. My regular mechanic says that it isn't the transmission. It just sounds like it needs to shift to a higher gear. I will get a Tach today and get it hooked up and record the RPM and each 10 MPH and then get back to you. Once again thanks for your ideas and response to my questions.

Larry Derouin

You also have an additional alternative. a secondary Over/Underdrive tranny. They usually have a 20% change and are electric. They'll hook up after the transfer case. Doing it this way will give you a 20% overdirve at the rear only which will work out to about a 3.28. Cost is about $2000 but is a good alternative if you plan on keeping it for a LONG time. Other than that to get RPMs down, you could out in the 700R4 which will give you about a 3.50 when in 4th or change the rear and the front.

Larry

Westcm

Have you had the rearend checked? Your Pinion bearing may be worn out, cuasing your noise.

Also, I replaced my muffler on my 89 sub. once from a RV series 3 chamber flowmaster to a standered 3 chamber Flowmaster (shorter) w/it dumping down right after the rearend, and it sounded great until I would get onto the freeway! It would resenate through the cab so bad you would get an instant headache. I changed it back to a RV series to resolve the problem.
So, not knowing what exuast system you have, you may want to take it into consideration

mbumgua

I had a 87 3/4 ton 454 suburban which I swapped out 4:10 gears for 3:42 gears and really improved the top end performance. The rear end in these are a 14-bolt full floater. I had an extra rear end with 3:42 gears . I swapped out the pinion and carrier myself. If you are not experienced with setting up rearends I would recommend taking it to a shop to have it done. Other option is to swap the entire axle with one from wrecking yard with 3:42 gears. You don't have to worry about a transfer case or front gears as you have a 2-wheel drive suburban. Also the 454 has enough power you don't have to worry about loss of performance.